Polymers for neural implants

Neural implants are technical systems that restore sensory or motor functions after injury and modulate neural behavior in neuronal diseases. Neural interfaces or prostheses have lead to new therapeutic options and rehabilitation approaches in the last 40 years. The interface between the nervous tissue and the technical material is the place that determines success or failure of the neural implant. Recording of nerve signals and stimulation of nerve cells take place at this neuro‐technical interface. Polymers are the most common material class for substrate and insulation materials in combination with metals for interconnection wires and electrode sites. This work focuses on the neuro‐technical interface and summarizes its fundamental specifications first. The most common polymer materials are presented and described in detail. We conclude with an overview of the different applications and their specific designs with the accompanying manufacturing processes from precision mechanics, laser structuring and micromachining that are introduced in either the peripheral or central nervous system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Polymer coatings on magnesium-based implants for orthopedic applications

Nowadays, the need for bio-implants, which can gradually degrade after fulfilling the therapeutic tasks is continuously increasing. Under such situation, magnesium (Mg) and its alloys have been proposed and intensively studied as the new-generation medical implants due to their favorable biodegradability and biocompatibility. However, their swift corrosion in physiological environments can always cause an early fracture and further the surgical failure, greatly hindering their broad applications. Therefore, great efforts have been made to alter the degradation behaviors of Mg-based implants. Biodegradable polymeric surface coatings have been revealed to be a straightforward and effective strategy for retarding the fast degradation and improving the bioactivity of Mg and its alloys. This article reviews the recent progress of polymer-based coatings on Mg substrates, regarding the coating strategies, coating properties, and their performance in corrosive protection and biocompatibility promotion via in vitro as well as some in vivo models. The specific pros and cons of different polymeric coatings are also discussed. Finally, we put forward some perspectives on the future direction of polymeric coatings on biomedical Mg-based implants to better adapt to clinical trials.     

UV-cured coatings for functional protection

Photopolymerizing formulations of urethane-acrylate and epoxy-acrylate oligomers with active diluents of varied functionality and molecular mass were studied. It was found that the functionality of the monomers strongly affects the mechanism by which protective properties of a coating are formed. The limits of the range of optimal concentrations of the active monomers were found. It was confirmed that the maximum protective properties of the coatings are observed when unifunctional and bifunctional active diluents are used in the mixture formulation in a stoichiometric or nearly so ratio. The possibility of creating formulations with nanosize particles of functional additives determining the purpose of a formulation (anticorrosive, decorative) was revealed and substantiated.     

Powder coatings for corrosion protection

Powder coatings found a wider use in corrosion protection of steel structure. In Europe very often double-layer systems are used, based on an adhesion promoting epoxy (EP) primer and a weathering stable top coat, mostly polyester (SP) sometimes EP/SP-hybrid powders. An interesting development is the use of zinc filled EP powders as primer to offer a cathodic protection to the steel surface. Powder systems with and without zinc were compared to proved coating systems based on liquid paint materials, where powder coating systems showed results comparable to these systems. Besides many advantages of powder coatings for corrosion protection there are still some problems. The workshops carring out the powder coating have to be in control of the surface pretreatment like chromating, but espescially phosphating and the work with the chromate-free pretreatment methods for galvanized steel. As always in the field of corrosion protection it is the surface pretreatment and preparation which determines the quality of the whole coating system decisively. This problem can be solved by appropriate working. In some years the problem with the general maintenance of powder coatings after weathering and ageing will be actual. This problem should be solved because of the homogeneous coatings on larger areas. Of importance will be the adhesion on the old coating and the appearance of the maintenance coating. The touch up of smaller parts as transport damages will be much more difficult in order to the appearance.     

dM-Dim for carboxylic acid protection

The 1,3-dithian-2-yl-methyl (Dim) and its analogous groups including dimethyl-Dim (dM-Dim) can provide a new dimension of orthogonality for carboxylic acid protection. They can be deprotected under nearly neutral oxidative conditions. In this paper, the protection of carboxylic acid with dM-Dim, deprotection of dM-Dim ester with sodium periodate, stability of dM-Dim protected carboxylic acid under acidic and basic conditions, and selective deprotection of dM-Dim protected carboxylic acids in the presence of tertiary butyl and methyl esters are presented.     

Hydrogel ophthalmic implants

A new nontoxic spongy hydrogel material containing immobilized α-chymotrypsin has been obtained via precipitation polymerization of hydroxyethyl methacrylate. From this material, drains for the therapy of secondary glaucoma and eyeball endoprostheses have been made. The positive results of biomedical studies and sanitary-chemical evaluation of the material have made it possible to recommend the obtained products for clinical use.     

