chapter 8 Design parameters 8.1 Biomaterials: Relative Properties 8.2 Bulk (Mechanical) and Surface Properties 8.3 Reactivity: Molecular Interactions 8.4 Bioadhesion(Tissue Bonding: Physical and Chemical mechanisms 8.5 Factors Affecting Biomaterials
CHAPTER 8 Design Parameters 8.1 Biomaterials: Relative Properties 8.2 Bulk (Mechanical) and Surface Properties 8.3 Reactivity: Molecular Interactions 8.4 Bioadhesion (Tissue Bonding): Physical and Chemical Mechanisms 8.5 Factors Affecting Biomaterials
8.1 BIOMATERIALS: RELATIVE PROPERTIES ADⅤ ANTAGES DISADVANTAGES METALS Stainless steel Strengt Potential for corrosion Ease of manufacturing High modulus of elasticity availability Cobalt-Chromium Strength Unknown long-term effects of Corrosion resistance Co and Cr ions Relative wear resistance High modulus Titanium(6A1-4V) Strength Low wear resistance Corrosion resistance CERAMICS Alumina Resistance to chemical degradation Low tensile and flexural strength Wettability Resistance to wear Calcium Phosphates(Slightly Soluble and resorbable Hydroxyapatite Bone-bonding Low tensile and flexural strength Slight solubility Slight solubility Whitlockite Bone-bonding Low tensile and flexural strength solubility Solubility Natural(resorbable) Bone Apatite Bone-bonding Low strengt Resorbabil
8.1 BIOMATERIALS: RELATIVE PROPERTIES ADVANTAGES METALS Stainless Steel Strength Ease of manufacturing Availability Cobalt-Chromium Strength Corrosion resistance Relative wear resistance Titanium (6Al-4V) Strength Low modulus Corrosion resistance CERAMICS Alumina Resistance to chemical degradation Wettability Resistance to wear Calcium Phosphates (Slightly Soluble and Resorbable) Hydroxyapatite Bone-bonding Slight solubility Whitlockite Bone-bonding Solubility Natural (Resorbable) Bone Apatite Bone-bonding Resorbability DISADVANTAGES Potential for corrosion High modulus of elasticity Unknown long-term effects of Co and Cr ions High modulus Low wear resistance Low tensile and flexural strength Low tensile and flexural strength Slight solubility Low tensile and flexural strength Solubility Low strength
POLYMERS Syntheti Thermoplastics PTFE ( Teflon Resistance to chemical degradation Low wear resistance Hydrophobicity Hydrophobic Low friction Does not display typical thermoplastic flow behavior UHMWPE Relatively high wear resistance Subject to oxidatio PET (Dacron) Subject to hydrolysis Low MW contaminants PMMA Polymerization in vivo Low fatigue strength ( for load-bearing appl PSF High strength thermoplast Water absorption (dec strength in water) PEEK High strength( PsF) Unproven C/PSF. C/PEEK Very high strength Unproven Relatively low modulus Elastomers PDMS High flex life Low wear resistance Ease of manufacture Release of low Mw PDms Range of mechanical properties Immunogenicity?
POLYMERS Synthetic Thermoplastics PTFE (Teflon) Resistance to chemical degradation Low wear resistance Hydrophobicity Hydrophobic Low friction Does not display typical thermoplastic flow behavior UHMWPE Relatively high wear resistance Subject to oxidation PET (Dacron) PMMA Polymerization in vivo PSF High strength thermoplastic PEEK High strength (> PSF) Low water absorption C/PSF; C/PEEK Very high strength Relatively low modulus Elastomers PDMS High flex life Ease of manufacture Subject to hydrolysis Low MW contaminants Low fatigue strength (for load-bearing applications) Water absorption (dec. strength in water) Unproven Unproven Low wear resistance Release of low MW PDMS Range of mechanical properties Immunogenicity?
