Bone matrix production in hydroxyapatite-modified hydrogels suitable for bone bioprinting

Abstract

Though bioprinting is a forward-looking approach in bone tissue engineering, the development of bioinks which are on the one hand processable with the chosen printing technique, and on the other hand possess the relevant mechanical as well as osteoconductive features remains a challenge. In the present study, polymer solutions based on methacrylated gelatin and methacrylated hyaluronic acid modified with hydroxyapatite (HAp) particles (5 wt%) were prepared. Encapsulation of primary human adipose-derived stem cells in the HAp-containing gels and culture for 28 d resulted in a storage moduli significantly increased to 126% ± 9.6% compared to the value on day 1 by the sole influence of the HAp. Additional use of osteogenic media components resulted in an increase of storage module up to 199% ± 27.8%. Similarly, the loss moduli was increased to 370% ± 122.1% under the influence of osteogenic media components and HAp. Those changes in rheological material characteristics indicate a distinct change in elastic and viscous hydrogel properties, and are attributed to extensive matrix production in the hydrogels by the encapsulated cells, what could also be proven by staining of bone matrix components like collagen I, fibronectin, alkaline phosphatase and osteopontin. When using the cell-laden polymer solutions as bioinks to build up relevant geometries, the ink showed excellent printability and the printed grid structure's integrity remained intact over a culture time of 28 d. Again, an intense matrix formation as well as upregulation of osteogenic markers by the encapsulated cells could be shown. In conclusion, we demonstrated that our HAp-containing bioinks and hydrogels on basis of methacrylated gelatin and hyaluronic acid are on the one hand highly suitable for the build-up of relevant three-dimensional geometries with microextrusion bioprinting, and on the other hand exhibit a significant positive effect on bone matrix development and remodeling in the hydrogels, as indicated by rheological measurements and staining of bone components. This makes the developed composite hydrogels an excellent material for bone bioprinting approaches.

Recent Advances in Photo-Crosslinkable Hydrogels for Biomedical Applications

“…By adding MeHA, heparin or gellan gum into the GelMA hydrogel construct, chondrocytes encapsulated in such 3D hybrid hydrogels maintain their chondrogenic phenotypes and increase the deposition of collagen type II [8285]. For bone tissue engineering applications, GelMA hydrogel loaded with nanosilicate or hydroxyapatite was shown to enhance the osteogenic differentiation of mesenchymal stem cells and bone mineralization in the absence of any osteoinducting factors [77,86]. Moreover, by incorporating a bioprinted vascular tissue construct into the nanosilicate-modified GelMA hydrogel, osteogenic potential of mesenchymal stem cells and bone mineralization were further enhanced in the presence of osteoinducting factors and VEGF, suggesting that this vascularized 3D bone tissue construct could be potentially used as a bone transplant for bone regeneration [68].…”

Beyond the Modification Degree: Impact of Raw Material on Physicochemical Properties of Gelatin Type A and Type B Methacryloyls

“…Formulations of GM(A) with adjusted properties are also increasingly used for sophisticated fabrication techniques such as inkjet‐printing, robotic dispensing, fused deposition modeling, or two‐photon polymerization . Differences in mechanical properties of resulting GM hydrogels and tissue‐specific additives are utilized to emulate most diverse tissues such as bone, cartilage, adipose tissue, cardiac tissue, and as matrix for formation of capillary structures . GM hydrogels with different cross‐linking densities were also utilized for drug delivery applications …”

Improved vasculogenesis and bone matrix formation through coculture of endothelial cells and stem cells in tissue‐specific methacryloyl gelatin‐based hydrogels

“…Gelatin can be modified with various amounts of methacryl groups to obtain covalently crosslinked gels that are stable under physiologic conditions and can be tuned in their mechanical properties (Hoch, Schuh, Hirth, Tovar, & Borchers, ). Hydrogels based on such methacryloyl‐modified gelatin (GM) have recently been used by our group for the engineering of various types of tissue equivalents like fatty tissue (Huber, Borchers, Tovar, & Kluger, ), cartilage (Hoch, Tovar, & Borchers, ), or bone (Wenz, Borchers, Tovar, & Kluger, ).…”