Composite Biomaterials

composite material

-material system composed of two or mor physically distinct phases whose combination produces aggregate properties that are different from those of its constituents

-two or more chemically distinct materials which when combined have improved properties over the individual materials

-natural or synthetic

-can be particle reinforced, fiber reinforced, structural

terminology/classification

continuous phase (matrix)

-purpose to transfer stress to other phases, protect phases from the environment

-classification: MMC, CMC, PMC (metal/ceramic/polymer matrix composites)

dispersed phase (filler)

-purpose to enhance matrix properties

-classification: particle, fiber, structural

composite structural organization

affected by concentration, size, shape, distribution, orientation of dispersed phase

benefits by type

-CMCs have increased toughness

-PMCs have increased Young’s modulus over density (E/p)

-MMCs have increased creep resistance

applications

primary motive of varying the type and distribution of reinforcing phase of the composites is to obtain:

-suitable mechanical and biological properties

-optimizing the structure and performance of biomedical devices

-improvement of the device with surrounding tissue

-composites offer greater potential of structural biocompatibility than homogeneous monolithic material

advantages

polymer composites

-low modulus but high strength, suitable for orthopedic application

metal composites

-no corrosion, release of allergenic metal ions (i.e. nickel or chromium)

-high fracture toughness

-high resistance against fatigue failure

dentistry: better aesthetic characteristics, more economical than metal

particle-reinforced

-ex. concrete: gravel + sand + cement

-reinforced concrete: reinforced with steel rebar or remesh → increases strength even if cement matrix cracked

-prestressed concrete: remesh under tension during setting of concrete, tension release then puts concrete under compressive force → concrete much stronger under compression, applied tension must exceed compressive force

fiber-reinforced

-____ themselves are very strong

-provide significant strength improvement to material

-ex. ____-glass

-continuous glass filaments in a polymer matrix

-strength due to fibers

-polymer simply holds them in place and environmentally protects them

fiber materials

whiskers

-thin single crystals, large length to diameter ration

-graphite, SiN, SiC

-high crystal perfection, extremely strong, strongest known

-very expensive

fibers

-polycrystalline or amorphous

-generally polymers or ceramics

-can be aligned continuous; discontinuous (aligned vs. random)

-ex. Al2O3, aramid, E-glass, boron, UHMWPE

wires

-metals: steel, Mo, W

structural composites

stacked and bonded fiber-reinforced sheets

-balanced, in-plane stiffness

-stacking sequence: 0/90 or 0/45/90

sandwich panels

-low density, honeycomb core

-benefit: light weight, large bending stiffness

-face sheet, adhesive layer, honeycomb, adhesive, face sheet

hard tissue applications (bone plates)

-rigid internal fixation of bone

-common mats: carbon fiber fabric and epoxy matrix, carbon/polyetheretherketone (PEEK) and material system

-fully resorbable bone plates have limitations because they have low strength and low modulus

-needs further work to create bone plates that are synchronized in terms of resorption of the plate and healing rate of bone

hard tissue applications (bone fracture repair)

-as simple as bandage (bandage is composite)

-casting material for bandage incl woven cotton fabrics, plaster of Paris

-casting material include fiber glass and advanced water activated polyurethane resin system

hard tissue applications (intramedullary nail)

-used to fix long bone fractures i.e. fracture of femoral neck

-inserted into intramedullary cavity of the bone and fixed in position using screws, rods, pins

-most successful application of bioresorbable implant

-ex. glass fiber/PEEK

-also used in total hip replacement (THR) and total knee replacement (TKR) by using reinforced UHMWPE with carbon fiber or UHMWPE itself

hard tissue applications (dental applications)

-dental post used to reinforce the remaining tooth structure on which the core and crown are built

-ex. short glass fiber reinforced polyester and carbon fiber reinforced epoxy composites

-artificial tooth replacing tooth permanently (ex. carbon fiber/carbon)

-dental cement

hard tissue applications (bone cement)

-polymethyl methacrylate (PMMA) AKA ____, widely used for implant fixations in various orthopedic and trauma surgery

soft tissue applications (bulk space filler)

-used to restore cosmetic defects up to aesthetically satisfactory condition (ex. lip filler)

-also used for articular cartilage replacement due to osteoarthritis

-ex. woven carbon fiber fabric

soft tissue applications (artificial tendon and ligament)

-tendon-strong fibrous band of tissue that extends from a muscle to periosteum of the bone

-ligament: connective tissue band that links bones in vicinity of every synovial joint

-ex. reinforcing hydrogel matrix poly (PHEMA) with helically wound rigid PET fibers

artificial leg

-consist of socket, shaft, foot

-ideally lightweight, corrosion resistant, fatigue resistant, aesthetic and easy to fabricate

-thermoset polymer composites reinforced with glass, carbon, Kevlar fibers are common mats

medical instrumentation

-moving table for MRI or CT-carbon fiber reinforced polymer composites

-others: surgical clamp, x-ray film cassettes