Structural changes in PVDF fibers due to electrospinning and its effect on biological function

Polyvinylidine fluoride (PVDF) is being investigated as a potential scaffold for bone tissue engineering because of its proven biocompatibility and piezoelectric property, wherein it can generate electrical activity when mechanically deformed. In this study, PVDF scaffolds were prepared by electrospinning using different voltages (12-30 kV), evaluated for the presence of the piezoelectric β-crystal phase and its effect on biological function. Electrospun PVDF was compared with unprocessed/raw PVDF, films and melt-spun fibers for the presence of the piezoelectric β-phase using differential scanning calorimetry, Fourier transform infrared spectroscopy and x-ray diffraction. The osteogenic differentiation of human mesenchymal stem cells (MSCs) was evaluated on scaffolds electrospun at 12 and 25 kV (PVDF-12 kV and PVDF-25 kV, respectively) and compared to tissue culture polystyrene (TCP). Electrospinning PVDF resulted in the formation of the piezoelectric β-phase with the highest β-phase fraction of 72% for electrospun PVDF at 25 kV. MSCs cultured on both the scaffolds were well attached as indicated by a spread morphology. Cells on PVDF-25 kV scaffolds had the greatest alkaline phosphatase activity and early mineralization by day 10 as compared to TCP and PVDF-12 kV. The results demonstrate the potential for the use of PVDF scaffolds for bone tissue engineering applications.

Polyimide Copolymers Containing Various Levels Of The 6F Moiety For High Temperature And Microelectronic Applications

Trifluoromethyl group-containing polyimides not only show extraordinary electrical properties, but they also exhibit excellent long-term thermo-oxidative stability. Among the most thermomechanically stable structural polyimides are those from 6F dianhydride (6FDA) and 6F diamines. The effects of substituting non-fluorine containing monomers such as BTDA, mPDA and 4,4′-DADPS for the hexafluoroisopropylidene monomers on the dielectric, thermo-oxidative, thermal and mechanical properties of the copolymers were studied.

Characterization and in vitro cytocompatibility of piezoelectric electrospun scaffolds

Previous studies have shown that electrical charges influence cell behavior (e.g. enhancement of nerve regeneration, cell adhesion, cell morphology). Thus, piezoelectric scaffolds might be useful for various tissue engineering applications. Fibrous scaffolds were successfully fabricated from permanent piezoelectric poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) by the electrospinning technique. Scanning electron microscopy and capillary flow analyses verified that the fiber mats had an average fiber diameter of 970 +/- 480 nm and a mean pore diameter of 1.7 microm, respectively. Thermally stimulated depolarization current spectroscopy measurements confirmed the piezoelectric property of the PVDF-TrFE fibrous scaffolds by the generation of a spontaneous current with the increase in temperature in the absence of an electric field, which was not detected in the unprocessed PVDF-TrFE powder. Differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction and Fourier transform infrared spectroscopy results showed that the electrospinning process increased the crystallinity and presence of the polar, beta-phase crystal compared with the unprocessed powder. Confocal fluorescence microscopy and a cell proliferation assay demonstrated spreading and increased cell numbers (human skin fibroblasts) over time on PVDF-TrFE scaffolds, which was comparable with tissue culture polystyrene. The relative quantity of gene expression for focal adhesion proteins (measured by real-time RT-PCR) increased in the following order: paxillin < vinculin < focal adhesion kinase < talin. However, no differences could be seen among the TCPS surface and the fibrous scaffolds. Future studies will focus on possible applications of these cytocompatible PVDF-TrFE scaffolds in the field of regenerative medicine.

