Free-standing multilayer films as growth factor reservoirs for future wound dressing applications

Chronic skin wounds place a high burden on patients and health care systems. The use of angiogenic and mitogenic growth factors can facilitate the healing but growth factors are quickly inactivated by the wound environment if added exogenously. Here, free-standing multilayer films (FSF) are fabricated from chitosan and alginate as opposing polyelectrolytes in an alternating manner using layer-by-layer technique. One hundred bilayers form an about 450 μm thick, detachable free-standing film that is subsequently crosslinked by either ethyl (dimethylaminopropyl) carbodiimide combined with N-hydroxysuccinimide (E-FSF) or genipin (G-FSF). The characterization of swelling, oxygen permeability and crosslinking density shows reduced swelling and oxygen permeability for both crosslinked films compared to non-crosslinked films (N-FSF). Loading of fibroblast growth factor 2 (FGF2) into the films results in a sustained release from crosslinked FSF in comparison to non-crosslinked FSF. Biocompatibility studies in vitro with human dermal fibroblasts cultured underneath the films demonstrate increased cell growth and cell migration for all films with and without FGF2. Especially G-FSF loaded with FGF2 greatly increases cell proliferation and migration. In vivo biocompatibility studies by subcutaneous implantation in mice show that E-FSF causes an inflammatory tissue response that is absent in the case of G-FSF. N-FSF also represents a biocompatible film but shows early degradation. All FSF possess antibacterial properties against gram+ and gram- bacteria demonstrated by an agar diffusion disc assay. In summary, FSF made of alginate and chitosan crosslinked with genipin can act as a reservoir for the sustained release of FGF2, possessing high biocompatibility in vitro and in vivo. Moreover, G-FSF promotes growth and migration of human dermal fibroblasts and has antibacterial properties, which makes it an interesting candidate for bioactive wound.