Comparative characterization of oligomeric precursors intended for injectable implants

The use of injectable materials is a simple approach for drug delivery and tissue repair, in, e.g. minimally invasive surgery applications. If these materials are used past their glass transition temperature and have a low viscosity, they will be able to flow while delivered in situ. Whether these materials are to be used as low viscosity drug carriers or further crosslinked for tissue repair, there is a need for a better understanding of their handling properties. In this study, oligo(trimethylene carbonate) (oTMC) and oligo[D,L‐lactide‐co‐(ε‐caprolactone)] (oDLLA‐co‐CL) of various molecular weights within a relevant injectability range were synthesized via ring‐opening polymerization. The materials were comparatively characterized by ¹H NMR spectroscopy, differential scanning calorimetry, gel permeation chromatography, and rheological measurements. After comparing the viscosities and molecular weights of the materials, it was concluded that oDLLA‐co‐CLs were, generally, better suited as an injectable in situ crosslinking network, whereas oTMCs were found to be better candidates as injectable drug carriers. This study provides useful data and guidelines on the use of these and other similar oligomers intended for injectable implants. Copyright © 2012 John Wiley & Sons, Ltd.     

Ultrathin organic layers for corrosion protection

The adsorption and self-organisation process of alkyl-phosphonic acids and phosphoric acid monoalkyl esters on technical aluminium surfaces have been investigated by different surface sensible techniques: Grazing angle FT-IR- spectroscopy, angle dependent XPS and Auger- spectroscopy. The aim of these studies was to replace the present technical procedure for pretreatment of aluminum surfaces with Chromate acid in order to improve the corrosion inhibition and the coating adhesion. The ability for self-assembly is given by substances which have a surface reactive group and a long-aliphatic or aromatic spacer and a supramolecular order is built-up between these spacers. The results show that these molecules are able to adsorb spontaneously onto the aluminum surface and subsequently a structured molecular order is formed. These effects were confirmed by industrial linked adhesion and corrosion tests.     

Vibrational spectroscopy of implants

The results of systematic spectral studies of polymers in ophthalmology are presented. The spectral criteria of selection of intraocular lens (IOL; implants of long service in an organism have been defined for poly(methylphenylsiloxane). Non-inflammatory implantation of IOL, when the manufacturing of lenses is performed under spectral control at several stages, has been realized. New siloxane–polyurethane block copolymers promising for ophthalmology have been studied and passivated surfaces have been obtained.     

Block copolymers for corrosion protection of aluminium

In this work, poly(n-butyl acrylate-b-trifluoroethyl methacrylate) (PBA-b-PTFEMA) and poly(n-butyl acrylate-b-heptadecafluorodecyl methacrylate) (PBA-b-PHFEMA) diblock copolymers synthesized by controlled radical polymerisation are used as a monolayer to protect aluminium against corrosion.Contact angle measurements show hydrophobic behaviour that can be attributed to the presence of a fluorinated block. The preferential orientation of the fluorinated block at the coating/air interface can explain the high hydrophobicity behaviour. Finally, corrosion resistance has been investigated by Electrochemical Impedance Spectroscopy (EIS). The results show that the PBA-b-PHFEMA copolymer provides excellent anti-corrosion barrier properties, even after 60 days of immersion in a solution of 3% NaCl.     

Near-infrared fluorescence probes for surgical navigation

Optical imaging is a promising tool for visualizing fundamental biological processes including disease progression, detection of tumors, and therapeutic monitoring non-invasively. Unlike visible light, near-infrared fluorescence (NIRF) imaging (beyond 700–1,700 nm) offers a competitive advantage to yield high-resolution images within a certain penetration depth (few millimeters to centimeters depending on NIR window). The last few years have witnessed rapid development of new NIRF probes within the span of whole NIR window, including small-molecule dyes, inorganic nanoparticles, and organic macromolecules. Benefitted by this, we observe a continual surge in the number of preclinical and clinical studies of NIRF imaging in surgery and related applications. At present, NIRF-guided imaging has emerged as a quintessential procedure to assist surgeons for intraoperative delineation and resection of tumors. Moreover, NIRF imaging is also used to improve the intraoperative staging, identify the hidden lesion in diseased organs, map lymph node metastases, detect tumor margins, and highlight vital organs intraoperatively. Considering rapid advancement of this field, we review recent progress in the development of NIRF probes, cancer-targeting strategies and their application for surgical navigation, particularly for the sentinel lymph node mapping, detection of tumors, and angiography. Moreover, we spotlight surgical navigation instrumentation that is currently used for intraoperative tumor detection.     

