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14 Infection, Tumorigenesis and Calcification of Biomaterials CHAPTER

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1 14 Infection, Tumorigenesis and Calcification of Biomaterials CHAPTER
14-1 Introduction: Overview of Other Potential Problems with Biomaterial Implantation Biomaterials and pathogenic responses 14-2 Infection 1. Presence of biomaterial and/or damaged underlying ECM 2. Bacterial colonization of tissue 3. Resistance to host defense mechanism and antibiotic therapy 4. Presence of characteristic bacteria type 5. Transformation of innocuous bacteria into virulent organisms 6. Presence of multiple bacteria species 7. Persistence of infection until removal of the substratum 8. Absence of integration of the biomaterial with the host 9. Presence of cell damage or necrosis

2 14.2.1 Common Pathogens and Categories of Infection
Gram+: Staphlococcus aureus, Staphlococcus epidermidis Gram -: Enterobacteriaceae, Psudomonas aeriginosa, Candida spp. (종류) Superficial immediate infection / Deep immediate infection / Late infection Steps to Infection Bacterial attachment reversible and nonspecific interaction (2) Adhesion irreversible & nonspecific and specific receptor-ligand (3) Aggregation extracellular polysaccharide slime (Biofilm) (4) Dispersion shear forces or blood flow secondary infection Race for the surface (proteins, cells, pathogens)

3 14.2.3 Characteristics of the Bacterial Surface, the Biomaterial Surface,
and the Media (1) Bacterial surface properties: G+ and G- bacteria G+: single bilayered PL memb. + thick cell wall (peptidoglycan) ECM binding G-: double PL memb. + peptidoglycan in between outer and inner memb. Fimbriae or pili / flagella for locomotion (2) Cell capsule and Biofilm Cell capsule: polysaccharide-based outer layer of G+ and G- Biofilm: microzone for ion trapping mushroom-like appearance without surface attachment

4 Hard to remove the adherent bacteria
1) Physical barrier to phagocytic cells 2) T and B cell formation (-) 3) Ab production and bacterial opsonization (-) 4) Antibiotic resistance 5) Bacterial surface properties (growth condition) (3) Biomaterial surface properties protein adsorbed and bacterial attachment cell attached sruface --- no bacteria attachment (hydrophilic groups) grooves and valleys --- bacteria trapping (4) Media properties proteins in media solvent --- ions --- adsorption thermodynamics

5 14.2.4 Specific and Non-specific Interactions involved in Bacterial Adhesion
Non-specific binding: DLVO theory Specific binding: Microbial surface components recognizing adhesive matrix mol. (MSCRAMMs) ECM molecules Summary of Implant-Associated Infections (1) Transformation of innocuous bacteria into virulent forms (2) Pre-implantation sterilization (3) Anti-infective materials [initial bacterial adhesion (-), slime forming bacteria (-)] (4) Infection-resistant materials 14-3 Techniques for Infection Experiments surface properties of biomaterials and bacteria ---- adhesion & infection Bacterial Surfaces (1) Surface Hydrophobicity a. Contact angle measurements b. Microbial adherence to hydrocarbon (MATH) c. Hydrophobic interaction chromatography (HIC) (2) Surface Charge a. electrophoretic mobility test velocity (Helmholtz-Smoluchowski eq.) b. electrostatic interaction chromatography (EIC)

6 14.3.2 In Vitro and In Vivo Models of Infection
biomaterial’s proclivity to infection (1) In vitro bacterial adhesion static or well-defined flow conditions / well-controlled wash step microscope / control materials (2) Ex vivo and In vivo infection models - Ex vivo model shunts / biomaterials with pathogen inoculated - In vivo model small and large animals (cage implant system) - histology and SEM of explants at various time points leukocytes and lymphocytes bacterial cell wall antibodies Limulus-Amebocyte Lysate (LAL) assays ---- LPS detection 14-4 Tumorigenesis Definition and Steps of Tumorigenesis - Biomaterials ---- tumor (uncontrolled growth, mass, metastasis) - Neoplasia: excessive and uncontrolled cell proliferation - Tumor: benign vs. malignant (metastasis) - Carcinogen: complete carcinogen / pro-carcinogen / co-carcinogen

7 Tumorigenesis initiation / latency / promotion Chemical vs. Foreign Body Carcinogenesis - Chemical carcinogenesis near biomaterials / distant organ / hydrocarbon-based molecules - Foreign body carcinogenesis solid materials with large size materials provoking inflammatory responses Timeline for Foreign Body Tumorigenesis (FBT) (1) FBT with large implants Implants --- foreign body response --- cellular proliferation --- fibrous capsule --- pre-neoplastic cells Causes of FBT 1. bulk chemical properties of the implant 2. physicochemical surface properties of the implant 3. viral contamination 4. interruption of cellular communication due to the implant 5. local tissue damage leading to insufficient nutrient exchange 6. disturbed cellular growth

8 (2) FBT with small implants
asbestos fibers --- mesothelioma cell memb penetration --- mechanical damage on nucleus Summary of Biomaterial-Related Tumorigenesis Disruption of cell-cell communication Physical damage Chemicals leached out DNA damage and tumor 14-5 Techniques In Vitro Models (1) Mutagenic potentials Ames test In Vivo Models (1) general biocompatibility w/ final shape of device (2) Animal type and Implantation location

9 14-6 Pathologic Calcification
Introduction to pathologic calcification - Pathologic calcification --- disrupt device function - ECM-derived materials and synthetic polymers - Mineral deposits --- mechanical properties (brittle --- premature fracture) - Extent of calcification structure and chemistry of the biomaterial host metabolic factors mechanical environment of the implant Mechanism of Pathologic Calcification Natural materials with glutaraldehyde or formaldehyde --- intact ECM ---- less immunogenic 1. Calcium deposits on dead cells or cell memb fragments 2. Non-viable cells 3. Fixing agents 4. Localized mechanical forces 5. Collagen 6. Negatively charged, non-collagenous proteins

10 14.6.3 Summary and Techniques to Reduce Pathologic Calcification
Targeting calcium phosphate crystal initiation trivalent cations (Fe3+, Al3+): inhibitors of Ca-P crystal formation soaking biomaterials with ethanol and surfactants 14-7 Techniques for Pathologic Calcification Experiments In Vitro Model - Materials in a bath with a particular chemical composition of in vivo location - Liquid in either static and continuously circulating Implant in motion or remaining immobile In Vivo Models of Calcification 1. Subcutaneous implantation 2. Insertion of the final device directly at the target location Sample Assessment 1. Biochemical assays 2. Sectioning and histological tech 3. Radiography 4. Microcomputed tomography non-destructive, X-ray sample rotation --- 3D image


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