E. Schacht | Ghent University (original) (raw)

Papers by E. Schacht

Plasma Processes and Polymers, 2009

ABSTRACT

Acta Tropica, 1999

Two trials were carried out in order to compare the prophylactic effect of a subcutaneously impla... more Two trials were carried out in order to compare the prophylactic effect of a subcutaneously implanted sustained release device (SRD) containing a mixture of a biodegradable copolymer, poly(caprolactone-co-L-lactide), and isometamidium (ISMM) with that obtained after intramuscular injection of the drug. In a first experiment under controlled conditions, two groups of cattle were treated with 0.5 mg/kg isometamidium either as a SRD or intramuscularly (i.m.), and exposed at monthly intervals to Glossina morsitans morsitans infected with Trypanosoma congolense. The average protection period was at least 24 months in the SRD treated against 5.7 months in the i.m. treated group. Using an ISMM enzyme-linked immunosorbent assay, the drug could be detected until 140 days post-treatment in the latter group, whereas in the former group, traces of the drug were detectable until 330 days after treatment. Furthermore, a field trial was carried out at the Madina Diassa ranch in Mali involving three groups of N'Dama cattle, each containing 23 or 24 : S 0 0 0 1 -7 0 6 X ( 9 9 ) 0 0 0 1 0 -8 S. Geerts et al. / Acta Tropica 73 (1999) 49-58 50 animals. Two groups were treated with 1 mg/kg ISMM either as a SRD or i.m. and a third group served as untreated control. Twelve months after treatment, the cumulative infection rates were 56.5, 87.8 and 91.6% in the SRD implanted, the i.m. treated and the control groups, respectively. The ISMM concentrations were slightly lower than in the laboratory trial, but the overall pattern of drug disappearance from the sera of the SRD treated cattle was very similar in both trials. Statistical analysis showed that the incidence of trypanosomiasis was significantly lower in the SRD treated than in the i.m. treated group.

Journal of Controlled Release, Jan 1, 1996

Azo-linked polymeric prodrugs of 5-aminosalicylic acid (5-ASA) were prepared and evaluated in sim... more Azo-linked polymeric prodrugs of 5-aminosalicylic acid (5-ASA) were prepared and evaluated in simulated human intestinal microbial ecosystem. Release of 5-ASA was demonstrated. Polyamides containing azo groups in the backbone were prepared and tested in vitro in a reductive buffer or in the bioreactor medium. It was demonstrated that for the hydrophobic polymer reduction stops at the hydrazine stage whereas for a hydrophilic analogue reduction with formation of amines occurred.

In the present work, we report on the biofunctionalisation of silanised Ti-surfaces with gelatin.... more In the present work, we report on the biofunctionalisation of silanised Ti-surfaces with gelatin. In recent years, a large number of papers have been published about the silanisation of different substrates including Ti-surfaces for biomedical applications. However, a comparative study evaluating the effects of different pre-treatment methods (cleaning and/or oxidation) and the efficiency of different silanisation reactions has to our information not yet been published. Since a clean and reproducible surface is required for studying structure-property relations, all Ti-surfaces were subjected to a three step procedure including a cleaning step, an oxidation step and a silanisation step. XPS analysis and contact angle measurements revealed that the pre-treatment of the Ti samples (cleaning + oxidation) had a drastic effect both on the surface composition and its wettability. A detailed study on the effect of different silanisation parameters indicated that the siloxane concentration, the siloxane type, the solvent and a catalyst affect the coupling efficiency of siloxanes to Ti-surfaces. Stability studies revealed a dependency between the siloxane type and the stability of the siloxane coating against hydrolytic cleavage from a Ti-surface. Since Ti-surfaces modified with a methacrylate containing silane possessed the highest hydrolytic stability, these surfaces were selected for the subsequent immobilisation of methacrylamide-modified gelatin via high energy irradiation induced cross-linking. The present work clearly demonstrates the need of a proper reaction strategy for immobilising ligands on Ti-surfaces.

Surface and Coatings Technology, 2009

Atomic force microscopy (AFM) Fourier transform infrared spectroscopy (FTIR) PACVD Hexamethyldisi... more Atomic force microscopy (AFM) Fourier transform infrared spectroscopy (FTIR) PACVD Hexamethyldisiloxane (HMDSO) Recently, plasma-polymerization at atmospheric pressure has become a promising technology due to its reduced equipment costs and its possibility of in-line processing. This paper focuses on plasma deposition by an atmospheric pressure dielectric barrier discharge (DBD) using hexamethyldisiloxane (HMDSO) as gaseous precursor. HMDSO plasma-polymerized films are deposited onto polyethylene terephthalate (PET) films using argon and different argon/air mixtures as carrier gases. The chemical and physical properties of the obtained coatings are discussed using contact angle measurements, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Contact angle and FTIR results show that the composition of the gas phase and the chemical structure of the obtained coatings are clearly correlated. When pure argon is used as working gas, the film is polymeric with a structure close to [(CH 3 ) 2 -Si-O] n . However, with increasing air content, a gradual change is observed from organic polydimethylsiloxane-like coatings to inorganic, quartzlike deposits. AFM results clearly indicate that with increasing air content, the deposition rate decreases, while the surface of the deposited films becomes rougher. From this point of view, the capability of controlling both chemical and physical properties of the plasma-polymerized films by varying operation conditions opens interesting perspectives.

