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Characterization of bone matrix development in gelatin-based hydrogels

: Wenz, Annika; Tovar, Günter; Borchers, Kirsten; Kluger, Petra

Bionanomaterials 17 (2016), Nr.s1, S.S51
ISSN: 2193-0651
ISSN: 2193-066X
German Society for Biomaterials (Annual Conference) <2016, Aachen>
Deutsche Gesellschaft für Biomaterialien (DGBM Jahrestagung) <2016, Aachen>
Fraunhofer IGB ()

For the fabrication of bone tissue equivalents via tissue engineering and bioprinting approaches, one crucial element is the used biomaterial which on the one hand should support and enhance the function of the used cells, and on the other hand guarantee processability with the chosen manufacturing technique. The use of gelatin-based hydrogels for cell encapsulation provides the positive properties of the base material collagen, and offers the possibility of adjusting composition as well as characteristics like viscosity and gelling behavior [1,2]. Further modification of the material with components like hydroxyapatite (HAp) was shown to have a positive impact on processability with bioprinting approaches and properties of the material as well as its bioactivity [3,4,5]. In the current study, bioinks based on methacrylated gelatin (GM) and modified with HAp particles were used and analyzed for said parameters.
The viscosity of the bioinks was measured, as well as water uptake by the hydrogels and the gels’ mechanical properties. Human mesenchymal stem cells from adipose tissue (hASCs) of three donors were encapsulated in differently modified GM hydrogels, and matrix development during culture for 28 days in standard and osteogenic media was examined. To prove the development of a bone matrix, the mechanical properties of the hydrogels were analyzed, and the hydrogels were stained for bone matrix markers like collagen type I and osteocalcin. Further analysis of matrix composition was conducted via Raman spectroscopy.
The modification with HAp led to improved properties of the bioinks as well as the resulting hydrogels, as being shown by increased ink viscosity and mechanical properties of the hydrogels. The degree of water uptake, however, was not influenced. The staining of the hASC-laden hydrogels cultured under osteogenic conditions showed an increased deposition of bone components like collagen and non-collagenous proteins like osteocalcin in the modified hydrogels compared to the control GM gels after 28 days of culture. Surprisingly, this increase was also seen in the HAp-containing gels cultured under standard conditions (Fig. 1A), what illustrated the significant positive impact of the added HAp onto osteogenesis. Similarly, the spectroscopic analysis of said hydrogels on day 1 and day 28 of culture revealed peaks resulting from typical bone components like the collagen-related amino-acid proline (853/869/1067 cm-1) or carbonate which is found in the biological mineral phase of bone (1074 cm-1) (Fig. 1B). The developing bone matrix could also be detected by a rising storage module of the gels, resulting in an increase between 25% and 100% compared to day 1 (Fig. 1C) and representing the mechanical strength of the newly formed matrix.
In the current study, we could show the suitability of a GM-based material for the use in bone tissue engineering. The properties of the analyzed inks and resulting hydrogels could be modified by the addition of HAp, and the osteoinductive impact of the added mineral phase leading to a significant increase in osteogenesis in the hydrogels was shown. We therefore anticipate that the material will be highly suitable as a bioink for the bioprinting of bone tissue equivalents.