Healthcare consumers are demanding more functional and more complex devices for treatment of medical conditions (). The medical device industry is expected to significantly increase over the coming decades due to aging populations in the United States, the United Kingdom, Germany, France, Italy, China, Japan, and Korea ().
The use of biomaterials, which are nonviable materials used in medical devices for interaction with biological systems, is nearly as old as human civilization itself (). Gold was used in dental applications by several ancient societies over two millenia ago (). For example, the Etruscans created dental appliances out of gold in the seventh century B.C.; these appliances were used to stabilize teeth or retain false teeth (). Around 500 B. C., the Phoenicians used gold wire for tooth fixation (). Ancient Central American cultures, including the Mayans, used jade and obsidian as inlay materials for tooth decoration (). In the eighteenth century, Fauchard described the use of gold foil and tin foil in dental fillings (). Cox et al. noted that the recently excavated remains of a British nobleman contained several dental restorations, including two fillings created using gold foil (). In 1829, Levert performed a series of in vivo studies involving a canine model, which compared the biocompatibility of sutures made out of gold, lead, platinum, and silver. His work indicated that platinum was associated with the least amount of irritation (). In 1829, Taveau described the development of an amalgam that contained mercury and coin silver ().
Lister's “Antiseptic Principle in the Practice of Surgery” facilitated the growth of medical device technology by showing the surgical community that metal in itself was not a source of gangrene (). Lister used silver wire for treatment of fractures (). In 1878, Edward Huse used magnesium wires to end bleeding of blood vessels in human patients. In this work, he noted the biodegradable nature of magnesium (). In 1890, Gluck performed the first joint replacement; he used a hinged prosthesis fashioned out of ivory to treat a knee joint that was afflicted by tuberculosis (). In 1895, Lane described the use of steel screws for treatment of simple fractures involving the fibula and the tibia (). In 1912, Sherman used a canine model to examine bone plates that were made out of vanadium steel (). Zierold performed an in vivo study involving implantation of various metals within canine tibia; he showed that stellite, a cobalt-chromium alloy, was noncorrosive and well tolerated by the surrounding tissue (). Since that time, cobalt-chromium alloy has been a mainstay of implantable medical devices, particularly orthopaedic prostheses. In 1940, Bothe et al. published a study in which pure titanium was implanted within feline femoral shafts; they noted that titanium was well tolerated and that bone formed an attachment to it (). Branemark et al. subsequently described the direct contact between bone and titanium using the term osseointegration (). In the 1960s, Sir John Charnley developed a hip prosthesis in which a small metallic head interacted with an ultrahigh molecular weight polyethylene cup; these components were cemented in place using polymethylmethacrylate bone cement (). Although this implant was highly successful, concerns were raised regarding tissue response to ultrahigh molecular weight polyethylene wear debris. Prostheses containing ceramic (e.g., alumina) components were developed in response to this concern (). The shape memory properties of equiatomic nickel-titanium alloy, known as Nitinol, were discovered in 1962 (, ). Due to its shape memory and superelastic properties, this material has been used in orthodontic archwires since the 1970s and self-expanding stents since the 1980s.
Since the mid-twentieth century, significant advances in polymeric and ceramic biomaterial technology have taken place. In the late 1940s and early 1950s, Sir Harold Ridley used polymethylmethacrylate to create the intraocular lens for treatment of cataracts (, ). A variety of materials were used as blood vessel substitutes during the last century, including paraffin-coated glass and aluminum, polymethylmethacrylate, Vinyon-N plastic fabric, and knitted Dacron (). In 1969, Hench developed a bioactive glass known as Bioglass; intrafacial bonds were shown to form between this material and the surrounding bone ().
Recent research efforts have involved the development of biodegradable materials and artificial tissues. For example, physicians and researchers have sought to create biodegradable implants, including stents, out of magnesium and magnesium alloys (, ). In addition, efforts have been underway since the 1970s to develop artificial tissues and organs, including substitutes for cartilage and skin. These artificial tissues and organs involve seeding of cells and incorporation of bioactive factors within scaffold materials such as bioactive ceramics, biodegradable polymers, carbon nanotube-containing composite materials, and natural materials (). Significant research efforts are underway to optimize the properties of the scaffold materials. As noted by Agrawal, scaffold materials must be porous, biocompatible, and biodegradable (). In addition, these materials must encourage cell growth and exhibit appropriate mechanical properties. In recent decades, polymers have also been used for controlled release of pharmacologic agents (). For example, polymer-coated stents and pegylated interferon alpha have been translated to clinical use ().
The ASM Handbook of Materials for Medical Devices describes the properties of metals, ceramics, polymers, and composite materials used in medicine and dentistry. Degradation of biomaterials and cell-material interactions are also considered. These chapters indicate that many biomaterials operate under very demanding and highly corrosive conditions (). Above all, improving cell-material interactions and tissue-material interactions is necessary to enhance the performance of conventional medical devices and enable the development of medical devices with novel functionalities ().
Roger J. Narayan
University of North Carolina