Polyurethane High flex life Uncertain molecular structure- Range of mechanical properties property relationships Surface radically different from ulk(high mobility of"soft segments") Low MW contaminants Subject to hydrolysis, oxidation, d calcification Hydrogel P-HEMA Low reactivity Low strength Absorbable PLA/PGA Programmable absorption Uncertain biological response to Metabolizable degradation products bolus-release of metabolites Collag Replicates eCm components Immunogenicity Halt Replicates ECM component U Chitosan Substitutes for GAG(e.g, hyaluronan) Unproven PTFE polytetrafluoroethylene, UHMWPE, ultra high molecular weight polyethylene PET polyethylene terephthalate; PMMA, polymethyl methacrylate; PSF, polysulfone; PEEK, polyetheretherketone; PDMS polydimethyl siloxane; P-HEMA, poly hydroxyethyl methacrylate; PLA, polylactic acid; PGA
Polyurethane High flex life Uncertain molecular structureRange of mechanical properties property relationships Surface radically different from bulk (high mobility of "soft segments") Low MW contaminants Subject to hydrolysis, oxidation, and calcification Hydrogel P-HEMA Low reactivity Transparent Absorbable PLA/PGA Programmable absorption Metabolizable degradation products Natural Collagen Replicates ECM components Hyaluronan Replicates ECM component Low strength Uncertain biological response to bolus-release of metabolites Low strength Immunogenicity? Unproven Chitosan Substitutes for GAG (e.g., hyaluronan) Unproven PTFE polytetrafluoroethylene, UHMWPE, ultra high molecular weight polyethylene PET polyethylene terephthalate; PMMA, polymethyl methacrylate; PSF, polysulfone; PEEK, polyetheretherketone; PDMS, polydimethyl siloxane; P-HEMA, poly hydroxyethyl methacrylate; PLA, polylactic acid; PGA, polyglycolic acid
8.2 BULK (MECHANICAL) AND SURFACE PROPERTIES 8.2.1 Properties Dependent on Atomic Bonding in the Bulk and Surface of Materials BULK URFACE mechanical Mechanical Elasticity/Plasticity/Viscoelasticity Friction/Lubrication Wear(Abrasive and Fatigue) Chem -Corrosion -Oxidation hydroly zymolysiS Dissolution Bioadhesion Mechanical Chemica
8.2 BULK (MECHANICAL) AND SURFACE PROPERTIES 8.2.1 Properties Dependent on Atomic Bonding in the Bulk and Surface of Materials BULK Mechanical -Strength -Elasticity/Plasticity/Viscoelasticity -Wear (Abrasive and Fatigue) SURFACE Mechanical -Wear (Adhesive) -Friction/Lubrication Chemical -Corrosion -Oxidation -Hydrolysis -Enzymolysis -Dissolution Bioadhesion -Mechanical -Chemical
8.2.2 Bulk( Mechanical)and Surface Properties SURFACE Mechanical Mechanical Chemical Strength Modulus Reactivity (MPa) (G 0-++++)(0-++++) Comment METALS Stainless steel 500-1000200 T Cobalt-Chromium 700 240 Titanium(6A1-4V)900 +++ CERAMICS umina 4000 Compress 259 Tension Calcium Phosphates Hydroxyapatite <900 NA ++R Compress Whitlockite NA ++ Natural Bone apatite 140 +++* Compress POLYMERS Syntheti PTFE ( Teflon) 0.4 +++ UHMWPE 21 PET( Dacron) <40 0++ ++ PMMA 3 PEEK 90 3.6 T C/PSF: C/PEEK 500 60 Composites PDMS 2.4-7 +++ gretna 076.9 P-HEMA 0 PL NA ++++* PGA NA ++++*举 Natural Collagen ++++* hyaluronan NA NA NA Chitosan NA NA NA ++++*举 PTFE polytetrafluoroethylene, UHMWPE, ultra high molecular weight polyethylene Pet polyethylene terephthalate; PMMA, polymethyl methacrylate; PSF, polysulfone; PEEK, polyetheretherketone PDMS, polydimethyl siloxane; P-HEMA, poly hydroxyethyl methacrylate; PLA, polylactic acid; PGA Soluble Absorbable
