Table 1.

Benefits and drawbacks of materials used for bone repair

Material	Sub-class	Benefits	Drawbacks	Novel developments
Metals	Stainless steel, titanium	High load bearing	Permanent fixture Stress-shielding Risk of infection Secondary surgery to remove implant Limited osseointegration	Surface coatings Nanopatterned surfaces
	Magnesium	High load bearing Biodegradable	Rapid dissolution of metal Implant failure Risk of infection	Addition of other metal ions
	Zinc	Biocompatbile Antibacterial	Low mechanical properties Releases large zinc ions harmful to cells	Porous structures Calcium phosphate coatings
Ceramics	Bioglass	Bioactive Osteoconductive Integration with host bone Antibacterial	Brittle Low fracture toughness Poor osteoinductivity	Metal doping
	Calcium phosphates	Osteoinductive Resorbable Injectable as a cement, shapeable	Brittle Slow resorption Limited mechanical strength	Metal doping Addition to polymers as coatings
	Silica nanomaterials	Low cytotoxicity High porosity High mechanical strength Biocompatible Tunable pore size Drug delivery vehicles Osteogenic Promotes vasculature	Risk of infection Crystallinity impacts biocompatibility Aggregation of nanoparticles High concentrations can lead to particle setting and cytotoxic effects Concentration limits Risk of infection	Surface modifications Combination with polymers
Polymers	Polylactic acid (PLA)	Biocompatible Biodegradable Easily 3D-printed into specific shapes and porosities Shorter degradation time than PCL (6 + months) High mechanical properties	Acidic degradation products may cause inflammation Risk of infection	Coat with calcium phosphate Blend with multiple polymers
	Polycaprolactone (PCL)	Flexible Hydrophobic Biodegradable Biocompatible Easily 3D-printed into specific shapes and porosities Shape-memory fabrication	Low mechanical stiffness Long degradation times Acidic degradation products High transition temperature for shape actuation Risk of infection	Blend with multiple polymers Use different polymer conformations (star)
	Collagen	Tunable pore size Biocompatible Sequester growth factors easily	Low mechanical properties Disease transmission risk Need mineral to induce osteogenesis Risk of infection	Reinforce with stronger materials Collagen derived from marine sources Add calcium phosphate
	Chitosan	Antibacterial Anti-inflammatory	Poor mechanical properties Low cell attachment Poor osteoconductivity Need mineral to induce osteogenesis	Reinforce with stronger materials Modify fabrication (granular hydrogels)