Current biomaterial-based strategies explored to treat articular cartilage defects have failed to provide adequate physico-chemical cues in order to guide functional tissue regeneration. Here, it is hypothesized that atmospheric-pressure plasma (APPJ) treatment and melt electrowriting (MEW) will produce microfiber support structures with covalently-immobilized transforming growth factor beta-1 (TGFβ1) that can stimulate the generation of functional cartilage tissue. The effect of APPJ operational speeds to activate MEW polycaprolactone meshes for immobilization of TGFβ1 is first investigated and chondrogenic differentiation and neo-cartilage production are assessed in vitro. All APPJ speeds test enhanced hydrophilicity of the meshes, with the slow treatment speed having significantly less CC/CH and more COOH than the untreated meshes. APPJ treatment increases TGFβ1 loading efficiency. Additionally, in vitro experiments highlight that APPJ-based TGFβ1 attachment to the scaffolds is more advantageous than direct supplementation within the medium. After 28 days of culture, the group with immobilized TGFβ1 has significantly increased compressive modulus (more than threefold) and higher glycosaminoglycan production (more than fivefold) than when TGFβ1 is supplied through the medium. These results demonstrate that APPJ activation allows reagentfree, covalent immobilization of TGFβ1 on microfiber meshes and, importantly, that the biofunctionalized meshes can stimulate neo-cartilage matrix formation. This opens new perspectives for guided tissue regeneration.

Three-dimensional (3D) bioprinting, where cells, hydrogels, and structural polymers can be printed layer by layer into complex designs, holds great promise for advances in medicine and the biomedical sciences. In principle, this technique enables the creation of highly patient-specific disease models and biomedical implants. However, an ability to tailor surface biocompatibility and interfacial bonding between printed components, such as polymers and hydrogels, is currently lacking. Here we demonstrate that an atmospheric pressure plasma jet (APPJ) can locally activate polymeric surfaces for the reagent-free covalent attachment of proteins and hydrogel in a single-step process at desired locations. Polyethylene and poly-ε-caprolactone were used as example polymers. Covalent attachment of the proteins and hydrogel was demonstrated by resistance to removal by rigorous sodium dodecyl sulfate washing. The immobilized protein and hydrogel layers were analyzed using Fourier transform infrared and X-ray photoelectron spectroscopy. Importantly, the APPJ surface activation also rendered the polymer surfaces mildly hydrophilic as required for optimum biocompatibility. Water contact angles were observed to be stable within a range where the conformation of biomolecules is preserved. Single and double electrode designs of APPJs were compared in their characteristics relevant to localized surface functionalization, plume length, and shape. As a proof of efficacy in a biological context, APPJ-treated polyethylene functionalized with fibronectin was used to demonstrate improvements in cell adhesion and proliferation. These results have important implications for the development of a new generation of 3D bioprinters capable of spatially patterned and tailored surface functionalization performed during the 3D printing process in situ.

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