Macromolecular Bioscience, 2010

In the last decade, substantial research in the field of post-plasma grafting surface modificatio... more In the last decade, substantial research in the field of post-plasma grafting surface modification has focussed on the introduction of carboxylic acids on surfaces by grafting acrylic acid (AAc). In the present work, we report on an alternative approach for biomaterial surface functionalisation. Thin poly-ε-caprolactone (PCL) films were subjected to a dielectric barrier discharge Ar-plasma followed by the grafting of 2-aminoethyl methacrylate (AEMA) under UV-irradiation. X-ray photoelectron spectroscopy (XPS) confirmed the presence of nitrogen. The ninhydrin assay demonstrated, both quantitatively and qualitatively, the presence of free amines on the surface. Confocal fluorescence microscopy (CFM), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to visualise the grafted surfaces, indicating the presence of pAEMA. Static contact angle (SCA) measurements indicated a permanent increase in hydrophilicity. Furthermore, the AEMA grafted surfaces were applied for comparing the physisorption and covalent immobilisation of gelatin. CFM demonstrated that only the covalent immobilisation lead to a complete coverage of the surface. Those gelatin-coated surfaces obtained were further coated using fibronectin. Osteosarcoma cells demonstrated better cell-adhesion and cell-viability on the modified surfaces, compared to the pure PCL films.

Macromolecular Bioscience, 2009

In the present work, the gelatin/fibronectin affinity was evaluated using SPR, QCM and radiolabel... more In the present work, the gelatin/fibronectin affinity was evaluated using SPR, QCM and radiolabelling. The results indicate that type A gelatin films possess a higher affinity for Fn compared to type B gelatin. This is due to a combined hydrophobic and electrostatic interaction between gelatin type A and Fn. In a second part, the affinity of Fn for porous gelatin scaffolds was evaluated. The scaffolds were prepared by a cryogenic treatment and subsequent freeze-drying yielding type I and type II scaffolds which possess different pore geometries/sizes. The results indicate that the Fn density on the scaffolds can be fine-tuned by varying the Fn concentration, the gelatin type (A vs. B), the pore size/geometry (type I vs. type II scaffolds).

Macromolecular Bioscience, 2008

The application of ozonization and cyclic voltammetry for the regeneration of gold chips containi... more The application of ozonization and cyclic voltammetry for the regeneration of gold chips containing a chemisorbed gelatin layer is reported. The efficiency of the regeneration process was analyzed using various surface analysis techniques indicating a complete removal of the biopolymer layer. The current findings open up perspectives for regeneration and multiple application of gold chips for SPR measurements.

Journal of Materials Science: Materials in Medicine, 2008

The design, development and evaluation of biomaterials that can sustain life or restore a certain... more The design, development and evaluation of biomaterials that can sustain life or restore a certain body function, is a very important and rapidly expanding field in materials science. A key issue in the development of biomaterials is the design of a material that mimics the natural environment of cells. In the present work, we have therefore developed hydrogel materials that contain both a protein (gelatin) and a glycosaminoglycan (chondroitin sulphate) component. To enable a permanent crosslinking, gelatin and chondroitin sulphate were first chemically modified using methacrylic anhydride. Hydrogels containing modified gelatin (gel-MOD) and/or chondroitin sulphate (CS-MOD) were cryogenically treated as optimised earlier for gel-MOD based hydrogels (Van Vlierberghe et al., Biomacromolecules 8:331-337, 2007). The cryogenic treatment leads to tubular pores for gel-MOD based systems. For CS-MOD based hydrogels and hydrogels containing both gel-MOD and CS-MOD, a curtain-like architecture (i.e. parallel plates) was observed, depending on the applied CS-MOD concentration. In our opinion, this is the first paper in which such well-defined scaffold architectures have been obtained without using rapid prototyping techniques.

