A Simple Method to Functionalize PCL Surface by Grafting Bioactive Polymers Using UV Irradiation

Background

Polycaprolactone (PCL) is a biodegradable polymer which is used in tissue engineering applications thanks to its many favorable characteristics. However, PCL surfaces are known as hydrophobic leading to a lack of favorable cell response. To overcome this problem, PCL surfaces will undergo a surface functionalization by grafting bioactive polymers bearing ionic groups.

Implication of the Nature and Texturation of Silicone Surfaces on the Grafting of PolyNaSS,a Bioactive Polymer

ObjectiveThe publication aims to characterize the particularities of breast implant outer shells' structure and roughness. Then, it seeks to study the implication of the topography and the type of silicone on the grafting of the bioactive polymer under UV irradiations.Material & methodsPolyNaSS was grafted on silicone surfaces via a radical polymerization under 365 nm UV irradiation. Surface characterizations were accessed using scanning electron microscopy (topography), water contact angle measurements, infrared spectroscopy, and colorimetric assays (grafting density). A viability test was carried with L929 fibroblasts using MTT reagent.ResultsPolydiphenylsiloxane (PDPS) has improved the grafting protocol thanks to the reactivity of phenyl groups under UV irradiation compared to polydimethylsiloxane (PDMS) but exhibits low viability rates in contact with fibroblasts.ConclusionThe roughness of silicone surfaces or the nature of silicone influence the grafting quality. PDPS could not be considered as an alternative to PDMS from a biological point of view.     

Inhibition de l'adhérence de Porphyromonas gingivalis sur la surface de titane greffé de poly(styrène sulfonate de sodium)

Dental implant-associated infections as peri-implantitis represent one of the major causes of osteointegration failures of oral implants. Adhesion of Porphyromonas gingivalis, one of the bacterial strains mainly involved in such infections, is tightly dependent on the topographical and/or physico-chemical properties of the implant surfaces. As a matter of fact, we showed that the grafting of one bioactive polymer such as poly(sodium styrene sulfonate) onto titanium implant surfaces allowed a sensitive decrease of Staphylococcus aureus adhesion (> 40%). The aim of the study consists in evaluating the adhesion of P. gingivalis onto titanium surfaces grafted with poly(sodium stryrene sulfonate) in order to elaborate implants exhibiting appropriate inhibiting properties towards the adhesion of periodontal pathogens. The grafting of poly(sodium stryrene sulfonate) onto titanium surfaces is carried out in two steps: chemical oxydation of titanium to initiate radical species then grafting of poly(sodium stryrene sulfonate) by radical polymerization. Chemical characterization of the surfaces is achieved by Fourier transformed infrared spectroscopy (FTIR). Bacterial adhesion was studied on grafted and non grafted (control) titanium surfaces, preadsorbed or not by plasmatic proteins. Protein adsorption as well as bacteria adhesion is followed by fluorescence spectroscopy by using proteins or bacteria previously labelled with fluorescence probes; the quantification of adsorption and bacteria adhesion are performed by image analysis. Results showed that protein adsorption is more important (~3 times) and that P. gingivalis adhesion is strongly inhibited (~73%) onto poly(sodium styrene sulfonate) grafted surfaces when compared to titanium control. Moreover, the inhibition of bacterial adhesion on grafted surfaces preadsorbed with plasma proteins is comparable to that observed on grafted surfaces preadsorbed with fibronectin. In conclusion, the obtained results evidenced that the grafting of titanium surface by poly(sodium styrene sulfonate) led to significant inhibition of P. gingivalis adhesion and that this inhibitory activity involved adsorbed proteins. Poly(sodium styrene sulfonate) grafted titanium surfaces present a high interest for the elaboration of oral implants in various clinical dental applications.     

Évaluation clinique et biologique d’un ligament synthétique bioactif chez la brebis

The anterior cruciate ligament, which plays a key role in the knee stabilization, is commonly injured mainly during sport practicing such as soccer or skiing. Although it seems that ligament replacement by a tendon autograft is a better solution, the reconstruction with an artificial ligament provides a shorter recovery time. Polyethylene terephthalate (PET) is the best polymer to fabricate ligament prosthesis but its biocompatibility still needs to be improved. Radical graft polymerization of sodium salt of styrene sulfonate (NaSS) on PET surface was performed using the “grafting from” technique. The grafting ratio is about 5 μmol/g and found to be perfectly reproducible. Polymer grafted ligaments and non-grafted ligaments were implanted in sheep for a 3-month observation. The clinical and biological evaluation of the knee synovial liquid of implanted sheep evidenced an early functional recuperation and an excellent tolerance of pNaSS reflecting a significant absence of articular inflammation.     

