BIOMATERIALS WITH ENHANCED PROPERTIES AND DEVICES MADE THERFROM

UNITED STATES PATENT APPLICATION PUBLICATION

Cunanan et.al.

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•Inventors: 1) Crystal M. Cunanan, Mission Viejo, CA (US);2) John Joseph Higgins, Palmerston North (NZ);3) Saroja Nagaraj Guradzada, Palmerston North (NZ).

•App. No.: 13/217,234•Filled: Aug. 24, 2011•Pub. No.: US 2012/0059487 A1•Pub. Date: Mar. 8, 2012

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Title Page No.

1 Abstract 4

2 Background 5

3 Problems with existing Biomaterials 8

4 INVENTION 9

5 Advantages of Elastin 15

6 Process Treatment 16

7 Mitigate Calcification 19

8 Patches with Improved Properties 20

9 Reinforcement Strips with Improved Properties

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10 Characterization 23

11 Pepsin Solubilisation of Neonatal Calf Pericardium

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12 Summary 25

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Abstract• Improved properties of Biomaterials are very

important in Fabrication of Biomedical devices.• These enhanced properties can be attributed to

elevated level of elastin, altered collagen types, and other biochemical changes.

• Such enhanced materials can be sourced from specific populations of animals, such as neonatal calves, range –fed adult cattle, etc.

• In this embodiment, glutaraldehyde - fixed neonatal pericardial tissue is used to create leaflets in a percutaneous heart valves.

• Example of such devices which would be improved by use of such tissue includes heart valves like percutaneous heart valves, vascular grafts, patches and like.

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Background1) Chaim & Ruiz, Percutaneous Transcatheter

Aortic Valve Implantation, Journal of American College of Cardiovascular Interventions Volume 1, pp 341-50, 2008

•Current Medical Devices Fabricated from prior art biological tissues tend to suffer from various limitations , Due to limited properties of fabricated materials.

•Improved properties in biomaterials would enable development of new & enhanced devices.

2) Kroger et al, in Diameter of occluded superficialfemoral arteries limits per- cutaneous recanalization, Jounal of Endovascular Thera- peutics, volume 9, pp 369-74, 2002

• patients with peripheral arterial disease have an average femoral artery diameter of 4.5 mm in diseased vessels and a vessel diameter of 5.7 mm in non-diseased arteries

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• Therefore to treat patients without vessel disease, a percutaneous valve needs to be less than 5.7 mm in diameter & To treat patients with vessel disease, the compressed valve diameter should be less than 4.5 mm.

• The ability to provide this important new therapy to patients is the ability to reduce the collapsed size of the valve.

3) JHYoder et al, Nonlinear and anisotropic tensile properties ofgrafi materi- als used in soft tissue applications, Clinical Biomechanics, volume 25, pp 378-82, 2010.

• In the area of soft tissue repair and orthopedics, new biomaterials which are strong, durable, flexible and thin are needed.

• Currently extracellular matrix (ECM) graft materials are approved for augmentation or replacement of soft tissue structures, such as tendon and ligament repair, bladder and breast reconstruction, skin grafting, and general soft tissue reinforcement of defects in organ walls, such as abdominal and thoracic walls

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• the available ECM materials have limits on the critical properties needed for these applications, including strength, flexibility, durability or thickness, and are, therefore, less ideal for the intended repairs.

• For example, many allogenic skin graft materials do not have the desired strength for high stress applications requiring long term durability.

4) R P Lanza, R Lander, W L Chick, editors, Principles of Tissue Engineering Academic Press, 1997

• Tissue engineering is a large and growing field of research, and covers diverse applications in the areas of the cardiovascular system , musculoskeletal system , ophthalmology, the nervous system, wound repair .

• the ECM scaffold is a critically important element in all tissue engineered constructs. Providing adequate strength, durability, and flexibility during the remodelling process is essential for successful incorporation of a tissue engineered replacement tissue or organ.

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Problems with existing Biomaterials

•materials used as scaffolds in tissue engineering, are severely limited in application because of the lack of strength and durability

•Complicated pulsing or lowing bioreactors require complex equipment with long culturing times in order to generate tissues with some minimum mechanical strength.

•They degrade faster than the cells can synthesize replacement matrix, resulting in mechanical failure.

•Immunogenicity of Biomaterials.

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INVENTION• Embodiments are directed to new biomaterials with

enhanced properties which will enable the development of new and improved medical devices.

• These properties of enhanced strength, durability, flexibility and reduced thickness are due, in part, to identification and selection of materials having an elevated elastin content.

• An exemplary embodiment includes the use of neonatal tissue, harvested from juvenile cows, less than one year old, less than 6 months old, less than 3 months old and preferably less than 30 days old

• staining with elastin stain, like picrosirius red stain, the tissue is found to contain extensive amounts of elastin.

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Fig. 1 Fig. 2

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• the use of neonatal bovine pericardial tissues will improve the performance of transplanted tissues.

• Through analysis and screening, elevated elastin levels, improved collagen characteristics and other desirable parameters can also be found in adult bovine animals, particularly when those animals are free-range fed rather than fed in confinement at a feedlot.

• In a further embodiment, Neonatal or juvenile bovine pericardium is rich in altered collagen types, such as types II and III, while adult bovine pericardium is composed primarily of Type I Collagen.

• Such interconnections can provide important stress relieving mechanisms in a tissue which can help prevent tissue fatigue and degeneration.

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• graph of the ultimate tensile strength of a number of tissues used in tissue bioprostheses and soft tissue repair and reconstruction.• pericardium is an ideal choice for a strong tissue.

