CHAPTER
14
Infection,
Tumorigenesis
and Calcification
of Biomaterials
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
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
14.2.2 Steps to Infection
(1) 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)
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 GBiofilm: microzone for ion trapping
mushroom-like appearance without surface attachment
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
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
14.2.5 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
14.3.1 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)
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
14.4.1 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
Tumorigenesis
initiation / latency / promotion
14.4.2 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
14.4.3 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
(2) FBT with small implants
asbestos fibers --- mesothelioma
cell memb penetration --- mechanical damage on nucleus
14.4.4 Summary of Biomaterial-Related Tumorigenesis
Disruption of cell-cell communication
Physical damage
Chemicals leached out
DNA damage and tumor
14-5 Techniques
14.5.1 In Vitro Models
(1) Mutagenic potentials
Ames test
14.5.2 In Vivo Models
(1) general biocompatibility
w/ final shape of device
(2) Animal type and
Implantation location
14-6 Pathologic Calcification
14.6.1 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
14.6.2 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
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
14.7.1 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
14.7.2. In Vivo Models of Calcification
1. Subcutaneous implantation
2. Insertion of the final device directly at the target location
14.7.3 Sample Assessment
1. Biochemical assays
2. Sectioning and histological tech
3. Radiography
4. Microcomputed tomography
non-destructive, X-ray
sample rotation --- 3D image