AN ECONOMIC EVALUATION OF BUFFER PREPARATION PHILOSOPHIES

1

CONNECT COLLABORATE

ACCELERATE TM

AN ECONOMIC EVALUATION OF BUFFER PREPARATION

PHILOSOPHIES FOR THE BIOPHARMACEUTICAL

INDUSTRY

TM

Buffer preparation philosophies 2©BioPhorum Operations Group Ltd | December 2019

ContentsContents ............................................................................................................................................................................................................ 2

Lead Author ...................................................................................................................................................................................................... 4

1.0 Executive summary .......................................................................................................................................................................... 7

2.0 Introduction ....................................................................................................................................................................................... 9

3.0 Methodology ...................................................................................................................................................................................10

3.1 Scenarios ........................................................................................................................................................................................ 12

3.2 Model assumptions and input parameters ........................................................................................................................... 13

4.0 Buffer demand .................................................................................................................................................................................15

4.1 Impact of buffer philosophy on volumes to be handled .................................................................................................... 17

4.2 Raw material demand ................................................................................................................................................................. 18

4.2.1 Stock solutions ..........................................................................................................................................................................18

4.2.2 Powders .......................................................................................................................................................................................20

5.0 Buffer preparation .........................................................................................................................................................................21

5.1 Capital cost .................................................................................................................................................................................... 21

5.2 Operating cost .............................................................................................................................................................................. 23

5.2.1 Labor .............................................................................................................................................................................................25

5.2.2 Consumables .............................................................................................................................................................................27

5.2.3 Raw materials ............................................................................................................................................................................29

5.3 Footprint ......................................................................................................................................................................................... 30

5.4 Cost of buffer (technology comparison) ................................................................................................................................ 32

5.4.1 Cost of buffer .............................................................................................................................................................................32

5.4.2 Sensitivity analysis ...................................................................................................................................................................34

5.4.3 Return on investment .............................................................................................................................................................36

5.4.4 Net present cost ........................................................................................................................................................................37

6.0 Conclusion .........................................................................................................................................................................................38

References ......................................................................................................................................................................................................41

Acronyms ........................................................................................................................................................................................................42


List of tables

Table 1: Buffer preparation philosophies ................................................................................................................................................................................................................................................................... 9

Table 2: Buffer list ............................................................................................................................................................................................................................................................................................................. 11

Table 3: Stock solutions for buffer stock blending............................................................................................................................................................................................................................................... 11

Table 4: Process model scenarios ............................................................................................................................................................................................................................................................................... 12

Table 5: Stock solution and buffer preparation times ........................................................................................................................................................................................................................................ 13

Table 6: Concentration factors for buffers ............................................................................................................................................................................................................................................................. 14

Table 7: Recipe times for system clean-in-place ................................................................................................................................................................................................................................................... 14

Table 8: Sensitivity analysis parameters .................................................................................................................................................................................................................................................................. 34

Table 9: Net present cost assessment for buffer preparation philosophies ............................................................................................................................................................................................. 37

List of figures

Figure 1: Relative comparison of buffer preparation philosophies ................................................................................................................................................................................................................. 8

Figure 2: Process flow for recovery and purification (taken from the BioPhorum Technology Roadmap for the Biopharmaceutical Manufacturing Industry1) .................................. 10

Figure 3: Buffer requirements per kg of product ................................................................................................................................................................................................................................................. 15

Figure 4: Solution requirements per batch ............................................................................................................................................................................................................................................................. 16

Figure 5: Storage volumes at 2,000L bioreactor scale ....................................................................................................................................................................................................................................... 17

Figure 6: Storage volumes at 12,500L bioreactor scale ................................................................................................................................................................................................................................... 17

Figure 7: Stock solution demand per batch ............................................................................................................................................................................................................................................................ 18

Figure 8: Stock solution demand at 2,000L bioreactor scale .......................................................................................................................................................................................................................... 19

Figure 9: Stock solution demand at 12,500L bioreactor scale ........................................................................................................................................................................................................................ 19

Figure 10: Powder demand per batch ....................................................................................................................................................................................................................................................................... 20

Figure 11: Total installed cost for buffer preparation at 2,000L bioreactor scale ................................................................................................................................................................................. 21

Figure 12: Total installed cost for buffer preparation at 12,500L bioreactor scale............................................................................................................................................................................... 22

Figure 13: Operating cost (per batch) for buffer preparation at 2,000L bioreactor scale .................................................................................................................................................................. 23

Figure 14: Operating cost (per batch) for buffer preparation at 12,500L bioreactor scale ............................................................................................................................................................... 23

Figure 15: Cumulative operating costs at 2,000L bioreactor scale .............................................................................................................................................................................................................. 24

Figure 16: Cumulative operating costs at 12,500L bioreactor scale .......................................................................................................................................................................................................... 24

Figure 17: Labor requirements per batch for buffer preparation at 2,000L bioreactor scale........................................................................................................................................................... 25

Figure 18: Labor requirements per batch for buffer preparation at 12,500L bioreactor scale ........................................................................................................................................................ 25

Figure 19: Consumables cost per batch for buffer preparation at 2,000L bioreactor scale .............................................................................................................................................................. 27

Figure 20: Consumables cost per batch for buffer preparation at 12,500L bioreactor scale ........................................................................................................................................................... 27

Figure 21: Raw materials cost per batch for buffer preparation at 2,000L bioreactor scale ............................................................................................................................................................. 29

Figure 22: Raw materials cost per batch for buffer preparation at 12,500L bioreactor scale .......................................................................................................................................................... 29

Figure 23: Preparation and hold equipment footprint at 2,000L bioreactor scale ................................................................................................................................................................................ 30

Figure 24: Preparation and hold equipment footprint at 12,500L bioreactor scale ............................................................................................................................................................................. 30

Figure 25: Cost of buffer per liter at 2,000L bioreactor scale ......................................................................................................................................................................................................................... 32

Figure 26: Cost of buffer per liter at 12,500L bioreactor scale ...................................................................................................................................................................................................................... 32

Figure 27: Sensitivity results for buffer concentrates at 2,000L bioreactor scale with 5g/L titer .................................................................................................................................................. 34

Figure 28: Sensitivity results for buffer stock blending at 2,000L bioreactor scale with 5g/L titer................................................................................................................................................ 35

Figure 29: Return on investment for buffer stock blending at 2,000L bioreactor scale ..................................................................................................................................................................... 36

Figure 30: Return on investment for buffer stock blending at 12,500L bioreactor scale .................................................................................................................................................................. 36


Lead Author

AuthorsThe following member company participants are acknowledged for their efforts and contributions in the production of this document:

PM Group Kevin Gibson

Avantor Pranav Vengsarkar

Biogen Phil de Vilmorin

Biopharm Services Christian Jones Andrew Sinclair

CRB Steve Attig

Exyte Carl Carlson

GSK Hiren Ardeshna

Lonza Carrie Mason

Merck Russell Jones

Merck & Co Inc. Kenilworth, NJ Jeff Johnson

Sanofi Nathalie Frau

University College Cork Denis Ring

BioPhorum Danièle Wiseman

With thanks to Natraj Ramasubramanyan


About BioPhorumThe BioPhorum Operations Group’s (BioPhorum’s) mission is to create environments where the global biopharmaceutical industry can collaborate and accelerate its rate of progress, for the benefit of all. Since its inception in 2004, BioPhorum has become the open and trusted environment where senior leaders of the biopharmaceutical industry come together to openly share and discuss the emerging trends and challenges facing their industry.

