Surface functionalization of polypropylene (PP) by chitosan immobilization to enhance human fibroblasts viability

Driven by the market demand, several synthetic and natural grafts have been proposed during the last years for tendons regeneration. The synthetic grafts, which present a better mechanical performance than the natural ones, usually fail due to the lack of biocompatibility and bioactivity. Thus, chitosan (Cs) was immobilized on polypropylene (PP) surface, previously activated by plasma treatment, in order to improve the fibroblasts' adhesion and proliferation on it. The Orange II dye method and FTIR-ATR analysis proved the successful Cs immobilization on the PP surface. It was observed by SEM and optical profilometry analysis that the Cs concentration increase leads to a surface roughness (R_a value) increase, as well as to water contact angle (C.A.) decrease at least until 2% (w/V) of Cs. Using the 2% (V/V) Cs solution concentration, according to SEM analysis and resazurin assay, the developed functionalization was well succeeded in improving fibroblasts adhesion and proliferation on PP substrates surface over 7 days of culture.     

Sonochemical immobilization of silver nanoparticles on porous polypropylene

Silver nanoparticles were immobilized on the surface of polypropylene (PP) porous beads by an ultrasound‐assisted reduction method. The structure and properties of the silver–PP composite were characterized with XRD, TEM, HRSEM, EDX, XPS, and Raman spectroscopy. Water‐soluble polymers such as PEG, PVA, and PVP were used as stabilizing agents for preventing the agglomeration of the silver nanoparticles. With PVP, a homogeneous distribution of silver nanocrystals, 50 nm in size, on the PP surface was achieved. The mechanism proposed for the silver anchoring to the inert polymer accounts for a localized melting of the PP. The beads of the silver PP composite demonstrated good stability and high antibacterial activity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1719–1729, 2008     

Surface immobilization methods for aptamer diagnostic applications

In this review we examine various methods for the immobilization of aptamers onto different substrates that can be utilized in a diverse array of analytical formats. In most cases, covalent linking to surfaces is preferred over physisorption, which is reflected in the bulk of the reports covered within this review. Conjugation of aptamers with appropriate linkers directly to gold films or particles is discussed first, followed by methods for conjugating aptamers to functionally modified surfaces. In many aptamer-based applications, silicates and silicon oxide surfaces provide an advantage over metallic substrates, and generally require surface modification prior to covalent attachment of the aptamers. Chemical protocols for covalent attachment of aptamers to functionalized surfaces are summarized in the review, showing common pathways employed for aptamer immobilization on different surfaces. Biocoatings, such as avidin or one of its derivatives, have been shown to be highly successful for immobilizing biotin-tethered aptamers on various surfaces (e.g., gold, silicates, polymers). There are also a few examples reported of aptamer immobilization on other novel substrates, such as quantum dots, carbon nanotubes, and carbohydrates. This review covers the literature on aptamer immobilization up to March 2007, including comparison of different linkers of varying size and chemical structure, 3′ versus 5′ attachment, and regeneration methods of aptamers on surfaces.     

Surface crystallization of polypropylene

Crystallization of compression-molded isotactic polypropylene and polyethylene is invariably spherulitic; generally, nucleation occurs randomly throughout the sample. In a special case where nucleation predominates at the surface, spherulitic growth centers become crowded and are forced to propagate unidirectionally into the bulk (transcrystallinity). Conditions for the formation of transcrystallinity have been investigated by optical and scanning electron microscopy. The occurrence of transcrystallinity is attributed to heterogeneous nucleation induced at the mold surface. To be effective, the mold surface must have a nucleating efficiency equal to or greater than that of adventitious nuclei present in the polymer. As the crystallization temperature approaches the melting point, the activity of mold surfaces is found to increase leading invariably to transcrystalline formation. The degree of activity of various mold surfaces correlates with the known activity of specific dispersed nucleating agents having similar chemical structures. Contrary to claims in the literature, the surface energy of the mold surface and temperature gradients across the melt surface do not play a primary role in transcrystalline formation of polypropylene.     

Changes in morphology and activity of transglutaminase following cross-linking and immobilization on a polypropylene microporous membrane

Transglutaminase (TGase) was cross-linked with glutaraldehyde, and cross-linked crystalline transglutaminase was immobilized on a polypropylene microporous membrane by UV-induced grafting. Immobilized enzyme activity were calculated to be 0.128 U/cm2 polypropylene microporous membrane. The microstructure and enzyme characteristics of free, cross-linked and immobilized transglutaminase were compared. The optimum temperature of free transglutaminase was determined to be approximately 40 °C, while cross-linking and immobilization resulted in an increase to approximately 45 °C and 50 °C. At 60 °C, immobilized, cross-linked and free transglutaminase retained 91.7 ± 1.20%, 63.2 ± 1.05% and 37.9 ± 0.98% maximum activity, respectively. The optimum pH was unaffected by the state of transglutaminase. However, the thermal and pH stabilities of cross-linked and immobilized transglutaminase were shown to increase.     

