Abstract
The aim of this study was to exploit silk fibroin’s properties to develop innovative composite microcarriers for mesenchymal stem cell (MSCs) adhesion and proliferation. Alginate microcarriers were prepared, added to silk fibroin solution, and then treated with ethanol to induce silk conformational transition. Microcarriers were characterized for size distribution, coating stability and homogeneity. Finally, in vitro cytocompatibility and suitability as delivery systems for MSCs were investigated. Results indicated that our manufacturing process is consistent and reproducible: silk/alginate microcarriers were stable, with spherical geometry, about 400 μm in average diameter, and fibroin homogeneously coated the surface. MSCs were able to adhere rapidly onto the microcarrier surface and to cover the surface of the microcarrier within three days of culture; moreover, on this innovative 3D culture system, stem cells preserved their metabolic activity and their multi-lineage differentiation potential. In conclusion, silk/alginate microcarriers represent a suitable support for MSCs culture and expansion. Since it is able to preserve MSCs multipotency, the developed 3D system can be intended for cell delivery, for advanced therapy and regenerative medicine applications.
Highlights
In 1967, van Wezel introduced for the first time the concept of microcarriers as a method to produce large scale vaccines and to improve adherent mammalian cell growth [1]
When microcarriers act as a delivery system, cells are maintained for a longer time period in the lesion site [5], giving them the possibility to secrete growth factors and actively participate in tissue matrix deposition, promoting its regeneration [2,6]
In the present work we developed and characterized composite microcarriers constituted by a core of alginate and a silk fibroin shell, evaluating their in vitro cytocompatibility and suitability as a delivery system for ASCs in regenerative medicine applications
Summary
In 1967, van Wezel introduced for the first time the concept of microcarriers as a method to produce large scale vaccines and to improve adherent mammalian cell growth [1]. Employed for cell and drug/growth factor encapsulation [11,12,13,14], alginate is a bedrock biomaterial for cell transplantation [15] due to its properties of fast sol-gel transition in contact with divalent cations, in vivo biocompatibility, permeability, and dissolution [16]. Alginate surface is unsuitable for cell adhesion due to the presence of negative charges and its deficiency of integrin domains [17,18]. To overcome this inconvenience, alginate can be conjugated with an arginine-glycine-asparagine (RGD) sequence to increase its cell adhesion properties [19] or combined with natural proteins, such as silk fibroin. Silk fibroin is able to promote cell adhesion, proliferation and differentiation of mesenchymal stem/stromal cells (MSCs) [24,25,26,27,28,29,30,31]
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