Growing from an end-user group in 2008, BioPhorum now comprises 53 manufacturers

and suppliers deploying their top 2,800 leaders and subject matter experts to work in seven

focused Phorums, articulating the industry’s technology roadmap, defining the supply partner

practices of the future, and developing and adopting best practices in drug substance, fill finish,

process development, manufacturing IT, and Cell and Gene Therapy. In each of these Phorums,

BioPhorum facilitators bring leaders together to create future visions, mobilize teams of experts

on the opportunities, create partnerships that enable change and provide the quickest route to

implementation, so that the industry shares, learns and builds the best solutions together.

BioPhorum Technology RoadmappingBioPhorum Technology Roadmapping establishes a dynamic and evolving collaborative technology management process to accelerate innovation by engaging and aligning industry stakeholders to define future needs, difficult challenges and potential solutions. The Phorum involves biomanufacturers, supply partners, academia, regional innovation hubs and agencies, serving to communicate the roadmap broadly while monitoring industry progress.

For more information on the Technology Roadmapping mission and membership,

go to https://biophorum.com/phorum/technology-roadmapping/


Abstract

As the demand for multiproduct, flexible facilities grows, there is an increasing emphasis on support services such as buffer preparation, where overheads are increasing and bottlenecks are developing. The supply of buffer solutions accounts for a large proportion of a facility’s footprint, labor, equipment and operating costs in the biomanufacturing industry. To alleviate the potential bottlenecks and reduce the impact on capital and operational expenditure, alternative philosophies for buffer management must be considered. The BioSolve Process software application from Biopharm Services Ltd has been used to construct a process model to assess the economic impact of a buffer preparation philosophy on a facility’s cost, design and operation. This comparison of traditional buffer preparation, buffer concentrates (in-line dilution) and buffer stock blending has demonstrated the significant benefits of both buffer concentrates and buffer stock blending over traditional buffer preparation. Buffer stock blending has proved to be the most economically viable due to significant operational benefits, particularly regarding labor demand.


1.0

Executive summaryBuffer management presents a number of significant challenges for the biomanufacturing industry and accounts for a large proportion of a facility’s footprint, labor, equipment and operating costs. This paper will evaluate the economic aspects of the various approaches available for the supply of buffers and assess their impact on facility design and operation.

Three strategies for buffer preparation are considered:

• Traditional buffer preparation: preparation of multi-component buffer solutions in

fixed vessels or single-use (SU) mixers at the final required concentration ready for

delivery to the process

• Buffer concentrates (in-line dilution): preparation of multi-component buffer

solutions in fixed vessels or SU mixers at a higher concentration than that required by

the process, which must be subsequently diluted before use

• Buffer stock blending: preparation of buffers in-line from concentrated, single-

component stock solutions at the final required concentration ready for delivery

to the process. While buffer stock blending is considered in this paper, the general

philosophy and associated operational benefits are comparable to similar approaches

such as in-line conditioning.

The volume of buffer required by a facility is directly related to the bioreactor volume

and product titer. Process developments, such as improved upstream productivity and an

ever-increasing demand for more agile multiproduct facilities, place growing demands on

support areas such as buffer preparation. Traditionally, labor-intensive and logistically

inflexible buffer supply is now frequently identified as a cause for bottlenecks. This is

evidenced by the identification of buffer preparation as one of the technology needs in the

BioPhorum Technology Roadmap for the Biopharmaceutical Manufacturing Industry1.


The comparison of the buffer philosophies is illustrated in Figure 1. Buffer concentrates and buffer stock blending on

demand offer considerable advantages over the traditional approach. Aside from the high initial investment, buffer stock

blending outperforms even buffer concentrates, particularly regarding the labor demand for buffer supply.

While the absolute values for the various assessment categories shown in Figure 1 are facility and process-specific, the

relative comparisons and general trends are likely to remain valid. The optimum buffer management approach is likely to

consist of a combination of the various philosophies and will vary by facility. Given the demonstrated benefits of buffer

stock blending as a cost-effective and flexible approach, it should certainly be included as part of the implemented strategy,

particularly for high-volume buffers.

Figure 1: Relative comparison of buffer preparation philosophies

Description 2,000 L scale 12,500 L scale

Trad

itio

nal

In-l

ine

dilu

tion

Buf

fer

stoc

k bl

endi

ng

on d

eman

d

Trad

itio

nal

In-l

ine

dilu

tion

Buf

fer

stoc

k bl

endi

ng

on d

eman

d

Capital cost

Operating cost

Labor demand

Consumables cost

Footprint

Flexibility

Total cost of buffer

Net present cost

Key:

= High positive impact = Medium positive impact = Baseline = High negative impact


2.0

Introduction Buffer preparation is a key challenge for the biopharmaceutical industry and is one of the technology needs identified in the BioPhorum Technology Roadmap for the Biopharmaceutical Manufacturing Industry1. This paper will evaluate the economic aspects of the various approaches for the supply of buffers for use in biopharmaceutical manufacturing and assess their impact on facility design and operation.

There is significant pressure on the biopharmaceutical

industry to reduce the overall cost of supply while

ensuring that safety and quality are not compromised. This

has resulted in initiatives to improve productivity as well

as an overall increase in demand for highly flexible and

adaptable facilities.

In the drive to improve productivity, there have been

considerable technology developments that have resulted

in the creation of higher titer processes, increasing the

productivity per liter of bioreactor capacity2. This has

resulted in significant challenges being placed on support

services, such as the design and operation of buffer

preparation. As downstream purification operations

are product-mass-based, some of the most significant

advances that have impacted on downstream and

consequentially buffer demand have occurred upstream3.

The large volumes of buffer required present logistical

challenges and buffer production remains a significant

proportion of a facility’s footprint, labor requirements

and equipment costs. It has been reported that media and

buffer powder storage and preparation represent ≥20% of

the space and costs for larger facilities4.

The buffer preparation philosophies compared in this

paper are outlined in Table 1.

Philosophy Description

Traditional buffer preparation Preparation of multi-component buffer solutions at the final required concentration ready for delivery to the

process:

• Preparation in fixed vessels or SU equipment

• Requires a dedicated preparation for each final process buffer

• Requires dedicated hold equipment for each final process buffer.

Buffer concentrates (in-line dilution) Preparation of multi-component buffer solutions at a higher concentration than that required by the process, which

must be subsequently diluted before use:

• Preparation in fixed vessels or SU equipment

• Typically requires a dedicated preparation for each multi-component buffer solution (although in some cases, a

single buffer concentrate may be used to prepare multiple final process buffer solutions)

• Volumes to be prepared and stored are reduced due to the concentration factor. Dispensing and material handling

requirements for a preparation are not impacted as only the initial charge of water for injection (WFI) is reduced

• As buffer formulations are multi-component, the least soluble ion and the common ion effect will limit the

maximum concentration factor that can be attained.

Buffer stock blending Preparation of buffers in-line from concentrated, single-component stock solutions at the final required

concentration ready for delivery to the process:

• Concentrated, single-component liquid stock solutions blended in-line with WFI to produce final

process buffer solutions

• Final process buffer solutions may be prepared and supplied directly to the process without the need for

intermediate buffer storage (buffer stock blending on-demand)

• Final process buffer solutions may also be prepared ahead of time and held in intermediate storage before

delivery to the process (buffer stock blending ahead of time)

• A wide range of buffers may be prepared from a relatively small number of concentrated, single-component

stock solutions.