A comparison of degradable synthetic polymer fibers for anterior cruciate ligament reconstruction

We compared mechanical properties, degradation rates, and cellular compatibilities of two synthetic polymer fibers potentially useful as ACL reconstruction scaffolds: poly(desaminotyrosyl-tyrosine dodecyl dodecanedioate)(12,10), p(DTD DD) and poly(L-lactic acid), PLLA. The yield stress of ethylene oxide (ETO) sterilized wet fibers was 150 +/- 22 MPa and 87 +/- 12 MPa for p(DTD DD) and PLLA, respectively, with moduli of 1.7 +/- 0.1 MPa and 4.4 +/- 0.43 MPa. Strength and molecular weight retention were determined after incubation under physiological conditions at varying times. After 64 weeks strength decreased to 20 and 37% of the initial sterile fiber values and MW decreased to 41% and 36% of the initial values for p(DTD DD) and PLLA, respectively. ETO sterilization had no significant effect on mechanical properties. Differences in mechanical behavior may be due to the semicrystalline nature of PLLA and the small degree of crystallinity induced by mesogenic ordering in p(DTD DD) suggested by DSC analysis. Fibroblast growth was similar on 50-fiber scaffolds of both polymers through 16 days in vitro. These data suggest that p(DTD DD) fibers, with higher strength, lower stiffness, favorable degradation rate and cellular compatibility, may be a superior alternative to PLLA fibers for development of ACL reconstruction scaffolds.

The effect of processing history on physical behavior and cellular response for tyrosine-derived polyarylates

Polyarylates have shown promise as fully degradable polymers for drug delivery as well as for structural implant applications due to their range of physicomechanical properties. Processing history, however, could have a significant impact on their overall performance in biologically relevant environments. More specifically, structural changes at the molecular level can occur that will affect a polymer's physical properties and subsequent, cell attachment and growth. The present study was aimed at comparing cell growth on tyrosine-derived polyarylates with that of polylactic acid (PLLA) in their original state and after processing (i.e. undrawn and drawn forms). Two polyarylates having distinct molecular structures were chosen. Strictly, amorphous poly(DTE adipate), denoted as poly(DT 2,4), and poly(DTD) dodecandioate, denoted as poly(DT 12,10), having a more complex, non-crystalline organization, were compared with semi-crystalline PLLA. The degree of shrinkage, thermal characterization, air-water contact angle and surface morphology were determined for each polymer in its undrawn and drawn states. Poly(DT 2,4) and PLLA after processing resulted in greater shrinkage and a slight decrease in hydrophilicity whereas poly(DT 12,10) had minimal shrinkage and became slightly more hydrophilic in its drawn state. Surface morphology or roughness was also altered by processing. In turn, the rate of cell growth and overall cell numbers were reduced significantly on drawn forms of poly(DT 2,4) and PLLA, whereas more favorable growth rates were supported on drawn poly(DT 12,10). These findings indicate that processing effects in amorphous as well as oriented polymeric structures can significantly alter their biological performance.

Design of a Filamentous Polymeric Scaffold forin VivoGuided Angiogenesis

Angiogenesis is mandatory for reperfusion of viable tissues, and lack of vascularization may cause ischemia. The increasing disparity between the demand and availability of adequate substitutes for small-diameter human blood vessels has prompted an intensive search for artificial materials or biological allograft tissues, both of which usually fail in the long term. The objective of this study was to pioneer a novel model for in vivo guided angiogenesis based on a specific design process of a filamentous polymeric scaffold with endothelial cells in a 3-dimensional culture system. To our knowledge, this is the first report of an in vivo guided angiogenesis approach based on a 2-step model, composed of endothelial cells and a filamentous polymeric scaffold framework. Endothelial cells that had been cultured on a specifically designed filamentous polymeric scaffold within a regulated dynamic tissue culture system were shown in vivo to induce guided angiogenesis. Cells seeded on a biodegradable polymeric scaffold were implanted into mice. On day 28 after implantation, analysis revealed a guided angiogenic process along the path of the implanted polymeric scaffold as well as initial evidence for early maturation of engineered vessels, allowing red blood cells to flow through the forming lumina of new vessels as the polymer degraded. The authors conclude that in vivo guided angiogenesis can be achieved by combining endothelial cells with biodegradable filamentous polymeric scaffolds and that this model can lay the cornerstone for vascular engineering and future development of clinically available protocols aimed to treat life-threatening cardiovascular conditions.