Fungal biodegradation of lignopolystyrene graft copolymers.

White rot basidiomycetes were able to biodegrade styrene (1-phenylethene) graft copolymers of lignin containing different proportions of lignin and polystyrene [poly(1-phenylethylene)]. The biodegradation tests were run on lignin-styrene copolymerization products which contained 10.3, 32.2, and 50.4% (wt/wt) lignin. The polymer samples were incubated with the white rot fungi Pleurotus ostreatus, Phanerochaete chrysosporium, and Trametes versicolor and the brown rot fungus Gloeophyllum trabeum. White rot fungi degraded the plastic samples at a rate which increased with increasing lignin content in the copolymer sample. Both polystyrene and lignin components of the copolymer were readily degraded. Polystyrene pellets were not degradable in these tests. Degradation was verified for both incubated and control samples by weight loss, quantitative UV spectrophotometric analysis of both lignin and styrene residues, scanning electron microscopy of the plastic surface, and the presence of enzymes active in degradation during incubation. Brown rot fungus did not affect any of the plastics. White rot fungi produced and secreted oxidative enzymes associated with lignin degradation in liquid media during incubation with lignin-polystyrene copolymer.     

Fungal biodegradation of lignopolystyrene graft copolymers.

White rot basidiomycetes were able to biodegrade styrene (1-phenylethene) graft copolymers of lignin containing different proportions of lignin and polystyrene [poly(1-phenylethylene)]. The biodegradation tests were run on lignin-styrene copolymerization products which contained 10.3, 32.2, and 50.4% (wt/wt) lignin. The polymer samples were incubated with the white rot fungi Pleurotus ostreatus, Phanerochaete chrysosporium, and Trametes versicolor and the brown rot fungus Gloeophyllum trabeum. White rot fungi degraded the plastic samples at a rate which increased with increasing lignin content in the copolymer sample. Both polystyrene and lignin components of the copolymer were readily degraded. Polystyrene pellets were not degradable in these tests. Degradation was verified for both incubated and control samples by weight loss, quantitative UV spectrophotometric analysis of both lignin and styrene residues, scanning electron microscopy of the plastic surface, and the presence of enzymes active in degradation during incubation. Brown rot fungus did not affect any of the plastics. White rot fungi produced and secreted oxidative enzymes associated with lignin degradation in liquid media during incubation with lignin-polystyrene copolymer.     

A chitosan-based flocculant prepared with gamma-irradiation-induced grafting

A natural polymer, chitosan, was modified to prepare an efficient flocculant using grafting method initiated by gamma ray in acid-water solution. A vinyl monomer, acrylamide, was used as the grafted monomer. The graft copolymer obtained was characterized using Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. Effects of acetic acid concentration, total irradiation dose, dose rate and monomer concentration on the grafting percentage were investigated. Flocculation experiment results demonstrated that the graft copolymer produced was significantly superior to chitosan and polyacrylamide (PAM).     

Feasibility Study of the Elaboration of a Biodegradable and Bioactive Ligament Made of Poly(ε-caprolactone)-pNaSS Grafted Fibers for the Reconstruction of Anterior Cruciate Ligament: In Vivo Experiment

Background

The anterior cruciate ligament rupture is a common injury which mainly affects young and active population. Faced to this problem, the development of synthetic structures for ligament reconstruction is increasing. The most recent researches focused on the development of biodegradable structures that could be functionalized to enhance host integration. This work describes the elaboration of different poly(ε-caprolactone) prototypes for the rat anterior cruciate ligament replacement in order to found the best design for further in vivo assays.

Observation de ligaments artificiels de genou après implantation en MEB à pression variable

ObjectivesWe carried out a comparative study between two methods to prepare explanted artificial ligaments samples before their observation in the variable pressure scanning electron microscope (VP-SEM).Materials and methodsPoly(ethylene terephtalate) (PET) artificial ligaments grafted by a bioactive polymer, the poly(sodium styrene sulfonate) were implanted for three months in the knee of four ewes after section of the anterior cruciate ligament (ACL). The qualitative evaluation of the cellular and tissue colonization of the artificial ligaments was carried out on critical point-dried explants (observed by VP-SEM) or not (observed by VP-SEM–Peltier).Results and discussionThe results showed differences in the biointegration of the two types of studied ligaments. Only the MEB-VP–Peltier technique allowed obtaining images of excellent resolution with high magnification. For this reason the MEB-VP–Peltier technique is a promising method for the fast qualitative evaluation of the cellular and tissue integration of the artificial ligaments.     

