No abstract

Critical size bone defects are regularly treated by auto-and allograft transplantation. However, such treatments require to harvest bone from patient donor sites, with often limited tissue availability or risk of donor site morbidity. Not requiring bone donation, three-dimensionally (3D) printed implants and biomaterial-based tissue engineering (TE) strategies promise to be the next generation therapies for bone regeneration. We present here polylactic acid (PLA)-bioactive glass (BG) composite scaffolds manufactured by fused deposition modeling (FDM), involving the fabrication of PLA-BG composite filaments which are used to 3D print controlled open-porous and osteoinductive scaffolds. We demonstrated the printability of PLA-BG filaments as well as the bioactivity and cytocompatibility of PLA-BG scaffolds using pre-osteoblast MC3T3E1 cells. Gene expression analyses indicated the beneficial impact of BG inclusions in FDM scaffolds regarding osteoinduction, as BG inclusions lead to increased osteogenic differentiation of human adipose-derived stem cells in comparison to pristine PLA. Our findings confirm that FDM is a convenient additive manufacturing technology to develop PLA-BG composite scaffolds suitable for bone tissue engineering.

Biofabrication can be a tool to three-dimensionally (3D) print muscle cells embedded inside hydrogel biomaterials, ultimately aiming to mimic the complexity of the native muscle tissue and to create in-vitro muscle analogues for advanced repair therapies and drug testing. However, to 3D print muscle analogues of high cell alignment and synchronous contraction, the effect of biofabrication process parameters on myoblast growth has to be understood. A suitable biomaterial matrix is required to provide 3D printability as well as matrix degradation to create space for cell proliferation, matrix remodelling capacity, and cell differentiation. We demonstrate that by the proper selection of nozzle size and extrusion pressure, the shear stress during extrusion-bioprinting of mouse myoblast cells (C2C12) can achieve cell orientation when using oxidized alginate-gelatin (ADA-GEL) hydrogel bionk. The cells grow in the direction of printing, migrate to the hydrogel surface over time, and differentiate into ordered myotube segments in areas of high cell density. Together, our results show that ADA-GEL hydrogel can be a simple and cost-efficient biodegradable bioink that allows the successful 3D bioprinting and cultivation of C2C12 cells in-vitro to study muscle engineering.

Electroactive hydrogels can be used to influence cell response and maturation by electrical stimulation. However, hydrogel formulations which are 3D printable, electroactive, cytocompatible, and allow cell adhesion, remain a challenge in the design of such stimuli‐responsive biomaterials for tissue engineering. Here, a combination of pyrrole with a high gelatin‐content oxidized alginate‐gelatin (ADA‐GEL) hydrogel is reported, offering 3D‐printability of hydrogel precursors to prepare cytocompatible and electrically conductive hydrogel scaffolds. By oxidation of pyrrole, electroactive polypyrrole:polystyrenesulfonate (PPy:PSS) is synthesized inside the ADA‐GEL matrix. The hydrogels are assessed regarding their electrical/mechanical properties, 3D‐printability, and cytocompatibility. It is possible to prepare open‐porous scaffolds via bioplotting which are electrically conductive and have a higher cell seeding efficiency in scaffold depth in comparison to flat 2D hydrogels, which is confirmed via multiphoton fluorescence microscopy. The formation of an interpenetrating polypyrrole matrix in the hydrogel matrix increases the conductivity and stiffness of the hydrogels, maintaining the capacity of the gels to promote cell adhesion and proliferation. The results demonstrate that a 3D‐printable ADA‐GEL can be rendered conductive (ADA‐GEL‐PPy:PSS), and that such hydrogel formulations have promise for cell therapies, in vitro cell culture, and electrical‐stimulation assisted tissue engineering.

Hydrogels that allow for the successful long-term in vitro culture of cell–biomaterial systems to enable the maturation of tissue engineering constructs are highly relevant in regenerative medicine. Naturally derived polysaccharide-based hydrogels promise to be one material group with enough versatility and chemical functionalization capability to tackle the challenges associated with long-term cell culture. We report a marine derived oxidized alginate, alginate dialdehyde (ADA), and gelatin (GEL) system (ADA-GEL), which is cross-linked via ionic (Ca2+) and enzymatic (microbial transglutaminase, mTG) interaction to form dually cross-linked hydrogels. The cross-linking approach allowed us to tailor the stiffness of the hydrogels in a wide range (from <5 to 120 kPa), without altering the initial ADA and GEL hydrogel chemistry. It was possible to control the degradation behavior of the hydrogels to be stable for up to 30 days of incubation. Increasing concentrations of mTG cross-linker solutions allowed us to tune the degradation behavior of the ADA-GEL hydrogels from fast (<7 days) to moderate (14 days) and slow (>30 days) degradation kinetics. The cytocompatibility of mTG cross-linked ADA-GEL was assessed using NIH-3T3 fibroblasts and ATDC-5 mouse teratocarcinoma cells. Both cell types showed highly increased cellular attachment on mTG cross-linked ADA-GEL in comparison to Ca2+ cross-linked hydrogels. In addition, ATDC-5 cells showed a higher proliferation on mTG cross-linked ADA-GEL hydrogels in comparison to tissue culture polystyrene control substrates. Further, the attachment of human umbilical vein endothelial cells (HUVEC) on ADA-GEL (+) mTG was confirmed, proving the suitability of mTG+Ca2+ cross-linked ADA-GEL for several cell types. Summarizing, a promising platform to control the properties of ADA-GEL hydrogels is presented, with the potential to be applied in long-term cell culture investigations such as cartilage, bone, and blood-vessel engineering, as well as for biofabrication.