VIEWS: 20 PAGES: 11 POSTED ON: 5/15/2012
\tt\Table 1 Possible tissue responses to biomedical implants \tch\ Implant material Tissue response Applications characteristics Biologically inactive Fibrous tissue of variable No thickness forms(a) Biologically sustainable Cells are attached and Artificial organs (hybrid type) proliferated Porous … … Film/sheet/tubes Nutrition permeable Guided tissue generation Bond formation with bone tissues Porous Bone cell ingrowth Bone replacements Solid Bone cell attachment Bone substitutes Sol-gel conversion Stimulated bone cell Injectable gels for bone regeneration, without drug regeneration Biodegradable Surrounding tissue replaces Same as sustainable and material degradable materials Fixation to soft tissues Percutaneous devices Artificial cartilage or ligament \tfn\ (a) Because this material stimulates the formation of fibrous tissue or attachment, it is literally inadequate to denote it “inactive.” Some exceptions are known. For example, glass beads with a code YAS-89 (glass or glass-ceramic particles for cancer treatments) yield no fibrous tissue. Thus, the size and shape may be effective to induce the encapsulation. \tt\Table 2 Tissue attachment mechanisms for bioceramic implants \tch\Type of attachment Example Dense, nonporous, nearly inert ceramics attached by bone growth into surface Al2O3 (single-crystal and irregularities by cementing the device into the tissues, by press-fitting into a defect, or polycrystalline) LTI (low-temperature attachment via a sewing ring (morphological fixation) isotropic carbon) For porous inert implants, bone ingrowth occurs, which mechanically attaches the bone Al2O3 (polycrystalline) to the materials (biological fixation) Hydroxylapatite-coated porous metals Dense, nonporous, surface-reactive ceramics, glasses, and glass-ceramics attach directly Bioactive glasses by chemical bonding with the bone (bioactive fixation) Bioactive glass-ceramics Hydroxylapatite Dense, nonporous (or porous), resorbable ceramics are designed to be slowly replaced Calcium sulfate (plaster of paris) by bone Tricalcium phosphate Calcium phosphate salts \tt\ Table 3 Physical characteristics of Al2O3 ceramics \tch\ High-alumina ISO 6474 ASTM F 603(a) ceramics Alumina content, % <99.8 99.50 99.5 3.90 3 Density, g/cm >3.93 3.94 Average grain size, 3–6 <7 4.5(b) µm Surface roughness 0.02 ... ... (Ra), µm Vickers hardness 2300 >2000 18 GPa (2.5 106 psi) Compressive 4500 (650) ... 4000 (580) strength, MPa (ksi) Bending strength, 550 (80)(c) 400 (58)(c) 400 (58) MPa (ksi) Young’s modulus, 380 (55) ... 380 GPa (psi 106) Fracture toughness 5–6 (4.5–5.5) ... ... (KIc), MPa m ( ksi in . ) Weibull modulus ... ... 8 \tfn\ (a) As minimum physical characteristics of Al2O3 bioceramics. (b) Median grain size. (c) After testing in Ringer’s solution \tt\Table 4 Minimum physical characteristics of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) bioceramics in accordance with ASTM F 1873 \tst\Some properties of 3Y-TZP, 12Ce-TZP (Ref 13), and a typical zirconia-toughened alumina (ZTA), composed of 15% zirconia-85% alumina, are described for comparison. All zirconia components here are partially stabilized. \tch\ Y-TZP(a)(b) 3Y-TZP(a) 12Ce-TZP(a) ZTA(c) Zirconia 93.2 ~97 ~88 ~15 ZrO2 content, % Y2O3/Al2O3 4.5–5.4 ~3 ~12 ~85 