The formation of 3D electrospun mat structures from alginate-polyethylene oxide (PEO) solution blends is reported. These unique architectures expand the capabilities of traditional electrospun mats for applications such as regenerative medicine, where a scaffold can help to promote tissue growth in three dimensions. The mat structures extend off the surface of the flat collector plate without the need of any modifications in the electrospinning apparatus, are self-supported when the electric field is removed, and are composed of bundles of nanofibers. A mechanism for the unique formations is proposed, based on the fiber-fiber repulsions from surface charges on the negatively charged alginate. Furthermore, the role of the electric field in the distribution of alginate within the nanofibers is discussed. X-ray photoelectron spectroscopy is used to analyze the surface composition of the electrospun nanofiber mats and the data is related to cast films made in the absence of the electric field. Further techniques to tailor the 3D architecture and nanofiber morphology by changing the surface tension and relative humidity are also discussed.
We present here a systematic investigation to understand why aqueous sodium alginate can only be electrospun into fibers through a blend with another polymer; specifically, polyethylene oxide (PEO). We seek to examine and understand the role of PEO as the “carrier polymer”. The addition of PEO favorably reduces electrical conductivity and surface tension of the alginate solution, aiding in fiber formation. While PEO has the ability to coordinate through its ether group (−COC−) with metal cation like the sodium cation of sodium alginate, we demonstrate in this study using PEO as well as polyvinyl alcohol (PVA) that coordination may have little effect on electrospinnability. More importantly, we show that PEO as carrier polymer provides molecular entanglement that is required for electrospinning. Since the selected carrier polymer provides the necessary entanglement, this carrier polymer must be electrospinnable, entangled and of a high molecular weight (more than 600 kDa for PEO). On the basis of these requirements, we stipulate that the PEO–PEO interaction of the high molecular-weight entangled PEO is key to “carrying” the alginate from solution to fibers during electrospinning. Further, using the resulting understanding of the role of PEO, we were able to increase the alginate concentration by employing a higher molecular-weight PEO: up to 70 wt % alginate using 2000 kDa PEO and, with, the addition of Triton X-100 surfactant, up to 85 wt % alginate, higher than previously reported.
The reaction dynamics of biodegradable, photocrosslinkable sodium alginate hydrogels are studied by in situ, dynamic rheology. Alginate, chemically-modified with methacrylate groups, crosslinks by ultraviolet (UV) light exposure in the presence of a photoinitiator. The gel formation is monitored during UV irradiation from a light emitting diode (LED) bottom plate fixture on the rheometer. Material properties of the hydrogels, including gel points and relaxation exponent, are evaluated using the Winter-Chambon criteria. We also report a new, complementary empirical method for determining the gel point from the reduction in sample strain at the onset of gelation, via monitoring the strain curve. In addition, the crosslinking dynamics and hydrogel moduli are altered by changing the UV irradiation intensities (3-15 mW cm À2 ) and degree of methacrylation (5-25%). Dynamic rheological measurements of hydrogels as described in this paper are a potentially powerful tool to elucidate the dynamics of gelation and predict mechanical properties. This technique may aid in the design of polymer formulations with light-reactive chemical species, which have tunable properties that can be matched to a range of applications, including regenerative medicine.
Alginate, a natural polysaccharide that has shown great potential as a cell scaffold for the regeneration of many tissues, has only been nominally explored as an electrospun biomaterial due to cytotoxic chemicals that have typically been used during nanofiber formation and crosslinking. Alginate cannot be electrospun by itself and is often co-spun with poly(ethylene oxide) (PEO). In this work, a cell adhesive peptide (GRGDSP) modified alginate (RA) and unmodified alginate (UA) were blended with PEO at different concentrations and blending ratios, and then electrospun to prepare uniform nanofibers. The ability of electrospun RA scaffolds to support human dermal fibroblast cell attachment, spreading, and subsequent proliferation was greatly enhanced on the adhesion ligand-modified nanofibers, demonstrating the promise of this electrospun polysaccharide material with defined nanoscale architecture and cell adhesive properties for tissue regeneration applications.
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