New catalysts and processes for environment protection

The results of recent studies in environmental catalysis are considered: design of support and catalysts for processes in moving — and fluidized catalyst beds; design of catalysts and processes for catalytic incineration of fuels and wastes, purification of hydrogen sulfide containing gases via direct catalytic H₂S oxidation to sulfur; design of monolith ceramic honeycomb catalysts for gas purification.     

Bioconjugated nanoparticles for DNA protection from cleavage

We have developed a novel method to protect DNA from cleavage using bioconjugated nanoparticles. Positively charged amino-modified silica nanoparticles have been directly prepared using water-in-oil microemulsion. Plasmid DNA can be easily enriched onto the positively charged nanoparticle surface, and the DNA strands are well protected from enzymatic cleavage. When incubated with nuclease enzyme for enzymatic cleavage, free plasmid DNA strands are completely cleaved, while those on the nanoparticle surfaces are intact. Our results clearly demonstrate unique properties of nanomaterials when combined with biomolecules. Our simple bionanotechnology will be highly useful in DNA separation, manipulation, and detection, and possibly in genetic engineering and gene therapy, as plasmid DNA can be protected in cellular environments without any change in its property.     

A photolabile protection strategy for terminal alkynes

We present a strategy for photolabile protection of terminal alkynes. Several photo-caged alcohols were synthesized via mild copper(II)-catalyzed substitution between tertiary propargylic alcohols and 2-nitrobenzyl alcohol to build up robust, base stable o-nitrobenzyl (NB) photo-cleavable compounds. We compare the new photolabile protecting group with the commonly used alkyne protecting group, 2-methyl-3-butyn-2-ol and the results show that NB ethers are stable under the cleaving conditions for the cleavage of methylbutynol protected alkynes. Additionally, we present the synthesis of photo-cleavable NB derivatives containing thiol groups that can serve as agents for photoinduced surface functionalization reactions.     

New methods for side-chain protection of cysteine

[reaction: see text]. Cysteine sulfhydryl protection with either the Fmoc or the Fm group was accomplished in one step and in high yield using commercially available FmocCl or FmocOSu, respectively. Mechanisms for the Fmoc to Fm transformations are discussed. Additionally, Fmoc-Cys(Fmoc)-OH (7) was synthesized and used in amide bond forming reactions. The S-Fmoc group is cleaved selectively from peptides containing the N-Fmoc group.     

Fluorophores as Optical Sensors for Local Forces

The main aim of this study is to investigate correlations between the impact of an external mechanical force on the molecular framework of fluorophores and the resultant changes in their fluorescence properties. Taking into account previous theoretical studies, we designed a suitable custom‐tailored oligoparaphenylenevinylene derivative (OPV5) with a twisted molecular backbone. Thin foils made of PVC doped with 100 nM OPV were prepared. By applying uniaxial force, the foils were stretched and three major optical effects were observed simultaneously. First, the fluorescence anisotropy increased, which indicates a reorientation of the fluorophores within the matrix. Second, the fluorescence lifetime decreased by approximately 2.5 % (25 ps). Finally, we observed an increase in the emission energy of about 0.2 % (corresponding to a blue‐shift of 1.2 nm). In addition, analogous measurements with Rhodamine 123 as an inert reference dye showed only minor effects, which can be attributed to matrix effects due to refractive index changes. To relate the observed spectroscopic changes to the underlying changes in molecular properties, quantum‐chemical calculations were also performed. Semiempirical methods had to be used because of the size of the OPV5 chromophore. Two conformers of OPV5 (C₂ and C_i symmetry) were considered and both gave very similar results. Both the observed blue‐shift of fluorescence and the reduced lifetime of OPV5 under tensile stress are consistent with the results of the semiempirical calculations. Our study proves the feasibility of fluorescence‐based local force probes for polymers under tension. Improved optical sensors of this type should in principle be able to monitor local mechanical stress in transparent samples down to the single‐molecule level, which harbors promising applications in polymer science and nanotechnology.     

Local harmonic approximation for multidimentional density matrix

A method is established for the approximate calculation of the density matrix for a system of interacting anharmonic oscillators. An approximate analytical expression is obtained for the density matrix of a two-dimentional isotropic anharmonic oscillator. As an example the calculations for a two-dimensional quartic oscillator are demonstrated.