In recent years, three-dimensional (3D) bioprinting has attracted wide research interest in biomedical engineering and clinical applications. This technology allows for unparalleled architecture control, adaptability and repeatability that can overcome the limits of conventional biofabrication techniques. Along with the emergence of a variety of 3D bioprinting methods, bioinks have also come a long way. From their first developments to support bioprinting requirements, they are now engineered to specific injury sites requirements to mimic native tissue characteristics and to support biofunctionality. Current strategies involve the use of bioinks loaded with cells and biomolecules of interest, without altering their functions, to deliver in situ the elements required to enhance healing/regeneration. The current research and trends in bioink development for 3D bioprinting purposes is overviewed herein.

different in the distinct zones of the bilayered constructs, and the intermediate regions showed pre-hypertrophic chondrocyte gene expression, especially on the BdTCP constructs. Immunofluorescence analysis supported these observations. This study showed that the proposed bilayered scaffolds allowed a specific stimulation of the chondrogenic and osteogenic cells in the coculture system together with the formation of an osteochondral-like tissue interface. Hence, the structural adaptability, suitable mechanical properties, and biological performance of the hierarchical scaffolds make these constructs a desired strategy for OC defect regeneration.

In cartilage tissue engineering (TE), several processing technologies have been combined to create scaffolds for efficient tissue repair. In our study, we propose novel silk fibroin (SF) scaffolds derived from enzymatically crosslinked SF hydrogels processed by salt-leaching and freeze-drying technologies, for articular cartilage applications. Though these scaffolds, we were able to combine the elastic properties of hydrogel-based systems, with the stability, resilience and controlled porosity of scaffolds processed via salt-leaching and freeze-drying technologies. SF protein has been extensively explored for TE applications, as a result of its mechanical strength, elasticity, biocompatibility, and biodegradability. Thus, the structural, mechanical and biological performance of the proposed scaffolds potentiates their use as three-dimensional matrices for cartilage regeneration.

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Chemically functionalized multi-walled carbon nanotubes (CNTs) are used as carriers for laccase immobilization. In this work, CNTs were modified using different approaches with a combination of methods involving hydrothermal oxidation with nitric acid, treatment with 3-aminopropyltriethoxysilane, glutaraldehyde, N-ethyl-N-(3-(dimethylamino)-propyl) carbodiimide hydrochloride and N-hydroxysuccinimide. The enzyme immobilization efficiency and recovered activity were evaluated towards-azino-bis(3-ethylbenzathiazoline-6-sulfonic acid) biocatalytic oxidation. The best compromise between immobilization efficiency and recovered activity was obtained using the CNTs functionalized with 0.3 M HNO 3 , treated with N-ethyl-N-(3-(dimethylamino)propyl) carbodiimide hydrochloride and N-hydroxysuccinimide. This catalyst also showed the best thermal stability (at 50 and 60 ºC). The bioconjugate based on this material was characterized by vibrational spectroscopies (FTIR and Raman) and by N 2 adsorption. The results from reutilization tests showed that laccase activity was kept above 65% of its initial value after five consecutive cycles of reuse. The biocatalytic performance of the immobilized enzyme was evaluated for the degradation of a mixture of phenolic compounds in water containing phenol, resorcinol, 4-methoxyphenol and 4-chlorophenol. As means of cost efficient to enzyme reutilization, laccase was immobilized over polysulfone membranes blended with the functionalized CNTs and studied in the degradation of 4-methoxyphenol.

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Advanced strategies to bioengineer a fibrocartilaginous tissue to restore the function of the meniscus are necessary. Currently, 3D bioprinting technologies have been employed to fabricate clinically relevant patient-specific complex constructs to address unmet clinical needs. In this study, a highly elastic hybrid construct for fibrocartilaginous regeneration is produced by coprinting a cell-laden gellan gum/fibrinogen (GG/FB) composite bioink together with a silk fibroin methacrylate (Sil-MA) bioink in an interleaved crosshatch pattern. We characterize each bioink formulation by measuring the rheological properties, swelling ratio, and compressive mechanical behavior. For in vitro biological evaluations, porcine primary meniscus cells (pMCs) are isolated and suspended in the GG/FB bioink for the printing process. The results show that the GG/FB bioink provides a proper cellular microenvironment for maintaining the cell viability and proliferation capacity, as well as the maturation of the pMCs in the bioprinted constructs, while the Sil-MA bioink offers excellent biomechanical behavior and structural integrity. More importantly, this bioprinted hybrid system shows the fibrocartilaginous tissue formation without a dimensional change in a mouse subcutaneous implantation model during the 10-week postimplantation. Especially, the alignment of collagen fibers is achieved in the bioprinted hybrid constructs. The results demonstrate that this bioprinted mechanically reinforced hybrid construct offers a versatile and promising alternative for the production of advanced fibrocartilaginous tissue.

Hollow tubular conduits (TCs) with tunable architecture and biological properties are in great need for modulating cell functions and drug delivery in guided tissue regeneration. Here, a new methodology to produce enzymatically cross-linked silk fibroin TCs is described, which takes advantage of the tyrosine groups present in silk structure that are known to allow the formation of a covalently cross-linked hydrogel. Three different processing methods are used as a final step to modulate the properties of the silk-based TCs. This approach allows to virtually adjust any characteristic of the final TCs. The final microstructure ranges from a nonporous to a highly porous network, allowing the TCs to be selectively porous to 4 kDa molecules, but not to human skin fibroblasts. Mechanical properties are dependent both on the processing method and thickness of the TCs. Bioactivity is observed after 30 days of immersion in simulated body fluid only for the TCs submitted to a drying processing method (50 °C). The in vivo study performed in mice demonstrates the good biocompatibility of the TCs. The enzymatically cross-linked silk fibroin TCs are versatile and have adjustable characteristics that can be exploited in a variety of biomedical applications, particularly in guidance of peripheral nerve regeneration.