Composites Flashcards
What are composites?
• Materials composed of more than one base material – usually,
matrix and reinforcement
Reinforcement may consist of long or short fibres, platelets,
particles etc
• Long fibres: (i.e. carbon fibre / glass fibre) spars/masts
• Short fibres: injection moulded tennis rackets
• Platelets: some types of car filler, resin ornaments.
What are the biomedical applications of composites
Bradley Hip
• Consists of a metal core with
CFR-PEEK outer layer
HAPEX
• HAPEX is an artificial bone analogue composite
made from HA (hydroxyapatite) and polyethylene
• HAPEX is used for orthopaedic implants like
tympanic (middle ear) bones
What are Matrix Systems?
Polymeric Matrices (bioresorbable and non-bioresorbable)
Mostly thermoplastics
- Polysulfone
- Poly-ether-ether-ketone (PEEK)
- Polyethylenes (UHMWPE and HDPE)
- Poly-tetra-fluoro-ethylene (PTFE)
- Poly(methylmethacrylate)(PMMA)
- Polylactic acid (PLA)
- Poly(lactic-co-glycolic acid) (PLGA)
- Polycaprolactone (PCL)
- Hydrogels
Fibre Reinforcement
Length is much greater than cross-section
• Much more mechanically effective than particles
• Usually anisotropic due to fibre orientation
• Customisation to match application
Applications in Biomaterials:
• Arterial prostheses
• Intervertebral discs
• Fixation plates and Nails
Reinforcing Systems - Polymer fibres
Aramid (Aromatic Polyamide, Liquid Crystal Polymer)
• Kevlar®, Nomex®, (both by Dupont)
• Twaron® (Teijin/Twaron, Japan)
• Light, stiff, strong
• Absorb moisture (a disadvantage)
• Poor compressive strength
• Applications: Dentistry, ligament prostheses
Reinforcing Systems – Carbon Fibre
- Lightweight, High Strength, Radiolucent
- BUT – Poor Shear Strength
Examples:
• Short fibre Carbon reinforced UHMWPE in orthopaedic applications
• Aimed to increase longevity of bearing surfaces
• Osteolysis and failure of tibial inserts in knee prostheses
Scaffolding device for ligament repair
• Performed poorly, permanent wear debris in joint
Reinforcing Systems - Polymer fibres - UHMWPE
UHMWPE
• Spectra (Honeywell), Dyneema (DSM, Heerlen), Toyobo
(Toyobo, Japan)
• High modulus, strength, light weight
• Do not absorb water
• BUT adhere poorly to matrix, hence performance is not
fully realised
• Applications: Dentistry (reinforcing acrylic resins),
intervertebral disc prostheses, ligament augmentation
Reinforcing Systems - Polymer fibres - PET
PET (Poly-ethylene-terephthalate) • Dacron® • Used as fabrics for arterial grafts in cardiovascular surgery • Proposed applications • Artificial tendons and ligaments • Ligament augmentation (fibres alone or as composites) • Soft tissue prosthetics • Intervertebral discs • Plastic surgery
Reinforcing Systems - Polymer fibres - Biodegradable Polymers
Biodegradable polymers
• PLA, PGA, and co-polymers
• Used as reinforcement and self – reinforcement (due to variation
in crystallinity and molecular weight)
Applications
• Ligament reconstruction (as fibres)
• Scaffolds for tissue engineering (as fibres reinforcing tissues)
• Biodegradable intramedullary pins and plates (as composites)
• Biodegradable scaffolds for bone regeneration
Reinforcing Systems - Ceramics
Usually as particulate reinforcement
• Calcium Phosphates (tri-calcium phosphate and hydroxyapatite)
• Bioactive (integrate with tissue)
• HAPEX (HA-PE composite, marketed by Smith & Nephew)
• Also used: Al, Zn phosphates, Bioglass and glass-ceramics,
bone mineral
Reinforcing Systems - Glasses
Commercial glasses (S-glass, E-glass fibres)
• High strength/weight ratio
• Good dimensional stability,
• Resistant to heat, cold, moisture, corrosion
• Low cost
Applications
• Orthopaedics (hip stems, with carbon fibre)
• Dentistry
Reinforcing Systems - Glasses - Bio-Glass
Bio-Glass (45S5 glass)
• Bioactive (takes years to resorb)
• Composed of SiO2 Na2O, CaO and P2O5
Advantages
• Highly bioactive
• FDA approved and commercially available
• Tensile modulus similar to bone (30-35 GPa)
Disadvantages • Mechanical weakness (UTS 40-60 MPa) • Low fracture resistance • Limited to low load applications • Also, S53P4 available and clinically used
Reinforcing Systems - Glasses - Resorbable Phosphate-based glass
Resorbable Phosphate-based glass
• E = 48 GPa (compare to 72 GPa for s-glass)
• UTS = 500 MPa (4 GPa for s-glass)
• Used as reinforcement for bioresorbable polymers
to produce fully resorbable composites
Dental Composites
• Dental composite resins have replaced both types of materials used in anterior and posterior teeth restoration
• Silver and gold amalgams were used for posterior teeth restoration
• Anterior teeth used to be restored with acrylic resins and synthetic cements which were cosmetically more attractive than the metal amalgams but had a shorter life
• The inclusions were normally barium glass or silica. The inclusions
improved the stiffness and wear resistance
• The matrix was an additional reaction product of bis (4-hydroxyphenol), dimethylmethane, and glycidyl methacrylate called BIS-GMA
Dental Composites - Notes
• The use of colloidal silica allowed the composite to be polished,
which reduced wear and plaque accumulation
• However it can only be used at low wt % compared with other fillers
since it tends to increase the viscosity of the mix too much
NB:
• A 75 wt% filler corresponds to approximately 50% volume
• Notice the contraction…this is an issue for all dental fillings leading to problems associated with saliva and bacteria at the interface edges
• Other problems include creep during the first three hours when the stiffness increases by a factor 2.5 – 4. The other major problem is wear
