Three-dimensional bioprinting has rapidly paralleled many biomedical applications and assisted in advancing the printing of complex human organs for a better therapeutic practice. The objective of this systematic review is to highlight evidence from the existing studies and evaluate the effectiveness of using natural-based bioinks in skin regeneration and wound healing. A comprehensive search of all relevant original articles was performed based on prespecified eligibility criteria. The search was carried out using PubMed, Web of Science, Scopus, Medline Ovid, and ScienceDirect. Eighteen articles fulfilled the inclusion and exclusion criteria. The animal studies included a total of 151 animals with wound defects. A variety of natural bioinks and skin living cells were implanted in vitro to give insight into the technique through different assessments and findings. Collagen and gelatin hydrogels were most commonly used as bioinks. The follow-up period ranged between one day and six weeks. The majority of animal studies reported that full wound closure was achieved after 2–4 weeks. The results of both in vitro cell culture and in vivo animal studies showed the positive impact of natural bioinks in promoting wound healing. Future research should be focused more on direct the bioprinting of skin wound treatments on animal models to open doors for human clinical trials.

Skin substitutes can provide a temporary or permanent treatment option for chronic wounds. The selection of skin substitutes depends on several factors, including the type of wound and its severity. Full-thickness skin grafts (SGs) require a well-vascularised bed and sometimes will lead to contraction and scarring formation. Besides, donor sites for full-thickness skin grafts are very limited if the wound area is big, and it has been proven to have the lowest survival rate compared to thick- and thin-split thickness. Tissue engineering technology has introduced new advanced strategies since the last decades to fabricate the composite scaffold via the 3D-bioprinting approach as a tissue replacement strategy. Considering the current global donor shortage for autologous split-thickness skin graft (ASSG), skin 3D-bioprinting has emerged as a potential alternative to replace the ASSG treatment. The three-dimensional (3D)-bioprinting technique yields scaffold fabrication with the combination of biomaterials and cells to form bioinks. Thus, the essential key factor for success in 3D-bioprinting is selecting and developing suitable bioinks to maintain the mechanisms of cellular activity. This crucial stage is vital to mimic the native extracellular matrix (ECM) for the sustainability of cell viability before tissue regeneration. This comprehensive review outlined the application of the 3D-bioprinting technique to develop skin tissue regeneration. The cell viability of human skin cells, dermal fibroblasts (DFs), and keratinocytes (KCs) during in vitro testing has been further discussed prior to in vivo application. It is essential to ensure the printed tissue/organ constantly allows cellular activities, including cell proliferation rate and migration capacity. Therefore, 3D-bioprinting plays a vital role in developing a complex skin tissue structure for tissue replacement approach in future precision medicine.

3D bioprinting technology is a well-established and promising advanced fabrication technique that utilizes potential biomaterials as bioinks to replace lost skin and promote new tissue regeneration. Cutaneous regenerative biomaterials are highly commended since they benefit patients with larger wound sizes and irregular wound shapes compared to the painstaking split-skin graft. This study aimed to fabricate biocompatible, biodegradable, and printable bioinks as a cutaneous substitute that leads to newly formed tissue post-transplantation. Briefly, gelatin (GE) and polyvinyl alcohol (PVA) bioinks were prepared in various concentrations (w/v); GE (6% GE: 0% PVA), GPVA3 (6% GE: 3% PVA), and GPVA5 (6% GE: 5% PVA), followed by 0.1% (w/v) genipin (GNP) crosslinking to achieve optimum printability. According to the results, GPVA5_GNP significantly presented at least 590.93 ± 164.7% of swelling ratio capacity and optimal water vapor transmission rate (WVTR), which is <1500 g/m2/h to maintain the moisture of the wound microenvironment. Besides, GPVA5_GNP is also more durable than other hydrogels with the slowest biodegradation rate of 0.018 ± 0.08 mg/h. The increasing amount of PVA improved the rheological properties of the hydrogels, leading the GPVA5_GNP to have the highest viscosity, around 3.0 ± 0.06 Pa.s. It allows a better performance of bioinks printability via extrusion technique. Moreover, the cross-section of the microstructure hydrogels showed the average pore sizes >100 μm with excellent interconnected porosity. X-ray diffraction (XRD) analysis showed that the hydrogels maintain their amorphous properties and were well-distributed through energy dispersive X-ray after crosslinking. Furthermore, there had no substantial functional group changes, as observed by Fourier transform infrared spectroscopy, after the addition of crosslinker. In addition, GPVA hydrogels were biocompatible to the cells, effectively demonstrating >90% of cell viability. In conclusion, GPVA hydrogels crosslinked with GNP, as prospective bioinks, exhibited the superior properties necessary for wound healing treatment.

The purpose of this work is to investigate the microstructure and tensile strength of Ti6Al4V pre-alloyed powders produced by a direct metal laser sintering technique. Traditionally, Ti6Al4V products for biomedical applications were produced through hot working or machining of wrought semi-finished products. A change in the production route for manufacturing Ti6Al4V products, from the more traditional methods to an additive manufacturing route, requires an investigation of microstructure and mechanical properties because these are strongly influenced by the production route. The microstructure obtained through rapid solidification during laser sintering shows a very fine α+β lamellar morphology. There is also evidence of martensite which was expected due to high solidification rate of the liquid pool from a temperature above the β-transus during the laser sintering process. Structurally, good mechanical properties which are comparable to the bulk material were obtained.

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