8.2.2 Bulk (Mechanical) and Surface Properties METALS Stainless Steel Cobalt-Chromium Titanium (6Al-4V) CERAMICS Alumina BULK Mechanical Strength Modulus (MPa) (GPa) 500-1000 200 700 240 900 110 4000 380 259 Calcium Phosphates Hydroxyapatite <900 <100 Whitlockite Natural Bone Apatite 140 18 POLYMERS Synthetic PTFE (Teflon) 14-34 0.4 UHMWPE 21 1 PET (Dacron) <40 PMMA 55 3 PSF 70 2.5 PEEK 90 3.6 C/PSF; C/PEEK 500 60 PDMS 2.4-7 <.01 Polyurethane 1-69 .07-6.9 P-HEMA PLA PGA Natural Collagen Hyaluronan NA NA Chitosan NA NA SURFACE Mechanical Chemical Wear Reactivity (0-++++) (0-++++) Comment + + Tension + + ++ + 0 0 Compress. Tension NA ++* Compress. NA +++* NA +++* Compress. ++++ 0 ++ + +++ + +++ + Tension Tension Composites ++++ 0 NA 0 NA 0 NA ++++** NA ++++** NA ++++** NA ++++** NA ++++** PTFE polytetrafluoroethylene, UHMWPE, ultra high molecular weight polyethylene PET polyethylene terephthalate; PMMA, polymethyl methacrylate; PSF, polysulfone; PEEK, polyetheretherketone; PDMS, polydimethyl siloxane; P-HEMA, poly hydroxyethyl methacrylate; PLA, polylactic acid; PGA, polyglycolic acid. * Soluble **Absorbable
8.3 REACTIVITY: MOLECULAR INTERACTIONS 8.3.1 Surface Modifying/Degradative Interactions: Effects of the body on the biomaterial 8.3.1.1 Water 8.3.1. 1.1 Absorption(e.g, high water absorption by hydrogels is desired but even low water absorption by thermoplastics polymers can adversely affect mechanical properties 8.3. 1.1.2 Hydrolysis(.g, of ester linkage of polymers) 8.3.1.1. 3 Water as electrolyte solution facilitates corrosion of metal 8.3. 1 1.4 Dissolution of certain substances (e. g, calcium phosphates 8.3.1.2 Oxygen 8.3.1.2. 1 Oxide formation(e.g, on metals) 8.3. 1.2.2 Oxidative degradation of polymers 8.3. 1.2.3 Corrosion of metal(e. g, sites of depleted oxygen undergo anodic reaction) 8.3.1.3 Cations and Anions Contributing to Corrosion, Dissolution, and Precipitation (e.g, mineralization/calcification 8.3. 1.4 Enzymes(e.g, enzymolysis of natural polymers such as collagen) Macromolecule Absorption(e.g, lipid absorption) 8.3.2 Molecular interactions with biological molecules: Effects of the biomaterial on the 8.3.2.1 Water 8.3.2. 1 1 Hydrophobic interactions 8.3.2.2 Charge Interactions 8.3.2.2. 1 lonic(primary bonding) 8.3.2.2.2 Secondary 8.3.2.2.2. 1 Hydrogen bonding 8.3.2.2.2.2 Van der Waals interactions
8.3 REACTIVITY: MOLECULAR INTERACTIONS 8.3.1 Surface Modifying/Degradative Interactions: Effects of the Body on the Biomaterial 8.3.1.1 Water 8.3.1.1.1 Absorption (e.g., high water absorption by hydrogels is desired but even low water absorption by thermoplastics polymers can adversely affect mechanical properties) 8.3.1.1.2 Hydrolysis (e.g., of ester linkage of polymers) 8.3.1.1.3 Water as electrolyte solution facilitates corrosion of metal 8.3.1.1.4 Dissolution of certain substances (e.g., calcium phosphates) 8.3.1.2 Oxygen 8.3.1.2.1 Oxide formation (e.g., on metals) 8.3.1.2.2 Oxidative degradation of polymers 8.3.1.2.3 Corrosion of metal (e.g., sites of depleted oxygen undergo anodic, reduction, reaction) 8.3.1.3 Cations and Anions Contributing to Corrosion, Dissolution, and Precipitation (e.g., mineralization/calcification) 8.3.1.4 Enzymes (e.g., enzymolysis of natural polymers such as collagen) Macromolecule Absorption (e.g., lipid absorption) 8.3.2 Molecular Interactions with Biological Molecules: Effects of the Biomaterial on the Body 8.3.2.1 Water 8.3.2.1.1 Hydrophobic interactions 8.3.2.2 Charge Interactions 8.3.2.2.1 Ionic (primary bonding) 8.3.2.2.2 Secondary 8.3.2.2.2.1 Hydrogen bonding 8.3.2.2.2.2 Van der Waals interactions
