Such a strategy may readily be translated to the clinic as a construct loaded with cells and growth factor could be injected or implanted into a patient, and sustained release of the bioactive factor could preclude the need for future growth factor injections. 15 Sustained presentation of the growth factor from a biomaterial directly to encapsulated cells would alleviate these concerns, as the BMP-2 would be available to cells in the interior of the construct as well as those near its edges, while the biomaterial can serve the role of protecting and stabilizing the growth factor, thus maintaining its bioactivity. While extracellular matrix (ECM) proteins can bind BMP-2, 14 protecting and stabilizing the growth factor, this slows its diffusion, possibly keeping it from cells in the center of a tissue engineered construct. Such replenishment is not only inconvenient, but the total amount of protein used in all doses may be cost-prohibitive. 13 As a result, regular replenishment is required to maintain their bioactivity. When growth factors are injected intravenously their half-life is on the order of minutes, 11, 12 and, for BMP-2 specifically, it is on the order of hours in serum-containing culture medium at 37☌ in vitro.
10 However, delivery of free growth factors, either in cell culture media or to a bone defect site, is problematic as they are typically unstable in physiologic conditions with very short half-lives. With respect to hASCs, exogenous presentation of this growth factor in culture media has also been shown to induce osteogenesis by hASCs both in vitro 8– 10 and when injected periodically in vivo into defects filled with hASC-laden scaffolds. 7 Combined with their strong osteogenic capacity, these factors make hASCs a promising cell source for bone tissue engineering strategies.īone morphogenetic protein-2 (BMP-2) is a growth factor known for its role in bone tissue formation. 5 Compared with human bone marrow-derived mesenchymal stem cells (hMSCs), hASCs can more easily be obtained in larger numbers 6 and are more proliferative in culture. 2 These cells can be obtained in high number from both young and elderly patients, 3 possess immunomodulatory properties, 4 and are highly proliferative in vitro allowing for cell expansion. Human adipose-derived stem cells (hASCs) are multipotent adult stem cells that are easily isolated from adipose tissue and can differentiate down the osteogenic lineage both in vitro 1 and in vivo. Thus, the GelMA system is a promising biomaterial for BMP-2-mediated hASC osteogenesis. Taken together, these findings suggest that controlled delivery of BMP-2 from the GelMA enhances its osteogenic bioactivity compared to free growth factor presented in the media. There were no statistically significant differences in calcium content between groups with 25, 50, or 100 μg/mL loaded BMP-2, suggesting that using a lower growth factor dose may be as effective as a higher loading amount in this system. Expression of alkaline phosphatase was accelerated, and cells in hydrogels with loaded BMP-2 deposited more calcium at one, two, and four weeks than cells without BMP-2 or with the growth factor presented in the media. Both donors exhibited similar responses to the loaded and exogenous growth factor BMP-2 from the hydrogels had a statistically significant effect on hASC osteogenic differentiation compared to exogenous BMP-2. GelMA hydrogels were shown to provide sustained, localized presentation of BMP-2 due to electrostatic interactions between the growth factor and biomaterial after an initial burst release. Here, methacrylated gelatin (GelMA) hydrogels were evaluated as a system to deliver BMP-2 to encapsulated hASCs from two different donors, and BMP-2 delivered from the hydrogels was compared to BMP-2 presented exogenously in culture media. Bone morphogenetic protein-2 (BMP-2) has been reported to stimulate their osteogenic differentiation both in vitro and in vivo. Human adipose-derived stem cells (hASCs) show great potential for healing bone defects.