Deposition of thiol-rich coatings on nanofibrous scaffolds via atmospheric pressure DBD plasma for tissue engineering applications

Tissue engineering is a rapidly emerging aiming at overcoming the limitations of conventional transplantation methods through development of substitute structures so-called scaffolds for the restoration of damaged tissues. One of the promising approaches towards a successful tissue repair is fabrication of a scaffold mimicking the fibrous structure of the extracellular matrix (ECM) that governs a wide range of crucial cellular performances such as adhesion and proliferation. Electrospinning can be used as a simple, versatile and cost-effective biofabrication technique able to produce polymeric fibrous meshes simulating the ECM morphology. Several biodegradable polymers have been employed in the generation of scaffolds with polycaprolactone (PCL) being by far the most considered material due to its non-toxicity and history of safe clinical use. Despite the afore-mentioned advantages, PCL is a hydrophobic material that does not exhibit desirable bio-chemical properties promoting cell-surface interactions. Therefore, a surface modification putting into effect appropriate biochemical properties can solve the issue. The generation of thiolated surfaces is gaining a huge popularity in TE applications since thiol groups (-SH) are known to serve as highly selective anchoring sites for the subsequent covalent immobilization of biomolecules. This was previously done via self-assembly approaches that ahave some drawbacks such as the use of organic solvents, the long reaction times and the multi-step procedure. As an alternative, plasma-assisted polymerization of thiol-containing precursors can be employed to deposit thiol-rich coatings onto the scaffolds in a fast, solvent-free and eco-friendly way. In this research, PCL nanofibers are first using electrospinning. A plasma polymerization process was then performed to deposit a thiol-rich coatings on the electrospun fibers using a dielectric barrier discharge (DBD) with 1-propanethiol as precursor. An optimization of the process was carried out via an extensive parametric study involving the discharge power, gas flow rate, treatment time and pressure inside the DBD chamber

Polylactic Acid/Polyaniline Nanofibers Subjected to Pre- and Post-Electrospinning Plasma Treatments for Refined Scaffold-Based Nerve Tissue Engineering Applications

Composite biopolymer/conducting polymer scaffolds, such as polylactic acid (PLA)/ polyaniline (PAni) nanofibers, have emerged as popular alternative scaffolds in the electrical-sensitive nerve tissue engineering (TE). Although mimicking the extracellular matrix geometry, such scaffolds are highly hydrophobic and usually present an inhomogeneous morphology with massive beads that impede nerve cell-material interactions. Therefore, the present study launches an exclusive combinatorial strategy merging successive pre- and post-electrospinning plasma treatments to cope with these issues. Firstly, an atmospheric pressure plasma jet (APPJ) treatment was applied on PLA and PLA/PAni solutions prior to electrospinning, enhancing their viscosity and conductivity. These liquid property changes largely eliminated the beaded structures on the nanofibers, leading to uniform and nicely elongated fibers having average diameters between 170 and 230 nm. After electrospinning, the conceived scaffolds were subjected to a N2 dielectric barrier discharge (DBD) treatment, which significantly increased their surface wettability as illustrated by large decreases in water contact angles for values above 125° to values below 25°. X-ray photoelectron spectroscopy (XPS) analyses revealed that 3.3% of nitrogen was implanted on the nanofibers surface in the form of C–N and N–C=O functionalities upon DBD treatment. Finally, after seeding pheochromocytoma (PC-12) cells on the scaffolds, a greatly enhanced cell adhesion and a more dispersive cell distribution were detected on the DBD-treated samples. Interestingly, when the APPJ treatment was additionally performed, the extension of a high number of long neurites was spotted leading to the formation of a neuronal network between PC-12 cell clusters. In addition, the presence of conducting PAni in the scaffolds further promoted the behavior of PC-12 cells as illustrated by more than a 40% increase in the neurite density without any external electrical stimulation. As such, this work presents a new strategy combining different plasma-assisted biofabrication techniques of conducting nanofibers to create promising scaffolds for electrical-sensitive TE applications

Polylactic Acid/Polyaniline Nanofibers Subjected to Pre- and Post-Electrospinning Plasma Treatments for Refined Scaffold-Based Nerve Tissue Engineering Applications

Composite biopolymer/conducting polymer scaffolds, such as polylactic acid (PLA)/ polyaniline (PAni) nanofibers, have emerged as popular alternative scaffolds in the electrical-sensitive nerve tissue engineering (TE). Although mimicking the extracellular matrix geometry, such scaffolds are highly hydrophobic and usually present an inhomogeneous morphology with massive beads that impede nerve cell-material interactions. Therefore, the present study launches an exclusive combinatorial strategy merging successive pre- and post-electrospinning plasma treatments to cope with these issues. Firstly, an atmospheric pressure plasma jet (APPJ) treatment was applied on PLA and PLA/PAni solutions prior to electrospinning, enhancing their viscosity and conductivity. These liquid property changes largely eliminated the beaded structures on the nanofibers, leading to uniform and nicely elongated fibers having average diameters between 170 and 230 nm. After electrospinning, the conceived scaffolds were subjected to a N2 dielectric barrier discharge (DBD) treatment, which significantly increased their surface wettability as illustrated by large decreases in water contact angles for values above 125° to values below 25°. X-ray photoelectron spectroscopy (XPS) analyses revealed that 3.3% of nitrogen was implanted on the nanofibers surface in the form of C–N and N–C=O functionalities upon DBD treatment. Finally, after seeding pheochromocytoma (PC-12) cells on the scaffolds, a greatly enhanced cell adhesion and a more dispersive cell distribution were detected on the DBD-treated samples. Interestingly, when the APPJ treatment was additionally performed, the extension of a high number of long neurites was spotted leading to the formation of a neuronal network between PC-12 cell clusters. In addition, the presence of conducting PAni in the scaffolds further promoted the behavior of PC-12 cells as illustrated by more than a 40% increase in the neurite density without any external electrical stimulation. As such, this work presents a new strategy combining different plasma-assisted biofabrication techniques of conducting nanofibers to create promising scaffolds for electrical-sensitive TE applications