Table 1: Buffer preparation philosophies


3.0

Methodology The BioSolve Process software application from Biopharm

Services Ltd has been used to construct a process model

to assess the impact of a buffer preparation philosophy

on a facility’s design and operation. Biosolve Process is a

user-configurable, process-modeling software product

with cost of goods being one of the key outputs. It is widely

used in the biopharmaceutical industry (50+ companies),

more than 50% of which are manufacturing companies and

34% are suppliers using it to model the value and impact of

innovative technologies.

Biosolve version 7.5.0.28 was used to generate the process

models for this assessment. However, in the standard

software version, the evaluation of buffer stock blending

is not currently available. To facilitate this assessment, a

custom calculation sheet was developed that allowed for

the assessment of in-line buffer preparation. The methods

developed to model buffer stock blending will be included

in the standard BioSolve Process build in the next release.

For the assessment of buffer preparation, the

process flow (as per Figure 2) and assumptions

used in the BioPhorum Technology Roadmap for the

Biopharmaceutical Manufacturing Industry1 were used as

a basis. The associated Biosolve model is available on

the Biopharm Services Limited website.

Figure 2: Process flow for recovery and purification (taken from the BioPhorum Technology Roadmap for the Biopharmaceutical Manufacturing Industry1)

Centrifugation/ 1° depth filtration

2° depth filtration

Protein A Virus inactivation

Cation exchange

Anion exchange

Viral filtration Ultrafiltration / diafiltration

Final filtration

Yie

ld

87% 96% 97% 98% 97% 97% 98% 98% 98%

Flo

wC

om

men

ts Removed when using perfusion USP

200 LMH 400L/m2

Batch 35g/L PCC - 55 g/L

Batch 45g/L PCC - 100 g/L

200 g/L 250 LMH 600L/m2

40 LMH 300 LMH 250L/m2


Table 2 lists all of the buffers considered in the model along with their respective uses. This is a relatively simplified buffer

list with only 14 different buffers throughout the entire process.

Buffer Depth

filtration

Protein A

chromatography

Virus

inactivation

Cation exchange

chromatography

Anion exchange

chromatography

Viral

filtration

Ultrafiltration

/diafiltration

Final

filtration

50mM phosphate pH 7.4 Equilibration

Post-flush

Equilibration

Wash 2

50mM sodium acetate,

2% benzyl alcohol

Storage

1M NaOH Clean

0.5M NaOH Clean Clean

50mM acetic acid, pH 3.1 Elution

50mM phosphate,

500mM NaCl pH 7.4

Wash 1

0.1M NaOH Storage Storage Storage Storage

1.5M acetic acid pH adjust

1.5M tris base pH adjust


250mM NaCl pH 5.0

Elution


50mM NaCl pH 5.0

Equilibration


100mM NaCl pH 5.0

Wash

50Mm tris-acetate,

50mM NaCl pH 8.0

Equilibration

Wash

20mM histidine,

20mM acetic acid, 50g/L

sucrose pH 6

Post-

flush

Diafiltration Post-

flush

Table 2: Buffer list

Using buffer stock blending, a wide range of buffers can be prepared from a relatively small number of stock solutions.

The concentrated stock solutions used in the model are listed in Table 3

Stock solution Concentration

Sodium phosphate monobasic 2M

Acetic acid 3M

Sodium hydroxide 3M

Tris 2M

Benzyl Alcohol 2%

Sodium chloride 3M

Histidine 0.5M

Sucrose 500g/L

Table 3: Stock solutions for buffer stock blending


3.1 ScenariosTable 4 lists the scenarios that have been considered

to identify the optimum buffer preparation philosophy

across a wide range of process scales and titers. The

impact of a buffer preparation philosophy has been

considered for both large-scale stainless steel (12,500L

bioreactor) and intermediate scale (2,000L bioreactor)

facilities. Due to their complexity and the wide

variation in costs, all multi-component buffer solutions

are assumed to be made in-house (i.e. the purchase of

ready-to-use buffer solutions is not considered).

In the case of buffer stock blending, both preparation

on demand and ahead of time have been considered,

as well as the method of supplying single-component

stock solutions (prepared in-house or by purchasing

ready-made, single-component stock solutions).

Scenario # Mode of buffer preparation Preparation: on

demand/ahead of time

Bioreactor

volume (L)

Buffer hold Titer (g/L) Purchased or prepared

stock solutions

1 Buffer stock blending Ahead of time 2,000 All preparations

into hold

2–10 Purchased


into hold

2–10 Prepared

3 Buffer stock blending On demand 2,000 Buffer hold is

minimized

2–10 Purchased


minimized

2–10 Prepared

5 Final-use concentration (traditional) Ahead of time 2,000 All preparations

into hold

2–10 N/A

6 Buffer concentrates (in-line dilution) Ahead of time 2,000 All preparations

into hold

2–10 N/A


into hold

2–10 Purchased


into hold

2–10 Prepared


minimized

2–10 Purchased


minimized

2–10 Prepared

11 Final-use concentration (traditional) Ahead of time 12,500 All preparations

into hold

2–10 N/A

12 Buffer concentrates (in-line dilution) Ahead of time 12,500 All preparations

into hold

2–10 N/A

Table 4: Process model scenarios


3.2 Model assumptions and input parametersThe model has the following in-built assumptions and

input parameters:

1. The process model and assumptions used in the first

edition of the BioPhorum Technology Roadmap for

the Biopharmaceutical Manufacturing Industry1 have

been used as a basis. The model (containing detailed

information for each unit operation) is available on

the Biopharm Services Limited website

2. The model is based on a new-build commercial

facility (greenfield) to produce monoclonal

antibodies

3. For each scenario listed in Table 4, there are five

installed production bioreactors. The product

from each bioreactor is purified individually (i.e. no

pooling). There is a single downstream train

4. Target capacity utilization is set to 80% (total of

78 batches per year in all cases)

5 For the economic assessment, the facility’s capital

cost is distributed over eight years

6. The downstream process is operated in batch mode

7. All stock solutions and buffer preparations are

‘right first time’

8. Equipment availability is 100%. Equipment failure is

not considered

9. For fixed vessels, the material of construction is

assumed to be stainless steel in all cases. There is

no allowance for higher-grade alloys that would

be required for high-chloride buffers (as BioSolve

Process does not facilitate varying material of

construction selection on a per buffer basis)

10. For SU systems, it is assumed that the films used

are compatible with the stated concentrated,

single-component stock solutions and

concentrated multi-component buffers (meeting

the requisite extractable-leachable guidelines to

prevent quality issues)

11. The threshold for SU equipment for preparation and

hold is set at 2,000L. Above this value, stainless steel

equipment is used

12. Buffer and stock solution preparation is on a per-

batch basis (or per-use in the case of on demand).

Preparations do not cover multiple batches

13. The model only considers the direct stock solution

and buffer preparation. The results do not take

into account raw material storage and handling,

dispensing, quality control (QC) testing, etc.

