Properties of Biomaterials PDF

Properties of Biomaterials Master’s in Biotechnology Tandon School of Engineering New York University 09/19/2024 Prof. Giuseppe Maria de Peppo  Properties of (bio)materials BULK SURFACE/INTERFACE MECH...

Properties of Biomaterials Master’s in Biotechnology Tandon School of Engineering New York University 09/19/2024 Prof. Giuseppe Maria de Peppo  Properties of (bio)materials BULK SURFACE/INTERFACE MECHANICAL CHEMISTRY OPTICAL ROUGHNESS physical biological THERMAL ELECTROCHEM properties properties ELECTRICAL CHARGE MAGNETIC CRISTALLINITY Bulk Properties  Bulk properties Mechanical - Describe how materials behave under physiological loads and conditions Optical - Describe the interaction of materials with light Thermal - Describe the ability of a material to store and transfer heat Electrical - Describe how a material conduct electricity when subjected to an electric field Magnetic - Describe the material response to magnetic fields  Types of mechanical loading TENSION COMPRESSION SHEARING BENDING TORSION \ axial loading transversal loading  Young’s modulus The Young’s modulus (E), also called elastic modulus, is a material property that describe how much a material will deform when a load is applied to it. It is essentially a measure of how stiff a material is. CERAMIC Tensile test (uniaxial loading) E METAL Stress (σ) E σ F/A L0 E= = = P ε ΔL/L0 ΔL POLYMER E Strain (ε)  Stress-strain diagram The stress-strain diagram provide information on material strengths, ductility, toughness, and resilience. X CERAMIC (brittle) METAL Stress (Pa) (ductile) X POLYMER (plastic) X Strain (%)  Stress-strain diagram The stress-strain diagram provide information on material strengths, ductility, toughness, and resilience. X CERAMIC (brittle) METAL Stress (Pa) (ductile) X POLYMER (plastic) X Strain (%)  Material strength The strength is a measure of the stress a material can withstand - there are two types: 1) Yield strength: the stress at which the material begins to deform plastically 2) Ultimate strength: the maximum stress the material can withstand before fracturing Ultimate strength X Stress (Pa) Yield strength elastic plastic  Relationship between microstructure and strength MICROSTRUCTURE EFFECT ON STRENGTH MECHANISM Grain Size (Hall-Petch) Increases with smaller grain size Grain boundaries impede dislocation motion Dislocations Increases with more dislocations Dislocations hinder further dislocation motion Phase Composition Increases with multiple phases Second-phase particles block dislocation movement Alloying Increases with solute atoms Solute atoms create lattice distortions hindering dislocations Precipitation Hardening Increases with ne precipitates Precipitates obstruct dislocation motion Texture (Anisotropy) Varies with grain orientation Grain orientation affects dislocation movement in certain directions Inclusions Inclusions generally reduce strength Inclusions act as stress concentrators Amorphous Structure Increases but ductility decreases Lack of long-range order prevents dislocation movement Phase Transformation Signi cant increase in strength Phase transformation to martensite creates a distorted phase Porosity Decreases with increased porosity Pores act as stress concentrators promoting crack initiation fi fi  Toughness Toughness is the ability of a material to absorb energy and plastically deform without fracturing; it can be determined by integrating the stress-strain curve. X Stress (Pa) Toughness Strain (%) Materials that can absorb a lot of energy before fracturing have high toughness Relationship between microstructure and toughness MICROSTRUCTURE EFFECT ON TOUGHNESS Grain Size (Hall-Petch) Smaller grains improve toughness by hindering crack propagation Porosity High porosity reduces toughness, while controlled porosity can enhance it Phase Composition Multiple phases can improve toughness through crack de ection Fiber Reinforcement Fibers improve toughness by bridging and de ecting cracks Crack Tip Blunting Ductile phases or hierarchical structures improve toughness by dissipating energy Crosslinking Low crosslink density enhances toughness, while high density reduces it Graded/Hierarchical Structures Graded and hierarchical structures enhance toughness by distributing stress Crystallinity Semi-crystalline materials are tougher than highly crystalline ones fl fl  Ductility Ductility is the ability of a material to sustain signi cant plastic deformation before fracture; It can be quantitatively assessed using the percent elongation at break. X Stress (Pa) ΔL % EL = X 100 L0 Ductility fi Strain (%)  