Journal of Controlled Release, 2006

prepared by spray-coating. To assess vascular compatibility polymer-only-coated stents were impla... more prepared by spray-coating. To assess vascular compatibility polymer-only-coated stents were implanted in one of the two main vessels of the left coronary artery (LAD or CX) of pigs (N =8). Bare metal stents were used as a control group. At 4 weeks, the animals were sacrificed and the stented coronary artery segments were carefully dissected, processed where after histology and histomorphometric measurements were performed. In vitro elution testing of EES was performed by incubating EES in vials containing PB solution (pH 7.4, 37°C). At regular intervals, the dissolution medium was refreshed. 17βestradiol concentrations were quantified by HPLC using a reverse phase Symmetry C18 4.6 × 150 mm column, a mobile phase of acetonitrile/water (50/50), a flow rate of 0.8 ml/min and UV detection at 281 nm.

Journal of Controlled Release, 1984

Journal of Chromatography A, 2010

The synthesis of a T-2 toxin imprinted polymer and its application in food analysis are reported ... more The synthesis of a T-2 toxin imprinted polymer and its application in food analysis are reported for the first time. A molecularly imprinted polymer (MIP) for the selective recognition of T-2 toxin (T-2) was synthesized by bulk polymerization. Methacrylamide and ethyleneglycol dimethacrylate were applied as functional monomer and cross-linker, respectively. Molecularly imprinted solid-phase extraction (MISPE) procedures were optimized for further application in the analysis of T-2. Scatchard plot analysis revealed that two classes of imprinted binding sites were formed in the imprinted polymer. The dissociation constant (KD) of the higher affinity binding sites was 7.0 micromol/l, while the KD of the lower affinity binding sites was 54.7 micromol/l. The performance of the MIP throughout the clean-up of spiked maize, barley and oat sample extracts was compared with the results obtained when using non-imprinted polymer, OASIS HLB and immunoaffinity columns (IAC). Depending on the food matrix and the spiked concentration, recoveries after MISPE and non-imprinted solid-phase extraction varied respectively from 60% to 73% and from 21% to 57%. Recoveries obtained after clean-up using OASIS HLB and IAC were in the range of 74-104% and 60-85%, respectively. Although highest recoveries were obtained with OASIS HLB sorbents, the designed MIP and the IAC were superior regarding selectivity, cross-reactivity, matrix effect, limits of detection (LOD) and limits of quantification (LOQ). Depending on the matrix, LOD after MISPE ranged from 0.4 microg/kg to 0.6 microg/kg and LOQ from 1.4 microg/kg to 1.9 microg/kg. LOD and LOQ after OASIS HLB clean-up varied from 0.9 microg/kg to 3.5 microg/kg and from 3.1 microg/kg to 11.7 microg/kg, respectively. The LOD and LOQ values obtained with IAC were in the range of 0.3-2.3 microg/kg and 1.0-7.7 microg/kg, respectively. Analysis of 39 naturally contaminated samples (maize, barley and oat) by liquid chromatography tandem mass spectrometry revealed that the MIP could be an excellent alternative for clean-up of contaminated food samples.

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Journal of Bioactive and Compatible Polymers, 2004

Dendritic poly-[N-(2-hydroxyethyl)-L-glutamine] (PHEG) with different molecular weights were synt... more Dendritic poly-[N-(2-hydroxyethyl)-L-glutamine] (PHEG) with different molecular weights were synthesized by aminolysis of dendritic poly-(γ-benzyl-L-glutamate) (PBG), which was obtained by polymerization of the corresponding N-carboxyanhydride (NCA) with poly(amido amine) (PAMAM, starburst®) of the fourth generation as initiator. Dynamic light scattering (DLS) was used to determine the size of the polymeric carriers and to compare the dendritic polymer to the linear analogue. The body distribution and blood clearance of 125 I-radiolabelled linear and dendritic PHEG with similar molecular weight were investigated in female BALB/c mice.

European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences, 2003

We report here the physicochemical and biological evaluation of a series of polymethacrylates wit... more We report here the physicochemical and biological evaluation of a series of polymethacrylates with side groups of different pK(a) values, such as tertiary amines, pyridine groups, acid functions and imidazole groups as synthetic vectors for gene delivery. The ability of the different polymers to condense DNA was studied by ethidium bromide exclusion tests and agarose gel electrophoresis. The results show that all polymers are able to condense DNA. Both the molecular weight and the chemical composition of the polymers have an influence on the DNA condensation process. Furthermore, the biological properties of the polymer-DNA complexes were investigated, including their haemolytic activity, cytotoxicity and in vitro transfection efficiency. Complexes based on polymers containing only tertiary amines, have a transfection efficiency similar to that of poly(ethyleneimine) (PEI). Polymers containing pyridine groups have a reduced transfection efficiency compared to polymers containing ter...

