Three-dimensional printing of cell-laden hydrogels has evolved as a promising approach on the route to patient-specific or complex tissue-engineered constructs. However, it is still challenging to print structures with both, high shape fidelity and cell vitality. Herein, we used a synthetic nanosilicate clay, called Laponite, to build up scaffolds utilising the extrusion-based method 3D plotting. By blending with alginate and methylcellulose, a bioink was developed which allowed easy extrusion, achieving scaffolds with high printing fidelity. Following extrusion, approximately 70%-75% of printed immortalised human mesenchymal stem cells survived and cell viability was maintained over 21 days within the plotted constructs. Mechanical properties of scaffolds comprised of the composite bioink decreased over time when stored under cell culture conditions. Nevertheless, shape of the plotted constructs was preserved even over longer cultivation periods. Laponite is known for its favourable drug delivery properties. Two model proteins, bovine serum albumin and vascular endothelial growth factor were loaded into the bioink. We demonstrate that the release of both growth factors significantly changed to a more sustained profile by inclusion of Laponite in comparison to an alginate-methylcellulose blend in the absence of Laponite. In summary, addition of a synthetic clay, Laponite, improved printability, increased shape fidelity and was beneficial for controlled release of biologically active agents such as growth factors.

For both the incorporation of cells and future therapeutic applications the sterility of a biomaterial must be ensured. However, common sterilisation techniques are intense and often negatively impact on material physicochemical attributes, which can affect its suitability for tissue engineering and 3D printing. In the present study four sterilisation methods, autoclave, supercritical CO2 (scCO2) treatment, UV-and gamma () irradiation were evaluated regarding their impact on material properties and cellular responses. The investigations were performed on methyl cellulose (MC) as a component of an alginate/methyl cellulose (alg/MC) bioink, used for bioprinting embedded bovine primary chondrocytes (BPCs). In contrast to the autoclave, scCO2 and UV-treatments, the-irradiated MC resulted in a strong reduction in alg/MC viscosity and stability after extrusion which made this method unsuitable for precise bioprinting. Gel permeation chromatography analysis revealed a significant reduction in MC molecular mass only after-irradiation, which influenced MC chain mobility in the Ca 2+crosslinked alginate network as well as gel composition and microstructure. With regard to cell survival and proteoglycan matrix production, the results determined UV-irradiation and autoclaving as the best candidates for sterilisation. The scCO2-treatment of MC resulted in an unfavourable cell response indicating that this method needs careful optimisation prior to application for cell encapsulation. As proven by consistent FT-IR spectra, chemical alterations could be excluded as a cause for the differences seen between MC-treatments on alg/MC behaviour. This investigation provides knowledge for the development of a clinically appropriate 3D-printing-based fabrication process to produce bioengineered tissue for cartilage regeneration.

seen great progress over the last decades which led to some successful preliminary studies in humans [3,4] but is still not routinely implemented in the clinics, largely due to a shortage of donor organs. [5] Most trials in islet transplantation concentrated on injecting allogenic islets into the portal vein [6] and preventing rejection of donor islets with immunosuppressants. Since these tended to impair islet function [7,8] and in the liver islets are exposed to detrimental components in the blood, [5] soon thoughts turned to the possibility of protecting islets from the immune system by a thin coating of hydrogels. [9] Furthermore, protection from an immunological response might enable even xenotransplantation, for instance of porcine islets, [10] which could solve the problem of donor shortage.To achieve immune-isolating encapsulation, many researchers focused on alginate and alginate based hydrogel blends as coating, since this polymer cannot be digested in the human body lacking the relevant enzymes and has been shown to be nonimmunogenic if sufficiently purified. [11][12][13] Alginate is a polysaccharide extracted from brown algae, which can be crosslinked in different strengths by the addition of divalent cations such as Ca 2+ , Sr 2+ , or Ba 2+[14] and has been successfully used for encapsulation of different cell types in the past. [15] For pancreatic islets, either macro-or microencapsulation in alginate were established; in both cases islets have been found to retain their viability and functionality for a certain time, [16] but capsule size and composition definitely have an impact on function of islets, mainly as a function of diffusion distances. [17,18] Microcapsules only contain a single islet per capsule, encased in a thin layer of alginate, which decreases the distance between islets and the Transplantation of pancreatic islets is a promising strategy to alleviate the unstable blood-glucose control that some patients with diabetes type 1 exhibit and has seen many advances over the years. Protection of transplanted islets from the immune system can be accomplished by encapsulation within a hydrogel, the most investigated of which is alginate. In this study, islet encapsulation is combined with 3D extrusion bioprinting, an additive manufacturing method which enables the fabrication of 3D structures with a precise geometry to produce macroporous hydrogel constructs with embedded islets. Using a plottable hydrogel blend consisting of clinically approved ultrapure alginate and methylcellulose (Alg/MC) enables encapsulating pancreatic islets in macroporous 3D hydrogel constructs of defined geometry while retaining their viability, morphology, and functionality. Diffusion of glucose and insulin in the Alg/MC hydrogel is comparable to diffusion in plain alginate; the embedded islets continuously produce insulin and glucagon throughout the observation and still react to glucose stimulation albeit to a lesser degree than control islets.