Introduction: Engineering multilayer polyelectrolyte thin films to direct cell behavior represents a significant challenge but also an excellent opportunity toward a variety of cell contacting applications. Here we propose two new bioactive thin film biomaterials, one that contains a reservoir for biomolecules, such as growth factors, for an efficient local and controlled release, and one that is formed with biomolecules from the extracellular matrix, such as Fibronectin (Fn), in order to mimic the extracellular environment and promote cell behavior.
Materials and Methods: Thin films are formed by the Layer-by-Layer assembly of poly(L-lysine) and poly(L-glutamic acid) or Fn. Carboxy-functionalized latex nanoparticles (25 nm) are incorporated as template. Films are cross-linked (EDC/NHS) to increase mechanical rigidity. Tetrahydrofuran (THF) is used to dissolve nanoparticles and create porous films to enable loading of bioactive species, as BMP2.
Results and Discussion: We describe here two strategies to control cell behavior. First, a nanotemplating strategy toward porous, polyelectrolyte-based thin films capable of controlled biomolecular loading and release is presented. Films are formed via the Layer-by-Layer assembly of charged polymers and nanoparticles, chemically cross-linked to increase mechanical rigidity and stability, and finally exposed to tetrahydrofuran to dissolve the NP and create an intra-film porous network[1]. We report here on the loading and release of the growth factor bone morphogenetic protein 2 (BMP-2), and the influence of BMP-2 loaded films on contacting murine C2C12 myoblasts.
We observe nanotemplating to enable stable BMP-2 loading throughout the thickness of the film, and find the nanotemplated film to exhibit comparable cell adhesion, and enhanced cell differentiation, compared to a non-porous cross-linked film (where BMP-2 loading is mainly confined to the film surface)[2]. The second strategy consist in the direct incorporation of Fn as the anionic polymer during film assembly in order to generate a thin film enriched in Fn that could mimic the extracellular environment and influence the cell behavior. We investigate the influence of Fn on the film construction, physicochemical and mechanical properties as well as the influence on pre-osteoblastic cells. We observe that Fn-based thin films present a novel growth regime with a terminated growth, and are capable of enhancing cell adhesion, spreading and proliferation compared to a Fn monolayer. The Fn present in the films is reorganized into fibrils by contacting cells.
Conclusion: We engineer, design and construct bioactive thin films biomaterials able to direct the behavior of contacting cells. Nanotemplated polyelectrolyte films can be employed to spatially and temporally release bioactive molecules, such as BMP2. Fn incorporation within Layer-by-Layer films leads to Fn-rich films, which enhance cell adhesion, spreading and proliferation compared to a standard 2D Fn layer.
References:
[1] Wu et al., Adv. Funct. Mat. 23, 66-74, 2013
[2] Gand et al., Biomatter, 4, 8231-8239, 2014