14. Where on demand buffer stock blending is used,

buffers are only delivered directly to the process

for chromatography operations. In other cases (e.g.

diafiltration buffer), buffers are prepared ahead

of time (at final concentration) and held in storage

systems before delivery to the process

15. For the preparation of single-component stock

solutions (for use with buffer stock blending) and

multi-component buffers, the recipe times for

preparation are listed in Table 5

Single-use bag preparation (up to a

threshold of 2,000L)

Vessel preparation

Set-up time (hr) 1 1

Fill-time (hr) Variable

(Fill-rate of 1,000L/hr)

1

Fill-time for large volumes >10,000L (hr) N/A 2

Mixing time (hr) 2 2

Personnel 2 2

Table 5: Stock solution and buffer preparation times


16. In the case of buffer stock blending on demand,

a set-up time of 30 minutes (with two people) is

allowed for each stock solution and buffer outlet

connection. Where buffer stock blending is used to

prepare buffer solutions ahead of time, a set-up time

of 60 minutes (with two people) is allowed for each

stock solution and buffer outlet connection

17. Where buffer concentrates are used, the

maximum overall concentration factor for the

multi-component buffers is listed in Table 6.

The concentration factors for single-component

stock solutions are listed in Table 3.

Buffer Concentration Factor

50mM phosphate pH 7.4 10

0.5M NaOH (import) 6

50mM acetic acid, pH 3.1 10

50mM phosphate, 500mM NaCl pH 7.4 6

0.1M NaOH (import) 5

1.5M acetic acid 1

1.5M tris base 1

0.1M NaOH , 0.1 NaCl 10

50mM sodium acetate, 250mM NaCl pH 5.0 10

50mM sodium acetate, 50mM NaCl pH 5.0 10

50mM aodium acetate, 100mM NaCl pH 5.0 10

50Mm tris-acetate, 50mM NaCl pH 8.0 10

20mM histidine, 20mM acetic acid, 50g/L sucrose pH 6 1

50mM Sodium Acetate, 2% Benzyl Alcohol 1

Table 6: Concentration factors for buffers

18. For clean-in-place (CIP) of buffer preparation and hold equipment, the recipe times are listed in Table 7.

The CIP of major equipment only is included in the BioSolve model.

Table 7: Recipe times for system clean-in-place

Preparation and hold vessels Buffer stock blending system

CIP frequency After each use WFI rinse after each buffer (1 min)

Full CIP once per production batch

Flow rate 50 L/min/m of vessel circumference 60L/min

Length to diameter ratio for vessels 2 N/A

Total rinse time 30 min 30 min

CIP personnel 2 2


4.0

Buffer demandBuffer requirements associated with downstream operations are product-mass based (i.e. buffer demand depends on bioreactor scale and product titer). Buffer demand increases significantly with bioreactor volume and titer. This relationship is demonstrated in Figure 3 with approximately 1,100–1,600L of buffer required for every kilogram of product produced (varying with scale).

While an increase in scale and/or titer shall result in an increase in product output and a corresponding increase in buffer

demand, the ratio between them varies due to the process equipment and parameters selected (automatically) within

BioSolve Process (e.g. chromatography column diameter and number of cycles). This results in some apparent outliers in

Figure 3 (e.g. 2g/L at 10,000L scale) but the general ratio remains within the expected range.

Figure 3: Buffer requirements per kg of product


Figure 4: Solution requirements per batch


1000

2000

5000

10000

12500

0

20,000

40,000

60,000

80,000

100,000

120,000

1 2 3 4 5 6 7 8 9

Bio

reac

tor

volu

me

(L)

Bu

ffer

vo

lum

e (L

)

Titre (g/L)

100,000-120,000

80,000-100,000

60,000-80,000

40,000-60,000

20,000-40,000

0-20,000


1000

2000

5000

10000

12500

0

20,000

40,000

60,000

80,000

100,000

120,000

1 2 3 4 5 6 7 8 9

Bio

reac

tor

volu

me

(L)

Bu

ffer

vo

lum

e (L

)

Titre (g/L)

100,000-120,000

80,000-100,000

60,000-80,000

40,000-60,000

20,000-40,000

0-20,000


1000

2000

5000

10000

12500

0

20,000

40,000

60,000

80,000

100,000

120,000

1 2 3 4 5 6 7 8 9B

iore

acto

r vo

lum

e (L

)

Bu

ffer

vo

lum

e (L

)

Titre (g/L)

100,000-120,000

80,000-100,000

60,000-80,000

40,000-60,000

20,000-40,000

0-20,000

The demand for buffer (per batch) across various scales of production is demonstrated in Figure 4.

Typically, a large proportion of the total volume required

is accounted for by a relatively small number of buffers. In

this case, the top five buffers account for 65% of the total

buffer volume. While this percentage is particularly high

due to the simplified nature of the buffer list, it still reflects

an overall industry trend. Of the solution requirements

for a batch, approximately 17% are hydroxide solutions

(of various concentrations) with the remaining 83% being

buffer solutions.

The considerable demand for buffer in every batch places a

number of challenges on manufacturing facilities including:

• Considerable capital investment costs

• Large footprint requirements for buffer

preparation and hold equipment

• High levels of labor required to manage

• Utility system capacity (e.g. WFI demand)

Improvements to upstream titers (e.g. through cell

line or media optimization) have resulted in significant

improvements to product output. Critically, higher titer

upstream processes can still take place in the same

bioreactor set-ups as those used for lower titer processes5.

This has a particular impact on support services such as

buffer preparation. For example, take a 2g/L process at a

12,500L bioreactor scale, the total buffer demand by the

process (per batch) would be ~22,000L. Increasing the

product titer to 5g/L would result in the required buffer

volumes (per batch) increasing to ~52,000L.

The associated increase in buffer demand has a

consequential impact on a facility’s footprint, capital costs

and operating costs, as well as the labor requirements to

support the buffer preparation. For a greenfield facility

design, this increase poses many challenges, however,

for a legacy facility that has a higher level of upstream

productivity, buffer production can become a significant

bottleneck and prove difficult to change.


1000

2000

5000

10000

12500

0

20,000

40,000

60,000

80,000

100,000

120,000

1 2 3 4 5 6 7 8 9

Bio

reac

tor

volu

me

(L)

Bu

ffer

vo

lum

e (L

)

Titre (g/L)

100,000-120,000

80,000-100,000

60,000-80,000

40,000-60,000

20,000-40,000

0-20,000


4.1 Impact of buffer philosophy on volumes to be handledFigure 5 and Figure 6 demonstrate the volume of liquid

that must be held for a given batch for the various buffer

preparation philosophies. This includes both stock solution

and buffer that must be stored before delivery to the

process. In the case of buffer concentrates, only buffers

that are to be delivered to chromatography operations are

concentrated. For other buffers (e.g. diafiltration buffers),

these are prepared and stored at final-use concentrations.

Similarly, for buffer stock blending, only chromatography

buffers are prepared on demand (all others are stored at

final-use concentrations).

Both buffer concentrates and buffer stock blending offer

significant advantages over preparation at final-use

concentrations. Buffer stock blending, in particular, has the

lowest storage volumes with a reduction of ~15% when

compared with 10x buffer concentrates. This reduction

increases to ~40% when 5x buffer concentrates are used.

In the case of buffer concentrates, each buffer must be

stored independently. For buffer stock blending, the

number of storage systems required is reduced due to

the preparation of final process buffers from a much

smaller number of common, concentrated, single-

component stock solutions. Due to the multi-component

nature of buffers, the maximum concentration that may

be attained is limited by the common ion effect. The

common ion effect applies to the case where several

components of a buffer have a common ion. For example,

a solution containing both acetic acid and sodium

acetate would have a reduced overall solubility due

to the common acetate ion (which causes a shift in the

solution equilibrium as per the Le Chateliers principle).

Additionally, the maximum concentration will be limited

by the least soluble ion out of all of the components6.

