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ABSTRACT: The chemical composition of a substrate can influence the adhesion, viability and proliferation of cells seeded on the substrate. The aim of this work was to investigate the influence of different cationic or anionic moieties in acrylonitrile based copolymers on the interaction with fibroblasts. A series of ten different types of acrylonitrilebased copolymers with a random sequence structure was preparedusing a water born synthesis process to exclude potential residues of organic solvents. As charged comonomers cationic methacrylic acid-2-aminoethylester hydrochloride (AEMA), N-3-amino-propyl-methacrylamide-hydrochloride (APMA) and anionic 2-methyl-2-propene-1-sulfonic acid sodium salt (NaMAS) were utilized. By application of a specific sintering procedure the copolymer materials were processed into transparent disks for conducting cell tests in direct contact. The copolymers were analyzed with respect to their composition and surface properties. Cytotoxicity tests of the polymer extracts, as well as of the disks were performed with L929 mouse fibroblasts. All copolymers showed no cytotoxic effects Furthermore for higher molar ratios of AEMA and NaMAS (>4.4 and 9.9 mol-%) a reduction in cell growth could be observed, which might be a hint that higher charge densities are unfavorable for the proliferation of L929 cells.
Clinical hemorheology and microcirculation 09/2012; · 3.40 Impact Factor
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ABSTRACT: Background: The patency of small-diameter vascular prostheses is limited by several factors such as thrombogenicity, which is strongly influenced by surface roughness and chemical composition, or a mechanical mismatch between the elastic modulus of an artery and of the vascular prosthesis. A confluent layer of endothelial cells onto the inner surface of vascular prostheses could improve the hemocompatibiliy of the device. Biomaterials with adjustable elastic properties could be tailored to the values of human arteries so that a prothesis mismatch could be avoided. It was recently demonstrated that a co-culture of endothelial cells with angiogenically stimulated monocytes (aMO2) shows an accelerated formation of a functional confluent endothelial cell monolayer on soft hydrophobic poly(n-butyl acrylate) networks with elasticities of 250 kPa (cPnBA04) and 1100 kPa (cPnBA73). In addition, the cell compatibility with vascular smooth muscle cells and aortic fibroblasts, which are other important cell types of the vessel wall, is essential for a vascular prosthesis material and must therefore be explored. Purpose: Here we investigated the interaction of human vascular smooth muscle cells and aortic fibroblasts with cPnBA04 and cPnBA73. material and methods: Human primary vascular smooth muscle cells and aortic fibroblasts were seeded on the two cPnBAs with different elastic moduli over 72 h. A live-dead staining (fluorescein/diacetate/propium iodide) was performed to determine the morphology and viability of adherent cells. Furthermore, the extracellular matrix components, the actin cytoskeleton, the cell-material-contacts and the cytokine profiles were analysed. Results: Both cell types adhered and were viable on cPnBA04 and cPnBA73. The level of pro-inflammatory cytokine secretion (IFN-γ and TNF-α) by smooth muscle cells and vascular fibroblasts was comparable to that of cells cultivated on a control material. The release of these cytokines by human fibroblasts was higher on cPnBA73 compared to cPnBA04. Both cell types secreted an extracellular matrix comparable to cells seeded on a control material. Conclusion: The study revealed, that cPnBA with varying elastic moduli are not only suitable for the cultivation of endothelial cells, but also for human vascular smooth muscle cells and aortic fibroblasts. Therefore, cPnBA could be a potential candidate material for the development of cardiovascular prostheses.