Resilience Resilience (U) is the ability of a material to absorb energy when it is deformed elastically, and release that energy upon unloading. X Stress (Pa) σy2 U= Resilience 2E Strain (%)  Poisson’s ratio The Poisson's ratio (ν) is a measure of the the deformation (expansion or contraction) of a material in directions perpendicular to the speci c direction of loading. ε transverse v= ε longitudinal Most materials display Poisson’s ratios between 0 and 0.5 (metals ~ 0.3) fi  Tensile strength vs compressive strength TENSION COMPRESSION In ductile materials the tensile strength is similar to the compressive strength In brittle materials the tensile strength is lower than the compressive strength  Buckling under compressive stress Buckling is the sudden change in shape (deformation) of a component under compressive load.  Shear stress and strain Shear stress is a measure of how a material behaves when forces are applied parallel to its surface. F Δx A SHEAR STRESS G=F/A L SHEAR STRAIN θ τ = tan θ or Δx / L FIXED BASE  Bulk modulus The bulk modulus (B) of a material is a measure of its resistance to bulk compression bulk σ F/A V0 B= = = -P bulk ε - ΔV/V0 ΔV 1 Compressibility = B Mechanical loading on femoral implants STRESS TENSOR STRESS PLANES  Fatigue strength and limit The fatigue limit is the stress level below which an in nite number of loading cycles can be applied to a material without causing fatigue failure (crack). The fatigue strength is the maximum stress a material can withstand for a speci ed number of cycles before failure. S-N plot (Wohler plot) stainless steel Ti alloys fi fi Examples of fatigue fractures in vascular stents https://doi.org/10.1016/j.jmbbm.2012.11.006 Examples of fatigue fractures in xation plates https://doi.org/10.1186/s40001-021-00630-7 fi  Creep Creep is the tendency of a solid material to undergo slow deformation while subject to persistent mechanical stresses that are still below the yield strength of the material. Depending on the temperature and stress, different deformation mechanisms are activated: Bulk diffusion (Nabarro–Herring creep) Grain boundary diffusion (Coble creep) Glide-controlled dislocation creep: dislocations move via glide Climb-controlled dislocation creep: dislocations move via climb Harper–Dorn creep: a low-stress creep mechanism in some pure materials  Hardness Hardness is a measure of the resistance to localized plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by pressing or abrasion. Most common test: - Vikers: a diamond pyramid-shaped indenter is pressed into the material with a speci c load - Knoop: a rhombic-based diamond indenter is pressed into the material with a light load - Shore: a durometer is used to measure the resistance of a material to indentation. - Mosh: material’s hardness is determined by its ability to scratch another material - Nanoindentation: a tiny indenter is used to study hardness a very small scale fi  Relationship between microstructure and hardness MICROSTRUCTURE EFFECT ON HARDNESS Grain Size Smaller grains increase hardness by hindering dislocation motion Porosity Higher porosity reduces hardness by creating weak points in the material Phase Composition Hard phases increase hardness; soft phases reduce it Crystallinity Higher crystallinity results in higher hardness; amorphous regions reduce hardness Crosslinking Higher crosslink density increases hardness by reducing polymer chain mobility Fiber Reinforcement Fiber reinforcements improve hardness by distributing stress and resisting deformation Graded/Hierarchical Structures Graded and hierarchical structures enhance hardness through multi-scale optimization Inclusions Hard inclusions increase hardness; soft inclusions reduce it  Optical properties Transparency - Ability of a material to transmit light without significant scattering or absorption Refractive Index - A measure of how much light is bent or refracted when entering a material Absorption - Ability of a material to absorb light rather than transmitting or reflecting it Scattering - The redirection of light by small particles or irregularities within a material Fluorescence - Emission of light by a material after it has absorbed electromagnetic radiation Photostability - The ability of a material to maintain its optical properties under exposure to light over time  Interaction of light with matter TRANSMISSION REFLECTION Light Source ABSORPTION RIFRACTION SCATTERING FLUORESCENCE Material  Light refraction and refractive index The refractive index (n) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium normal speed of light in vacuum