Through the use of single-component stock solutions, it

is possible to maximize the concentration factor for each

stock solution.

Figure 5: Storage volumes at 2,000L bioreactor scale Figure 6: Storage volumes at 12,500L bioreactor scale


Figure 7: Stock solution demand per batch

4.2 Raw material demand

4.2.1 Stock solutions

The demand for stock solutions on a per-batch basis across various scales of production is demonstrated in Figure 7. For stock

solutions that have a relatively low demand per batch, there are opportunities for multi-batch preparation in order to optimize

the operation of the preparation area.


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Figure 8: Stock solution demand at 2,000L bioreactor scale




0

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Sodium phosphatemonobasic(2M)

Acetic acid (3M)

Sodium hydroxide(3M)

Tris (2M)

Sodium chloride (3M)

Histidine (0.5M)

Sucrose (500g/L)

Benzyl Alcohol (2%)

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Sucrose (500g/L)

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Tris (2M)


Histidine (0.5M)

Sucrose (500g/L)

Benzyl Alcohol (2%)

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Sucrose (500g/L)

Benzyl Alcohol (2%)



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Tris (2M)


Histidine (0.5M)

Sucrose (500g/L)

Benzyl Alcohol (2%)

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Acetic acid (3M)


Tris (2M)


Histidine (0.5M)

Sucrose (500g/L)

Benzyl Alcohol (2%)



0

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Tris (2M)


Histidine (0.5M)

Sucrose (500g/L)

Benzyl Alcohol (2%)

0

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Titre (g/L)


Acetic acid (3M)


Tris (2M)


Histidine (0.5M)

Sucrose (500g/L)

Benzyl Alcohol (2%)

Figure 8 and Figure 9 illustrate the breakdown of concentrated, single-component stock solution usage (per batch) for 2,000

and 12,500L scales.


4.2.2 Powders

In the case of preparation from solid raw materials, Figure 10 presents the powder quantities that are required on a per batch

basis for the preparation of the buffers considered in the process model.

Figure 10: Powder demand per batch


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0-200


5.0

Buffer preparation

5.1 Capital costFigure 11 and Figure 12 illustrate the total installed cost associated with buffer preparation and storage. This includes the

base equipment cost as well as built-in allowances for building, installation, control, pipework, utilities, electrical, and heating,

ventilation and air conditioning.

Figure 11: Total installed cost for buffer preparation at 2,000L bioreactor scale


Buffer concentrates (in-line dilution) typically result in

the lowest total installed cost. Taking an average of all

titers, there is a reduction of ~56% at the 2,000L scale

when compared with traditional buffer preparation. This

reduction increases to ~65% for the larger, stainless

steel facility scale. The relative cost reduction associated

with buffer concentrates increases with scale due to the

replacement of large fixed vessels with smaller SU systems.

When considering the total installed cost of buffer stock

blending, there are a number of considerations relating to

both the mode of operation (ahead of time or on demand)

and the stock solution philosophy (purchase ready-made

or prepare in-house). For a 2,000L SU facility, even though

a significant proportion of buffer hold is removed, the

capital cost of buffer stock blending on demand is higher

(~16%) than the scenario where buffers are prepared

ahead of time. This is due to the cost of the multiple buffer

stock blending skids required to support the process in an

on demand mode. When buffer stock blending is used to

prepare buffers ahead of time, it is possible to supply all

buffers for the specified process from a single skid. For a

larger stainless steel facility, the high cost associated with

buffer hold (due to the large volumes) results in buffer stock

blending on demand having a significantly lower capital cost

(~46%) when compared to preparation ahead of time.

The selected philosophy for stock solution supply has a

noticeable impact on the initial investment required for

a facility. For both on demand and ahead of time, capital

investment for stock solution preparation and storage

represents ~20% of the total investment required.

The most significant factor in the buffer stock blending

capital cost is the cost of the skid(s) itself (as the cost

associated with buffer hold is vastly reduced). As an

equivalent number of buffer stock blending skids are

required for both scales, the cost-benefit associated

with buffer hold reduction is much more evident at a

larger scale. At the 2,000L process scale, buffer stock

blending on demand (including stock solution preparation)

is more than three times more expensive than buffer

concentrates (in-line dilution). For the equivalent scenario

at the 12,500L scale, the costs are ~63% higher. The cost

difference between the philosophies decreases further

if stock solutions are purchased ready-made to the point

where buffer stock blending on demand has a lower capital

investment than buffer concentrates once the titer is

increased to 8g/L.

While the absolute investment cost will vary from facility

to facility, the trend that buffer stock blending is the most

expensive option generally remains true. This is in line with

previous publications that have discussed GE Healthcare

In-line Conditioning Systems6, 7.

Figure 12: Total installed cost for buffer preparation at 12,500L bioreactor scale


5.2 Operating costThe operating cost per batch at 2,000L and 12,500L scales are presented in Figure 13 and Figure 14. The operating costs

considered are only those associated with direct production (raw materials, consumables (e.g. SU bags), labor and WFI

costs). Costs associated with raw material storage and handling, dispensing and QC testing are not included for this study.

Figure 13: Operating cost (per batch) for buffer preparation at 2,000L bioreactor scale

Figure 14: Operating cost (per batch) for buffer preparation at 12,500L bioreactor scale


At both 2,000L and 12,500L scales, the operating costs

are lowest with buffer stock blending on demand. When

compared with traditional buffer preparation and buffer

concentrates, the margin of improvement associated with

buffer stock blending on demand is much greater at the

intermediate scale. At both scales, there is a considerable

reduction in labor requirements; however, at the larger

scale these are offset somewhat by the increase in

consumables costs (associated with replacing fixed vessels

with SU systems).

Buffer concentrates offer improvements over traditional

buffer preparation at the 2,000L scale. At the large scale,

the operating costs associated with buffer concentrates

are higher due to the increased use of SU technology due

to the smaller volumes being handled. There is a trade-off

between capital and operating expenditure (which can be

balanced through the adjustment of concentration factors

and optimum volumes). For a specific facility, the optimum

buffer management strategy could be a combination of the

various philosophies to achieve a balance between capital

and operating costs.

Figure 15 and Figure 16 demonstrate the cumulate

operating costs at both the 2,000L and 12,500L scales (for

a 5g/L process). At the 2,000L scale, buffer concentrates

offer significant cost savings when compared to traditional

buffer preparation (~23%). This reduction is primarily

related to lower consumables costs due to the reduction

in volumes being handled. The operating costs for buffer

stock blending when used to prepare buffers ahead of

time are comparable to this. When used to prepare buffers

on demand, the consumables cost is reduced by a further

~35% when compared with buffer concentrates (due to

labor and further consumables savings).

At the 12,500L scale, buffer concentrates have a higher

operating cost (~24%) when compared to traditional

buffer preparation. This is related to the increased use

of SU technology. As with the 2,000L scale, buffer stock

blending on demand results in the lowest operating

cost, although the margin of difference is significantly

lower (~7%). At the large scale, the consumables cost for

buffer stock blending are higher than preparation at final

concentration, but there is a significant reduction in labor.

The following sections give further insight into the labor

and consumables costs for the various philosophies.

Figure 15: Cumulative operating costs at 2,000L bioreactor scale Figure 16: Cumulative operating costs at 12,500L bioreactor scale


Figure 17: Labor requirements per batch for buffer preparation at 2,000L bioreactor scale

5.2.1 Labor

Figure 17 and Figure 18 illustrate the labor demand per batch associated with buffer preparation.