The immobilization of enzymes and cells of Bacillus stearothermophilus onto poly(maleic anhydride/styrene)-Co-polyethylene and poly(maleic anhydride/vinyl acetate)-Co-polyethylene

The graft copolymer, poly(maleic anhydride/styrene)-co-polyethylene was prepared. The copolymer immobilized bovine serum albumin (BSA), but the amount coupled appeared to be effected by the amount of styrene in the graft copolymer, temperature, and pH of the coupling medium. Competition existed between hydrolysis of the grafted anhydride groups and the protein. A graft copolymer with 66% add-on immobilized 4.5 mg/glucose oxidase/g copolymer, 4.6 mg alkaline phosphates/g copolymer and 0.2 mg cell of Bacillus stearothermophilus/g copolymer. A number of copolymers containing poly(maleic anhydride/vinyl acetate)-co-polyethylene were prepared to cover a range of grafting levels. These immobilized larger quantities of BSA, alkaline phosphatase, and cells of B. stearothermophilus than did the styrene graft copolymer. The copolymer was also hydrolyzed to release the hydroxyl group from the poly(vinyl acetate) component of the grafted chains. Using p-benzoquinone as the "activating agent," the copolymer coupled to BSA and to acid phosphatase. Using p-toluene-sulfonyl chloride, the copolymer was very effective in immobilizing trypsin.     

Synthèse et greffage de polymères bioactifs sur des surfaces en titane pour favoriser l’ostéointégration

Titanium is widely used in orthopedic and dental implants for its excellent resistance to corrosion and its biocompatibility. In order to improve the long-term osteointegration of titanium, bioactive polymers bearing ionics groups such as sulfonates (sodium polysytrene sulfonate, polyNaSS) are grafted by a covalent way onto titanium surface. The surface is chemically modified and then bioactive polymers are grafted by radical polymerization. The chemical composition of grafted surfaces is given by ATR/FTIR and XPS which certified the presence of sulfonate groups at the surface of grafted titanium. Quantitative grafting of polyNaSS is determined by a colorimetric method and evaluated at 5 μg/cm².In vitro study is performed in order to see the effect of these bioactive polymers on the mineralization of human osteoblast (line MG63). After 28 days of cultured cells on grafted titanium surfaces and non-grafted ones, the amount of calcium onto surfaces is quantified. The results show that the mineralization of these cells is improved with the presence of polyNaSS. The amount of calcium is increased on grafted surfaces compared to non-grafted ones. Cell adhesion was evaluated. Cells were seeded onto grafted and non-grafted titanium and then subjected to detachment forces. The results show that the attachment of human osteoblasts-like cells is increased for grafted titanium with polyNaSS. A study on titanium surface grafted by polymers bearing ionics groups such as carboxylate and phosphate is in progress.     

Radical graft polymerization of styrene sulfonate on poly(ethylene terephthalate) films for ACL applications: "grafting from" and chemical characterization

The purpose of this study is to develop a reliable method of functionalizing poly(ethylene terephthalate) with bioactive polymers to produce a "biointegrable" artificial anterior cruciate ligament. Radical graft polymerization of the sodium salt of styrene sulfonate (NaSS) onto poly(ethylene terephthalate) (PET) films was performed using the "grafting from" technique. Prior to the grafting, the surfaces of poly(ethylene terephthalate) films were activated by ozonation to generate peroxide and hydroperoxide reactive species on the PET film surfaces. The radical polymerization of NaSS was initiated by thermal decomposition of the hydroperoxides. The grafted PET surfaces were characterized by a toluidin blue colorimetric method, X-ray photoelectron spectroscopy, contact angle measurements, and atomic force microscopy. The influence of ozonation time, monomer concentration, and temperature on NaSS grafting ratios was examined. A total of 30 min of ozonation followed by grafting from a 15% NaSS solution at 70 degrees C for 90 min or more resulted in attachment of poly(NaSS) chains to the PET film surfaces.     