Methodology for the immobilization of enzymes onto mesoporous materials

Cytochrome c and xylanase were adsorbed onto two mesoporous materials, SBA-15 (a pure silicate) and MSE (an organosilicate), with very similar physical properties but differing chemical compositions. A methodical order was developed whereby the influences of surface area, pore size, extent of order, particle size, surface potentials, isoelectric points, pH, and ionic strength on immobilization were explored. In silico studies of cytochrome c and xylanase were conducted before any immobilization experiments were carried out in order to select compatible materials and probe the interactions between the adsorbents and the mesoporous silicates. The stabilities of the mesoporous materials at different pH values and their isoelectric points and zeta potentials were determined. Electrostatic attraction dominated protein interactions with SBA-15, while weaker hydrophobic interactions are more prominent with MSE for both cytochrome c and xylanase. The ability of the immobilized protein/enzyme to withstand leaching was measured, and activity tests and thermostability experiments were conducted. Cytochrome c immobilized onto SBA-15 showed resistance to leaching and an enhanced activity compared to free protein. The immobilized cytochrome c was shown to have higher intrinsic activity but lower thermostability than free cytochrome c. From an extensive characterization of the surface properties of the silicates and proteins, we describe a systematic methodology for the adsorption of proteins onto mesoporous silicates. This approach can be utilized in the design of a solid support for any protein.     

Photo-responsive polymer materials for biological applications

In this review, we briefly summarized the remarkable progress of photo-responsive polymer materials from zero-dimensional micelles, twodimensional surfaces to three-dimensional hydrogels with irreversible or reversible moieties. Based on the photo-responsiveness, polymer have been designed, synthesized and applied for various biological fields including drug delivery and cell manipulation.     

3D thermoplastic elastomer microfluidic devices for biological probe immobilization

Microfluidics has emerged as a valuable tool for the high-resolution patterning of biological probes on solid supports. Yet, its widespread adoption as a universal biological immobilization tool is still limited by several technical challenges, particularly for the patterning of isolated spots using three-dimensional (3D) channel networks. A key limitation arises from the difficulties to adapt the techniques and materials typically used in prototyping to low-cost mass-production. In this paper, we present the fabrication of thin thermoplastic elastomer membranes with microscopic through-holes using a hot-embossing process that is compatible with high-throughput manufacturing. The membranes provide the basis for the fabrication of highly integrated 3D microfluidic devices with a footprint of only 1 × 1 cm(2). When placed on a solid support, the device allows for the immobilization of up to 96 different probes in the form of a 10 × 10 array comprising isolated spots of 50 × 50 μm(2). The design of the channel network is optimized using 3D simulations based on the Lattice-Boltzmann method to promote capillary action as the sole force distributing the liquid in the device. Finally, we demonstrate the patterning of DNA and protein arrays on hard thermoplastic substrates yielding spots of excellent definition that prove to be highly specific in subsequent hybridization experiments.     

Preparation of cellulosic fibers with biological activity by immobilization of trypsin on periodate oxidized viscose fibers

In this study, a biologically active fibrous material was designed by immobilizing trypsin on viscose fibers. The viscose yarn was first oxidized with sodium periodate to produce aldehyde groups and then employed as a support for subsequent immobilization of trypsin through bovine serum albumin. The oxidation by sodium periodate caused changes in the chemical and physical properties of the modified yarn samples, which were evaluated by determining the aldehyde group content, fineness and tensile strength of yarn. The viscose fibers oxidized under the most severe conditions (0.4 % NaIO₄, 360 min) exhibited the maximum amount of introduced aldehyde groups (1.284 mmol/g), but also the highest decrease in tensile strength. The trypsin activity was assayed with N-α-benzoyl-DL-arginine p-nitroanilide hydrochloride, whereas the amount of bound trypsin was determined by Bradford method. Trypsin immobilized on oxidized viscose yarn retained 97.3 and 83.8 % of the initial activity over 60 days of storage at 4 and 25 °C, respectively, and remained firmly attached to the carrier. The potential application of obtained bioactive fibers is in the treatment of wounds.     

