LoftinAH _Smart_ Coatings for Spine Implant-Related Infection

A novel implant coating to de l i ver an t ib io t ic through an active trigger mechanism in a spine infection mouse model

UCLA Department of

Orthopaedic Surgery

“Smart” Coatings: Amanda

H. Loftin

AALAS Annual Meeting

Wednesday Nov. 4th, 2015

Despite advances in aseptic surgical technique & perioperative antibiotic use...

Chahound  et.  al.  Front  Med.  2014  

.5 -18.8% of patients

post- operative infection is

reported to still occur in approximately

Undergoing spine surgeries. �

Surgical site infection following spine surgery is a dreaded complication with significant:

Negative outcomes for the patient

Detrimental effects on the healthcare system

Economic burden

1

2

3

Stavrakis et. al. Front Med. 2015

NEGATIVE FOR THE PATIENT

OUTCOMES

Neurological Compromise

Morbidity & Mortality

Disability

Abey  DM  et  al  J.  Spinal  Disord.  1995  Glassman  SD  et  al  Spine  1996  

Levi  ADO  et  al  J.  Neurosurg.  1997  Roberts  FJ  et  al  Spine  1998  

Several patient hospitalizations

Repeat surgeries

Long course of intravenous

followed by oral antibiotics

1

2

3

Detrimental EFFECTS ON THE HEALTHCARE SYSTEM

Stavrakis et. al. Front Med. 2015

This amounts to huge costs, with the treatment of a single

implant-associated spinal wound infection potentially costing

more than $900,000

Stavrakis  et  al.  Front  Med.  2015  

7

Clinical Presentation

1 year post-op

Bardis, Alexander. (2014). Late Post-operative Spinal Infections [PowerPoint Slide]. Retrieved from http://www.slideshare.net/AlexanderBardis/postoperative-spinal-infection-65o-eexot?related=3

1 year post-op

Bardis, Alexander. (2014). Late Post-operative Spinal Infections [PowerPoint Slide]. Retrieved from http://www.slideshare.net/AlexanderBardis/postoperative-spinal-infection-65o-eexot?related=3

Staphylococcus aureus remains that leading agent of spine implant

infections, responsible for around 50% of cases1

1.  Chahoud et al. Front Med. 2014 2.  Stavrakis et. al. Front Med. 2015

Staphylococcus epidermidis & Propionibacterium acnes

are also common pathogens 1-2

BIOFILM FORMATION 1. Attachment of S. aureus to implanted surface

2. Growth Formation of an extracellular matrix that is not susceptible to antimicrobial killing.

3. Dispersal of further establishes the biofilm making treatment extremely difficult

Biofilms block penetration of immune cells and antimicrobials, promoting bacterial survival

Orthopedic spinal implant infections are unique in that the implant is typically retained to prevent destabilizing

the spine making treatment more challenging

Bardis, Alexander. (2014). Late Post-operative Spinal Infections [PowerPoint Slide]. Retrieved from http://www.slideshare.net/AlexanderBardis/postoperative-spinal-infection-65o-eexot?related=3

13

��

Implants provide an avascular

surface for bacteria to form biofilm1-3

1. Cappen DA et al Orthop. Clin North Am 1996 2. Massie JB et al C. O. R.R., 1992 3. Knapp DR et al C. O. R.R. 1988

Bardis, Alexander. (2014). Late Post-operative Spinal Infections [PowerPoint Slide]. Retrieved from http://www.slideshare.net/AlexanderBardis/postoperative-spinal-infection-65o-eexot?related=3

��

The use of instrumentation increases the risk

of infection1-3

1. Cappen DA et al Orthop. Clin North Am 1996 2. Massie JB et al C. O. R.R., 1992 3. Knapp DR et al C. O. R.R. 1988

Bardis, Alexander. (2014). Late Post-operative Spinal Infections [PowerPoint Slide]. Retrieved fromhttp://www.slideshare.net/AlexanderBardis/postoperative-spinal-infection-65o-eexot?related=3

�The incidence of

spine implant related infection is:

