Genetic potential of interfacial guided osteogenesis in implant devices

Abstract

The purpose of this review is to summarise recent advances in the design and composition of bioactive surface layers of implantabile biomaterials, and thus the genetic potential of osteoprogenitor cells to recognize and respond to these diverse implanted biomaterials. Changes applied to a biomaterial's surface, in general, could improve its biocompatibility, osseointegration and durability properties, which are required for long-term implantation in the living body. In this review, the implant-bone interface was evaluated and interpreted on the basis of osteoblast cell cultures, i.e., on the genetic potential of osteoblasts to express different phenotype markers depending on the type of biomaterials used. The interface formed by in vitro-grown osteoblasts may be used to identify components of the in vivo implant-bone interface. Over the years, a large number of implant systems consisting of many different biomaterials have been introduced in dentistry and orthopaedics. This paper discusses the performance of currently used metals and other biomaterials, by focusing on the events which occur immediately after implantation and on their impact on the bone-implant interface. The review demonstrates that continuous improvements in composition, surface modality and design of implants may benefit osseointegration and clinical longevity of such implants. No load-bearing conditions or clinical status are discussed. Titanium (Ti) and calcium phosphate ceramics are regarded as the most biocompatible synthetic substances known to be used in hard tissue implantation. These biomaterials are osteoconductive, and do not induce ectopic bone formation. Nonetheless, they provide a physical matrix which is suitable for the deposition of new bone and may guide both the growth and extension of the bone. Comparative investigation evaluated that Ti implant systems appear to be apposed by more bone than ceramic systems, although alternatives concerning the type of Ti alloy and bioactive surface layer engineering, generate extremely diverse osseointegration results. Manufacturers have created an extensive range of inorganic or ceramic coatings on Ti implants in order to achieve better bone healing and osteoconduction. Biologically active molecules, added to the implant surface, represent breakthroughs in guided interfacial osteogenesis. This methodology offers an enormous potential of genetic controlling and promoting osteogenesis. The bone growth factors are not fully understood, but most researchers agree that the contact between the bioactive surface layer of the implant and bone is not static but dynamic and that the above factors may maximise the implant osseointegration.