Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Processing and characterization of biodegradable soy plastics: Effects of crosslinking with glyoxal and thermal treatment
    Vaz, C.M. ; Doeveren, P.F.N.M. van; Yilmaz, G. ; Graaf, L.A. de; Reis, R.L. ; Cunha, A.M. - \ 2005
    Journal of Applied Polymer Science 97 (2005)2. - ISSN 0021-8995 - p. 604 - 610.
    mechanical-properties - protein plastics - water-absorption - collagen - glutaraldehyde - films - bioprostheses - cytotoxicity - composites - extrusion
    Processing and modification routes to produce and to improve properties of biodegradable plastics from soy isolate were studied. Soy isolate, acid-treated and crosslinked soy were subsequently compounded, extruded, and injection molded. Acetic acid and glyoxal were examined concerning their suitability for acid treating and crosslinking of soy, and their effect on the final properties of the obtained materials. Heat treatment was also used as a possible methodology to crosslink the protein structure. The molded specimens were tested in terms of their tensile properties and solubility at different pHs, and were also evaluated for the degree of crosslinking and molecular weight distributions. The obtained plastics were rigid and brittle with stiffness ranging from 1436 MPa for soy, to 1229 MPa for glyoxal crosslinked soy, up to 2698 MPa for heat-treated soy. The differences in stiffness were discussed in terms of the crosslinking efficiency and spatial distribution. The solubility profiles were studied as a function of the pH of the immersion solutions and the crosslinking degree of each material. A reduction in protein solubility with decreasing pH was observed, with a minimum between pH 4 and 5 and a resolubilization of the protein at pHs lower than pH 4 and greater than 8. Higher levels of crosslinking resulted in a decrease of the solubility and an aggregation of the protein molecules. The soy plastics proved to be very versatile materials with potential to be used in applications where quite demanding performances are expected, such as in the biomedical field.
    pH-sensitive soy protein films for the controlled release of an anti-inflammatory drug
    Vaz, C.M. ; Graaf, L.A. de; Reis, R.L. ; Cunha, A.M. - \ 2004
    Materials Research Innovations 8 (2004)3. - ISSN 1432-8917 - p. 149 - 150.
    in-vitro - albumin microspheres - delivery system - acrylic-acid - glutaraldehyde - hydrogels - chitosan - microencapsulation - microcapsules - theophylline
    Controlled delivery with bi-layer matrix devices produced by co-injection moulding
    Vaz, C.M. ; Doeveren, P.F.N.M. van; Dias, G.R. ; Reis, R.L. ; Cunha, A.M. - \ 2004
    Macromolecular Bioscience 4 (2004)8. - ISSN 1616-5187 - p. 795 - 801.
    protein-based thermoplastics - controlled drug-delivery - order release kinetics - biomedical applications - in-vitro - behavior - systems - tablets - diffusion - solute
    The aim of this study was to design new soy protein-based bi-layered co-injection moulded matrix systems aimed to achieve controlled drug delivery. The devices consisted of a drug-free outer layer (skin) and a drug-containing core. The systems overcame the inherent disadvantage of non-linear release associated with diffusion-controlled single-layer matrix devices by providing additional releasing area with time to compensate for the decreasing release rate. As expected, the bi-layer devices presented a significant decrease in drug release rate when compared with a correspondent single layer matrix system. The skin thickness and the degree of crosslinking of the core appeared to be very important tools to tailor the release patterns. Furthermore, due to the amphoteric nature of the soy protein, the developed devices evidenced a pH-dependent behaviour. The mechanisms of drug release were also elucidated at two different pH values: i) pH 5.0, near the isoelectric point of soy (low matrix solubility); and ii) pH 7.4, physiological pH (high matrix solubility). Consequently, changing the release medium from pH 5.0 to pH 7.4 after two hours, led to an abrupt increase in drug release and the devices presented a typical controlled drug delivery profile: slow release/fast release. These evidences may provide for the development of individual systems with different release onsets that in combination may exhibit drug releases at predetermined times in a pre-programmed way. Another possibility is the production of three-layer devices presenting bimodal release profiles (fast release/slow release/fast release) by similar technologies.
