Hydrogels: There is always room for Jello

Transcription

1 Hydrogels: There is always room for Jello Soft-solids and the evolution of medical device design Gavin Braithwaite, 56 Roland Street, Suite 310 Boston, MA Cambridge Polymer Group, Inc. Testing, Consultation, and Instrumentation for Polymeric Materials 7-17 Presentation (10/1/2010)

2 Gels: the fourth phase of matter Solid Permanent shape, fixed volume Elastic recovery Liquid Fixed volume, conformable shape No recovery (viscous) Gas Volume expands to fill container Gel Properties between solids and liquids Fixed volume and shape (like solids) while static Often turn liquid when agitated Partially elastic, partially viscous (viscoelastic) 2

3 Gel microstructure Gels and hydrogels Gel gelatus: frozen, immobile Gels structure continuous solid supporting a discontinuous solvent Solid is usually a crosslinked or associated network of molecules Liquid is anything compatible with the network Chemistry of network is critical solubility of the network draws in solvent to fill the network must be balanced by a restraining force generated within the network Network can t expand beyond the length of the chain 3

4 Soft solids Xerogel Liquid is removed leaving air Insulators Organogel Liquid is organic fluid Network is hydrophobic polymer Silicone gels Hydrogel Liquid is water Network is hydrophilic polymers or particles Collagen (jello, cartilage) Pectin (jam) phema (contact lenses) Poly(acrylic acid) (diapers) 4

5 Characteristics of hydrogels High water content Free water allows diffusion of solutes Viscous damping of mechanical deformation Density matched to water Very low solids content Network structure Can be static or dynamic Permanent crosslinks (contact lenses) Thermally sensitive (jello) labile (hair-gel) Contains and confines water in 3d shape Provides elastic recovery Provides support for attaching active ingredients 5

6 Soft-solids: Natures solution Hydrogels are ubiquitous in the body Mucus and tear films Cartilage Vitreous humor and cornea Tendon Microstructure critical function 6

7 Current uses of hydrogels in medicine Predominantly as a carrier or protector Drug release e.g. drug eluting stents smart gels e.g. enteric coatings (lower stomach targeted delivery) Tissue guides Nerve regeneration guides Vision Contact and intraocular lenses Tissue bulking Soft solid supports tissue Provides fluid motion Flexible and conformable Cartilage replacement Load-bearing lubricious 7

8 Urinary incontinence Urinary Incontinence profound quality of life impact million people in US 35%+ of adult women have some measure Often results from pregnancy Can also impact children during development Results from loss of muscle tone around sphincter Usually due to distortion of the urethra Current treatments conservative Subset require surgical intervention Soft solid re-closes the sphincter at rest 8

9 Stroke mitigation Myocardial infarction occurs when part of heart dies Due to blockage of blood flow to heart muscle Can be survived by leads to chronic problems Muscle wall looses strength and gradually deforms Stretches the internal structure of the heart Distorts valves Ultimately leads to mitral regurgitation (blood flow reversal) Injection of a soft-solid in to the heart wall Stiffens wall Preserves geometry 9

10 Expanding the applications Soft tissue replacement and augmentation Conceptually simple Easy application Limited demands on material Larger market Aging demographics Demand mobility Minimal surgery Load bearing applications Cartilage mimic 10

11 Engineering Solutions Solution: Designs based on simple engineering models Existing joints simple Hinge (knee) Ball-and-socket (hip, shoulder) easy to design Well understood materials simple fixation easy to validate Highly successful Hips now > 20 years Very low failure rates 11

12 What is wrong? Irreversible Tissue preserving Support structures and bone removed Not biomechanically compatible Bearing surface optimized for wear Fixation methods require anchors 12

13 What is missing? Conformable lubricious surface Native cartilage cushions, lubricates and spreads loads Naturally low friction Reduced contact stresses Conforms under loads Minimally invasive Current procedures require tissue excision To allow the joint to operate To allow easier access and operation To allow fixation Biomechanically compatible Current devices change way joint operates e.g. meniscus and ligaments removed Solution Cartilage replacement i.e. hydrogels 13

14 Permeability Tunable microstructures 20%-65%* Loading Curve E Elastic Modulus [MPa] DP DP DP AG RSA3 AG RSA3 AG RSA3- PEG 14 AG RSA3- PEG 1FT 5FT 5FT %

15 Compression loading of hydrogels Viscoelastic response Strain [mm/mm] PEG MPa 1 hr 20% 5 FT 0.5 MPa 1 hr MPa 1 hr Time [hours] 15

16 Ultra-low friction High lubricity Coefficient of friction, [ ] PVA freeze-thaw gel CPG PVA gel DATA CPG modified PVA gel Contact stress [MPa] 16

17 Thank you is a contract research laboratory specializing in polymers and their applications. We provide outsourced research and development, consultation and failure analysis as well as routine analytical testing and custom test and instrumentation design., Inc. 56 Roland St., Suite 310 Boston, MA (617) info@campoly.com 17