Kirill Feldman

Collagen nerve conduits releasing the neurotrophic factors GDNF and NGF

Artificial nerve conduits (NC) can clinically be instrumental for facilitating the surgery of damaged peripheral nerves. To improve axonal regeneration of injured peripheral nerves, we have developed collagen nerve conduits (NC) releasing glial cell line-derived neurotrophic factor (GDNF) alone or in combination with nerve growth factor (NGF), which exert synergistic action on axonal growth. Degradation of the NC and their mechanical and drug release properties were controlled by two means: (i) cross-linking the collagen tubes by physical means, through a dehydro-thermal treatment (DHT), before loading with the neurotrophic factors (NTFs) GDNF or GDNF/NGF; and (ii) coating the drug-loaded collagen tubes with layers of poly(lactide-co-glycolide) (PLGA). Non-cross-linked collagen NC (C-NC) released high amounts of NTFs during the initial 2-3 days of incubation, whereas the DHT-treated collagen NC (C(dht)-NC) did not show a prominent burst effect. The release kinetics was similar for GDNF alone and GDNF co-delivered with NGF. Within 30 days, the C-NC released 78% and 83% of the total doses of GDNF and NGF, respectively, whereas the C(dht)-NC released only 68% of GDNF and 56% of NGF. The bioactivity of the NTFs released up to 30 days was confirmed by an in vitro bioassay using chicken embryonic dorsal root ganglion (DRG) explants. The C(dht)-NC also possessed adequate mechanical resistance against radial compression, the pull-out of a suture thread, and loss of patency upon bending. Modulus and pull-out strength increased in the order of C-NC, C(dht)-NC approximately Neuragen, and Neurolac, with the latter two products being commercially available collagen and polyester NC, respectively. In vitro degradation time upon incubation with collagenase increased in the same order for the collagen-based NC. In conclusion, co-delivery of synergistically acting GDNF and NGF from structurally improved NC may be a promising tool for the successful repair of peripheral nerve defects.

Atom Transfer Radical Polymerization as a Tool for Surface Functionalization

Atom transfer radical polymerization (ATRP) is receiving increasing attention as a method for surface functionalization. In this paper we discuss a simple way, based on the hydrophilicity of the substrate, for discriminating between surface and bulk polymerization in materials having a homogeneous distribution of initiator groups. This concept could allow a consistent simplification of the processing techniques and is therefore of high significance for the applicability of ATRP.

Low toxic, thermoresponsive dendrimers based on oligoethylene glycols with sharp and fully reversible phase transitions.

Novel first (G1) and second (G2) generation dendrimers based on three-fold branched oligoethylene glycol dendrons are efficiently synthesized which show characteristic thermoresponsive behavior and negligible cytotoxicity (for G2).

Solid-state replication of relief structures in semicrystalline polymers

The feasibility of structuring the surfaces of semicryst. polymers is explored using poly(tetrafluoroethylene-co-hexafluoropropylene) as a model material. Hot embossing was performed in the polymer melt at 330 Deg after which the samples were quenched at room temp. [on SciFinder (R)]

Solid‐State Processing of Organic Semiconductors

By Mohammed A. Baklar , elix F Koch , Avinesh Kumar , Ester Buchaca Domingo , Mariano Campoy-Quiles , Kirill eldman , F Liyang u , Y Paul Wobkenberg , James Ball , Rory M. Wilson , Iain McCulloch , Theo Kreouzis , Martin Heeney , Thomas Anthopoulos , Paul Smith ,

Surface forces, surface chemistry and tribology

Scanning probe methods have been applied to the investigation of tribological phenomena on the nanometre and nanonewton scale. The systems studied have included parallel investigation of identical tribosystems on the macro and nano scales, where the inherent differences in the AFM/LFM and flat-on-disk experiments have been compared; oxide-covered surfaces in contact under electrolytes, where the adhesion hysteresis and frictional behaviour was shown to be strongly dependent on the solution pH; and polymer surfaces, where advantage can be taken of variations in the interactions between the scanning tip and different polymers, to perform chemically sensitive, high-resolution surface imaging of polymer blends.

Light-curable polymer/calcium phosphate nanocomposite glue for bone defect treatment

Light-curable, methacrylate-based resins are clinically used for complex defect repair in dentistry (Heliobond). The present study investigates how such easy-to-apply polymers may be used on a much broader range of applications, particularly for gluing wet bone. We investigate the significantly improved adhesion of the polymer to wet bone surfaces in a close to in vivo setup using freshly cut cow hip bone as a model. The use of a reactive filler (20 wt.% amorphous, glassy calcium phosphate nanoparticles, a-CaP) allows for combination of the properties of the polymer (strength; light-curing) and the reactive filler (recrystallization of amorphous CaP to hydroxyapatite within minutes). This filler alone has been earlier suggested for use as an injectable bone cement since it reacts under in vivo conditions within 10-15 min. Our study transfers this reactivity into a composite, thus using the reactive CaP phase to establish an improved adhesion of the composite to wet bone surfaces. Additional in vitro bioactivity tests, compressive and tensile strength suggest use of such light-curable nanocomposites for complex-shaped load-bearing implant materials and fracture repair.

Method for fabricating pixelated, multicolor polarizing films

Pixelated, multicolor polarizing filters--of potential use in full-color displays--were produced by what we believe to be a novel method, i.e., masked evaporation of silver and gold onto glass substrates partially covered with separated sub-micrometer-wide strips of oriented poly(tetrafluoroethylene) (PTFE), prepared by friction deposition. The evaporated metal films preferentially nucleated at the glass surface and, consequently, formed parallel arrays in between the PTFE strips. The structures thus produced feature a strong angle-dependent absorption of polarized visible light, allowing for optical switching between red and blue and between green and yellow.

Alignment of liquid crystals on self-assembled monolayers using ultra-thin gold films

Thin films (1-100 .ANG.) of Au were sputtered on glass substrates coated with an ITO layer, a non-rubbed polyimide planarization layer, and a Cr adhesion interlayer. Then, self-assembled monolayers (SAMs) of the thiols 1-dodecanethiol, 1-hexadecanethiol, and 11-mercapto-1-undecanol were deposited on these substrates. The samples were characterized by AFM, polarized optical microscopy, and UV-vis spectroscopy. Furthermore, display cells were constructed, filled with the liq. crystals and characterized by measurements of their electrooptical properties. For the apolar thiols, a monolithic homeotropic alignment was obsd., while, the alkanethiols with a polar end group exhibited a monolithic planar liq.-crystal alignment. The transparency of the SAMs was enhanced. [on SciFinder (R)]

Tailoring of mechanical properties of derivatized natural polyamino acids through esterification and tensile deformation

Tensile deformation was applied to the naturally produced poly-γ-glutamic acid, which can be enzymatically degraded and is, therefore, of interest for biomedical use. However, natural polyamino acids have a similar chemical structure to synthetic polyamides (“nylons”), which are known to feature strong inter-molecular hydrogen bonding that prevents large-scale molecular motion in their solid state. Through esterification, this hydrogen bonding was partially shielded, allowing orientation of the polyamino acid macromolecules through tensile deformation. An increase in Youngs modulus and tensile strength was achieved of solution-cast films of the chemically modified poly-γ-glutamic acids, consistent with enhanced uniaxial polymer chain orientation. The latter was confirmed by both wide-angle X-ray scattering and polarized Raman spectroscopy. The films thus produced were found to be non-cytotoxic. These mechanically tailorable, biocompatible polymers may be excellent candidates for use in musculoskeletal tissue engineering applications that have different loading requirements within the body.