Figure 18: Labor requirements per batch for buffer preparation at 12,500L bioreactor scale


The use of buffer concentrates (in-line dilution) offers

some advantages over traditional buffer preparation.

Buffer concentrates do not reduce the dispensing and

material handling requirements for a preparation (as only

the initial charge of WFI is reduced) and do not reduce

the number of preparations (as a preparation is still

required for each dedicated buffer). However, savings

are still observed due to the replacement of some fixed

vessels with SU equipment. Single-use technology is

more amenable to buffer concentrates due to the smaller

volumes being handled.

Buffer stock blending on demand results in a labor

reduction of ~39% when compared to the preparation

of buffer concentrates (assuming stock solutions are

prepared in-house). This is due to the reduced number

of preparations (eight single-component stock solutions

instead of individual preparations for each of the 14

buffers). The percentage savings are similar for both

scales, but the absolute value is greater at the larger scale

due to the increased volumes being handled. If stock

solution preparation is outsourced, these savings increase

greatly (~90%). The majority (~80%) of the direct labor

hours associated with buffer stock blending relate to the

preparation of the stock solutions.

In this study, there are 14 different buffers used by

the process, all of which can be produced from eight

stock solutions in the case of buffer stock blending. If

the number of different buffers is increased (as would

be expected for a typical manufacturing facility), the

savings will be increased (due to the additional number

of preparations that would be required for both buffer

concentrates and traditional buffer preparation). The

benefits associated with labor increase in proportion to

the number of different buffers (this remains true even

as additional stock solutions become necessary). As labor

hours are directly related to the number of preparations,

the impact of stock simplification is also significant. For

a process that has a small number of stock solutions,

the number of preparations and associated labor and

equipment demand is significantly lower when compared

with a more complex process.

While the absolute values will vary depending on

specific facility and process requirements, it is clear that

buffer stock blending is far less demanding in terms of

labor requirements when compared with traditional

buffer preparation. A study by Kedrion BioPharma has

demonstrated similar labor benefits when using a GE

Healthcare In-line Conditioning System. In this case study,

four in-line conditioning systems are used by the facility

to produce 26 different buffers from 11 stock solutions.

In this case, the reported reduction in preparation time

is 69%8. Another case study of a large-scale biologics

manufacturer demonstrated that reduced labor demand

for in-line conditioning resulted in a reduction of 4.5 full-

time equivalent staff6.


5.2.2 Consumables

Figure 19 and Figure 20 illustrate the consumables cost per batch for buffer preparation. The consumables costs in these

cases are primarily associated with SU bags (for preparation and hold).

Figure 19: Consumables cost per batch for buffer preparation at 2,000L bioreactor scale

Figure 20: Consumables cost per batch for buffer preparation at 12,500L bioreactor scale


At the 2,000L bioreactor scale, the use of buffer

concentrates offers a reduction (~29%) in consumables cost

when compared to preparation at final-use concentrations.

This is expected due to the smaller volumes being prepared

and stored. The consumables costs for buffer concentrates

are in line with buffer stock blending when used ahead of

time (where preparation of stock solutions is included).

The use of buffer stock blending on demand has the most

impact on consumables costs. When used on demand,

the consumables cost is reduced by a further ~41% when

compared with the use of buffer concentrates. If stock

solutions are purchased ready-made, this reduction

increases to more than 90%.

Buffer stock blending offers a number of advantages over

the use of buffer concentrates in terms of the volumes to be

prepared and stored. When used on demand, the buffer hold

associated with chromatography buffers can be completely

eliminated. Instead, stock solutions will be connected to the

buffer stock blending system.

At the 12,500L bioreactor scale, the use of buffer

concentrates results in an increase in consumables

cost per batch. Due to the smaller volumes being

processed, fixed vessels are replaced with SU

preparation and hold equipment.

Again, buffer stock blending is favorable when

compared with the use of buffer concentrates. Where

stock solutions are prepared in-house, the consumables

costs are increased by ~57% when compared to

traditional buffer preparation; but when compared

to buffer concentrates, there is a ~33% reduction.

In this study, only SU equipment and fixed vessels

are considered. Alternative strategies using non-SU

delivery forms could be further considered to address

the higher consumables cost when compared against

traditional buffer preparation. Where stock solutions

are bought in, buffer stock blending on demand results

in the lowest overall consumables cost.


5.2.3 Raw materials

The raw material costs associated with buffer preparation are presented in Figure 21 and Figure 22. At all scales, it can be seen

that the cost of buying in ready-made stock solutions is more expensive than preparing them in-house by ~60%.

Figure 21: Raw materials cost per batch for buffer preparation at 2,000L bioreactor scale

Figure 22: Raw materials cost per batch for buffer preparation at 12,500L bioreactor scale


5.3 FootprintFigure 23 and Figure 24 illustrate the equipment footprint associated with buffer preparation and hold equipment.

Figure 23: Preparation and hold equipment footprint at 2,000L bioreactor scale

Figure 24: Preparation and hold equipment footprint at 12,500L bioreactor scale


The use of buffer concentrates (with in-line dilution)

offers significant footprint savings when compared to

traditional buffer preparation (due to smaller volumes

being handled). There is a reduction of approximately

~50% in equipment space at the 2,000L scale and

approximately ~41% at the 12,500L scale.

Buffer stock blending (on demand) offers a further reduction

in footprint (~20%). As with previous comparisons,

purchasing ready-made stock solutions again offers a further

reduction in footprint (due to the removal of preparation

equipment). It should be noted that this footprint is within

the production area only and excludes warehouse space.

In the Kedrion BioPharma study, a footprint reduction

of 61% was reported8. The results of this facility-specific

study are very much in line with the Biosolve results

observed. In the case of buffer stock blending being

compared to preparation of buffers at final concentration,

buffer stock blending demonstrates a footprint reduction

of 62% at the 2,000L and 53% at the 12,500L scales (based

on an average of all titers).


5.4 Cost of buffer (technology comparison)

5.4.1 Cost of buffer

Figure 25 and Figure 26 illustrate the cost per liter of buffer at the 2,000L and 12,500L scales. This cost per liter takes into

account the amortized capital cost as well as ongoing operational costs (such as labor, consumables, raw materials, utilities, etc.).

Figure 25: Cost of buffer per liter at 2,000L bioreactor scale

Figure 26: Cost of buffer per liter at 12,500L bioreactor scale


As expected, at the 2,000L scale, the use of buffer

concentrates has a large impact on the buffer costs when

compared with preparation at final concentration with a

reduction in the price per liter of ~27%. At the larger scale,

the cost per liter for buffer concentrates is equivalent to

the cost of traditional buffer preparation. This is due to the

higher consumables cost associated with the increased use

of SU technology.

At the 2,000L scale, buffer stock blending (with in-house

preparation of stock solutions) results in a ~19% reduction

in the cost of buffer per liter when compared with buffer

concentrates. At the 12,500L scale, the cost reduction is

~16%. The difference in percentage is as a result of the

quantities of buffer being produced at both scales. The

increased volume of buffer at the 12,500L scale results in a

significantly lower cost per liter of buffer in general.

While there are considerable operational savings

associated with buffer stock blending, the positive impact

on buffer cost per liter is limited by the scale of the initial

investment. Even though the capital cost is amortized over

time, there is still a significant impact on the cost of buffer

per liter. As the technology develops, initiatives to reduce

the equipment supply cost would have a considerable

impact on this initial investment cost and consequently

reduce the buffer cost per liter.

