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PEEK has several approving mechanical properties; however, for certain demanding applications such as automotive, PEEK does not exhibit the required strength. Moreover, if the PEEK parts are developed by Fused Filament Fabrication (FFF)-based 3D Printing, there is a high chance of having PEEK parts with decreased mechanical properties. Carbon Fiber (CF) reinforcement is a well-known method of mitigating the low mechanical properties of PEEK. Hence, in the present study, we attempted to develop CF-reinforced PEEK (CFR-PEEK) parts via FFF. First, we developed homogeneous CFR-PEEK mixtures via ball milling and explored the effects of different milling duration and speeds on the extent of uniform dispersion of the CFs in the PEEK matrix. Next, we fed the CFR-PEEK milled powders into a high-temperature extrusion setup to develop uniform-diameter CFR-PEEK filaments. We analyzed the effects of different extrusion parameters on the uniform-diameter CFR-PEEK filament quality to make it suitable for 3D Printing. Finally, the CFR-PEEK filaments were used in a high-temperature FFF setup to develop design-specific parts. Our results indicate that 400 rpm and 4h were apt for developing uniform CFR-PEEK mixtures. Interestingly, increasing the CF content above 10 vol% resulted in brittle filaments. The extrusion temperature, speed, and cooling rate played a major role in forming the uniform-diameter CFR-PEEK filaments. Finally, the 3D printed CFR-PEEK parts exhibited a tensile strength of 49MPa, lesser than unfilled PEEK. We indicate that poor interfacial bonding of the CF with the PEEK matrix is a primary reason for this reduced strength. In addition, printing defects such as pores also contributed to the reduced strength of the CFR-PEEK parts.

Volumetric muscle loss (VML), which involves the loss of a substantial portion of muscle tissue, is one of the most serious acute skeletal muscle injuries in the military and civilian communities. The injured area in VML may be so severely affected that the body loses its innate capacity to regenerate new functional muscles. State-of-the-art biofabrication methods such as bioprinting provide the ability to develop cell-laden scaffolds that could significantly expedite tissue regeneration. Bioprinted cell-laden scaffolds can mimic the extracellular matrix and provide a bioactive environment wherein cells can spread, proliferate, and differentiate, leading to new skeletal muscle tissue regeneration at the defect site. In this study, we engineered alginate–gelatin composite inks that could be used as bioinks. Then, we used the inks in an extrusion printing method to develop design-specific scaffolds for potential VML treatment. Alginate concentration was varied between 4–12% w/v, while the gelatin concentration was maintained at 6% w/v. Rheological analysis indicated that the alginate–gelatin inks containing 12% w/v alginate and 6% w/v gelatin were most suitable for developing high-resolution scaffolds with good structural fidelity. The printing pressure and speed appeared to influence the printing accuracy of the resulting scaffolds significantly. All the hydrogel inks exhibited shear thinning properties and acceptable viscosities, though 8–12% w/v alginate inks displayed properties ideal for printing and cell proliferation. Alginate content, crosslinking concentration, and duration played significant roles (p < 0.05) in influencing the scaffolds’ stiffness. Alginate scaffolds (12% w/v) crosslinked with 300, 400, or 500 mM calcium chloride (CaCl2) for 15 min yielded stiffness values in the range of 45–50 kPa, i.e., similar to skeletal muscle. The ionic strength of the crosslinking concentration and the alginate content significantly (p < 0.05) affected the swelling and degradation behavior of the scaffolds. Higher crosslinking concentration and alginate loading enhanced the swelling capacity and decreased the degradation kinetics of the printed scaffolds. Optimal CaCl2 crosslinking concentration (500 mM) and alginate content (12% w/v) led to high swelling (70%) and low degradation rates (28%) of the scaffolds. Overall, the results indicate that 12% w/v alginate and 6% w/v gelatin hydrogel inks are suitable as bioinks, and the printed scaffolds hold good potential for treating skeletal muscle defects such as VML.

Fused Filament Fabrication (FFF)-based 3D printing is an efficient technique for developing medical implants, but it is not very useful in developing small yet mechanically robust design-specific fixtures such as dental implants (15 mm). Specifically, it is challenging to 3D print robust Polyetheretherketone (PEEK) small implants due to PEEK's high melting temperature and melt viscosity. However, in this study, we efficiently utilize high-temperature FFF to develop the first-of-its-kind patient-specific robust PEEK dental implants with high print resolution. Specifically, we explore the effects of critical FFF processing conditions on the mechanical properties of the implants and subsequently determine an optimized set of processing conditions that are essential in developing durable dental implant systems. Our results indicate that the 3D printed dental implants exhibit good fatigue properties and suffice the clinical and industrial requirements for dental implants. Furthermore, we prove that the 3D printed implants exhibit adequate mechanical durability even after simulated (accelerated) aging of 30 years.