Incorporation of growth factors into medical devices via biomimetic coatings

Abstract

Orthopaedic and dental surgeons are fully aware of the need for implants to bond well with the surrounding living bone if long-lasting clinical success is to be achieved. For example, well-bonded hip implants have a 10 year failure rate, which is lowered fivefold if bonding is poor or absent. The techniques that are currently available to impart implant surfaces with the desired osteoconductive properties are essentially limited. To overcome the inherent difficulties, we have developed a 'biomimetic' coating process. By this means, implants with complex surface geometries, such as porous spinal implants, can be furnished with a bone-bonding surface. Furthermore, these coatings can be rendered osteoinductive as well as osteoconductive (by incorporating osteogenic agents). Using this facility, we have induced bone formation at an ectopic site in rats, and have accelerated osseointegration (bone bonding) at an orthotopic dental site in adult miniature pigs. Our preliminary results indicated that these osteoinductive dental implants bond with surrounding bone within one week instead of the usual three weeks. We believe that surfaces coated with biomimetic coatings into which osteogenic growth factors are incorporated hold great potential for use in clinical orthopaedics and dentistry.

Advances in Biomimetic Apatite Coating on Metal Implants

“…The incorporated BMP-2 which retained its biological activity was gradually released from the coating and induced the formation of bone tissue not only upon the implant surface but also within its immediate surroundings(Y. Liu et al, 2006). Apart from coating implants with apatite in vitro, the bioactive implants which could induce bone-like apatite in vivo also had the ability to induce ectopic bone formation.…”

“…By this technique, biologically active molecules can be coprecipitated with apatite crystals onto metal implants rather than being merely adsorbed on its surface(Y. Liu et al, 2001Liu et al, , 2003Liu et al, , 2006Wen et al, 1999). Therefore, the biomimetic apatite coating can be used as the carriers for biologically active molecules.…”

“…Its biological performance will be described later(Y. Liu et al, 2006). Uchida et al immobilized laminin on titanium by immersion the AH -treated titanium in a calcium phosphate solution containing laminin at 25°C for 1 day .…”

“…After implantation in vivo, the degradation of these biomimetic coatings would lead to the gradual exposure and release of incorporated molecules from these coatings rather than in a single rapid burst, which also renders the biomimetic coatings of great potential value as a drug-carrier system in orthopedics(Y. Liu et al, 2006). Liu et al first biomimetically precoated titanium alloy implants with a thin and dense layer of calcium phosphate, and then incubated in a supersaturated solution of calcium phosphate with bovine serum albumin (BSA) at various concentrations under physiological conditions for 48 h. BSA successfully coprecipitated with the Ca 2+ and PO 4 3-ions on the surface of Ti alloy implants, and the release of this protein from the biomimetic coatings took place gradually over the span of several days.…”

Evaluation of PLAGA/n-HA Composite Scaffold Bioactivity in vitro

“…In particular, RMSCs proliferation on PLAGA/n-HA scaffolds was accelerated in the first week of cell culture. Since it has been well documented that hydroxyapatite had extremely high affinity to a diverse range of proteins and other biomolecules, the cell proliferation of RMSC might be stimulated by the enrichment of proteins and growth factors by n-HA on scaffold surface [29,30]. We also found that the osteogenic differentiation of RMSCs on the composite scaffolds was largely enhanced as shown in Figure 3B and C. n-HA trapped in PLAGA microspheres might release certain amount of calcium ions before they reach equilibrium with the local microenvironment, this might play an important role during RMSC differentiation.…”