The building parameters of three-dimensional (3D) printed polylactic acid/hydroxyapatite (HA) composite bone plates were optimized by an orthogonal experiment, and the effects of the layer thickness, printing speed, filament feeding speed, and HA content on the bending strengths of the specimens were analyzed. The deformation characteristics of the specimens were studied by 3D full-field strain analysis, and the internal defects of the specimens were analyzed. The effects of different combinations of the process parameters on the cross-sectional shape of the single deposited line, printing temperature, and pressure of the molten material were further analyzed. The results showed that the factors affecting the bending properties were the layer thickness, printing speed, filament feeding speed, and HA content, successively. The optimized process parameters were an HA content of 10%, a layer thickness of 0.1 mm, a printing speed of 30 mm/s, and a filament feeding speed of 0.8 mm/s, and the optimized specimen bending strength was 103.1 ± 5.24 MPa. The deposited line with a flat section shape and width greater than the print spacing helped to reduce the porosity of the specimens. The process parameters that resulted in large high-temperature areas and a high extrusion pressure could better promote material fusion.

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A continuous polyglycolic acid (PGA) fiber-reinforced polylactic acid (PLA) degradable composite was proposed for application in biodegradable load-bearing bone implant. The fused deposition modeling (FDM) process was used to fabricate composite specimens. The influences of the printing process parameters, such as layer thickness, printing spacing, printing speed, and filament feeding speed on the mechanical properties of the PGA fiber-reinforced PLA composites, were studied. The thermal properties of the PGA fiber and PLA matrix were investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The internal defects of the as-fabricated specimens were characterized by the micro-X-ray 3D imaging system. During the tensile experiment, a full-field strain measurement system was used to detect the strain map and analysis the fracture mode of the specimens. A digital microscope and field emission electron scanning microscopy were used to observe the interface bonding between fiber and matrix and fracture morphologies of the specimens. The experimental results showed that the tensile strength of specimens was related to their fiber content and porosity. The printing layer thickness and printing spacing had significant impacts on the fiber content. The printing speed did not affect the fiber content but had a slight effect on the tensile strength. Reducing the printing spacing and layer thickness could increase the fiber content. The tensile strength (along the fiber direction) of the specimen with 77.8% fiber content and 1.82% porosity was the highest, reaching 209.32 ± 8.37 MPa, which is higher than the tensile strength of the cortical bone and polyether ether ketone (PEEK), indicating that the continuous PGA fiber-reinforced PLA composite has great potential in the manufacture of biodegradable load-bearing bone implants.

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