Clinical hemorheology and microcirculation 09/2012; · 3.40 Impact Factor
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Reactive and Functional Polymers 01/2012; 72(8):533-541. · 2.48 Impact Factor
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eXPRESS Polymer Letters 01/2012; 6(1):26-40. · 1.77 Impact Factor
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ABSTRACT: Here we introduce a multifunctional copolymer network system with adjustable thermomechanical properties, which is also capable to show a substantial water uptake and in this way should allow the additional alteration of the overall elastic properties besides the variation of the crosslinking density. The swelling capacity in water, the thermal properties as well as the crystallinity of a series of grafted copolymer networks named CLEG composed of water swellable poly(ethylene glycol) (PEG) side chains and crystallizable poly(ε-caprolactone) (PCL) segments acting as covalent crosslinker were explored in an aqueous environment. The water swelling capability of the CLEG polymer networks was found to increase from 120% to 240% with increasing weight content of PEG. In contrast to the dry state, where two well separated melting temperatures could be observed for all CLEG samples, in aqueous environment only one melting temperature slightly above 40°C, was obtained, whereby the overall crystallinity after swelling with water was strongly related to the PCL content in the CLEG polymer networks. © 2012 Materials Research Society.
Materials Research Society Symposium ProceedingsMaterials Research Society Symposium Proceedings, Boston, MA; 01/2012
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ABSTRACT: Thermo-sensitive shape-memory polymers (SMP), which are capable of memorizing two or more different shapes, have generated significant research and technological interest. A triple-shape effect (TSE) of SMP can be activated e.g. by increasing the environmental temperature (T env), whereby two switching temperatures (T sw) have to be exceeded to enable the subsequent shape changes from shape (A) to shape (B) and finally the original shape (C). In this work, we explored the thermally and magnetically initiated shape-memory properties of triple-shape nanocomposites with various compositions and particle contents using different shape-memory creation procedures (SMCP). The nanocomposites were prepared by the incorporation of magnetite nanoparticles into a multiphase polymer network matrix with grafted polymer network architecture containing crystallizable poly(ethylene glycol) (PEG) side chains and poly(ε- caprolactone) (PCL) crosslinks named CLEGC. Excellent triple-shape properties were achieved for nanocomposites with high PEG weight fraction when two-step programming procedures were applied. In contrast, single-step programming resulted in dual-shape properties for all investigated materials as here the temporary shape (A) was predominantly fixed by PCL crystallites. © BME-PT.
eXPRESS Polymer Letters 01/2012; 6(1):26-40. · 1.77 Impact Factor
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Clinical hemorheology and microcirculation 01/2012; 50(1):153. · 3.40 Impact Factor
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ABSTRACT: The need for engineered devices to treat cardiovascular diseases is increasing due to an aging population and a changing lifestyle. Soft poly(n-butyl acrylate) (cPnBA) networks were recently described as polymer networks with adjustable mechanical properties and suggested as soft substrates for cells, which could potentially be used for cardiovascular implants. Vascular prostheses designed to be implanted in arteries should have an elasticity similar to blood vessels (elastic modulus at body temperature between 100 and 1200 kPa). Therefore, cPnBA networks with E-moduli of 250 kPa (cPnBA0250) and 1100 kPa (cPnBA1100) were developed. Recently, it was shown that both materials were non-cytotoxic for murin fibroblasts, human primary endothelial cells and human monocytes. However, before such newly developed polymers can be used in vivo, it has to be assured that the sterilized materials have a very low endotoxin load to avoid an unspecific activation of the immune system, which otherwise might cause local or systemic inflammatory responses and could lead to severe pathologies. In this study we investigated the immuno-compatibility of sterilized cPnBA0250 and cPnBA1100 with the help of an immuno-competent macrophage cell line as well as with whole human blood.
