The effects of micromachined surfaces on formation of bonelike tissue on subcutaneous implants as assessed by radiography and computer image processing B. Chehroudi/ D. McDonnell/ and D. M. Brunette 1 * Departments of lOral Biology and 20ral Medical and Surgical Sciences, University of British Columbia, 2199 Wesbrook Mall, Vancouver, British Columbia V6T 1Z3, Canada Surface topography varies widely among commercially available orthopedic and dental implants. While it is gener- ally accepted that the surface topography of an implant in- fluences the formation of bone and affects its performance, few systematic studies have dealt with this important feature. Quantification of the mineralized tissue at the implant inter- face has typically been attempted using histologic methods or conventional radiographic procedures. However, histologic methods are often technically demanding and time consum- ing, whereas conventional radiographic procedures lack res- olution and sensitivity to identify small areas of mineraliza- tion. The objective of this study was to study systematically the effects of micromachined surfaces on bone formation by applying digital radiographic techniques to identify and quantify mineralized tissue. Titanium-coated epoxy replicas of 19 different micromachined grooved or pitted surfaces that ranged between 30 and 120 ,urn deep, as well as smooth control surfaces, were implanted percutaneously and fixed to the parietal bone of rats. After 8 weeks the implants and attached tissue were removed and processed for light and electron microscopy. A total of 316 implant surfaces were processed, radiographed using conventional and digital INTRODUCTION It is generally agreed that bone-contacting biomateri- als, such as those used in orthopedic or dental im- plants, must integrate firmly with bone to achieve a successful, long-term clinical result. Although a range of metallic and polymeric materials permit bone- cell growth and calcified-matrix production both in vivo and in vitro,l-s many of these materials allow bone growth by providing a permissive surface for osteogenic-cell adhesion and do not necessarily stimu- late or induce mineralized-tissue formation. Selection of materials for bone-contacting applications of im- plants has largely been evaluated by trial-and-error optimization, an approach that stands in contradistinc- *To whom correspondence should be addressed. techniques, and sectioned for histologic observations. The area of the bonelike tissue and its density were calculated using National Institutes of Health Image software. Mineral- ization was frequently noted at the interface of some types of micromachined surface but rarely on smooth surfaces. The presence of bone in histologic sections and areas identified as bone through digital radiography and image processing correlated strongly. The frequency of bonelike foci formation decreased as the depth of the grooves increased. In contrast, mineralization occurred more frequently as the depth of the pit increased. In addition, bonelike foci were oriented along the long axis of the grooves. It is thus feasible that the bonelike tissue is shaped, directed, or engineered to a predetermined configuration which is dictated by the surface topography. This study indicated that surface topography influences the frequency as well as the amount of bone deposited adjacent to implants, and mineralized product can be guided by the surface topography. Moreover, digital radiography and im- age processing can be used reliably to identify and quantify mineralized tissue at the implant interface. © 1997 John Wiley & Sons, Inc. tion to tissue engineering, where materials are de- signed to fulfil certain functions. A more logical ap- proach to a predictable and clinically successful surface for bone-contacting implants would be to engineer im- plant surfaces capable of actively producing the de- sired bone-cell responses. In his presidential address to the Society of Biomaterials, Ratner,6 in advocating an engineering approach to biomaterials application, stated that some existing biomaterials can be compared to dinosaurs poised for extinction. One approach to producing biomaterials with bone- promoting capabilities is to manipulate surface chemis- try to stimulate bone production. Examples of this ap- proach include implants made of hydroxyapatite and bioactive glasses which are thought to act by means of specific surface chemical properties. 3 ,7,8 Although these materials accelerate and promote bone formation at their surface, concerns have been expressed about their Journal of Biomedical Materials Research, Vol. 34, 279-290 (1997) © 1997 John Wiley & Sons, Inc. CCC 0021-9304/97/030279-12