Instructive coatings for biological guidance of bone implants

• Surface modifications enhance the performance of load-bearing implants.
• Coating compounds should actively participate in the biological processes.
• Especially compromised health conditions require optimized surface properties.

Synthetic inorganic and organic materials have been extensively investigated in the field of bone regeneration in an attempt to mimic the composition and structure of the extracellular matrix (ECM) of bone tissue with the ultimate aim of generating suitable synthetic bone substitute materials and modifying the surface of bone implants. For load-bearing applications, bone implants are generally made of a bioinert metal with appropriate mechanical properties and a modified surface (i.e. roughened, coated or a combination thereof), to enhance the surface biocompatibility and osteoconductivity. Currently, biomaterials research is evolving from the use of bioinert and biologically passive implants toward interactive implants that stimulate tissue regeneration. Therefore, surface physico-chemical properties of bone implants need to be optimal and capable to biologically instruct and stimulate the regeneration of bone tissue.This review is focused on surface modification approaches in the field of bone regeneration for load-bearing bone implants with emphasis on the use of inorganic and organic coating compounds that actively participate in the biological processes that occur upon implantation. The review shows that appropriate surface modifications can be helpful to achieve desired tissue responses in healthy as well as compromised conditions.