Clinical hemorheology and microcirculation 01/2012; 50(1-2):131-42. · 3.40 Impact Factor
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ABSTRACT: Soft hydrophobic poly(n-butyl acrylate) networks (cPnBA) were developed as entropy elastic substrates for passive mechanical stimulation of cells, where the elastic modulus of the cPnBAs could be systematically adjusted by variation of the cross-link density. The networks were synthesized by thermally-induced radical polymerization from n-butyl acrylate, with poly(propylene glycol) dimethacrylate (PPGDMA) acting as cross-linker, whereby the purity of the cPnBAs was confirmed by (1)H-NMR spectroscopy and gas chromatography. In this work two cPnBA polymer networks with an elastic modulus around 200 kPa and 1 MPa were investigated having an elastic modulus similar to that of arteries. Both cPnBAs exhibited an almost smooth surface with a surface roughness (R(q)) in the wet state ranging from 17 to 37 nm and a similar zeta-potential, indicating an almost identical chemical composition within the topmost surface layer in terms of functional groups. In contrast, wettability of the samples was found to be different with an advancing angle (θ(advancing)) of 123±3.8° for cPnBA0250, while for cPnBA1100 significantly lower values for θ(advancing) (111±3.8°) were obtained. First in vitro tests were performed with primary endothelial cells (HUVEC) to study its effects on vascular cell functions. Within the time period of cultivation (72 h), the cells on the cPnBA samples reached subconfluence and showed a viability rate of almost 100%. Although cell density differed after 72 h with more cells on cPnBA0250 than on cPnBA1100, both materials showed no significant effect on the cell morphology, the cellular LDH-release, which was used as marker for the integrity of the cell membrane, and the organisation of the VE-cadherin. However, lower cell density and less actin stress fibre formation on cPnBA1100 might indicate that cell-material interaction was weaker on cPnBA1100 than on cPnBA0250. The secretion of the vasoactive cytokines prostacyclin (PGI2) and thromboxane A2 (TXA2) was low compared to previously reported values. However, the anti-thrombogenic ratio of PGI2/TXA2 - which is balanced under physiological conditions - with much higher PGI2 compared to TXA2 (up to 17.6-fold after 72 h for cPnBA1100) suggests that this material might be effective to preventing thrombosis.
Journal of Biomaterials Science Polymer Edition 03/2011; · 1.69 Impact Factor
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ABSTRACT: Small calibre vascular prostheses (<6 mm) still lack medium and long term patency. Inelasticity of the prosthesis is one of the characteristics, which is involved in the mechanisms of failure (e.g. the development of neointimal hyperplasia at the distal anastomosis). Here we report about covalently crosslinked poly(n-butyl acrylate) networks (cPnBA) with adjustable elastic moduli, which can be tailored to values of human arteries (between 100 and 1000 kPa). Motivated by the potential application of such polymer networks as cardiovascular prosthesis, adhesion, activation and thrombus formation of human platelets on cPnBA networks were evaluated. All cPnBA-samples displayed a high thrombogenicity compared to the control (silicone). Significantly less platelets adhered on the surface of the soft cPnBA04 than on cPnBA73. All cPnBA samples displayed a higher number of platelet aggregates and a lower number of inactivated platelets in comparison to the control. While the elastic modulus of cPnBA networks could be successfully adjusted to that of human arteries, the tested polymers did not show an optimal hemocompatibility. Future studies aim at improving the biofunctionality by surface modification of these polymer networks.
Clinical hemorheology and microcirculation 01/2011; 49(1-4):375-90. · 3.40 Impact Factor
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ICCM International Conferences on Composite MaterialsICCM International Conferences on Composite Materials; 01/2011
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ABSTRACT: Mechanical conditioning can serve as a potent tool to influence mechano-responsive cells, which plays a prominent role during formation and regeneration of functional tissue. Recently, the differentiation of mesenchymal stem cells could be influenced by the local stiffness of hydrogels used as 2D substrates. However, the mechanical properties and the swellability of hydrogels in physiological liquids are difficult to control precisely as their properties strongly depend on physical parameters like ionic strength or pH value. Here, we explored amorphous, hydrophobic poly(n-butyl acrylate) networks (cPnBA) as soft substrates for cell culture system with adjustable mechanical properties. cPnBAs were synthesized via bulk radical polymerization from n-butyl acrylate (nBA) and poly(propylene glycol) dimethacrylate (PPGDMA) as crosslinker. The Young's modulus for cPnBAs determined by tensile tests could be systematically adjusted from 100 kPa to 10 MPa by increasing the PPGDMA-content at ambient temperature, while the glass transition temperature (Tg) was found to increase from −46 to −22°C. All cPnBAs exhibited similar surface properties with a surface roughness (Rq) in the range from 1.4 to 0.4 µm and advancing contact angles from 115° to 100°, which remained constant after ethylene oxide sterilization. The extracts of sterilized materials were tested for cytotoxic effects with L929 cells. All tested samples were non-cytotoxic. The functional integrity of cell membranes and mitochondrial activity stayed unaffected. The investigated polymer networks are promising candidates as soft substrates for passive mechanical stimulation of cells in vitro in cell culture devices or in vivo as implant coatings. Copyright © 2010 John Wiley & Sons, Ltd.
