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matrix polymer chemistry, filler type, and matrix–filler interaction. This article discusses current efforts and focuses on key research challenges in the emerging usage of polymer nanocomposites for potential biomedical applications.

Nanocomposites for Biomedical Applications

Hydroxyapatite–Polymer Nanocomposites

Rohan A. Hule and Darrin J. Pochan Abstract Bionanocomposites have established themselves as a promising class of hybrid materials derived from natural and synthetic biodegradable polymers and organic/inorganic fillers. Different chemistries and compositions can lead to applications from tissue engineering to load-bearing composites for bone reconstruction. A critical factor underlying biomedical nanocomposite properties is interaction between the chosen matrix and the filler. This article discusses current efforts and key research challenges in the development of these materials for use in potential biomedical applications.

Introduction and Challenges Bionanocomposites form a fascinating interdisciplinary area that brings together biology, materials science, and nanotechnology. New bionanocomposites are impacting diverse areas, in particular, biomedical science. Generally, polymer nanocomposites are the result of the combination of polymers and inorganic/organic fillers at the nanometer scale. The extraordinary versatility of these new materials springs from the large selection of biopolymers and fillers available to researchers. Existing biopolymers include, but are not limited to, polysaccharides, aliphatic polyesters, polypeptides and proteins, and polynucleic acids, whereas fillers include clays, hydroxyapatite, and metal nanoparticles.1 The interaction between filler components of nanocomposites at the nanometer scale enables them to act as molecular bridges in the polymer matrix. This is the basis for enhanced mechanical properties of the nanocomposite as compared to conventional microcomposites.2 Bionanocomposites add a new dimension to these enhanced properties in that they are biocompatible and/or biodegradable materials. For the sake of this review, biodegradable materials can be described as materials degraded and gradually absorbed and/or eliminated by the body, whether

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degradation is caused mainly by hydrolysis or mediated by metabolic processes.3 Therefore, these nanocomposites are of immense interest to biomedical technologies such as tissue engineering, bone replacement/repair, dental applications, and controlled drug delivery. Table I lists some biopolymers commonly used in biomedical applications. Current opportunities for polymer nanocomposites in the biomedical arena arise from the multitude of applications and the vastly different functional requirements for each of these applications. For example, the screws and rods that are used for internal bone fixation bring the bone surfaces in close proximity to promote healing. This stabilization must persist for weeks to months without loosening or breaking.3 The modulus of the implant must be close to that of the bone for efficie