8.4 BIOADHESION (TISSUE BONDING): PHYSICAL AND CHEMICAL MECHANISMS 8.4.1 Physical/Mechanica 8.4.1.1 Entanglement of macromolecules(nm scale 8.4.1.2 Interdigitation of ECM with surface irregularities/porosity(um scale) 8. 4.2 Chemical 8.4.2. 1 Primary 8.4.2.2.1 Ionic 8.4.2.2 Secondary 8.4.2.2. 1 Hydrogen bonding 8.4 2.2.2 Van der Waals 8.4.2.3 Hydrophobic Interactions
8.4 BIOADHESION (TISSUE BONDING): PHYSICAL AND CHEMICAL MECHANISMS 8.4.1 Physical/Mechanical 8.4.1.1 Entanglement of macromolecules (nm scale) 8.4.1.2 Interdigitation of ECM with surface irregularities/porosity (mm scale) 8.4.2 Chemical 8.4.2.1 Primary 8.4.2.2.1 Ionic 8.4.2.2 Secondary 8.4.2.2.1 Hydrogen bonding 8.4.2.2.2 Van der Waals 8.4.2.3 Hydrophobic Interactions
8. 4.3 Size and time scales for bioadhesion Tissue Mechanism Ime eve of Bonding Constant Measurement(s) mm-cm Organ Interference Fit Weel Radiographic Grouting Agent Months -Years (qualitative) Tissue(B Mechanical Testing growth (quantitative) Chemical Bonding mm Tassi ght Microscopy/Histology Scanning Electron Microscopy (qualitative and quantitative) lm Cell Integrin Days-Weeks Histology Transmission electron nm Protein Secondary Bonding Seconds-Minutes- Immunohistochemisty GAG Hydrophobic Hours-Days Interactions Adsorption Isotherm nm Mineral epitaxy Seconds-Minutes- Transmission Electron crystallites Ionic Bonding Hours-Days Microscopy In vitro Precipitat (quan)
8.4.3 Size and Time Scales for Bioadhesion Size Tissue Mechanism Scale Level of Bonding mm-cm Organ Interference Fit Grouting Agent Tissue (Bone) Ingrowth Chemical Bonding mm Tissue Same mm Cell Integrin nm Protein Secondary Bonding GAG Hydrophobic Interactions nm Mineral Epitaxy crystallites Ionic Bonding Time Constant WeeksMonths-Years Weeks Days-Weeks Seconds-MinutesHours-Days Seconds-MinutesHours-Days Measurement(s) Radiographic (qualitative) Mechanical Testing (quantitative) Mechanical Testing Light Microscopy/Histology (qualitative) Scanning Electron Microscopy (qualitative and quantitative) Histology Transmission Electron Microscopy (qual.) Immunohistochemisty (qual.) Adsorption Isotherm (quan.) Transmission Electron Microscopy In vitro Precipitation (quan.)
8.4.4 Characteristics of Porous Materials for Selected Applications Device Function Pore Geometry/ Purpose Tissue Cell Process(es)Size(um) Orientation Facilitate dermal regeneration/ 3-D)Isotopic or Prevent contraction Dermis Fibroblast Contraction20-120 planar isotropic(?) Facilitate nerve regeneration/Axon elongated Nerve Nerve Migration 1-10 Uniaxial Attachment of bone/Bone Bone Osteoblast Mitosis 100-600 Isotropic ingrowth Synthesis
m 8.4.4 Characteristics of Porous Materials for Selected Applications Device Function/ Purpose Tissue Cell Cell Process(es) Pore Size (mm) Pore Geometry/ Orientation Facilitate dermal regeneration/ Prevent contraction Dermis Fibroblast Contraction 20-120 (3-D) Isotopic or planar isotropic (?) Facilitate nerve regeneration/Axon elongation Nerve Nerve Migration 1-10 Uniaxial Attachment of prosthesis to bone/Bone ingrowth Bone Osteoblast Mitosis Synthesis 100-600 Isotropic
