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Three-dimensional printing technologies exhibit tremendous potential in the advancing fields of tissue engineering and regenerative medicine due to the precise spatial control over depositing the biomaterial. Despite their widespread utilization and numerous advantages, the development of suitable novel biomaterials for extrusion-based 3D printing of scaffolds that support cell attachment, proliferation, and vascularization remains a challenge. Multi-material composite hydrogels present incredible potential in this field. Thus, in this work, a multi-material composite hydrogel with a promising formulation of chitosan/gelatin functionalized with egg white was developed, which provides good printability and shape fidelity. In addition, a series of comparative analyses of different crosslinking agents and processes based on tripolyphosphate (TPP), genipin (GP), and glutaraldehyde (GTA) were investigated and compared to select the ideal crosslinking strategy to enhance the physicochemical and biological properties of the fabricated scaffolds. All of the results indicate that the composite hydrogel and the resulting scaffolds utilizing TPP crosslinking have great potential in tissue engineering, especially for supporting neo-vessel growth into the scaffold and promoting angiogenesis within engineered tissues. Graphic abstract

In recent years, 3D bioprinting has attracted broad research interest in biomedical engineering and clinical applications. However, there are two issues need to be solved urgently at present, the development of ink is the first pressing thing for 3D printing tissue engineering scaffold, other thing is the promotion of angiogenesis in the scaffold. Therefore, a gelatin/sodium alginate‐based hydrogel with protein‐rich is developed here, which is prepared by gelatin, sodium alginate, and soy protein/soy peptide powder. The prepared inks exhibit excellent shear‐thinning behavior, which contribute to extrusion‐based printing; also shown good crosslinking ability by calcium chloride. The macroporous composite scaffolds are printed by 3D printing using the developed ink and the physicochemical properties of the scaffolds are evaluated. Moreover, the cytocompatibility of printed scaffold is characterized by using human umbilical vein epidermal cells, results show that the scaffolds with soy protein and soy peptide powder can promote cell attach, spread, migration, and proliferation. The further research of chicken embryo allantoic membrane assay and animal experiment are carried, and results present that the scaffold can promote the growth of neo‐vessels in the scaffold, which means the developed ink with soy protein and soy peptide powder has great potential for angiogenesis.

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Three dimensional printable formulation of self‐standing and vascular‐supportive structures using multi‐materials suitable for organ engineering is of great importance and highly challengeable, but, it could advance the 3D printing scenario from printable shape to functional unit of human body. In this study, the authors report a 3D printable formulation of such self‐standing and vascular‐supportive structures using an in‐house formulated multi‐material combination of albumen/alginate/gelatin‐based hydrogel. The rheological properties and relaxation behavior of hydrogels were analyzed before the printing process. The suitability of the hydrogel in 3D printing of various customizable and self‐standing structures, including a human ear model, was examined by extrusion‐based 3D printing. The structural, mechanical, and physicochemical properties of the printed scaffolds were studied systematically. Results supported the 3D printability of the formulated hydrogel with self‐standing structures, which are customizable to a specific need. In vitro cell experiment showed that the formulated hydrogel has excellent biocompatibility and vascular supportive behavior with the extent of endothelial sprout formation when tested with human umbilical vein endothelial cells. In conclusion, the present study demonstrated the suitability of the extrusion‐based 3D printing technique for manufacturing complex shapes and structures using multi‐materials with high fidelity, which have great potential in organ engineering.

