INTRODUCTION

Experiential fracture stabilization training is a cornerstone of veterinary surgical education. Cadaveric bone, the traditional training substrate, has several well-recognized limitations, including anatomical variability, the potential risk of disease transmission, chemical hazards associated with preservation, and high procurement and maintenance costs [1–4]. Consequently, synthetic canine composite bone models (CBMs) have gained increasing acceptance as supplementary educational tools because they provide reproducibility, improve animal welfare by reducing cadaver use, and offer greater logistical convenience [5, 6]. To function as effective surgical surrogates, CBMs should reproduce the hierarchical mechanical architecture of natural canine bone, comprising a dense cortical shell with a stiffness of 7.5–21 GPa and a tensile strength of approximately 251 MPa [7], surrounding a porous trabecular core optimized for compressive load absorption [8]. Epoxy resin (E), polyester resin (R), and polyurethane (PU) foam are commonly used to fabricate such models because of their low-cost, ease of processing, and versatility. However, these materials exhibit inherent brittleness and do not fully replicate the mechanical behavior of native bone, thereby limiting their effectiveness for advanced orthopedic procedural training [9–14].

Fiber reinforcement has been widely employed to improve the stiffness and fracture toughness of polymer composites while maintaining relatively low production costs [15–19]. Nevertheless, increasing fiber content also increases resin viscosity, making it difficult to cast composites into the small and geometrically complex molds required for canine bone models. Compared with human bone analogs, canine-specific molds require tighter dimensional tolerances within substantially smaller casting volumes, and the mechanical behavior of fiber-reinforced composites under these manufacturing conditions cannot be directly extrapolated from studies of human bone models [20, 21]. Therefore, identifying a fiber weight fraction that simultaneously provides adequate resin workability and desirable biomimetic mechanical properties remains a major challenge for developing canine-specific CBM.

Veterinary institutions across the Association of Southeast Asian Nations (ASEAN) are progressively aligning their curricula with international Day-1 Competency standards, resulting in an increasing demand for simulation-based surgical training [22, 23]. However, commercially available bone simulators remain prohibitively expensive for many veterinary schools, particularly in resource-limited settings. Hand-pour casting using locally available E or R together with PU foam represents a practical and economical fabrication approach. PU foam is particularly suitable as a cancellous bone analog because of its adjustable density, established application in orthopedic simulation, and widespread commercial availability in Thailand [13, 14]. Previous studies have shown that fiber reinforcement can improve the stiffness and fracture resistance of open-cast polymer composites within the 0.5–5 wt% range; however, increasing fiber content progressively compromises resin flowability, mold filling, and structural integrity [15, 18, 24]. The optimal balance between mechanical enhancement and manufacturing feasibility for canine-sized CBM has not yet been established.

Although previous investigations have evaluated fiber-reinforced polymer composites and commercially available synthetic bone models, most have focused on human orthopedic applications or general composite material characterization rather than canine-specific surgical simulation [9, 10, 15–21]. Furthermore, existing studies have largely emphasized improvements in mechanical properties without simultaneously considering casting workability, specimen reproducibility, and cost-effectiveness under hand-pour fabrication conditions. As a result, there remains insufficient evidence regarding the optimal fiber weight fraction for E- and R-based composites intended for low-cost canine CBMs that can reproduce the mechanical hierarchy of cortical and cancellous bone while remaining practical for routine fabrication in veterinary teaching institutions.

Therefore, this study aimed to optimize hand-pour fabricated fiber-reinforced E and R composites for developing affordable canine CBMs by systematically evaluating fiber weight fractions of 1, 3, and 5 wt%. The tensile mechanical properties of the reinforced resin systems were compared with those of PU foam as a cancellous bone analog and with published mechanical properties of natural canine cortical and trabecular bone. The findings were used to identify the composite formulation that provides the most appropriate balance between mechanical performance, manufacturing reproducibility, casting feasibility, and economic affordability for veterinary orthopedic training. To the best of our knowledge, this is the first study to systematically optimize fiber weight fractions in E and R composites specifically for hand-pour fabrication of canine orthopedic training models.