Over the years, the field of bioprinting has attracted attention for its highly automated 16 fabrication system that enables the precise patterning of living cells and biomaterials at pre-17 defined positions for enhanced cell-matrix and cell-cell interactions. Notably, vat polymerization 18 (VP)-based bioprinting is an emerging bioprinting technique for various tissue engineering 19 applications due to its high fabrication accuracy. Particularly, different photo-initiators (PIs) are 20 utilized during the bioprinting process to facilitate the crosslinking mechanism for fabrication of 21 high-resolution complex tissue constructs. The advancements in VP-based printing have led to a 22 paradigm shift in fabrication of tissue constructs from cell-seeding of tissue scaffolds (non-23 biocompatible fabrication process) to direct bioprinting of cell-laden tissue constructs 24 (biocompatible fabrication process). This paper, presenting a first-time comprehensive review of 25 the VP-based bioprinting process, provides an in-depth analysis and comparison of the various 26 biocompatible PIs and highlights the important considerations and bioprinting requirements. This 27 review paper reports a detailed analysis of its printing process and the influence of light-based 28 curing modality and PIs on living cells. Lastly, this review also highlights the significance of VP-29 based bioprinting, the regulatory challenges and presents future directions to transform the VP-30 Page 1 of 47 AUTHOR SUBMITTED MANUSCRIPT -BF-102156.R2based printing technology into imperative tools in the field of tissue engineering and regenerative 31 medicine. The readers will be informed on the current limitations and achievements of the VP-32 based bioprinting techniques. Notably, the readers will realize the importance and value of 33 highly-automated platforms for tissue engineering applications and be able to develop objective 34 viewpoints towards this field.
The purpose of 4D printing is to embed a product design into a deformable smart material using a traditional 3D printer. The 3D printed object can be assembled or transformed into intended designs by applying certain conditions or forms of stimulation such as temperature, pressure, humidity, pH, wind, or light. Simply put, 4D printing is a continuum of 3D printing technology that is now able to print objects which change over time. In previous studies, many smart materials were shown to have 4D printing characteristics. In this paper, we specifically review the current application, respective activation methods, characteristics, and future prospects of various polymeric materials in 4D printing, which are expected to contribute to the development of 4D printing polymeric materials and technology.
In this study, we synthesized strontium-contained calcium silicate (SrCS) powder and fabricated SrCS scaffolds with controlled precise structures using 3D printing techniques. SrCS scaffolds were shown to possess increased mechanical properties as compared to calcium silicate (CS) scaffolds. Our results showed that SrCS scaffolds had uniform interconnected macropores (~500 µm) with a compressive strength 2-times higher than that of CS scaffolds. The biological behaviors of SrCS scaffolds were assessed using the following characteristics: apatite-precipitating ability, cytocompatibility, proliferation, and osteogenic differentiation of human mesenchymal stem cells (MSCs). With CS scaffolds as controls, our results indicated that SrCS scaffolds demonstrated good apatite-forming bioactivity with sustained release of Si and Sr ions. The in vitro tests demonstrated that SrCS scaffolds possessed excellent biocompatibility which in turn stimulated adhesion, proliferation, and differentiation of MSCs. In addition, the SrCS scaffolds were able to enhance MSCs synthesis of osteoprotegerin (OPG) and suppress macrophage colony-stimulating factor (M-CSF) thus disrupting normal bone homeostasis which led to enhanced bone formation over bone resorption. Implanted SrCS scaffolds were able to promote new blood vessel growth and new bone regeneration within 4 weeks after implantation in critical-sized rabbit femur defects. Therefore, it was shown that 3D printed SrCS scaffolds with specific controllable structures can be fabricated and SrCS scaffolds had enhanced mechanical property and osteogenesis behavior which makes it a suitable potential candidate for bone regeneration.
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