Three-dimensional microextrusion bioprinting has attracted great interest for fabrication of hierarchically structured, functional tissue substitutes with spatially defined cell distribution. Despite considerable progress, several significant limitations remain such as a lack of suitable bioinks which combine favorable cell response with high shape fidelity. Therefore, in this work a novel bioink of alginate-methylcellulose (AlgMC) blend functionalized with egg white (EW) was developed with the aim of solving this limitation. In this regard, a stepwise strategy was proposed to improve and examine the cell response in low-viscosity alginate inks (3 %, w/v) with different EW concentrations, and in high-viscosity inks after gradual methylcellulose (MC) addition for enhancing printability. The rheological properties and printability of these cell-responsive bioinks were characterized to obtain an optimized formulation eliciting balanced physicochemical and biological properties for fabrication of volumetric scaffolds. The bioprinted AlgMC+EW constructs exhibited excellent shape fidelity while encapsulated human mesenchymal stem cells (MSC) showed high post-printing viability as well as adhesion and spreading within the matrix. In a proof-of-concept experiment, the impact of these EW-mediated effects on osteogenesis of bioprinted primary human pre-osteoblasts (hOB) was evaluated. Results confirmed a high viability of hOB (93.7 ± 0.15 %) post-fabrication in an EW-supported AlgMC bioink allowing cell adhesion, proliferation and migration. EW even promoted the expression of osteogenic genes, coding for bone sialoprotein (IBSP) and osteocalcin (BGLAP) on mRNA level. To demonstrate the suitability of the novel ink for future fabrication of multi-zonal bone substitutes, AlgMC+EW was successfully co-printed together with a pasty calcium phosphate bone cement biomaterial ink to achieve a partly mineralized 3D volumetric environment with good cell viability and spreading. Along with the EW-mediated positive effects within bioprinted AlgMC-based scaffolds, this highlighted the promising potential of this novel ink for biofabrication of bone tissue substitutes in clinically relevant dimensions.

One of the biggest hindrances in tissue engineering in recent decades has been the complexity of the prevascularized channels of the engineered scaffold, which was still lower than that of human tissues. Another relative difficulty was the lack of precision molding capability, which restricted the clinical applications of the huge engineered scaffold. In this study, a promising approach was proposed to prepare hydrogel scaffold with prevascularized channels by liquid bath printing, in which chitosan/β-sodium glycerophosphate served as the ink hydrogel, and gelation/nanoscale bacterial cellulose acted as the supporting hydrogel. Here, the ink hydrogel was printed by a versatile nozzle and embedded in the supporting hydrogel. The ink hydrogel transformed into liquid effluent at low temperature after the cross-linking of gelatin by microbial transglutaminase (mTG). No residual template was seen on the channel surface after template removal. This preparation had a high degree of freedom in the geometry of the channel, which was demonstrated by making various prevascularized channels including circular, branched, and tree-shaped networks. The molding accuracy of the channel was assessed by studying the roundness of the cross section of the molded hollow channel, and the effect of the mechanical properties by adding bacterial cellulose to the supporting hydrogel was analyzed. Human umbilical vein endothelial cells were injected into the aforementioned channels which formed a confluent and homogeneous distribution on the surface of the channels. Altogether, these results showed that this approach can construct hydrogel scaffolds with complex and accurate molding prevascularized channels, and hs great potential to resolve the urgent vascularization issue of bulk tissue-engineering scaffold.

The meshes for hernia repair result in many problems that are related to complications including chronic pain and limited movement due to inadequate mechanical strength, non‐absorbability, or low elasticity. In this study, degradable polylactic acid (PLA), synthetic thermoplastic polyurethane (TPU), and acellular dermal matrix (ADM) powders are combined to prepare a novel PLA/TPU/ADM mesh with three different topological structures (square, circular, and diamond) by 3D printing. The physicochemical properties and structural characteristics of mesh are studied, the results show that the diamond structure mesh with the pore size of 3 mm has sufficient elasticity and tensile strength, which provides the efficient mechanical strength required for hernia repair (16 N cm−1) and the value more than polypropylene(PP) mesh. Besides, in vitro and in vivo experiments demonstrate human umbilical vein endothelial cells could successfully proliferate on the PLA/TPU/ADM mesh whose biocompatibility with the host is shown using a rat model of abdominal wall defect. In conclusion, the results of this study demonstrate that the PLA/TPU/ADM mesh may be considered a good choice for hernia repair as its potential to overcome the elastic and strength challenges associated with a highly flexible abdominal wall, as well as its good biocompatibility.