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• Tissue thickness is an important parameter in some applications, such as percutaneous tissue valves

• Neonatal bovine pericardium is the thinnest of the pericardial tissues.

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• shows the modulus of several tissues used in soft tissue reconstruction. The data show that neonatal bovine pericardium has an unexpectedly high modulus, given its relative thinness

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Advantages of Elastin• higher elastin content exhibit improved flexibility,

greater elasticity, and longer durability.• Devices fabricated from such tissues would be more

resistant to fatigue-related failure by reducing the mechanical stress on the tissues during use, thereby reducing the degradation rate of the collagen in the tissues.

• Elastin is a very hydrophobic molecule and contains about 30% glycine, arranged randomly along its chain,& Because of that it does not form helices, but is rather amorphous.

• It acts like a spring, stretching out when stress is applied to it, and recoiling to its original shape when the stress is released.

• Therefore tissues with higher elastin content can better withstand shear stress

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Process TreatmentHarvest the tissue

Rinse in isotonic buffered solution to wash away any residual blood.

ship to an off-site manufacturing location for further processing.

inspected for integrity and damage, and rinsed further to reduce any incoming bioburden

each tissue is laid out on a cutting board and large patches are isolated for fixation

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The tissues are fixed in a dilute solution of isotonic-buffered glutaraldehyde (0.625% in isotonic

phosphate buffered saline at pH 7-7.4)

Glutaraldehyde - fixed neonatal bovine pericardial tissues have a shrinkage

temperature of 84° C

Leaflets are fabricated into valves through an assembly pro-

cess which is specific to the valve design

exemplary percutaneous valve design fabricated from

prior art bovine pericardial leaflets

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• A significant reduction in tissue profile and volume enables the valve to be compressed into a catheter or less, ensuring its delivery via the peripheral arterial system, which is the most minimally invasive means to deliver a percutaneous valve.• After delivery, the valve will demonstrate improved

performance & not only is the implantation less traumatic for the patient, enabling faster recovery and fewer post-operative complications, also enable the valve to perform better hemodynamically

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Mitigate Calcification

• Reducing calcification is a key objective in obtaining a more durable, long-lasting surgical valve.

• calcification mitigation treatment is to use AOA (alpha-amino oleic acid) as a capping agent to reduce reactivity of residual aldehydes after the glutaraldehyde fixation step ( U.S. Pat. No. 4,976,733, issued Dec. 11, 1990).

• calcification treatments by using surfactants (U.S. Pat. No. 4,885,005, issued Dec. 5, 1989,)

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Patches with Improved Properties

• A pericardial patch can be used for general surgical reconstruction in the heart.

• Such patches can be chemically cross linked or simply disinfected.

• Patches may be treated to alter their calcification properties, promote adhesion, or minimize adhesion, as required for the desired application.

• Patches may be adhered to the tissue or organ being repaired using sutures, staples, or the like.

• A further advantage to patches made with the embodiments is the higher burst strength of these patches compared to traditional patch materials.

• Patches with elevated elastin levels are better able to resist burst forces and exhibit higher burst strengths.

Reinforcement Strips with Improved Properties

• Strips of extracellular matrix materials (ECM) are helpful in gastrointestinal surgery, particularly in minimally-invasive procedures where staples are used.

• Including a strip of ECM material in the suture or staple area helps ensure integrity of the staple-line.

• The burst strength of tissues from the embodiments described herein is much greater than the burst strength of tissues from the prior art.

• These two factors together, improved burst strength and improved suture pull-out strength, will ensure a higher performance for reinforced sutures, staple-lines, and other mechanical interfaces where disparate mechanical properties can result in failure.

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Characterization• Adult and neonatal bovine pericardium tissues fixed

with glutaraldehyde were characterized by SAXS (Small Angle X-Ray Spectroscopy) to examine their microstructure.

• The more aligned fibrils with shorter spacing is the result of the altered collagen types in neonatal pericardium compared to adult pericardium.

• Structure of collagenous tissues can be characterized by small angle X-ray scattering (SAXS) thereby yielding a quantitative measure of fibril orientation and of the collagen fibril.

• As noted glutaraldehyde fixed neonatal bovine pericardium is more highly aligned compared to similarly-processed adult pericardium as measured by the Small Angle X-Ray Scattering (SAXS) technique.

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Pepsin Solubilisation of Neonatal Calf Pericardium

• The adult and neonatal tissue was solubilised with pepsin and dried and the weight of the remaining tissue is taken and values are given below:

Pepsin digestion % tissue remaining

Adult tissue 21.1 (mean) Neonatal 11.52 (mean)• It show that the adult pericardial tissue has more

mature collagen crosslinks that are resistant to pepsin than the neonatal pericardial tissue .

• The presence of Type III collagen is strongly indicated by the amino acid data and the data suggest that differences in physical and biochemical properties between calf and adult tissue.

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SummaryWhat they claimed is;• An isolated portion of calf pericardium tissue

comprising an elastin content of greater than 0.25 micrograms per milligram dry weight , a ratio of hydroxyproline to proline greater than 1.0 , and wherein the calf is less than 12 months old.

• The isolated tissue portion of claim having a thickness of between approximately 0.05-0.250 mm.

• The isolated tissue portion of claim having a pepsin digestion of more than 20%.

• The isolated tissue portion of claim having a modulus greater than 20 Mpa.

• The isolated tissue portion of claim wherein the tissue is a component of a prosthetic heart valve.

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Thank You.....!!!!