This paper presents a comprehensive effort to develop and analyze first-of-its-kind design-specific and bioactive piezoelectric scaffolds for treating orthopedic defects. The study has three major highlights. First, this is one of the first studies that utilize extrusion-based 3D printing to develop design-specific macroporous piezoelectric scaffolds for treating bone defects. The scaffolds with controlled pore size and architecture were synthesized based on unique composite formulations containing polycaprolactone (PCL) and micron-sized barium titanate (BaTiO3) particles. Second, the bioactive PCL-BaTiO3 piezoelectric composite formulations were explicitly developed in the form of uniform diameter filaments, which served as feedstock material for the fused filament fabrication (FFF)-based 3D printing. A combined method comprising solvent casting and extrusion (melt-blending) was designed and deemed suitable to develop the high-quality PCL-BaTiO3 bioactive composite filaments for 3D printing. Third, clinical ultrasonic stimulation (US) was used to stimulate the piezoelectric effect, i.e., create stress on the PCL-BaTiO3 scaffolds to generate electrical fields. Subsequently, we analyzed the impact of scaffold-generated piezoelectric stimulation on MC3T3 pre-osteoblast behavior. Our results confirmed that FFF could form high-resolution, macroporous piezoelectric scaffolds, and the poled PCL-BaTiO3 composites resulted in the d33 coefficient in the range of 1.2–2.6 pC/N, which is proven suitable for osteogenesis. In vitro results revealed that the scaffolds with a mean pore size of 320 µm resulted in the highest pre-osteoblast growth kinetics. While 1 Hz US resulted in enhanced pre-osteoblast adhesion, proliferation, and spreading, 3 Hz US benefited osteoblast differentiation by upregulating important osteogenic markers. This study proves that 3D-printed bioactive piezoelectric scaffolds coupled with US are promising to expedite bone regeneration in orthopedic defects.
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.
Polyetheretherketone (PEEK) is a high-performance polymer material for developing implants for orthopedic, spinal, cranial, maxillofacial, and dentistry applications. However, the major limitation of PEEK implants is their bioinertness, i.e., their...
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