Table 3 Key findings and key insights from different methods of loading growth factors with different materials

Physical adsorption

Scaffold

Hydrogel

Simple, fast, with a noticeable burst of release

Simple, fast, with sudden release

Growth factors are exposed and their activity is susceptible to environmental influences and uncontrolled release rates

Growth factors are not directly exposed, they are more active, and the sustained-release rate is poorly controlled

Chemical bonding

PCL

PVA-Tyr

Poly(oligo (ethylene glycol) methacrylate) (POEGMA) modified PCL was covalently bound (amide bonded) to growth factors

Extensive covalent binding (bisphenol bonding) to growth factors

Chemical modification is required to provide the active moiety first, and the effect on growth factor activity is unknown

Multiple growth factors can be achieved by combining multiple growth factors to achieve multiple growth factors together for slow-release therapy

Microsphere encapsulation

Gelatin

PLGA

Chitosan

Biocompatible and can be loaded with a wider range of growth factors depending on the charge carried by the A and B types

Long sustained release time. Degradation produces acidic substances that produce undesirable effects

It can be made into nanoscale microspheres, but 80% of it is released abruptly in the first 4 h

The combination of types A and B allows for the co-retardation of multiple growth factors

Neutralisation of acids in combination with alkaline materials, e.g. simultaneous use with MnO2 microspheres

It can be combined with PLGA, etc. to prepare novel composite microspheres