Nanofibrillar Scaffolds Research Articles

Nanostructured Polymers Prepared Using a Self-Assembled Nanofibrillar Scaffold as a Reverse Template

We describe the preparation of nanostructured polymeric materials by polymerizing a monomer within a scaffold composed of self-assembled nanofibrils. 1,3:2,4-Dibenzylidene sorbitol (DBS) is an inexpensive sugar derivative that can form nanofibrillar networks in a variety of organic solvents at relatively low concentrations. Here, we induce DBS nanofibrils in styrene and then thermally initiate the free-radical polymerization of the monomer. The polymerization proceeds without any evidence of macroscopic phase separation, ultimately yielding a transparent solid of polystyrene. Within this material, intact DBS nanofibrils (diameter 10-100 nm) are preserved, as shown by atomic force microscopy (AFM). The DBS fibrils can also be subsequently extracted from the polymer, leaving behind a network of nanoscale pores. The porosity of the resulting polymer has been characterized by the BET technique.

Increased FGF-2 secretion and ability to support neurite outgrowth by astrocytes cultured on polyamide nanofibrillar matrices

An electrospun nonwoven matrix of polyamide nanofibers was employed as a new model for the capillary basement membrane at the blood-brain barrier (BBB). The basement membrane separates astrocytes from endothelial cells and is associated with growth factors, such as fibroblast growth factor-2 (FGF-2). FGF-2 is produced by astrocytes and induces specialized functions in endothelial cells, but also has actions on astrocytes. To investigate potential autocrine actions of FGF-2 at the BBB, astrocytes were cultured on unmodified nanofibers or nanofibers covalently modified with FGF-2. The former assumed an in vivo-like stellate morphology that was enhanced in the presence of cross-linked FGF-2. Furthermore, astrocyte monolayers established on unmodified nanofibers were more permissive for neurite outgrowth when cultured with an overlay of neurons than similar monolayers established on standard tissue culture surfaces, while astrocytes cultured on FGF-2-modifed nanofibers were yet more permissive. The observed differences were due in part to progressively increasing amounts of FGF-2 secreted by the astrocytes into the medium; hence FGF-2 increases its own expression in astrocytes to modulate astrocyte–neuron interactions. Soluble FGF-2 was unable to replicate the effects of cross-linked FGF-2. Nanofibers alone up-regulated FGF-2, albeit to a lesser extent than nanofibers covalently modified with FGF-2. These results underscore the importance of both surface topography and growth factor presentation on cellular function. Moreover, these results indicate that FGF-2-modified nanofibrillar scaffolds may demonstrate utility in tissue engineering applications for replacement and regeneration of lost tissue following central nervous system (CNS) injury or disease.

Quantitative Investigation of FGF-2-Modified Nanofibrillar Prosthetic for Neural Cell System Re-establishment

Recent advances in regenerative medicine have improved understanding of the materials properties of nanofibrillar scaffolds used to aid cell system re-establishment. A picture is emerging that a successful scaffold has a defined set of physical properties including mechanical properties, topographical properties, and growth factor inclusion, and that the weighting of each may vary depending on the cell system and its functionality. In the present work, results from investigations of a slowly biodegradable nanofiber prosthetic for neural cell system re-establishment are presented. Preliminary data from in-vivo investigations (rat model) indicate that a nanofiber prosthetic device of FGF-2-modified nanofibers contributes to system re-establishment including aligned guidance for regenerating axons across an injury gap, and angiogenesis. Research by Meiners’ group also demonstrated that FGF-2 retains biological activity significantly longer when immobilized on nanofibers than when presented as a soluble molecule [1]. The present investigations use atomic force microscopy operated in a new mode, Scanning Probe Recognition Microscopy (SPRM) [2], developed by Ayres’ group, to quantitatively investigate properties of FGF-2-modified nanofibers. The SPRM system is given the ability to auto-track on regions of interest through incorporation of recognition-based tip control realized using algorithms and techniques from computer vision, pattern recognition and signal processing fields. Statistically meaningful numbers of reliable data points are extracted using an automatic procedure that maintains uniformity of experimental conditions. Properties under quantitative SPRM investigation include nanofiber stiffness and surface roughness, nanofiber curvature, nanofiber mesh density and porosity, and growth factor presentation and distribution. Each of these factors has been demonstrated to have global effects on cell morphology, function, proliferation, morphogenesis, migration, and differentiation.[1] A. Nur-E-Kamal et al., Mol Cell Biochem 309 (2008) 157-166.[2] Y. Fan et al., Int. J. Nanomedicine 2 (2007) 651-661.

Quantitative Investigations of Nanoscale Elasticity of Nanofibrillar Matrices

AbstractRecent research indicates that nanophysical properties as well as biochemical cues can influence cellular re-colonization of a tissue scaffold. It has also been shown nanoscale elasticity can strongly influence cellular responses. In the present work, quantitative investigations of the elasticity of a nanofibrillar matrix scaffold that has demonstrated promise for spinal cord injury repair are compared with complementary transmission electron microscopy investigations, performed to assess nanofiber internal structures. Interpretive model improvements are identified and discussed.