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Synthetic bone grafts (Metal foams (No bioactivity and so no regeneration,…
Synthetic bone grafts
Metal foams
Tailored porosity to minimise stress shielding
Good cyclic loading
Used in load-bearing applications
Spinal fusion cages
No bioactivity and so no regeneration
Ti + NaOH -> TiOH on surface
Ti surface is usually TiO2
If placed in supersaturated solution HCA forms
Coating not bioactivity
Polymer composites
Problems
Polymer matrix may mask bioactivity
Difficult to match degradation rate
Bonding?
Polymer breaks down and releases HA
HAPEX
HA + HDPE
Blending and coextrusion
Not bioresorbable
Fibrous encapsulation
No structural composites are available
General
Requirements
Biocompatible & bioactive
No immunorejection
No infection
No formation of fibrous capsule
Easily produced and sterilised
Mechanical properties similar to host tissue
Ideally
Act as a template for tissue growth in 3D
interconnected macroporus network
Vascularisation, tissue ingrowth and nutrient delivery
Bond to host tissue without formation of scar tissue
Resorb at the same rate as repair
Provide signals to cells
Able to be shaped to fit a range of defect geometries
Upscalable for mass production
Applications
Spinal Fusion
Non-union of fractures
Repair after tumour removal
Maxillofacial defects
Cranioplasty
Bioactive ceramics
Weak to cyclic loads
Non-load bearing sites
Bone graft replacement
Bone graft extension
Cage filler (spinal fusion)
Manufacture of scaffold
Corraline HA
97% CaCO3
Highly porus
Specific species
Correct composition and structure
Approved by governing bodies
Difficult to reliably source
Hydrothermal conversion to HA
260 C
15,000 psi
Ammonium phosphate
Scaffold sintering
Porogens mixed into powder
Usually PMMA spheres
Control of pore size
Fraction of solid in slurry
Volume fraction of porogen
Size of porogen
Limited by particle size
Difficult to get good distribution
Poor interconnection
Simple process
Polymer foam reticulation
Polymer foam + ceramic slurry
Heated to burn out polymer
Sintering to form ceramic foam
Problems
Sifficult to sinter well
Hard to scale
Slurry gets stuck in the foam
Hollow structure (weak)
Gel-cast foaming
Process
Vigorous agitation
Surfactant stabilises bubbles
Pour into moulds
Polymer curing (in-situ polymerisation)
Drying and sintering (burns out polymer)
Particle slurry + polymer gelling agent + surfactant
Problems
Difficult to control
Not reproducable
Product sold in 3mm granules
Could use 3D printing?
Bioactive glasses
Small sintering window
Cannot be made porus
New solution required
Crystallisation occurs readily with low silica
Low silica is needed for bioactivity
Add network modifiers (Sr, K, Mg)