Preparation of cassava starch grafted with polystyrene by suspension polymerization

Cassava starch grafted with polystyrene (PS-g-starch) copolymer was synthesized via free-radical polymerization of styrene by using suspension polymerization technique. Potassium persulfate (PPS) was used as an initiator and water was used as a medium. The graft copolymer was characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, X-ray diffraction and scanning electron microscopy. The sub-micron spherical beads of PS were observed on the surface of starch granules. SEM micrographs showed porous patches of PS adhering on the starch granules after Soxhlet extraction. FTIR spectra also indicated the presence of PS-g-starch copolymer. XRD analysis exhibited insignificant changes in crystalline structure and degree of crystallinity. The effects of starch:styrene weight ratio, amount of PPS, reaction time and reaction temperature on the percentage of grafting – G (%), were investigated. G (%) increased with increasing starch content. Other variables showed their own individual optimal values. The optimum condition yielding 31.47% of G (%) was derived when the component ratio was 1:3 and reaction temperature and time were 50 °C and 2 h, respectively. Graft copolymerization did not change granular shape and crystallinity of starch. This study demonstrated the capability of polymerization of styrene monomer on the granular starch without emulsifier and the synthesis of graft copolymer without gelatinization of starch.     

Synthesis and properties of carrageenan grafted copolymer with poly(vinyl alcohol)

The aim of this work was to prepare a carrageenan-g-poly(vinyl alcohol) (CG-g-PVA) polymer using potassium persulphate as an initiator. The effect of different ratios of the polymer blends on the parameters of the grafted polymer was investigated. The grafting ratio decreased with an increase of the CG content in the graft copolymer. The resulting CG-g-PVA was characterized by ATR-FTIR, tensile strength, elongation at break, swelling ratio, contact angle and biodegradation in soil. From the ATR-FTIR the 3,6-anhydride-galactose of the CG showed a peak at 927 cm⁻¹ that was absent in the CG-g-PVA and the ether linkage of PVA-g-CG between the hydroxyl group of PVA and the 3,6-anhydride-galactose of CG showed a peak at 1089 cm⁻¹ in the graft copolymer. The tensile strength and elongation at break decreased with an increase of the CG due to its phase separation. The highest tensile strength was observed at 2:8 CG/PVA. In addition, the swelling ratio decreased and the contact angle increased as a function of the increase of the CG in the grafted copolymer. The best ratio of CG-g-PVA was 2:8 CG/PVA. This graft copolymer was easily biodegraded in natural soil.     

Adapting Mechanical Characterization of a Biodegradable Polymer to Physiological Approach of Anterior Cruciate Ligament Functions

Background and objectiveOver the past decades, anterior cruciate ligament injuries have become a considerable public health issue. Due to specific physiological conditions such injuries often demand replacement surgery and can take up to two years to a complete recovery. Using biomaterials able to accelerate the healing process could represent a remarkable progress in the field. The main goal of this article is, therein, to evaluate the mechanical properties of poly(ε-caprolactone) (PCL) fibers with biological properties enhanced by poly(sodium styrene sulfonate) (PNaSS) grafting when subjected to mechanical stress in different conditions.Materials and methodsPCL fibers were thermal grafted with PNaSS. The grafting density was estimated by the toluidine blue colorimetric assay (TB). The influence of the grafting on in vitro primary ACL fibroblast behavior was evaluated by cell proliferation and fluorescence microscope images. The mechanical behavior was evaluated by tensile experiments in air and water, fatigue experiments and simulated walk efforts.ResultsThe results show that poly(ε-caprolactone) bundles have their mechanical behavior changed by the different surface treatments and nature of mechanical stress. Although, compared with the values of the natural ligament, the poly(ε-caprolactone) has shown superior mechanical properties (Young's Modulus, elastic deformation and ultimate tensile stress) in all studied scenarios. In addition, the pNaSS-grafted surfaces presented a positive influence in the cell proliferation and morphology.ConclusionThe pNaSS-grafted PCL has responded mechanical and biological requests for suitable ligament prosthesis material and could be considered as a promising alternative for ACL reconstruction.     

Presence of sulfonate groups on Ti6Al4V surfaces enhances osteoblastic attachment strength at the interface

The application of the titanium alloy Ti6Al4V in the biomedical field is not new. It has been used for more than 50 years with excellent results. Nonetheless, the interactions developed at the interface biomaterial-cell still present some challenges during implantation. The use of bioactive polymers bearing anionic groups in combination with titanium-based materials has been shown to be an excellent solution. In this study, we demonstrated the impact of the poly(sodium styrene sulfonate) (or poly(NaSS)) chemical grafting on Ti6Al4V surfaces by following the attachment strength of the osteoblastic cells MC3T3-E1, in their initial moments of interaction, and by afterward examine their differentiation. The grafting process was proved to be successful by measuring the poly(NaSS) concentration on the Ti6Al4V using the toluidine blue colorimetric method. The cells morphology was observed without changes being detected between substrates. On the other hand, the presence of the sulfonate groups enhanced the strength of the cellular bond, enabling the MC3T3-E1 to resist to shear stress of 10 dyn/cm² of magnitude. The poly(NaSS) was found to enhance the osteoblastic cells differentiation by increasing the alkaline phosphatase concentration and, consequently, the cells metabolic activity. This in vitro study proved once again the poly(NaSS) to be suitable for biomedical applications.     

