Fabrication of individual scaffolds based on a patient-specific alveolar bone defect model

Abstract

Fabricating individualized tissue engineering scaffolds based on the three-dimensional shape of patient bone defects is required for the successful clinical application of bone tissue engineering. However, there are currently no reported studies of individualized bone tissue engineering scaffolds that truly reproduce a patient-specific bone defect. We fabricated individualized tissue engineering scaffolds based on alveolar bone defects. The individualized poly(lactide-co-glycolide) and tricalcium phosphate composite scaffolds were custom-made by acquiring the three-dimensional model through computed tomography, which was input into the computer-aided low-temperature deposition manufacturing system. The three-dimensional shape of the fabricated scaffold was identical to the patient-specific alveolar bone defects, with an average macropore diameter of 380 μm, micropore diameters ranging from 3 to 5 μm, and an average porosity of 87.4%. The mechanical properties of the scaffold were similar to adult cancellous bone. Scaffold biocompatibility was confirmed by attachment and proliferation of human bone marrow mesenchymal stem cells. Successful realization of individualized scaffold fabrication will enable clinical application of tissue-engineered bone at an early date.

Introduction

Dental implant restorations have become the standard method for reconstructing occlusions (Yamada et al., 2004). Sufficient bone volume in the implant area is a prerequisite for implant insertion, and is a critical factor for ensuring successful dental implantation (Ueda et al., 2001). However, alveolar bone defects stem from a variety of processes (such as disused absorption of alveolar bone after tooth loss, trauma, tumors, and periodontal diseases), resulting in insufficient bone volume in the implant area and the inability to implant. A number of approaches have attempted to repair alveolar bone defects in the implant area, including guided bone regeneration, distraction osteogenesis, and bone grafting techniques such as autologous iliac transplantation (Aghaloo and Moy, 2007). Recently, bone tissue engineering on porous three-dimensional (3D) scaffolds (Scheller et al., 2009) has shown great promise as a potential technique for alveolar bone defect repair.

Tissue engineering is dedicated to the development of biosubstitutes for restoring, maintaining, or improving the morphology and functions of damaged tissues or organs (Langer and Vacanti, 1993). While tissue engineering has been employed to repair damaged organs such as livers, hearts, and bones, bone tissue engineering may be one of the first techniques to enjoy successful clinical application (Service, 2000). Controlled 3D biodegradable scaffolds that serve as templates for initial cell attachment and subsequent tissue regeneration are critical for the success of bone tissue engineering (Vozzi et al., 2003). Since there are individual variations among patients and differences in damaged parts, bone tissue engineering scaffolds need to be custom-made to meet individual patient needs. Fabricating scaffolds precisely according to the 3D shape of the patient's bone defects will also improve the biocompatibility of scaffolds following implantation (Uchida et al., 2008). Although various attempts have been made to fabricate scaffolds according to the shape of patient bone defects (Dyson et al., 2007, Hollister et al., 2000, Sanz-Herrera and Garcia-Aznar, 2009, Wang et al., 2009, Wettergreen et al., 2005), scaffolds have not been formulated that truly reproduce patient-specific bone defects.

Traditional methods for the fabrication of bone tissue engineering scaffolds include particulate leaching, electro-spinning, multilayer lamination, and molding (Borden et al., 2002). Since these methods are limited by manual intervention, discordant fabrication processes, weak ductility, and the use of pore-forming agents (Leong et al., 2003), microscopic and macroscopic 3D scaffold shapes are unable to meet patient-specific clinical application needs. Recent advances in computer science and its integration with biomaterials and engineering have led to the emergence of new rapid prototyping technologies for producing 3D constructs, including stereolithography (Chu et al., 2002), fused deposition modeling (Chen et al., 2005, Hutmacher et al., 2001, Kalita et al., 2003, Zein et al., 2002), 3D printing (Chumnanklang et al., 2007, Lam et al., 2002, Tay et al., 2007), and selective laser sintering (Goodridge et al., 2007, Leong et al., 2003, Tan et al., 2003). These technologies produce controlled porous architectures less than 200 μm in size, but are limited at the 200–500 μm scale necessary for vascularization and bone tissue regeneration. Recently, our laboratory established a unique method based on the layer-by-layer manufacturing principle of solid freeform fabrication for 3D bone tissue engineering scaffolds (Xiong et al., 2001, Xiong et al., 2002, Yan et al., 2005). This method generates custom-made bone tissue engineering scaffolds according to the 3D shapes of patient bone defects, and easily produces controlled porous architectures in the range of 200–500 μm.

The aim of this study was to fabricate patient-specific alveolar bone tissue engineering composite scaffolds made of poly(lactide-co-glycolide) (PLGA) and tricalcium phosphate (TCP). A 3D model of the patient's alveolar bone defect was obtained from a computed tomography (CT) scan of the mandibular bone of a volunteer who lost the left mandible premolar and experienced heavy absorption of alveolar bone. Computer-aided low-temperature deposition manufacturing (LDM) was used to successfully tailor the PLGA/TCP composite scaffolds. The resulting PLGA/TCP scaffolds were characterized by scanning electron microscopy (SEM), liquid displacement, and mechanical bend testing, and biocompatibility was confirmed by attachment and proliferation of human bone marrow mesenchymal stem cells (HBMSCs).