Al2O3 content, % 6.0 3 Density, g/cm … … 4.1 Median grain 0.6 ~0.3 … ~10 size, µm Vickers 1200 … … 1750 hardness, HV Flexural 800 (116) ~1000 (145) ~600 (87) 760 (110) strength, MPa (ksi) Elastic modulus 200 (29) … … 310 (45) GPa (psi 106) Weibull 10 … … … modulus Fracture ~8 (7.2) … ~16 (14.5) 6–12 (5.5–11) toughness (KIc), MPa m ( ksi in . ) \tfn\(a) Partially stabilized. (b) ASTM F 1873. (c) Data from Ceram Research Ltd., 2001, as an engineering ceramic \tt\Table 5 Processes for introducing porous microstructures \tch\Key process Porogen Examples other than porous ceramics Phase separation Separated phases, Silica gel, poly(lactic acid)- droplets/interconnected glass Freeze and dry Frozen particles, air Organic-inorganic hybrids Dissolution Water-soluble crystals Organic-inorganic hybrids (sucrose, NaCl) Melting Low-melting crystals: NaCl, Inverse opal structure, coating naphthalene, camphor Calcining/burn Particles: polyethylene, Coating poly(styrene), active carbon Foaming Air, foam: surfactants … Templates Coral, urethane sponge, Nanotubes, nanofibrils collagen or cotton fibrils \tt\Table 6 Examples of glasses and glass-ceramics for biomedical applications \tch\ Bioglass Code13-93 Ceravital Bioverit II Cerabone (A-W GC) Developers Hench Day et al. Brömer, Gross Hölland et al. Kokubo, Yamamuro, et al. Examples of 45SiO2-24.5CaO- 13-93: 53SiO2- 46SiO2-5Na2O- 45SiO2- 46MgO·45CaO· compositions 24.5Na2O-6.0P2O5 20CaO-6Na2O- 0.5K2O-3MgO- 30Al2O3- 34SiO216P2O5·1 and (45S5) and related 12K2O-5MgO-4P2O5; 33CaO-12.5P2O5 12MgO- CaF2 precipitated derivatives (Fig. 6) 13-93B3: 53B2O3- (KGC); apatite 9(Na+K)2O-4F; (apatite and - phases 20CaO-6Na O- 2 apatite; Mg- CaSiO3) 12K2O-5MgO-4P O mica 2 5 (glass) (phlogopite) Principal Biodegradable Biodegradable; Biodegradable Machinable Greater bending chemical and soft-tissue strength mechanical attachment properties Clinical Ossicles; bone- Scaffolds for soft Ossicles Petrosa, middle Vertebra, iliac applications defect-filling tissue ear, zygoma, bone; bone granules or cones nasal bone, etc. cement filler (e.g., endosseous ridge) Young’s Y: 35 GPa (5.0 Fiber compacts B: 100–150 MPa Y: 70–90 GPa Y: 118 GPa modulus (Y); 106 psi) (14–21 ksi) (10 to 13 106 (17 106 psi) bending B: 42 MPa (6 ksi) psi) B: 214 MPa (31 strength (B) B: 90–140 MPa ksi) (13–20 ksi) \tfn\Note: Cortical bone: Y: 7–30 GPa (1.0 to 4.4 10 psi); B: 50–150 MPa (7–22 ksi). Cancellous bone: Y: 0.5–0.05 6 GPa (0.07 to 0.007 106 psi); B: 10–20 MPa (1.5–3.0 ksi). Source: Ref 4–6 \tt\ Table 7 Examples of genes activated by ions released from 45S5 Bioglass \tch\Groups Units Transcription factors and cell cycle regulators G1/S-specific cyclin D1 (CCND1) 26S protease regulatory subunit 6A Cyclin-dependent kinase inhibitor 1 (CDKN1A) DNA synthesis, repair and recombination DNA exclusion repair protein (ERCC1) mut L protein homolog High-mobility group protein (HMG-1) Replication factor C 38-kDa subunit (RFC38) Apoptosis regulators Defender against cell death 1 DAD-1 Deoxyribonuclease II (Dnase II) Growth factors and cytokines Insulin-like growth factor II (IGF2) Bone-derived growth factor 1 (BPGF1) Macrophage-specific colony-stimulating factor (CSF-1; MCSF) Vascular endothelial growth factor (VEGF) Extracellular matrix components Matrix metalloproteinase 14 precursor (MMP14) Matrix metalloproteinase 2 (MMP2) Bone proteoglycan II precursor; decorin Cell surface antigens and receptors CD44 antigen hemoatopoietic form precursor Fibronectin receptor beta subunit; integrin 1 Vascular cell adhesion protein I precursor (V- CAM 1) \tt\Table 8 Present uses of bioceramics \tch\ Application Material(s) used Orthopaedic load-bearing applications Al2O3, yttria-toughened zirconia, zirconia- toughened alumina Coatings for chemical bonding (orthopaedic, HA, surface-active glasses and glass-ceramics dental and maxillary prosthetics) Dental implants Al2O3, HA, surface-active glasses Alveolar ridge augmentations Al2O3, HA, HA-autogenous bone composite, HA-PLA composite, surface-active glasses Otolaryngological applications Al2O3, HA, surface-active glasses and glass- ceramics Artificial tendons and ligaments PLA-carbon-fiber composites Coatings for tissue ingrowth (cardiovascular, Al2O3 orthopaedic, dental, and maxillofacial prosthetics) Temporary bone space fillers Trisodium phosphate, calcium and phosphate salts Periodontal pocket obliteration HA, HA-PLA composites, trisodium phosphate, calcium and phosphate salts, surface-active glasses Maxillofacial reconstruction Al2O3, HA, HA-PLA composites, surface- active glasses, bioactive glass-ceramics Percutaneous access devices Bioactive glass-ceramics Orthopaedic fixation devices PLA-carbon fibers, PLA-calcium/phosphorus- base glass fibers \tfn\ Note: HA, hydroxyapatite, PLA, poly-l-lactic acid \tt\ Table 9 Examples of organic and inorganic components \tch\ Biodegradable hybrids Biosustainable hybrids Polymer component Natural polymers Synthetic polymers Chitosan, gelatin, collagen PDMS, poly(lactic acid) Inorganic component Silanes with polymerizable or reactive groups X-Z(OR)3, where Z = Si, Ti; OR = alkoxy groups, X = polymerizing groups (vinyl, glycidoxy, methacryloxy), or groups active against proteins or tissues (e.g., amino group) Applications Solid bodies Tissue-defect fillers for Tissue-defect fillers for regeneration reconstruction Porous bodies (beads, Tissue-defect fillers Artificial organs with living granules sheets, tubes) Tissue engineering scaffolds cells Wound-healing agents Bioreactors Tissue engineering scaffolds Gelling sols, gels Injectable sols Injectable sols Tissue-defect fillers Tissue-defect fillers \tfn\Note: PDMS, polydimethylsiloxane \tt\Table 10 Properties of biomedical carbons [Typist: Insert Table 8 from p 149 of the first edition of the book.] \tt\Table 11 Successful applications of glassy, low-temperature isotropic (LTI), and vapor-deposited ultralow-temperature isotropic (ULTI) carbons \tch\Application Material Mitral and aortic heart valves LTI Dacron and Teflon heart valve sewing rings ULTI Blood-access device LTI/titanium Dacron and Teflon vascular grafts ULTI Dacron, Teflon, and polypropylene septum ULTI and aneurism patches Pacemaker electrodes Porous glassy carbon-ULTI-coated porous titanium Blood oxygenator microporous membranes ULTI Otologic vent tubes LTI Subperiosteal dental implant frames ULTI Dental endosseous root form and blade LTI implants Dacron-reinforced polyurethane aloplastic ULTI trays for alveolar ridge augmentation Percutaneous electrical connectors LTI Hand joints LTI \tfn\ Dacron and Teflon, E.I. DuPont de Nemours & Co., Inc.