Evaluation of focal adhesion mediated subcellular curvature sensing in response to engineered extracellular matrix

Fibril curvature is bioinstructive to attached cells. Similar to natural healthy tissues, an engineered extracellular matrix can be designed to stimulate cells to adopt desired phenotypes. To take full advantage of the curvature control in biomaterial fabrication methodologies, an understanding of the response to fibril subcellular curvature is required. In this work, we examined morphology, signaling, and function of human cells attached to electrospun nanofibers. We controlled curvature across an order of magnitude using nondegradable poly(methyl methacrylate) (PMMA) attached to a stiff substrate with flat PMMA as a control. Focal adhesion length and the distance of maximum intensity from the geographic center of the vinculin positive focal adhesion both peaked at a fiber curvature of 2.5 μm-1 (both ∼2× the flat surface control). Vinculin experienced slightly less tension when attached to nanofiber substrates. Vinculin expression was also more affected by a subcellular curvature than structural proteins α-tubulin or α-actinin. Among the phosphorylation sites we examined (FAK397, 576/577, 925, and Src416), FAK925 exhibited the most dependance on the nanofiber curvature. A RhoA/ROCK dependance of migration velocity across curvatures combined with an observation of cell membrane wrapping around nanofibers suggested a hybrid of migration modes for cells attached to fibers as has been observed in 3D matrices. Careful selection of nanofiber curvature for regenerative engineering scaffolds and substrates used to study cell biology is required to maximize the potential of these techniques for scientific exploration and ultimately improvement of human health.

Gelatin-polytrimethylene carbonate blend based electrospun tubular construct as a potential vascular biomaterial

The present work details the fabrication of electrospun tubular scaffolds based on the biocompatible and unexploited blend of gelatin and polytrimethylene carbonate (PTMC) as a media (middle layer of blood vessel) equivalent for blood vessel regeneration. An attempt to resemble the media stimulated the selection of gelatin as a matrix (substitution for collagen) with the inclusion of the biodegradable elastomer PTMC (substitution for elastin). -The work highlights the variation of electrospinning parameters and its assiduous selection based on fiber diameter distribution and pore size distribution to obtain smooth microfibers and micropores which is reported for the first time for this blend. Electrospun conduits of gelatin-PTMC blend had fibers sized 6-8 μm and pores sized ~100-150 μm. Young's modulus of 0.40 ± 0.045 MPa was observed, resembling the tunica media of the native artery (~0.5 MPa). An evaluation of the surface properties, topography, and mechanical properties validated its physical requirements for inclusion in a vascular graft. Preliminary biological tests confirmed its minimal in-vitro toxicity and in-vivo biocompatibility. MTT assay (indirect) elucidated cell viability above 70% with scaffold extract, considered to be non-toxic according to the EN ISO-10993-5/12 protocol. The in-vivo subcutaneous implantation in rat showed a marked reduction in macrophages within 15 days revealing its biocompatibility and its possibility for host integration. This comprehensive study presents for the first time the potential of microporous electrospun gelatin and PTMC blend based tubular construct as a potential biomaterial for vascular tissue engineering. The proposed media equivalent included in a bilayer or trilayer polymeric construct can be a promising off-shelf vascular graft.

Poly(l-lactide) and Poly(l-lactide- co-trimethylene carbonate) Melt-Spun Fibers: Structure-Processing-Properties Relationship

l-Lactide/trimethylene carbonate copolymers have been produced as multifilament fibers by high-speed melt-spinning. The relationship existing between the composition, processing parameters and physical properties of the fibers has been disclosed by analyzing how the industrial process induced changes at the macromolecular level, i.e., the chain microstructure and crystallinity development. A poly(l-lactide) and three copolymers having trimethylene carbonate contents of 5, 10 and 18 mol % were synthesized with high molecular weight ( M_n) up to 377 kDa and narrow dispersity. Their microstructure, crystallinity and thermal properties were dictated by the composition. The spinnability was then assessed for all the as-polymerized materials: four melt-spun multifilament fibers with increasing linear density were collected for each (co)polymer at a fixed take-up speed of 1800 m min^-1 varying the mass throughput during the extrusion. A linear correlation resulted between the as-spun fiber properties and the linear density. The as-spun fibers could be further oriented, developing more crystallinity and improving their tensile properties by a second stage of hot-drawing. This ability was dependent on the composition and crystallinity achieved during the melt-spinning and the parameters selected for the hot-drawing, such as temperature, draw ratio and input speed. The crystalline structure evolved to a more stable form, and the degree of crystallinity increased from 0-52% to 25-66%. Values of tensile strength and Young's modulus up to 0.32-0.61 GPa and 4.9-8.4 GPa were respectively achieved.