This investigation employed Taguchi experimental design method and ASTM three-point bending test to determine the parameters that influence the flexural strength of a material composed of a thin layer fabricated by a rapid prototyping (RP) machine and coated with a layer of unsaturated polyester resin (UPR). Since current rapid prototyping machines use a layer-based process to manufacture products, this will result in RP products liable to break along forming layers when bending load is applied. A type of resin-reinforced RP transtibial socket is proposed to strengthen the flexural strength so that the abrupt collapse can be prevented if a transtibial prosthetic socket made by an RP machine. This study proposed wrapping a layer of unsaturated polyester resin around a preliminary thin RP socket manufactured by a fused deposition modeling (FDM) machine to reinforce its flexural strength. Factors affecting the strength of the resin-reinforced RP socket include thickness and forming orientation of the preliminary RP socket, thickness of the UPR layer, and type of material used to make the preliminary RP socket. Employing Taguchi experimental design method and ASTM three-point bending test standard, the parameters that influence the flexural strength of the resin-reinforced RP prosthetic socket can be determined. Based on the appropriate parameters, including thickness of the RP layer and UPR layer, the RP material and RP fabricating orientation, the preliminary thin RP prosthetic sockets can be fabricated by an FDM machine. And the thin layer preliminary RP sockets were then wrapped with cotton socks and laminated UPR layer to form resin-reinforced RP sockets. To confirm the effectiveness of the resin-reinforced sockets developed in this study, a volunteer subject with unilateral left below-knee amputation is recruited to implement the experiment. The pressures at residual limb/socket interface were measured by using a pressure distribution measurement system and movement was captured by a motion analysis system while a volunteer patient wears the resin-reinforced RP socket. The experimental results demonstrated that the applicability of the proposed type of material and a resin-reinforced RP transtibial socket has been verified. A prosthetist may use the interface pressures exerting on stump and gait pattern during walking to assess the suitability of this type of RP socket based on clinical expertise. Further trial use and more subjects are needed to validate the durability of the proposed RP socket.

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