The costs included in this study are only the direct

costs for preparation and do not include dispensing,

materials storage/handling and QC testing. In

demonstrating the comparative benefits of one

technology over another, it is the relative difference

between the numbers that is more important to

overall trends as opposed to the absolute value.

5.4.1.1 Variability in cost of buffer

There are a number of factors that vary between facilities

and specific processes that have a significant impact on

the final cost of a buffer. These factors include quantity

of buffers, complexity of buffers (and associated raw

material costs), utility costs, labor costs, equipment costs,

etc.). In this case, a relatively simple process with a limited

number of buffers is used which results in a low cost per

liter. Even for the same raw materials, there is a significant

variation in the cost of goods between end-users4.

The variability in buffer costs due to the factors above

is reflected in the wide range of published buffer

costs. A simple sodium hydroxide buffer could have a

cost of $3.50–5.75 per liter for a given scale9. This is

contrasted by the much higher costs of $11.13–19.72

per liter that were identified through interviewing

bioprocessing professionals10. While the absolute

values differ, the general trends in cost remain, such as

a reduced cost when operating at larger scales and the

impact of buffer preparation philosophy on the relative

cost of buffer preparation.

5.4.1.2 Stock solution supply

In the case of buffer stock blending, a key decision is

the supply of stock solutions. These can be purchased

ready-made or prepared in-house. While the initial

capital outlay will be smaller for ready-made solutions,

the added cost of raw materials will typically result in a

higher cost of goods, although some suppliers claim that

outsourced costs can be lower11.

In terms of raw materials, the cost of purchasing ready-

made liquids is about twice as much as purchasing

powders. At a smaller scale, costs are ~$5/L for powders

and ~$13/L for ready-made liquids4. These values reduce

as scale increases but the relative difference is similar.

The higher raw material costs (including shipping) are

counteracted somewhat by the reduced capital and

labor costs. Given the simplified buffer list in this study,

the cost of buying in ready-made stock solutions is

more cost-effective. This indicates the potential impact

of standardizing on a relatively small number of stock

solutions across the industry.

Most publications have considered the case of purchasing

ready-made buffers. In the case of stock solutions, the

volumes required are reduced and the single-component

nature reduces the complexity and associated cost. This

also provides significant opportunities when developing

standardized stock solutions throughout the industry.

Aside from the cost of goods, there are a number of

other considerations when it comes to outsourcing stock

solution or buffer preparation. There are clear advantages

when it comes to simplifying work practices, reducing

labor, and reducing equipment and space requirements

within the production area9. There are also potential

benefits in the reduction of process and employee risks

associated with in-house preparation (such as repetitive

weighing, employee exposure to chemicals and facility

exposure to dust). While space requirements within the

production area will reduce, the warehousing space will

likely be increased as liquid storage requires more space11.

The loss of control over preparation can be seen as a

negative, but it brings with it some advantages such as

the removal of responsibility to deal with ongoing stock

solution production issues.


5.4.2 Sensitivity analysis

To provide a better understanding of the impact of input variables, a one-at-a-time sensitivity analysis has been performed

whereby the sensitivity is assessed relative to the baseline values as per Table 8. The basis for comparison is the impact on

buffer cost per liter.

Parameter Low High

Buffer per batch (L) -30% +30%

Total installed capital cost ($) -20% +100%

WFI cost per liter ($) -20% +50%

Number of buffers -29% +43%

Number of stock solutions -25% +50%

Consumables cost -30% +30%

Labor hours per preparation -30% +30%

Raw materials cost -30% +30%

Table 8: Sensitivity analysis parameters

Figure 27: Sensitivity results for buffer concentrates at 2,000L bioreactor scale with 5g/L titer

WFI cost per liter (+50%)

Capital cost (+100%)

Raw material costs per batch (+30%)

Labor hours per batch (+30%)

Consumables cost per batch (+30%)

No. buffers per batch (+43%)

Buffer requirements per Kg product (-30%)

WFI cost per liter (-20%)

Capital cost (-20%)

Raw material costs per batch (-30%)

Labor hours per batch (-30%)

Consumables cost per batch (-30%)

No. buffers per batch (-29%)

Buffer requirements per Kg product (+30%)

2.26 2.76 3.26 3.76 4.26 4.76 5.26

Buffer cost per liter ($)


As demonstrated in Figure 27, at the 2,000L scale, the cost of supplying buffer using buffer concentrates is highly

sensitive to the number of different buffers required by the process, as well as the volumes to be handled (including

the maximum concentration factor that can be used). This is noteworthy as it gives an insight into the ability of buffer

preparation to respond to changes to the core process. Increasing the number of buffers from 14 to 20 results in an

increase of 20% in the buffer cost per liter.

In contrast to buffer concentrates, buffer stock blending is not highly sensitive to the number of different buffers

required by the process. The same increase in the number of buffers only results in a 2% increase in the cost of buffer

per liter. This demonstrates that buffer stock blending is less susceptible to becoming a bottleneck as a result of changes

to the core process. Increasing the number of stock solutions has a more significant impact than increasing the number

of buffers, but this is less likely to have a significant facility impact (as the likelihood of a significant number of additional

stock solutions is lower).

Buffer stock blending is highly sensitive to the total installed capital cost, much more so than other preparation

philosophies. In the design of a facility, this is an important consideration as initiatives to reduce the installation cost

would have a significant impact.

Figure 28: Sensitivity results for buffer stock blending at 2,000L bioreactor scale with 5g/L titer

No. buffers per batch (+43%)

Labor hours per batch (+30%)

Consumables cost per batch (+30%)

WFI cost per liter (+50%)

Capital cost (+100%)

No. stock solutions per batch (+50%)

Buffer requirements per Kg product (-30%)

No. buffers per batch (-29%)

Labor hours per batch (-30%)

Consumables cost per batch (-30%)

WFI cost per liter ( -20%)

Capital cost ( -20%)

No. stock solutions per batch (-25%)

Buffer requirements per Kg product (+30%)

0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40

Buffer cost per liter ($)


5.4.3 Return on investment

As stated previously in section 5.1, the capital cost associated with buffer stock blending is significantly higher than

other philosophies. When deciding to invest in buffer stock blending, this increase in capital investment is counteracted

by operational savings. At the 2,000L scale, the operational savings associated with buffer stock blending recover the

additional investment over traditional buffer preparation after 60 batches. When compared with buffer concentrates,

the additional capital investment is recovered in 190 batches.

In the case where an existing facility was to switch from buffer concentrates to buffer stock blending, it would take

275 batches to recover the full investment associated with buffer stock blending.

Figure 29: Return on investment for buffer stock blending at 2,000L bioreactor scale

Figure 30: Return on investment for buffer stock blending at 12,500L bioreactor scale


At the 12,500L scale, the capital investment for buffer stock blending is lower than preparation at final concentration and

there are significant operational savings per batch. When compared with buffer concentrates, the initial capital outlay is

higher, but again this is counteracted by lower ongoing operating costs. The operational savings associated with buffer

stock blending recover the additional investment over buffer concentrates after 161 batches.

If an existing facility were to switch from buffer concentrates to buffer stock blending, it would take 360 batches to recover

the full investment associated with buffer stock blending.