    Soy matrix drug delivery systems obtained by melt-processing techniques
    Vaz, C.M. ; Doeveren, P.F.N.M. van; Reis, R.L. ; Cunha, A.M. - \ 2003
    Biomacromolecules 4 (2003)6. - ISSN 1525-7797 - p. 1520 - 1529.
    mechanical-properties - controlled-release - sustained-release - water-absorption - formulation - pellets - tablet
    The aim of this study was to develop new soy protein drug delivery matrix systems by melt-processing techniques, namely, extrusion and injection moulding. The soy matrix systems with an encapsulated drug (theophylline, TH) were previously compounded by extrusion performed at two different pH values, (i) pH 4 (SIpDtp) and (ii) pH 7 (SIDtp), and further injection-moulded into a desired shape. During the extrusion process the matrixes SIDtp were also cross-linked with glyoxal (0.6X-SIDtp) and reinforced with a bioactive filler, hydroxylapatite (SI-HADtp). The obtained mouldings were used to study the drug-release mechanisms from the plastic soy¿TH matrixes. In an isotonic saline solution (ISS) buffered at pH 5.0 (200 mM acetate buffer), the resulting release kinetics could be described using the Fick's second law of diffusion. Because the diffusion coefficients were found to be constant and the boundary conditions to be stationary, these systems are drug-diffusion controlled. Conversely, the dominant phenomena in an isotonic saline solution buffered at pH 7.4 (200 mM Tris/HCl buffer) are more complex. In fact, because of the higher polymer solubility, the resulting matrix is time-variant. So, the drug release is affected by swelling, drug diffusion, and polymer dissolution, being faster when compared to ISS¿200 mM acetate buffer, pH 5.0. The changes in the formulation composition affecting the correspondent release rates were also investigated. At pH 7.4, increasing the cross-linking degree of the polymer matrix (via reaction with glyoxal or heat treatment) or decreasing the net charge (extruding at pH near its isoelectric point) led to lower release rates. The incorporation of ceramic filler caused the opposite effect. Because of the low solubility of the matrix at pH 5.0, no significant variations were detected with variations in the selected formulations. These systems, based on a nonstandard protein-based material, seem to be very promising to be used as carriers for drug delivery.
    Casein and soybean protein-based thermoplastics and composites as alternative biodegradable polymers for biomedical applications
    Vaz, C.M. ; Fossen, M. ; Tuil, R.F. van; Graaf, L.A. de; Reis, R.L. ; Cunha, A.M. - \ 2003
    Journal of Biomedical Materials Research Part A 65A (2003)1. - ISSN 1549-3296 - p. 60 - 70.
    soy-protein - wheat gluten - films - biomaterials - sponges - isolate
    This work reports on the development and characterization of novel meltable polymers and composites based on casein and soybean proteins. The effects of inert (Al2O3) and bioactive (tricalcium phosphate) ceramic reinforcements over the mechanical performance, water absorption, and bioactivity behavior of the injection-molded thermoplastics were examined. It was possible to obtain materials and composites with a range of mechanical properties, which might allow for their application in the biomedical field. The incorporation of tricalcium phosphate into the soybean thermoplastic decreased its mechanical properties but lead to the nucleation of a bioactive calcium-phosphate film on their surface when immersed in a simulated body fluid solution. When compounded with 1% of a zirconate coupling agent, the nucleation and growth of the bioactive films on the surface of the referred to composites was accelerated. The materials degradation was studied for ageing periods up to 60 days in an isotonic saline solution. Both water uptake and weight loss were monitored as a function of the immersion time. After 1 month of immersion, the materials showed signal of chemical degradation, presenting weight losses up to 30%. However, further improvement on the mechanical performance and the enhancement of the hydrolytic stability of those materials will be highly necessary for applications in the biomedical field
    Effect of crosslinking, thermal treatment and UV irradiation on the mechanical properties and in vitro degradation behavior of several natural proteins aimed to be used in the biomedical field
    Vaz, C.M. ; Graaf, L.A. de; Reis, R.L. ; Cunha, A.M. - \ 2003
    Journal of Materials Science-Materials in Medicine 14 (2003)9. - ISSN 0957-4530 - p. 789 - 796.
