Selective laser sintering of polymer biocomposites based on polymethyl methacrylate
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Materials and processes used for medical applications should have specific attributes. For bone repair and reconstruction, controlled open porosity and osteoconductivity are essential apart from mechanical strength and biocompatibility. Several forms of calcium phosphates are often used for these applications, considering properties similar to bone minerals, but often in combinations with other biopolymers. Polymethyl methacrylate (PMMA) and b-tricalcium phosphate (b-TCP) are identified as a suitable combination for the current research, considering specific properties both individually and in combinations, when processed by different means for specific medical applications. Specific responses of the biocomposite material formed by mechanically mixing the two materials in the powder form to selective laser sintering (SLS) under varying conditions are investigated. The results indicate the suitability of the material system for SLS, while controlled porosity and mechanical property combinations are possible by optimizing material composition and process parameters.
I. INTRODUCTION
Ceramics and their composites are used for medical applications such as repair of bone fractures and attachment of bone plates, apart from being substitute materials in dental and orthopedic requirements.1,2 The material used as a bone substitute should be biocompatible, easily available, and easy to process, apart from having the compressive strength necessary to serve as the base material for new bone growth. While ideal material systems are yet to evolve, porous ceramics based on calcium phosphate possess properties similar to bone minerals and exhibit unique characteristics as bone substitutes, compared to other biomaterials. They also induce biological responses during bone remodeling, involving the resorption of old bone minerals coupled with the formation of the new bone. During resorption, the degradation products of calcium phosphate bioceramics (calcium and phosphate ions) are naturally metabolized and they do not induce abnormal calcium or phosphate levels in the organs of the body.3 The primary constitution of the natural bone includes 60% of calcium phosphate minerals and hence calcium phosphate has the osteoconductive property to be a bone substitute.4 Calcium phosphates were shown to exhibit a variety of forms, but from the chemical point of view, hydroxyapatite (HA),5 b-tricalcium phosphate (TCP),6 multiphasic bioglass, biphasic calcium phosphate (BCP), and octacalcium a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.211 J. Mater. Res., Vol. 29, No. 17, Sep 14, 2014
phosphate (OCP) have evolved over time and have been investigated both in vitro and in vivo.7 Among these, TCP has better biodegradability and is most commonly used in bone surgery. It has two major distinct phases of anhydrous crystals: monoclinic a-TCP (low-temperature polymorph) and rhombohedral b-TCP (high-temperature polymorph). Further, considering better biocompatibility, osteoconductivity, and cell-med
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