Radiolysis of chitosan derivatives exhibiting antimutagenic activity

The radiolysis of antimutagens extracted from natural biopolymer chitosan was studied by the EPR method. It was shown that addition of gallic acid (2 mol %) to quaternized chitosan results in a 2.5-fold decrease in the radiation-chemical yield of radicals and a nearly complete inhibition of the formation of ion radicals. Gallic acid units likely play the role of a stabilizer that protects the polycation from radiation damage and, hence, the structure of the cationogenic units from changes, thereby improving the antimutagenic properties of the system.     

Radiolysis of polycationic systems exhibiting antimutagenic activity

The radiolysis of synthetic (based on diallyldimethylammonium) and natural (based on the biopolymer chitosan) polycations as antimutagens was studied by means of the ESR technique. It was shown that the introduction of gallic acid units into a polymer structure leads to stabilization of the macromolecule toward radiation and a reduction in radical formation during γ-irradiation, a change that correlates with a considerable increase in the antimutagenic activity of the modified polycations. Approaches to the targeted synthesis of effective animutagens and optimization of their composition were developed.     

Renewable vegetable raw materials as a base for preparing versatile functional nanocomposites

A power-saving technology was developed for preparing functional nanocomposites from renewable vegetable raw materials and nanosized elements.     

Surface modification of polypropylene materials by the cobalt complex of 5,10,15,20-tetrakis-(4-methylpyridyl)porphyrin tetratosylate

The process of immobilization of cobalt(II) 5,10,15,20-tetrakis(4-methylpyridyl)porphyrin tetratosylate on chemically activated surface of polypropylene materials was studied using infrared spectroscopy of multiple frustrated total internal reflection, electron spectroscopy, and atomic force microscopy. The modified materials were shown to have a sorption activity with respect to nitrogen bases, the structural analogs of blood toxines.     

Surface immobilization of biomolecules by click sulfonamide reaction

Alkyne-modified biomolecules can be immobilized site- and chemoselectively on sulfonylazide slides under very mild conditions by means of the click sulfonamide reaction.     

Porous chromatographic materials as substrates for preparing synthetic nuclear explosion debris particles

Several porous chromatographic materials were investigated as synthetic substrates for preparing surrogate nuclear explosion debris particles. Eighteen metals, including some of forensic interest, were loaded onto materials by immersing them in metal solutions (556 mg/L of each metal) to fill the pores, applying gentle heat (110 °C) to drive off water, and then treating them at high temperatures (up to 800 °C) in air to form less soluble metal species. High-boiling-point metals were uniformly loaded on spherical controlled-pore glass to emulate early fallout, whereas low-boiling-point metals were loaded on core–shell silica to represent coated particles formed later in the nuclear fallout-formation process. Analytical studies characterized material balance and the formation of recalcitrant species. Metal loading was 1.5–3 times higher than expected from the pore volume alone, a result attributed to surface coating. Most metals were passively loaded; that is, solutions filled the pores without active metal discrimination. However, niobium and tin concentrations were lower in solutions after pore filling, and were found in elevated concentrations in the final products, indicating selective loading. High-temperature treatments caused reduced solubility of several metals, and the loss of some volatile species (rhenium and tellurium). Sample preparation reproducibility was high (the inter- and intra-batch relative standard deviations were 7.8 and 0.84 %, respectively) indicating suitability for use as a working standard for analytical methods development. We anticipate future standardized radionuclide-loaded materials will find use in radioanalytical methods development and/or serve as a starting material for the synthesis of more complex nuclear explosion debris forms (e.g., Trinitite).     

Criteria for the development of biological reference materials

Summary A review is presented of factors to be considered in the development of biological reference materials. Some guidelines are offered regarding approaches to the generation of the varied materials required for analytical quality control. Major considerations in such an endeavour are the goal of the undertaking and role of the final product, selection of candidate materials, preparation, characterization and certification. Selection of materials should be from those important to commerce and consumers, and related to various regulatory, clinical, environmental, and research activities. They should adequately represent the different choices and types of foodstuffs, clinical materials and environmental materials, such as soils, sewage sludges, plant and animal tissues, of interest in different regions of the world.Acquisition can be from commercial sources or the result of in-house preparation, with attention to stability enhancement if required and maintenance of native analyte levels by minimization of contamination. The approach to chemical and physical characterization relies on the measurement philosophy, selection of analytes, their speciation, and selection of analytical methods and analysts for establishment of homogeneity and quantitative levels. Throughout the overall task of RM development there is a requirement for a critical approach by critical analytical and measurement scientists and the involvement of national RM agencies in order to produce top quality control materials.

---

Kriterien für die Entwicklung von biologischen Referenzmaterialien

---

Contribution No. 88-50 from Land Resource Research Centre