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					\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.

				
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