Plasma polymer-based deposition of coatings with high primary Amine content on PCL/PLGA nanofibers for tissue engineering applications

In the tissue engineering field, the surface modification of hydrophobic nanofibers (NFs) to introduce cell-interactive chemical functionalities remains a challenge. Therefore, this study explores a novel three-step plasma based-method to synthesize coatings with a higher chemical selectivity in comparison to conventional plasma polymers. First, hexamethyldisiloxane (HMDSO) plasma polymerization was performed on NFs (blend of poly-$\epsilon$-caprolactone and poly(D,L-lactide-co-glycolide), after which the samples were exposed to a helium plasma. Both steps were performed in a medium-pressure dielectric barrier discharge. Scanning electron microscopy (SEM) showed that the plasma-based steps did not damage the NFs, while X-ray photoelectron spectroscopy (XPS) and water contact angle measurements showed that a hydrophilic silanol-rich layer was formed. This layer was used in the final step, in which (3-aminopropyl) triethoxysilane (APTES) was grafted on the plasma polymer to introduce primary amine groups onto the surface, which was confirmed by XPS. This APTES-based layer could be partially removed, but the remaining stable layer enhanced Schwann cell responses in live/dead, The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), immunofluorescent, and adhesion assays in comparison to the untreated and HMDSO-based coated NFs. As such, the fabricated coatings with selective functionality on PCL/PLGA NFs are a promising candidate to use in the tissue engineering field

Nonthermal plasma processing for nanostructured biomaterials and tissue engineering scaffolds : a mini review

Traditional wet chemistry offers a great magnitude of methods for surface modification and surface coatings for nanostructured materials. However, most methods require solvents and purification steps, and generate waste and byproducts. An interesting alternative set of methods involves the use of nonthermal or low-temperature plasmas (LTP) toward making and modifying nanostructured biomaterials. In this current opinion piece, some of the recent literature in this area is highlighted, and current perspectives are given. Emphasis is noted for the role of LTP for surface modification of nanofibrous scaffolds and plasma electrolytic oxidation (PEO) for surface-nanostructuring of metallic implants. The morphological nanofeaturing in fibrous mats as an extracellular matrix mimicking scaffold is presented along with recent perspectives of using LTP and plasma electrolytic oxidation for surface structuring for enhanced biointegration via cell/surface interactions with plasma processed implants/scaffolds constructs

Multifaceted polymeric nerve guidance conduits with distinctive double-layered architecture and plasma-induced inner chemistry gradient for the repair of critical-sized defects

Despite tissue engineering advances, current nerve guidance conduits (NGCs) are still failing in repairing critical-sized defects. This study aims, therefore, at tackling large nerve gaps (2 cm) by designing NGCs possessing refined physicochemical properties enhancing the activity of Schwann cells (SCs) that support nerve regeneration over long distances. As such, a combinatorial strategy adopting novel plasma-induced surface chemistry and architectural heterogeneity was considered. A mechanically suitable copolymer (Polyactive®) was electrospun to produce nanofibrous NGCs mimicking the extracellular matrix. An innovative seamless double-layered architecture consisting of an inner wall comprised of bundles of aligned fibers with intercalated random fibers and an outer wall fully composed of random fibers was conceived to synergistically provide cell guidance cues and sufficient nutrient inflow. NGCs were subjected to argon plasma treatments using a dielectric barrier discharge (DBD) and a plasma jet (PJ). Surface chemical changes were examined by advanced X-ray photoelectron spectroscopy (XPS) micro-mappings. The DBD homogeneously increased the surface oxygen content from 17 % to 28 % on the inner wall. The PJ created a gradient chemistry throughout the inner wall with an oxygen content gradually increasing from 21 % to 30 %. In vitro studies revealed enhanced primary SC adhesion, elongation and proliferation on plasma-treated NGCs. A cell gradient was observed on the PJ-treated NGCs thus underlining the favorable oxygen gradient in promoting cell chemotaxis. A gradual change from circular to highly elongated SC morphologies mimicking the bands of Büngner was visualized along the gradient. Overall, plasma-treated NGCs are promising candidates paving the way towards critical nerve gap repair

Non-thermal plasma activation of BPDA-PPD polyimide for improved cell-material interaction

Biocompatible BPA-PPD polyimide is widely used in the packaging of implantable devices. Plasma activation can improve its interaction with the surrounding tissue upon implantation. The influence of He, air, N2 and Ar plasma activation on polyimide's surface hydrophilicity, roughness, topography, composition and cell-surface interaction was evaluated, along with the influence of hydrophobic recovery on such properties. All plasma activations increased the surface hydrophilicity but neither the roughness nor topography changed. The increase was attributed to the incorporated O- and N-functionalities. 24 h after the activations the surface hydrophilicity decreased while maintaining the functionalities, due to the functionalities’ reorientation/migration towards the bulk of polyimide. Air and N2 activations improved the cell-surface interactions with fibroblasts. These were equally influenced by the surface hydrophilicity and the surface functionalities availability. The hydrophobic recovery lowered the initial cell adhesion but not the cell proliferation, as the hydrophobic recovery was progressively reversed in the culture media