Chapter 4 - Materials for Bioprinting

Biomaterials

non-viable materials typically used in therapeutic and diagnostic systems that are in contact with tissue or biological fluids

Biomaterials can be categorized into

polymers (natural and synthetic), ceramics, metals (alloys), glasses, carbons and composites comprised of various combinations of the above material types

Biomaterial characteristics

nontoxic and noncarcinogenic, chemically stable and resistant to corrosion, able to sustain large and variable stresses in human body, able to shape/manufacture into intricate geometries → fabrication, form, function, integration with body

requirements of biomaterials in tissue engineering

formability, biocompatibility, suitable mechanical properties, biodegradability, biodegradation product, bioactivity, sterilization considerations

formability

bioprinting techniques highly specialized technologies in terms of material formability - each technique requires specific material characteristics such as viscosity, shear-thinning property, response and transition time, sol-gel transition stimulus

biocompatibility

critical property for biomaterial - quality of not having toxic or injurious effects on biological systems, ability of material to perform with an appropriate host response in a specific application

biocompatibility - not an intrinsic property

biocompatibility of material refers to specific application in which material used, no material definitely biocompatible, property is process-dependent, no FDA-approved materials

biocompatibility - continuously perform a function

material implanted in human body is expected to perform a specific function as opposed to staying there, also considered as ability of material to continuously perform a function

biocompatibility - host response

appropriate/acceptable host responses allowed, which indicate biocompatible material not necessarily required to generate no response

suitable mechanical properties - metal

primary metallic strength attributes include tensile yield, modulus of elasticity, ultimate strength and fatigue endurance; other mechanical properties should also be addressed for specific applications

suitable mechanical properties - polymer

principal mechanical properties are tensile, fatigue and creep strengths as well as modulus; excessive wear can result in premature mechanical failure

biodegradability

ideally, material degradation rate is synchronized with rate of tissue regrowth so that scaffold will be remodeled and replaced by new cells and extracellular matrix

degradation-absorption rate influenced by several factors

degree of crystallinity, hydrophilicity of polymer backbone, volume of porosity, surface area, presence of catalysts

biodegradation product

degradation products of biodegradable polymers are known as largely non-cytotoxic, however for some polymer, fast degradation of polymer leads to local acidification which is detrimental for cell viability and migration

bioactivity