    soy-protein - films - glutaraldehyde
    Gelatine (GEL), soy (SI), casein (CAS) and sodium-caseinate (NaCAS) solutions were cast to produce protein films. All the proteins were chemically modified by adding glyoxal to the film-forming solutions in amounts varying from 0 to 0.9% (w/w based on the protein content). After casting, the same films were also submitted to a heat treatment performed at 80°C or UV irradiation. The effect of those chemical/physical modifications on the mechanical properties and on the hydrolytic stability of the protein films was evaluated. As a result, a large variety of protein films with different mechanical properties and degradation profiles were developed. CAS and NaCAS even when chemically/physically modified do not resist to hydrolysis longer than 2 weeks. GEL, only when chemically modified with glyoxal, become water resistant. Due to its hydrolytic stability, SI become a very attractive material for biomedical applications where long term treatments are a requisite.
    In vitro degradation behaviour of biodegradable soy plastics : effects of crosslinking with glyoxal and thermal treatment
    Vaz, C.M. ; Graaf, L.A. de; Reis, R.L. ; Cunha, A.M. - \ 2003
    Polymer Degradation and Stability 81 (2003)1. - ISSN 0141-3910 - p. 65 - 74.
    water-soluble carbodiimide - dermal sheep collagens - mechanical-properties - cross-linking - protein - glutaraldehyde - cytotoxicity - composites - carbonate - release
    In-vitro degradation of soy-derived protein materials, non-crosslinked (SItp), crosslinked with glyoxal (X-SItp) or submitted to heat treatment (24TT-SItp), was studied with either an isotonic saline solution without enzymatic activity or containing bacterial collagenase. The changes in weight of the samples during the in-vitro degradation were studied and compared with the variations of the mechanical properties. The weight loss of SItp, X-SItp and 24TT-SItp were more pronounced when using collagenase. After 24 h of immersion, SItp lost 10.6 f its initial weight whereas 0.6X-SItp and 24TT-SItp lost 1.7 and 5.7°respectively. In every case, the weight loss was found to be directly proportional to the respective crosslinking degree: 2.4 or SItp, 44 or 0.6X-SItp and 27.8 or 24TT-SItp. Consequently, the susceptibility of the soy materials towards enzymatic degradation could be controlled by varying the degree of crosslinking of the samples. The mechanical properties proved to be more sensitive to the loss of plasticiser (glycerol) during immersion than to the degradation of the polymeric matrices. After 24 h of immersion all the materials presented an increase in stiffness and brittleness due to the complete leaching of glycerol from the matrices. SItp, X-SItp and 24TT-SItp proved to be suitable materials for either load-bearing applications or temporary applications such as tissue engineering scaffolds or drug delivery systems.
    Development and design of double-layer co-injection moulded soy protein based drug delivery devices
    Vaz, C.M. ; Doeveren, P.F.N.M. van; Reis, R.L. ; Cunha, A.M. - \ 2003
    Polymer 44 (2003)19. - ISSN 0032-3861 - p. 5983 - 5992.
    order sustained-release - biomedical applications - biodegradable polymers - mechanical-properties - diffusional matrices - in-vitro - kinetics - thermoplastics - extrusion - behavior
    Novel double-layer delivery devices based on soy protein derived materials were designed and produced using an innovative two material co-injection moulding technique. It was demonstrated that the viscosity ratio between core and skin layer materials played an important role in the formation of the interfacial shape, namely the skin thickness and uniformity of the bi-materials. The adequate selection of the materials used and the optimisation of the respective processing conditions enabled an accurate control of the relative thickness of the layers of the device. The preliminary results confirmed the potential of these systems to achieve a controlled drug delivery.
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