Table 4: Current strategies for growth factor delivery in bone tissue engineering and the associated advantages and drawbacks.

Delivery systemRelease characteristicsAdvantagesDrawbacks

Supercritical CO2Sustained releaseGood encapsulation efficiency
Very high bioactivity retention
Solvent less formation
Limited available scaffold conformations suitable for bone tissue engineering
Complex equipment requirement for manufacture

ElectrospinningVarying releaseRapid fabrication of scaffold
Large number of polymers available for electrospinning
Limited available scaffold conformations suitable for bone tissue engineering
Requires organic solvents which can denature GFs and reduce bioactivity
Limited information on encapsulation efficiency
Limited information on release characteristics

Nano/microspheresInitial burst then slow sustainSeveral techniques available for fabrication
Easy to combine with other scaffold fabrication techniques
Limited available scaffold conformations suitable for bone tissue engineering
Requires organic solvents which can denature GFs and reduce bioactivity
Classical formation techniques have poor encapsulation efficiency

HydrogelsShort-term releaseCan be injected into wound sites (in situ formation)
Good encapsulation efficiency
Solvent less formation
Easy to combine with other techniques
Rapid degradation of most commonly used hydrogels
Unsuitable mechanical characteristics for bone tissue engineering

Functionalisation of surfaces,
for example, polyelectrolyte systems
nanocoating, and so forth.
Short-term releaseCan be applied to scaffolds with good mechanical properties
High bioactivity retention
Technique is time intensive
Alters existing surface chemistry