Xanthan-g-poly(acrylamide): Microwave-assisted synthesis,characterization and in vitro release behavior

Xanthan-g-poly(acrylamide) was synthesized employing microwave-assisted and ceric-induced graft copolymerization, and was characterized by FT-IR, DSC, XRD and SEM studies. Matrix tablets of diclofenac sodium were formulated using graft copolymer as the matrix by direct compression technique. Release behavior of the graft copolymer was evaluated using USP type-II dissolution apparatus in 900 ml of phosphate buffer (pH 6.8), maintained at 37 °C and at 50 rpm. Microwave-assisted grafting provided graft copolymer with higher % grafting in a shorter time in comparison to the ceric-induced grafting. The % grafting was found to increase with the increase in the power of microwave and/or time of exposure. The matrix tablets were found to release the drug by zero-order kinetics, and the faster release of drug was observed from the graft copolymer matrix as compared to the xanthan gum matrix. It was observed that grafting reduces the swelling, but increases the erosion of xanthan gum.     

Intermediates in nickel(0)-phosphine complex catalyzed dehydrogenative silylation of olefins

Nickel(0) complexes 1-4 containing π-coordinated olefin and triphenylphosphine (tricyclohexylphosphine) (starting from Ni(cod)₂) were prepared and the X-ray structures of 1 and 2 were resolved. The complexes appeared as efficient catalysts in dehydrogenative silylation of styrene and vinyltris(trimethylsiloxy)silane, but only after prior oxygenation of phosphine ligand. Stoichiometric studies of Ni(0) complexes with substrates showed that the bis(silyl)nickel(II) complex was a key intermediate in both reactions examined. A scheme of catalysis by Ni(0) complex involving olefin insertion into Ni-Si bond, as a crucial step, is presented.     

Graft copolymers of starch and its application in textiles

The graft copolymerization of styrene (ST), methyl methacrylate (MMA)/butyl acrylate (BA) with starch was carried chemically using ferrous ion-peroxide redox system. The grafting was performed at 60 °C and the monomer ratios of ST/MMA and ST/BA was varied with their % composition as 80/20, 50/50 and 20/80 parts by weight. The effect of initiator concentration, starch concentration and the monomer ratio on the grafting efficiency was studied. The grafted starch granules (GSG) were further analyzed for their particle size, bulk density and by sizing on cotton yarn for its physico-mechanical properties such as tensile strength, elongation at break, etc. The rheological properties of the resulting granular product in water as well as the starch graft copolymer emulsion were studied.     

Photoswitching of ligand association with a photoresponsive polymer-protein conjugate

Light-regulated molecular switches that reversibly control biomolecular function could provide new opportunities for controlling activity in diagnostics, affinity separations, bioprocessing, therapeutics, and bioelectronics applications. Here we show that site-specific conjugation of light-responsive polymers near the biotin-binding pocket of streptavidin provides control of ligand binding affinity in response to UV and visible light irradiation. Two different light-responsive polymers were utilized that display opposite photoresponsive solubility changes under UV or visible (vis) light irradiation in aqueous solutions. At 40 degrees C, the N,N-dimethylacrylamide (DMA)-co-4-phenylazophenyl acrylate (AZAA) copolymer (DMAA) was soluble under UV irradiation and precipitated under visible light, while the DMA-co-N-4-phenylazophenyl acrylamide (AZAAm) copolymer (DMAAm) was soluble under visible irradiation and precipitated under UV light. Both polymers were synthesized with a vinyl sulfone terminus and conjugated to the Glu116Cys (E116C) streptavidin mutant via thiol coupling. The DMAA-streptavidin conjugate bound biotin efficiently when the polymer was in the soluble state under UV irradiation, but under visible irradiation, the polymer collapsed and blocked free biotin association. Furthermore, if biotin was allowed to bind when the polymer was in the soluble state under UV irradiation, then when the polymer was collapsed by visible light, the streptavidin released the bound biotin. The DMAAm-streptavidin conjugate showed the opposite response, with association of biotin allowed under visible light irradiation and blocked under UV irradiation. The photoresponses of the streptavidin conjugates thus correspond to the original photoresponsive phase transition properties of the polymer switches triggered by the cis-trans isomerization of the diazo chromophores.