Optimization of fiber reinforcement in hand-pour epoxy composites for developing low-cost canine composite bone models: Mechanical characterization and material selection.

Abstract

Background and aim: Synthetic canine bone models are increasingly used in veterinary orthopedic education as reproducible and ethically acceptable alternatives to cadaveric specimens. However, commercially available models remain expensive, and low-cost fabrication methods that provide suitable mechanical performance are limited. This study aimed to optimize fiber-reinforced epoxy resin (E) and polyester resin (R) composites fabricated by a hand-pour casting technique for the development of affordable canine composite bone models by comparing their tensile mechanical properties and identifying the most suitable cortical bone analog material.

Materials and methods: E and R were reinforced with chopped E-glass fiber at 0%, 1%, 3%, and 5% (wt/wt), whereas polyurethane (PU) foam was evaluated as a cancellous bone analog. Dumbbell-shaped specimens were fabricated using silicone molds according to American Society for Testing and Materials D638-14 and tested under uniaxial tension using a universal testing machine. Elastic modulus, yield strength, yield strain, ultimate stress, and ultimate strain were determined from stress-strain curves. Mechanical properties were compared using one-way analysis of variance followed by Tukey's honestly significant difference test, with statistical significance set at p < 0.05.

Results: Fiber reinforcement significantly improved the elastic modulus of epoxy composites in a concentration-dependent manner, reaching 1,513.12 ± 67.85 MPa at 5 wt%, whereas polyester composites showed no significant stiffness improvement. Epoxy composites demonstrated markedly lower specimen-to-specimen variability than polyester composites, with coefficients of variation for elastic modulus ranging from 1.4% to 4.5%. Although ultimate stress and ultimate strain decreased with increasing fiber content in both resin systems, epoxy reinforced with 3 wt% E-glass fiber provided the most favorable balance between stiffness, reproducibility, and casting workability. PU foam exhibited an elastic modulus of 57.72 ± 7.69 MPa, providing a 23-fold stiffness difference from the selected cortical analog and supporting its suitability as a cancellous core material. The estimated raw material cost of the proposed composite bone model was approximately 7% of the equivalent commercial product.

Conclusion: E reinforced with 3 wt% chopped E-glass fiber is the preferred material for low-cost hand-pour fabrication of canine composite bone models because it offers the optimal combination of mechanical performance, manufacturing consistency, and processing feasibility. Combined with PU foam, this formulation provides an economical platform for veterinary surgical simulation. Future studies should validate the bilayer construct under compressive loading, drilling, and screw pull-out testing before clinical educational application.