���

1. Stavrakis et. al. Front Med. 2015 2. Chahoud et a. Front Med. 2014 3. Smith et. al. Spine. 2011.

1% without instrumentation1

3.4-10% with instrumentation1

One study reports a 28% higher infection rate with instrumentation

 Once biofilm is formed,

bacteria are 100-1,000 times less susceptible to

antibiotics1

Olsen  et.  al.  J  Neurosurg.  2003  

Prevention and

Treatment

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Modification of the host is difficult and often

beyond the surgeons control

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Reduction of preoperative risk factors is: timely, requires extreme patient compliance, and often impossible

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Diabetes ���Malnutrition���Obesity���Steroid therapy���Smoking������

Previous Spine Surgery���Cardiovascular problems Age >65���Steroid use���Immunosuppression���Gender���

Patient Risk Factors

Some surgical risk factors can be modified by the surgeon to decrease risk of infection,

but this may compromise the intended benefit of the procedure

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In Implant Infection Prevention

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Antibiotics

Implant

Host

Modifiable Factors

Current methods of local antibiotic delivery

Short-lived Vancomycin powder

Via passive release from suboptimal loading vehicles

Antibiotic loaded beads

23

Bardis, Alexander. (2014). Late Post-operative Spinal Infections [PowerPoint Slide]. Retrieved from ttp://www.slideshare.net/AlexanderBardis/postoperative-spinal-infection-65o-eexot?related=2

24

No antibiotic barrier is present on the implant itself to protect it from

bacterial colonization and subsequent biofilm formation

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Develop a novel, non-toxic, biodegradable poly (ethylene

glycol )-propylene sulfide (PEG-PPS) polymer coating that can be used

As a vehicle to deliver antibiotics locally through both a passive and active mechanism. To actively release antibiotic in response to the reactive oxygen cascade initiated by the presence of bacteria, allowing the “smart” polymer to release

antibiotic where it is needed most.

Existing animal models OUR NOVEL IN VIVO MOUSE MODEL

Inexpensive preclinical screen tool to evaluate the efficacy of treatments

Accurate

Rapid Large animals: 1. Costly 2.

Minimal engineering

options Histology based 1. Significant euthanasia 2. Requires large numbers 3. Labor intensive

EVALUATION OF EXISTING

ANIMAL MODELs

Mouse Surgical model

Combines the use of bioluminescent bacteria and genetically modified mice with advanced imaging to

noninvasively monitor infection and inflammation in real time, without requiring euthanasia. Provides a rapid, accurate, and inexpensive in vivo

preclinical screening tool to evaluate the efficacy of potential strategies to prevent or treat implant related spine infections.

Strengths of our model

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Postoperative evaluation of infection and inflammation

Bioluminescence and fluorescence

imaging

PODs* 0, 1, 3, 5, 7, 10, 14, 18,

21, 28, 35

POD 35

24 lysEGFP mice (12 wks., male)

POD 35

Evaluation of bacterial burden

& immune response

Visualization of biofilm on implant

Colony forming units (CFUs)

harvested from implant and joint tissues

Variable Pressure Scanning Electron

Microscopy (VP-SEM)

ex vivo confirmation of bacterial

burden

POD 0: Intraoperative inoculation of

S. aureus Xen36

Provides a rapid, accurate, and

inexpensive in vivo preclinical screening

tool to evaluate the efficacy of potential strategies to prevent or

treat implant related spine infections.

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Discussion & Conclusions

This model has unique elements that may: Complement or provide an alternative to previous

animal models of spine implant infections.

1x103 CFU is the ideal inoculum

of S. aureus Xen 36 to establish

a chronic implant-related infection as higher doses cause wound breakdown and lower doses can be cleared by the immune system.

Replace euthanasia with noninvasive real-time

in vivo imaging and provides a direct measurement

of bacterial burden and host neutrophilic inflammatory

response longitudinally in the same animals in real-time.

Mouse model as a platform to test clinical aims Mechanism- p a t h w a y a n a l y s i s

Applicability-coatings Innovation-new antimicrobials

Evaluation of antibiotic & antimicrobial coatings

Immune response to chronic implant related spine infection

Can we redesign orthopedic antibiotics

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“Smart” Coatings

PEG-PPS Coating

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OO

OHm

OO S

SS

S Nm n

NaH

OO

Om

Br

AIBNSH

O

OO

O S

OS

OO S

SS

m n

N S S N

1. 2.

