MSE/BMED 4751 Handout # 1 Guidelines for reviewing concepts from Chpt 1.4 on your own

Classification of materials used as biomaterials (Chpt 1.4)

Class Type of 1o Bonding

Composition & Structure Properties Processing Approaches* Examples

Metals

metallic

Electropositive atoms (3 or fewer valence electrons -> “extra e- donated to bulk mat’l)

Generally polycrystalline

Strong, but malleable (can be hammered) and

Ductile – can be drawn or bent

Tough – can absorb energy of large applied loads without fracture occurring

Casting – involves a Liquid (L)→ Solid (S) phase transformation

Fe,

Ti – joint replacements, bone grafts

Ceramics

Mostly ionic

Stoichiometrically balanced cations & anions (ionic solid)

Polycrystalline or noncrystalline/amorphous (glass)

Hard, but usually not tough → brittle (affects failure mechanism and requires smaller loads)

Often processed as a particle suspension (L+S) – e.g. slip casting – then allowed to dry to form solid

Bioactive glass (orthopaedic & dental coatings)

Polymers

Typically covalent

Typically organic (contains carbon)

Chains of atoms

e.g. -(CH2-CH2)n-

repeat unit & degree of polymerization, n

Generally amorphous, but can be crystalline or otherwise “organized” (self-assembly)

Often flexible (elastomers especially)

Often fairly tough

Some are biodegradable

Extrusion

Casting – e.g. cast “slabs” of hydrophilic polymer network swollen in water (hydrogel)

Synthetic PEG

Poly(lactide-co-glycolide)

PMMA

Advantage Large quantities, sterilization, tailored properties are possible

Disadvantage Need to remove toxic, left-over monomer (starting material)

Naturally-derived (biologically active, but not viable alone)

Derived outside body (e.g plant-derived alginate)

Proteins (e.g. collagen, fibrin)

Advantages Can mimic biological environment

Disadvantages xenogeneic (“foreign derived” or originating from a different species) effects of animal-derived products can cause undesirable immune response

See Tables 1.2, 1.3, & 1.4 for other examples of biomaterials & their applications *Note: We will not focus on Processing Approaches in this course.