Nanoceramics in Biomedical Applications

An improved understanding of the interactions at the nanoscale level between the bioceramics in medical impl~ntsand th.ehard or soft tissues in the human body could contribute significantly to the design of new-generation prostheses and postoperative patient management strategies. Overall, the benefits of advanced ceramic materials in biomedical applications have been universally accepted, specifically in terms of their strength, biocompatibility, hydrophilicity, and wear resistance in articulating joints. The cqntil)uqus development of new-generation implants utilizing nanocoatings with novel nanosensors and devices is leading to better compatibility with human tissue and improved well-being and longevity fqr patients. This article gives a short overview of bloceramlcs and reexamines key issues of concern for processing and applying nanoceramics as biomaterials. Keyryords: bioceramics, biomaterials, implants, nanoceramics, nanostructure. Introduction At present, the most common materials in clinical use are those chosen from a handful of well-characterized and available biocompatible ceramics, metals, polymers, and their combinations as composites or hybrids. Advances in the fundamental understanding of cell and molecular biology, tissue engineering, targeted drug delivery, wound healing, and other biomedical processes, together with the development of new enabling technologies such as microscale, nanoscale, and bio-inspired fabrication (biomimetics) and surface modification methods, have the potential to drive at an unprecedented rate the design and development of new biomaterials useful for medical applications. The current focus is on the production of new nanoceramics relevant to a broad range of applications such as implantable surfacemodified medical devices for better hardand soft-tissue attachment, increased bioactivity, tissue regeneration and engineering, cancer treatment, drug and gene delivery, treatment of bacterial and viral infections, delivery of oxygen to damaged tissues, imaging, and materials for mini28 mally invasive surgery. A more futuristic view includes nanorobotics, nanobiosensors, and micro-nanodevices for a wide range of biomedical applications. The opportunity to significantly improve the clinical usefulness ofbiomaterials, particularly on the nanoscale, provided by these advances should be seized by promoting and supporting research and development of novel new-generation biomaterials with improved bioactivity and mechanical properties. Specifically, these new concepts and strategies for fabrication methods and improved tissue interactions could lead to biomaterials that are truly biocompatible and bioresponsive at a nanoscale level, similar to biogenic (natural) materials. Abiomaterial by definition is a nondrug substance suitable for inclusion in systems that augment or replace the function of bodily tissues or organs. A century ago, artificial devices made from materials as diverse as gold and wood were developed to a point where they could replace various components of the human body. These materials are capable of being in contact with body fluids and tissues for prolonged periods of time while eliciting little if any adverse reaction. 1 The main factors in any biomaterial's clinical success are its biocompatibility and biofunctionality, which are directly related to tissue/implant interface interactions. Improvement of interface bonding by nanoscale coatings, based on biomimetics, has been of worldwide interest during the last decade. Currently, a number of companies are in the commercialization stages of new-generation nanoscalemodified implants for orthopedic, ocular, and maxillofacial surgery and for hardand soft-tissue engineering (e.g., Iso'Iis BV,ApaTech Ltd., £lex Corp.). The worldwide biomaterials market is valued at close to $24 billion. Orthopedic and dental applications represent approximately 55% of the total biomaterials market. Sales of orthopedic products worldwide exceeded $13 billion in 2000, an increase of 12% over 1999 revenues.' Expansion in these areas is expected to continue, due to a number of factors including the aging population, an increasing preference by younger to middle-aged candidates to undergo surgery, improvements in technology, a better understanding of biomechanics, the desire to improve one's appearance, and the demand by patients for better performance from orthopedic products. Biomaterials and Bioceramics It has been long accepted that no foreign. material placed within a living body is completely compatible with it. The only substances that conform completely are those manufactured by the body itself (autogenous); any other substance that is recognized as foreign initiates some type of reaction. The question for biomaterials researchers is, with our ability to control surfaces at the nanoscale level, and with the range of new-generation novel "nanotreatments" being developed, can we somehow deceive the body into allowing synthetic materials to be accepted as biogenic or autogenic? When a synthetic material is implanted in the human body, the tissue reacts in a variety of ways, depending on the material used. The mechanism of tissue interaction at the nanoscale depends on the tissue's response to the implant surface. In general, three terms describe or classify a biomaterial with respect to the tissue response: bioinert, bioresorbable, and bioactive.Abioinert material, such as alumina, is accepted by the body but does not interact or react with the physiological environment; a bioresorbable material, such as MRS BULlETIN/JANUARY 2004