NaOMe

star PEG-PPS

star PEG OHOHOHOH

SHSi

OOOOH

SHSiOCH3

OCH3

H3CO+

Implant

A B

Polyethylene glycol polymer

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•  Coating of optimal “timed” release •  Coating of targeted abx

!

!

S O OOSSPPS PEG

Antibiotic

0.5% Star PEG-PPSsolution at 4°C

Dry coat at 37°C

Implant

Implant

!

!Figure!7.!Antibiotic!loaded!implant!coating!process!using!star!PEG6PPS!polymer.!A!solution!of!star!0.5%!PEG6PPS!with!antibiotic!will!be!used!to!rapidly!coat!the!implant.!Metal!implants!will!first!be!silanized!to!introduce!–SH!(thiol)!groups.!Pictures!show:!(A)!uncoated!metal!implants!and!(B)!coated!implants!with!star!PEG6PPS/Rhodamine,!which!can!be!seen!as!a!purple/red6colored!coating!on!the!implant.!!

Titanium  Pins  Uncoated          3%  PEG-­‐PPS          6%  PEG-­‐PPS  

Polymer  is  low  profile:  nano-­‐micro  scale  

Covalent  linkage:  resistant  to  wear    

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Antibiotic Release

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7

Ti Pins: Cumulative Release Profile

6% PEG-PPS3% PEG-PPS

Days

!Daily Release (µg per pin/mL PBS) 3 % PEG-PPS 6 % PEG-PPS

1d 53.77 ± 25.85 136.89 ± 33.64

2d 2.47 ± 0.42 6.52 ± 3.19

3d 2.66 ± 0.62 2.01 ± 0.33

4d 2.25 ± 0.72 2.04 ± 0.04

5d 2.03 ± 0.17 1.82 ± 0.59

6d 2.32 ± 1.14 1.93 ± 0.07

7d 2.28 ± 1.65 1.08 ± 0.60

Daily release is above the minimum inhibitory concentration (MIC) for S. aureus

Surgical Procedure

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Do “smart” coatings work in vivo?

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In vivo efficacy of PEG-PPS coatings

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Ex Vivo Bacterial Counts

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0

1000

2000

3000

4000

5000

6000

Col

ony

Form

ing

Uni

ts

PEG Vanc Tig

Tissue Colony Forming Units Post-Operative Day 21

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PEG-PPS is an optimal vehicle to deliver antibiotics in the setting of spinal implants as it passively delivers antibiotics above the MIC and actively increases drug delivery in the presence of bacteria.

The Vanc impregnated PEG-PPS coating

prevented implant colonization by bacteria and

prevented implant infection completely

This novel coating shows promise in the prevention and/or treatment of orthopaedic spine implant infections and further large animal studies and biosafety studies are warranted.

Now that we have a vehicle to deliver antibiotics, can we redesign

antibiotics?

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Introducing Pentobra

Published in: Nathan W. Schmidt; Stephanie Deshayes; Sinead Hawker; Alyssa Blacker; Andrea M. Kasko; Gerard C. L. Wong; ACS Nano 2014, 8, 8786-8793. DOI: 10.1021/nn502201a Copyright © 2014 American Chemical Society

P. acnes

Special Thanks

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Bernthal Lab Alexandra Stavrakis Yan He Erik Dworsky Jannifer Manegold

Los Angeles Orthopaedic Hospital

Fabrizio Billi, PhD

CRUMP INSTITUTE OF MOLECULAR IMAGING

David Stout, PhD

Center for Experimental Medicine, University of Tokyo, Japan

Yoichiro Iwakura, D. Sc,

Cedars-Sinai George Liu, M.D., PhD Moshe Arditi, M.D.

Caliper Life Sciences

Kevin Francis, Ph.D. Department of Biomedical Engineering. UC. Davis

Scott Simon, Ph.D.

UCLA Orthopaedic Hospital Research Center

John Adams, MD Jeff Miller, MD

UCLA Department of Orthopaedic Surgery

Jeffrey Eckardt, MD Gerald Finerman, MD

Department of Microbiology and Immunology. Dartmouth Medical School

Ambrose Cheung, MD

Questions?

aloftin@g.ucla.edu

Amanda H. Loftin

AALAS Annual Meeting

Wednesday Nov. 4th, 2015