Poly‐l‐lactic acid (PLLA) has been used as a biodegradable polymer for many years; the key characteristics of this polymer make it a versatile and useful resource for regenerative medicine. However, it is not inherently bioactive. Thus, here, a novel process is presented to functionalize PLLA surfaces with poly(ethyl acrylate) (PEA) brushes to provide biological functionality through PEA's ability to induce spontaneous organization of the extracellular matrix component fibronectin (FN) into physiological‐like nanofibrils. This process allows control of surface biofunctionality while maintaining PLLA bulk properties (i.e., degradation profile, mechanical strength). The new approach is based on surface‐initiated atomic transfer radical polymerization, which achieves a molecularly thin coating of PEA on top of the underlying PLLA. Beside surface characterization via atomic force microscopy, X‐ray photoelectron spectroscopy and water contact angle to measure PEA grafting, the biological activity of this surface modification is investigated. PEA brushes trigger FN organization into nanofibrils, which retain their ability to enhance adhesion and differentiation of C2C12 cells. The results demonstrate the potential of this technology to engineer controlled microenvironments to tune cell fate via biologically active surface modification of an otherwise bioinert biodegradable polymer, gaining wide use in tissue engineering applications.

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In article number https://doi.org/10.1002/adhm.201801469 by Manuel Salmerón‐Sánchez, Marco Cantini, and co‐workers, functional poly(ethyl acrylate) brushes grafted on a biodegradable poly lactic acid scaffold, via surface‐initiated atomic transfer radical polymerization, trigger the formation of fibronectin nanonetworks that target cell adhesion and differentiation for application in regenerative medicine. The cover image was prepared by Mark Robert Sprott and Sara Trujillo.

Fibronectin (FN) mediates cell-material interactions during events such as tissue repair, and therefore the biomimetic modeling of this protein in vitro benefits regeneration. The nature of the interface is crucial in determining cell adhesion, morphology, and differentiation. Poly(ethyl acrylate) (PEA) spontaneously organizes FN into biological nanonetworks, resulting in exceptional bone regeneration in animal models. Spontaneous network organization of FN is also observed in poly(buthyl acrylate) (PBA) substrates that have higher surface mobility than PEA. C2C12 myoblasts differentiate efficiently on PEA and PBA substrates. In this study, we investigate if intermediate surface mobilities between PEA and PBA induce cell differentiation more efficiently than PEA. A family of P(EA-co-BA) copolymers were synthesized in the entire range of compositions to finely tune surface mobility between PEA and PBA. Surface characterization demonstrates that FN mobility steadily increased with the PBA content. All compositions allowed the biological organization of FN with similar exposure of cell binding domains. C2C12 myoblasts adhered well in all the materials, with higher focal adhesions in PEA and PBA. The increase of the interfacial mobility had an impact in cell adhesion by increasing the number of FAs per cell. In addition, cell differentiation decreased proportionally with surface mobility, from PEA to PBA.