Polyurethane Immobilization of Cells and Biomolecules

T. THOMSON, MS, is Director of Main Street Technologies. He was the founder and Chief Technical Officer of Hydrophilix, Inc., a technology-based firm specializing in the development of advanced medical devices, environmental remediation technologies and consumer products. Mr. Thomson is known for his expertise in the development of products based on hydrophilic polyurethane (HPUR), and his current research includes the application of polyurethane composites to developing scaffolds for cell growth. He wrote 3 books on the subject, holds 7 patents in synthetic chemistry and process control, and has sponsored several seminars on the medical applications of specialty polyurethanes.

• Preface ix1 Polyurethane Chemistry 1Introduction 1The Chemistry 2The Isocyanates 3The Polyol 5Cross-Linking 5The Water Reaction 6Process 8The One-Shot Process 8The Prepolymer Process 10Post Processing 12Architecture of Polyurethane Foam 14Grafting to the Polyurethane Foam 16Biodegradable PUR 19Mechanism of Biodegradation 23More Examples 24Conclusion 25References 262 Laboratory Practice 29Introduction 29Prepolymers 30Preparation of an Elastomer 30Preparation of Foam 32Hydrophobic Foams 32Hydrophilic Foams 34Custom Prepolymers, Foams, and Scaffolds 40Examples 43Structure–Property Relationships 48The Special Case of Hydrophilic Polyurethane Foams 50Physical and Chemical Testing 50Physical Testing 52Biocompatibility Testing 54Process Equipment 54Metering Pump 55Mixing Head 55Tank/Material Retaining Container 55Machine Manufacturers 56References 563 Scaffolds 59Introduction 59Bioscaffolds 61Examples of Biofilter 65Elimination of Tobacco Odor from a Cigarette-Manufacturing Plant 67Treatment of VOCs from an Industrial Plant 68The Liver as Biofilter 68Scaffolds for Medical Applications (In Vivo and Extracorporeal) 70The Liver Model 71The Extracellular Matrix as Scaffold 72The Physical Scaffold 73Design of an Ideal Scaffold 74Drug Discovery 75Materials of Construction 77Ceramics 77Metals 80Polymer Scaffolds 82Poly(lactic Acid) 82Poly(glycolic Acid) 82Polycaprolactone 83Polyurethanes 83The “Ideal” Scaffold 87Pore Size and Distribution 89Void Volume 91Interconnectedness 96Surface Area 98Mechanical Properties 100Surface Chemistry 100Specificationsof the Ideal Scaffold 101References 1054 Immobilization 109Introduction 109Methods of Immobilization 111Immobilization by Adsorption 113Biofiltration 113Biotrickling Filter Setup and Operating Conditions 115The Toluene Reactor 116The H2S Reactor 120Biological Treatment of Aquarium Tanks 123Protein Adsorption 125The Avidin–Biotin System 126Application of the Avidin–Biotin System to Cell Adhesion to a Scaffold 128Adsorption to a Tricalcium Phosphate (TCP) Scaffold Using the Avidin–Biotin System 128Hepatic Cells on a Fabricated Polycaprolactone Scaffold 131Summary of Immobilization by Adsorption 132Immobilization by Extraction 133Extraction of Pesticides 138Summary 144Immobilization by Entrapment 145Alginate Encapsulation 146Encapsulation of Pancreatic Islet Cells 148Encapsulation of Osteoblasts 148Introduction to the Pancreas Model 149The Pancreas Model 150Summary of Encapsulation 154Immobilization by Covalent Bonding 154Overview of Covalent Immobilization 156Substrates Used for Immobilization 157Alginates 158Albumin 159Collagen 159Synthetic Polymers as Supports 159Polyethylene 159Poly l-Lactic Acid 160Immobilization to Polyvinyl Chloride 161Ceramics 163Summary 163Polyurethane Immobilization 164Fundamental Principles 164Prepolymer Chemistry 168The Immobilization Chemistry 169Structure and Chemistry of Biomolecules 170Preparation of Immobilized Biomolecules 171Notable Uses of Polyurethane for Immobilization 174Organophosphates 174Lipases 177Fibroblasts 178Collagen 180Amyloglucosidase 182Novel Reactor System 184Endothelialization 185Creatinine 186Conclusion to Immobilization 187References 1895 Controlled Release from a Hydrogel Scaffold 195Introduction 195Release Rates 198Examples of Hydrogels Used for Controlled Release 198Polysaccharides 199Pectin 199Alginates 200Carrageenan 200Agar 200Starch 200Proteins 200Gelatin 200Casein 201Other Proteins 201ControlledRelease by Diffusion 201Reservoir Layer 202Diffusion Experiments 206Islet Encapsulation 208Other Controlled Release Examples 211Targeted Delivery 211Stomach 212Small Intestines 212Colon 212Summary and Conclusions 213References 213Index 215