n= speed of light in medium Snell’s Law  Refractive index in contact lenses Soft contact lenses - Example: hydrogel lenses made from materials like hydroxyethyl methacrylate (n = 1.42) Rigid gas permeable contact lenses - Example: lenses made from materials like fluorosilicone acrylate (n = 1.46 to 1.49) Hard contact lenses - Example: lenses made from polymethylmethacrylate (n = 1.49 to 1.50)  Types of contact lenses Contact lens Intraocular lens Corneal implant Surface Properties  Surface properties Wettability - Hydrophilic, hydrophobic, superhydrophobic Chemistry - Metals, ceramics, polymers, composites Surface charge - Negative, positive, zwitterionic Texture (roughness/topography) - Meso-, micro- and nano-features Crystallinity (polymers) Electrochemical - conductivity, ion permeability, capacitance, redox reactivity  Material surface Surface is the zone where the structure and composition differs from the average bulk (2D interface between the material and the surrounding environment) Main characteristics: 1) Surface have unique reactivity 2) Surface readily contaminate 3) Surface molecules can exhibit considerable mobility (polymers)  Surface energy and wettability Surface energy is assessed via contact angle (θ) measurement. It quanti es the wetting of a solid by a liquid. It is de ned geometrically as the angle formed by a liquid at the three-phase boundary point where a liquid, gas, and solid intersect SURFACE TENSION HYDROPHILIC SURFACE HYDROPHOBIC SURFACE Young’s Law solid solid If contact angle is low the surface shows good good wettability, adhesiveness, and high surface energy fi fi  Surface mobility (reversal) in different media Poly(2-hydroxyethyl methacrylate) pHEMA AIR CH3 CH2 C C=O CH2 CH2 WATER OH Surface roughness and topography Surface roughness and topography Wenzel model Cassie-baxter model  Surface wear mechanisms TYPE DESCRIPTION Abrasive Harder materials or particles scratch the surface of a softer material Adhesive Two surfaces slide over each other and material is transferred from one surface to the other Fretting Caused by repeated small amplitude cyclic motion between two surfaces leading to material degradation Fatigue Caused by repetitive stress cycles leading to crack formation and propagation Corrosive Wear that involves electrochemical reactions at the biomaterial surface Erosive Caused by the impact of particles or uid jets against a surface, leading to material loss over time Oxidative Material degradation due to oxidation processes on the surface fl  Implant wearing SURGICAL MECHANICAL IMPLANT PROCESS STRESS FIXATION PATIENT ANATOMICAL SUBOPTIMAL FACTORS LOCATION DESIGN Affatato, Saverio. “Wear of orthopaedic implants and arti cial joints.” (2012) fi  Implant wearing WEAR PARTICLES Consequences: in ammatory response, brous encapsulation, implant loosening, implant rejection fl fi  Example of implant wearing Worn retrieved PE tibial tray Worn surface of retrieved PE cup  Corrosion Corrosion is a slow electrochemical process which degrades metals overtime. It consist of oxidation and reduction reaction occurring at implant surface. e- METAL METAL 1 METAL 2 SELF-CORROSION GALVANIC CORROSION corrosion rate Localized corrosion and metal release (toxicity) Localized corrosion and metal release (toxicity) MECHANICAL FATIGUE FRETTING STRESS CREVICE INFLAMMAT. EFFECTS REACTIONS GALVANIC COMPLEX SHIELDING EFFECTS FORMATION EFFECT Abdelilah Asserghine, et al.npj Materials Degradation, 6(57), 2022 Localized corrosion and metal release (toxicity) Localized corrosion and metal release (toxicity) M+ M+ M+ e- M+ e- e- M+ M+ e- M+ M+ e- e- e- M+ M+ M+  Localized corrosion and metal release (toxicity) M+ M+ M+ e- M+ e- e- M+ M+ e- M+ M+ e- e- e- M+ M+ M+ Consequences: cytotoxicity, in ammation, bone resorption, allergic reaction, respiratory symptoms, anaphylaxis fl Examples of corrosion of dental implants  Adsorption of proteins The surface energy determines biomaterial interaction with molecules Adsorbed proteins and ions influence the interaction of biomaterials with the body Cells do not interact with biomaterials, unless they are functionalized to do so Protein adsorption is important for a variety of processes: - Clot formation - Foreign body response - Inflammation and immune response - Vascularization - Bioactivity and tissue growth - Bacterial colonization  Factors in uencing protein adsorption Protein-Related Factors Surface Characteristics Environment Size and structure Chemistry pH Isoelectric point Wettability Ionic strength Hydrophobicity Texture Temperature Concentration Functionalization Vroman effect fl Q&A