Types of Surface
While manufacturing of the prosthetic implants, the imparting required properties to their contact surfaces is hardly not more important than their construction (geometry). The characteristics of outer surface of the implant directly contacting the living tissue (mainly the bone) such as the degree of their roughness and porosity, chemical, biological purity (sterility) determine its capability forbiological integration with the osseous tissue (osseoconductivity) to a great extent.
At present, there is a number of technologies assuring attainment of implant surface having required osseoconductivity. Only such technologies, which now are the state-of-the-art for the attainment of SLA or RBM surfaces on titanium blanks from among them, are practiced at our ABM Technology enterprise.
A combination of sandblasting and acid etching of prosthetic implant underlies both technologies (SLA and RBM). The difference between them lies in the technological details, however leading to the result significantly differing in quality.
At the initial stage, SLA technology (Sand-blasted, Large grit, Acid-etched) provides for the attainment of the macroroughness over the contact surface of metal (titanium) implant. This macroroughness is attained by processing of product with the sandblasting equipment with hard grains of corundum (Al2O3). The next stage is its short-time acid etching with heated mixture of hydrochloric (HCl) and sulfuric (H2SO4) acids resulting in formation of the micropits 2 to 4 µm deep on its surface. This contact surface is not yet considered as the microporous one failing to give sufficient space for growth of a living osseous tissue. Moreover, the remnants (contaminants) of corundum particles having a bad effect on the quality andspeed of osseointegration occur on it. The use of hydrofluoric (HF) or nitric (HNO3) acids for etching results in the attainment of really microporous structure (the pits up to 5 to 10 µm deep) are formed, but the macroroughness attained while sandblasting is partially washed (“becomes blurred”). According to research, SLA surface demonstrates significantly better osseoconductivity as compared with the other implant processing technologies (such as titanium plasma spray, mechanical milling, and hydroxyapatite coating), but allows for RBM surface in this parameter.
For the attainment of required macroroughness, RBM technology (Resorbable Blast Media) provides for the initial sandblasting of titanium implant with hard grains of tricalcium phosphate (Ca3O8P2). This material is characterized by a high degree of resorption (capability for dissolution and resolution) in consequence of which a need for further treatment of such medical product with strong inorganic acids is eliminated. In RBM technology, the acid etching of implant surface is performed with the use of much less aggressive organic acids. This treatment results in the attainment of really microporous structure of contact surface of titanium implant with the optimum pits 5 to 10 µm deep for the integration of living osseous tissue with the retention of macroroughness after sandblasting and full absence of undesirable residual inclusions. The research shows that RBM surface on the prosthetic implants of chemically pure titanium demonstrates the best results in the speed of growing together with the osseous bone (osseointegration) having no drawbacks inherent in other processing technologies.