Processing of Organic/Inorganic Composites by Stereolithography
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ABSTRACT Ceramic StereoLithography (CSL) is used to fabricate complex shaped ceramic powder compacts by laser photocuringa concentratedceramic dispersion in photocuring solutions layer-by-layer. The main processingparametersin CSL such as layer thickness, resolution,hatch spacing, and overcure depend on knowledge of the light propagationin a concentrated dispersion. In studies dealing with the processing of ceramic-filled organics, we investigated the depth of curingfor model resin systems as a function of photoinitiatorconcentration.An optimal photoinitiatorconcentration that maximized the gel cure depth was observed The study showed that photoinitiatorplays a significant role in controlling the quality and performance of the formed gel network, with special regardto thickness of cured layers. This has potential applicationto fields as diverse as industriallycured coatings and dental fillings, and more generally, 3-dimensionalfabrication techniques.
INTRODUCTION Stereolithography is a sequential layering process that converts a "virtual" object into a real structure [1,2]. A 3-dimensional, computer-aided design (CAD) model is computationally sliced into a series of 2-dimensional, thin patterns. Each 2-D pattern is then transmitted to another computer which controls a scanning laser [1,2]. The laser is rastered across the surface of a photocurable monomer resin to solidify the layer in the shape of the 2-D pattern. A new layer of resin is swept across the surface, and the process repeated. By sequentially depositing layers in this layer-additive fashion, the entire structure is replicated in solid form [1,2]. By their very nature, composite materials encompass a wide range of applications. Since stereolithography lends itself especially well to the fabrication of complex shaped objects, we narrow our focus to the processing of organic/inorganic hybrids for use as biomaterials. A specific goal is to produce bone graft or implant materials with complex internal geometry tailor-designed by computer. We desire to produce composites that are biocompatible from an immunological point of view, as well as mechanically functional in supporting loads. Current bone graft techniques suffer from a series of drawbacks [3]. Autogenous strategies are limited by finite supply and issues of morbidity. Allografts often involve issues of immunogenicity (potential for viral transmission) as well as efficacy, depending on sterilization method [3]. Commercial products such as ultra high molecular weight polyethylene lack bone inductivity and/or strength [4]. In processing of organic/inorganic composites by stereolithography, we have taken a two-pronged approach. We have previously developed techniques to produce fully ceramic compacts [5], and since the stereolithography apparatus (SLA) is designed for
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pure polymeric constructs, we now marry both approaches to achieve the fabrication of ceramic/polymer hybrids. In developing these composites, we have found it n
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