Technological watch

Cartilage injuries and bone loss become increasingly prevalent in modern societies. Articular cartilage and menisci have low or no capacity for self-repair and none of the available treatments provide satisfactory, long-term outcomes. Additionally, despite self-regenerating capabilities of bone tissue, the mechanism may fail or become insufficient, creating the need for surgical bone replacement, which is restrained by natural graft accessibility. 3D bioprinting is a rapidly developing technology emerging as a promising remedial therapy in orthopedics. The extensive and ongoing studies in this field are focused on such topics as cartilage and bone biology, standardization of cell culture protocols, bioink formulation, and 3D bioprinting technology. Recent results of these examinations, focused on applications in orthopedics, are presented in this review.

https://www.sciencedirect.com/science/article/pii/S2405886619300399?dgcid=rss_sd_allhttps://www.sciencedirect.com/science/article/pii/S2405886619300399Design and characterisation of multi-functional strontium-gelatin nanocomposite bioinks with improved print fidelity and osteogenic capacityPublication date: June 2020

Source: Bioprinting, Volume 18

Author(s): Cesar R. Alcala-Orozco, Isha Mutreja, Xiaolin Cui, Dhiraj Kumar, Gary J. Hooper, Khoon S. Lim, Tim B.F. Woodfield

3D bioprinting of constructs for tissue engineering and regenerative medicine has steadily gained attention due to its potential to fabricate anatomically-precise living constructs, localise specific cell types and enable the regeneration of functional tissues in a clinical setting. However, the limited availability of bioinks that can be successfully 3D bioprinted with high fidelity and simultaneously provide encapsulated cells with a tailored, low-stiffness microenvironment supporting functional tissue formation remains an unmet challenge. To address both the physical and biological limitations of available bioinks, this study aimed to develop a nanocomposite bioink (Sr-GelMA) comprising of strontium-carbonate (Sr) nanoparticles and low concentration (5 w/v%) gelatin-methacryloyl (GelMA) hydrogel for extrusion-based 3D bioprinting of low-stiffness cell-laden scaffolds with high shape fidelity and bone-specific cell signalling factors. We systematically investigated the effect of Sr incorporation on hydrogel physico-chemical properties, print fidelity, scaffold shape retention, as well as cell viability, osteogenic differentiation and in vitro bone formation. Nanocomposite Sr-GelMA hydrogels retained their physical and mechanical properties, while rheological studies revealed a significant increase in viscosity profiles that led to notably enhanced printability compared to GelMA alone. Moreover, bioprinted Sr-GelMA scaffolds exhibited excellent shape fidelity evidenced by a defined pore geometry on the x-y-z axis, resulting in an interconnected bioink filament and pore network that was maintained even after long-term culture and osteogenic differentiation (28 days) of human mesenchymal stromal cells (hMSCs). The presence of clustered Sr nanoparticles in the cell-laden bioink allowed high quality bioprinting combined with high hMSC viability (>95%) post-fabrication. Furthermore, Sr addition resulted in enhanced osteogenic differentiation of hMSCs as revealed by higher alkaline phosphatase (ALP) levels, osteocalcin (OCN) and collagen type-I (Col I) expression, with mineralised nodule formation distributed homogenously throughout the bioprinted construct. This study demonstrated that strontium-based nanocomposite bioinks optimised for extrusion-based 3D bioprinting of osteoconductive scaffolds support long-term shape retention with promising potential for bone tissue regeneration.

https://www.sciencedirect.com/science/article/pii/S2405886619300417?dgcid=rss_sd_allhttps://www.sciencedirect.com/science/article/pii/S2405886619300417Multilayered microcasting of agarose–collagen composites for neurovascular modelingPublication date: March 2020

Source: Bioprinting, Volume 17

Author(s): Hossein Heidari, Hayden Taylor

The in vitro fabrication of vascular networks is one of the most complex challenges currently faced in tissue engineering. We describe a method to create multi-layered, cell-laden hydrogel microstructures with coaxial geometries and heterogeneous elastic moduli. The technique can be used to build in vitro vascular structures that are fully embedded in physiologically realistic hydrogels. Our technique eliminates rigid polymeric surfaces from the vicinity of the cells—overcoming a limitation of many microfluidic models—and allows layers of multiple cell types to be defined with tailored ECM composition and stiffness, and in direct contact with each other. We demonstrate channels with internal diameters as small as 175 ??m, and agarose–collagen (AC) gels whose Young’s moduli range from 1.4–8.3 ?kPa. We also show co-axial geometries with layer thicknesses as small as 125 ??m. One potential application of such structures is to simulate brain microvasculature. Towards this goal, the composition and mechanical properties of the composite AC hydrogels are optimized for cell viability and biological performance in both 2D and 3D culture. Seven-day viability of human microvascular endothelial cells (HMECs) and SY5Y glial cells is found to be maximized with a collagen content of 0.05% (w/v) when agarose content ranges between 0.25% and 1% (w/v). Additionally, we quantify the roles of type I bovine and rat-tail collagen, Matrigel, and poly-d-lysine–collagen–Matrigel coatings in promoting HMEC spreading, proliferation and confluence. 3D triple-layer vascular constructs have been fabricated, composed of a cannular monolayer of HMECs surrounded by two regions of SY5Ys with differing spatial densities. The endothelia are confluent and maintain trans-endothelial electrical resistance (TEER) values around 300 ?? ?cm2 over 11.5 days. This prototype opens the way for intricate multi-luminal blood vessels to be fabricated in vitro.

https://www.sciencedirect.com/science/article/pii/S2405886619300387?dgcid=rss_sd_allhttps://www.sciencedirect.com/science/article/pii/S2405886619300387Chondroprotective and osteogenic effects of silk-based bioinks in developing 3D bioprinted osteochondral interfacePublication date: March 2020

Source: Bioprinting, Volume 17

Author(s): Joseph Christakiran Moses, Triya Saha, Biman B. Mandal

Attributing cell instructive features and multifunctionality to biological inks (bioinks) employed for three-dimensional (3D) printing strategies is very much essential to bring about a paradigm shift in developing next generation smart intuitive 3D bioprinted constructs. Giving perspective to this notion, we explore here the feasibilities in developing multifunctional silk-based cartilage and bone bioinks for recreating heterogeneous complicated tissue constructs such as the osteochondral interface. In this regard, the developed silk based bioinks exhibit shear thinning behaviour with quick thixotropic recovery (~90% recovery) aiding in printing self-standing structures with decent print fidelity. The hydrogel network within the 3D bioprinted constructs present good permeability enabling in forming an undulating demarcation region at the bioprinted osteochondral interface. Furthermore, the cartilage and bone inks used for the microextrusion based bioprinting of osteochondral constructs facilitate the spatial maturation and differentiation of encapsulated stem cells towards osteogenic and chondrogenic lineages. The incorporation of strontium doped nano-apatites activates hypoxia inducible factor (HIF-1?) related genes, conferring proangiogenic and chondroprotective traits to the bioinks. Involvement of strontium in down regulating cyclooxygenase-2 via inhibiting prostaglandins (PGE2) pathway enabled anti-osteoclastic activity while favouring M2 macrophage biasness. Altogether, these findings corroborate the potential of the developed nanocomposite bioinks for fabricating clinically viable grafts for osteochondral defect repair associated with osteoporosis.

Graphical abstract