European Journal of Pharmaceutical Sciences, 2005

Polymethacrylates are vinyl-based polymers that are used for DNA transfection. Cationic polymetha... more Polymethacrylates are vinyl-based polymers that are used for DNA transfection. Cationic polymethacrylates efficiently condense DNA by forming inter-polyelectrolyte complexes. Their use for DNA transfection is, however, limited due to their low ability to interact with membranes. In order to increase their transfection efficiency, we combined polymethacrylates with Penetratin, a 16-residue water-soluble peptide that internalises into cells through membrane translocation. DNA condensation was assessed using physicochemical methods, while transfection efficiency and cellular internalisation were studied using Cos-1 cells. Agarose gel electrophoresis retardation, ethidium bromide exclusion tests and dynamic light scattering measurements showed that the stability of the polymethacrylate-DNA complexes is not affected by addition of Penetratin. Transfection efficiency of polymethacrylate-DNA complexes into Cos-1 cells increased by addition of Penetratin and was higher than that of polyethylenimine (PEI)-DNA complexes and comparable to Lipofectamine TM . Confocal microscopy and flow cytometry indicated that Penetratin mainly enhances endolysosomal escape polymethacrylate-DNA complexes and increases their cellular uptake. Since the cellular toxicity of polymethacrylate-DNA-Penetratin complexes remains low, especially compared to PEI, this transfection system opens new perspectives for gene therapy.

Biosensors and Bioelectronics, 2011

There is a lack of methods suitable for generation of data about the dynamics of effects on cell ... more There is a lack of methods suitable for generation of data about the dynamics of effects on cell membranes with a high sensitivity. Such methods are urgently needed to support the optimisation of interaction of substances, particles or materials with cell. The goal of this article is to use an improved microhole chip system to monitor the alterations of cells due to the interactions of polymer-DNA complexes. This should demonstrate exemplarily that subtoxic effect of biological relevant particles or substances at relevant concentrations can be monitored for several hours. By using a microhole cell chip and a microfluidic unit single cells can be electrically interfaced via microholes and the use of small electrodes with high impedances is not necessary. For separation and positioning of the cells onto the hole negative pressure is applied on the reverse side of the chip. Under cell culture conditions the cell starts to spread on the biocompatible insulating chip membrane resulting in a stable interface to an adherent growing cell. After the spreading process is finished, the polymer/polyplex solution is added and the impedance is measured with respect to time. To illustrate the cellular parameter which can affect the measured impedance a simple simulation based on the finite element method (FEM) is performed. It was shown for the first time that the impedance-based method predicated on the microhole chip can be used for biological relevant substances at relevant concentrations and that it is more sensitive than the well-established biological marker.

Biomaterials, 2011

Subretinal implants aim to replace the photoreceptor function in patients suffering from degenera... more Subretinal implants aim to replace the photoreceptor function in patients suffering from degenerative retinal disease by topically applying electrical stimuli in the subretinal space. Critical obstacles in the design of high-resolution subretinal implants include the proximity of stimulating electrodes to the target cells and enabling nutrient flow between the retina and the choroid. The present work evaluates the adhesion, migration and survival of retinal cells on an ultrathin (5 mm), highly porous (Ø 1 mm spaced 3 mm), gelatin-coated polyimide (PI) membrane. The biocompatibility was examined in mice indicating a good tolerance upon subcutaneous implantation with only a mild inflammatory response. In addition, organotypic cultures of rat retina evidenced that the porous membrane allowed the necessary nutrient flow for the retinal cell survival and maintenance. A transscleral implantation technique was applied to position the membrane into the subretinal space of rats. The effect on the obtained retinal integration was investigated in vivo using scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT). In 12 out of 18 rat eyes, the implant was successfully placed subretinally. SLO and OCT demonstrated complete retinal attachment and fluorescein angiography showed no retinal vascular abnormalities over and around the implant, immediately after and up to four weeks after the implantation. Histological examination of the eyes showed a close attachment of a thin fibrocyte layer to the implant, the occlusion of the pores by living cells and the survival of some photoreceptors at the implantation site.

Biomacromolecules, 2004

Recently, we have shown that polymethacrylates containing imidazole side groups (HYMIMMA) or acid... more Recently, we have shown that polymethacrylates containing imidazole side groups (HYMIMMA) or acid functions (MA), which have similar buffering properties as polyethyleneimine, were not able to transfect Cos-1 cells, whereas polymers containing only tertiary amines (DMAEMA) do transfect Cos-1 cells (Dubruel, P. et al. Eur. J. Pharm. Sci. 2003, 18 (3-4), 211-220). In the present work, we investigated to what extent the differences in transfection activity are related to differences in cellular internalization and/or subcellular localization. Therefore, we synthesized a series of polymethacrylates containing primary amine functions, used for the coupling of the fluorescent Oregon Green probe. The polymers containing acid functions were labeled with an amine containing fluorescein derivative (5-aminomethyl)fluorescein hydrochloride. It is demonstrated that the endosomal release of the MA and HYMIMMA-based complexes might be the limiting step in the gene transfer process in Cos-1 cells.