Three-dimensional printing (3DP) has been employed to fabricate scaffolds with advantages of fully controlled geometries and reproducibility. In this study, the scaffold structure design was established through investigating the minimum feature size and powder size distribution. It was then fabricated from the 3DP plaster-based powders (CaSO4·1/2H2O). Scaffolds produced from this material demonstrated low mechanical properties and a rapid degradation rate. This study investigated the effects of heat treatment on the mechanical and in vitro degradation properties of the CaSO4 scaffolds. The occurrence of dehydration during the heating cycle offered moderate improvements in the mechanical and degradation properties. By using a heat treatment protocol of 200°C for 30？min, compressive strength increased from 0.36 ± 0.13？MPa (pre-heat-treated) to 2.49 ± 0.42？MPa (heat-treated). Heat-treated scaffolds retained their structure and compressive properties for up to two days in a tris-buffered solution, while untreated scaffolds completely disintegrated within a few minutes. Despite the moderate improvements observed in this study, the heat-treated CaSO4 scaffolds did not demonstrate mechanical and degradation properties commensurate with the requirements for bone-tissue-engineering applications. 1. Introduction Bone defects larger than a critical size cannot be healed by normal bone remodelling processes and thus require bone substitution. The autograft, which is recognised as the “gold standard” for bone repair, has been widely used for decades. However, it still has noted drawbacks, including risk of disease transmission and limited availability compared to ever-increasing surgical demand [1]. In the United States, for example, there are annually more than 0.5 million surgical procedures which are related to bone repair [2]. One of the breakthroughs in bone tissue engineering was the development of 3D scaffolds that replace and restore the lost tissues. They serve as a template to allow cell seeding and carry cells to the desired site. Despite the initial success in the development of 3D scaffolds, researchers now face a greater challenge in repairing injured bone in load-bearing sites [3]. In order to maintain the function of load-bearing bones, the scaffold needs to exhibit appropriate mechanical properties. These properties are highly dependent on scaffold design and geometry. A general consensus for the optimal bone-tissue-engineered scaffold design is to mimic the architecture, mechanical, and biochemical properties of natural bone [4]. However, it is
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