5.4.4 Net present cost

To facilitate the comparison of the various buffer preparation philosophies, the net present cost (NPC) for the various

approaches has been calculated. NPC is the discounted cash flow of all costs for every year, discounted back by the discount

rate. In this assessment, a discount rate of 10% is used over a 15-year period with the full capital investment included in year

one. The results of the assessment are listed in Table 9.

As a result of the operational savings demonstrated in section 5.2, buffer stock blending on demand has the lowest NPC

offering advantages over traditional buffer preparation and buffer concentrates at both the intermediate and large scales.

Table 9: Net present cost assessment for buffer preparation philosophies

Net present cost ($ million)

2,000L scale 12,500L scale

Final-use concentration (traditional) 17 24

Buffer concentrates (in-line dilution) 13 26

Buffer stock blending 10 21


6.0

ConclusionProcess modeling offers significant insights into the effect of a buffer preparation philosophy on capital and operational expenditure. This study has demonstrated the impact of a buffer preparation philosophy on the capital and operating expenditure for manufacturing facilities. The selection of an appropriate buffer philosophy is particularly important given the large volumes associated with the supply of buffers to the downstream process and the relative ease with which buffer preparation can become a bottleneck.

Given the correlation between production scale, titer and buffer demand, the consideration

and selection of an appropriate philosophy are important for new greenfield facilities as well

as for legacy facilities where the buffer requirements may have changed (e.g. an increase in

upstream productivity).

In terms of total volumes of stock solution and buffer to be handled, both buffer concentrates

and buffer stock blending offer considerable advantages over traditional buffer preparation. The

reduced volumes of buffer to be handled have an impact on footprint, and capital and operational

expenditure. For a 12,500L scale process at 5g/L, the total volume of solutions to be prepared and

stored using traditional buffer preparation is ~52,000L. Using buffer concentrates, this can be

reduced significantly with volumes of ~10,000–15,000L (varying with the concentration factor

used). For buffer stock blending, the volumes are reduced even further to ~8,500L.

The use of buffer concentrates generally results in the lowest required capital investment due to

the replacement of fixed vessels with SU systems. For titers above 6g/L at the large scale, buffer

stock blending on demand can compete from a capital perspective if stock solutions are purchased

ready-made. At the intermediate scale, buffer concentrates also offer a reduction in the total

operating cost per batch (~23% reduction compared to traditional buffer preparation). Due to the

increased use of SU equipment, the consumables cost per batch is significantly higher for a large-

scale production facility to the point where total operating costs are higher than traditional buffer

preparation (~24% increase).


Buffer stock blending on demand generally requires a higher capital investment than buffer

concentrates. This is related to the requirement for multiple buffer stock blending systems to support

the facility. At the intermediate scale, the capital cost of buffer stock blending on demand would be

lower than that of traditional buffer preparation for titers above 7g/L if stock solutions were to be

purchased ready-made instead of prepared in-house. At the large scale, the capital investment for

buffer stock blending is lower than that of traditional buffer preparation.

At the 2,000L scale, the cost of buffer stock blending can be more than three times as expensive

than the use of buffer concentrates. The higher capital costs associated with buffer stock blending

are counteracted by significant operational savings, which are evident at all scales of manufacturing

considered. There is a considerable reduction in the labor requirements for buffer preparation

(~39% lower than buffer concentrates and ~66% lower than traditional buffer preparation).

The space required for buffer preparation and storage is also reduced when compared to other

preparation philosophies due to the smaller volumes being handled.

At all manufacturing scales considered, the use of buffer stock blending on demand results in the

lowest cost per liter for buffer preparation. At the intermediate scale, buffer concentrates offers

a reduction of ~27% when compared to traditional buffer preparation. Buffer stock blending on

demand results in a further reduction of ~19%. At the large scale, the cost of buffer concentrates

is equivalent to that of traditional buffer preparation (lower equipment costs are offset by higher

consumables costs) whereas buffer stock blending on demand offers a reduction in the cost

of buffer per liter by ~16%. In all considerations other than capital cost, buffer stock blending

outperforms other buffer preparation philosophies. As the technology develops, initiatives to reduce

the equipment supply cost would have a considerable impact on this initial investment cost and

consequently reduce the buffer cost per liter.

For a new build, the higher investment costs of buffer stock blending when compared to buffer

concentrates would be recouped in around two years. Even in the case of a retrofit installation, the

use of buffer stock blending would have a payback of three to four years (when compared with buffer

concentrates). The return on investment presented here is based on a simplified buffer list as a typical

manufacturing facility would have a higher number of unique buffers. As the number of buffers

required for a process increases, the payback time associated with buffer stock blending decreases.

The need for flexibility in biopharmaceutical facilities is increasing with a much greater demand

for agile multiproduct facilities10. This results in substantial challenges for support services such

as buffer preparation. As processes and titers change between batches, buffer preparation must

be easily adaptable to meet the needs of the process without significant modifications. This is

difficult to achieve with both traditional buffer preparation and buffer concentrates as each

solution requires a dedicated preparation. This is particularly evident at a large scale where fixed

vessels are used. Due to equipment and labor constraints, buffer preparation can very easily

become a bottleneck.


Buffer stock blending is inherently flexible as a small number of common stock solutions

are used to prepare a wide variety of buffers. They are prepared on demand and

connected directly to the process so restrictions on minimum and maximum preparation

and hold volumes do not exist, although consideration must be given to the selection

of an appropriately sized system to allow for flexibility in buffer flow demands (e.g. to

accommodate changing chromatography column linear flow rates). The flexibility of buffer

stock blending is demonstrated by the low sensitivity of the cost of buffer to the number

of different buffers required by a process. This contrasts to the high sensitivity of buffer

concentrates and preparation at final concentration. This sensitivity demonstrates how

susceptible the buffer preparation area is to become a bottleneck. To maximize the flexibility

and potential of buffer stock blending, it is essential to minimize the number of individual

stock solutions required through a simplification of the buffer recipes. The cost of buffer

stock blending is directly dependent on the number of unique stock solutions required

(e.g. equipment costs, labor demand and consumables costs).

The preparation of buffers on demand also protects against buffer waste associated

with failed preparations or buffers that have expired (e.g. due to delays in production).

Due to their highly concentrated nature, stock solutions are less likely to expire than

concentrated buffer solutions6.

Given the sensitivity of buffer costs to a wide range of factors, the selection of a buffer

preparation philosophy should be considered on a case-by-case basis depending on the

specific facility and product demands. The optimum buffer management strategy for a

particular facility will likely be a combination of all of the above philosophies. For example,

traditional buffer preparation will likely be used for small preparations (e.g. for viral

inactivation) while buffer stock blending may generally be used for other larger preparations,

particularly for chromatography buffers. Some buffers will not be suited to buffer stock

blending (e.g. the solution may have an excessive number of individual components or fall

outside the flow-range capability of a system). In these cases, buffer concentrates could be a

viable alternative (with the option of using a buffer stock blending system to dilute).

The absolute values presented in this paper will vary from case to case, although the

relative comparisons and general trends are likely to remain valid. Buffer stock blending is

demonstrated to be a more flexible and cost-effective technology for buffer preparation

and should be considered as part of an optimum buffer management strategy.

©BioPhorum Operations Group Ltd | December 2019 Buffer preparation philosophies 41

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Acronyms/ Abbreviation Definition

CIP Clean-in-place

NPC Net present cost

QC Quality control

SU Single-use

WFI Water for injection

Acronyms


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AN ECONOMIC EVALUATION OF BUFFER PREPARATION PHILOSOPHIES