Polymers for Advanced Technologies 11/2010; 22(1):126 - 132. · 2.01 Impact Factor
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ABSTRACT: The formation of functional tissue is strongly dependent on biochemical as well as physical signals. A common approach in tissue engineering is the application of passive scaffold systems with fixed morphology and stiffness. In this paper, we explored whether mechanically active scaffolds, exhibiting self-sufficient shape changes under physiological conditions, can be prepared from radio-opaque shape-memory polymer composites (SMPCs). The influence of different thermomechanical treatments on the kinetics of the shape change was studied. Radio-opaque SMPCs were obtained by incorporation of barium sulfate (BaSO4) microparticles (up to 40 wt%) into an amorphous polyether urethane (PEU) via co-extrusion technique. The shape-memory properties of the composites were investigated by cyclic, thermomechanical tensile tests consisting of a specific shape-memory creation procedure (SMCP), in which the programming temperature (Tprog) was varied, followed by recovery under stress-free condition, enabling the determination of the switching temperature (Tsw). An almost complete recovery with shape recovery rate (Rr) values ranging from 88% to 98% was realized within a small temperature interval of ΔTrec ≈ 30°C for all composites, while Tsw was found to be close to the applied Tprog. The feasibility of actively moving scaffolds was demonstrated using model scaffolds, where originally square-shaped pores were temporarily fixed in an expanded circular shape at different Tprog. We found that the kinetics of the shape change obtained under physiological conditions could be adjusted by variation of Tprog between 1 and 6 hr. Such radio-opaque scaffolds could serve as model scaffolds for investigating the active mechanical stimulation of cells in vitro or in vivo. Copyright © 2010 John Wiley & Sons, Ltd.
Polymers for Advanced Technologies 07/2010; 22(1):180 - 189. · 2.01 Impact Factor
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ABSTRACT: Various composites have been prepared to improve the mechanical properties of shape-memory polymers (SMPs) or to incorporate new functionalities (e.g. magneto-sensitivity) in polymer matrices. In this paper, we systematically investigated the influence of the programming temperature Tprog and the applied strain εm as parameters of the shape-memory creation procedure (SMCP) on the shape-memory properties of an amorphous polyether urethane and radio-opaque composites thereof. Recovery under stress-free conditions was quantified by the shape recovery rate Rr and the switching temperature Tsw, while the maximum recovery stress σmax was determined at the characteristic temperature Tσ, max under constant strain conditions. Excellent shape-memory properties were achieved in all experiments with Rr values in between 80 and 98%. σmax could be tailored from 0.4 to 3.7 MPa. Tsw and Tσ, max could be systematically adjusted from 33 to 71 °C by variation of Tprog for each investigated sample. The investigated radio-opaque shape-memory composites will form the material basis for mechanically active scaffolds, which could serve as an intelligent substitute for the extracellular matrix to study the influence of mechanical stimulation of tissue development.
Smart Materials and Structures 05/2010; 19(6):065019. · 2.09 Impact Factor
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Journal of Materials Chemistry 01/2010; 20(17):3404-3415. · 5.97 Impact Factor
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ABSTRACT: Acrylonitrile-based polymer systems (PAN) are comprehensively explored as versatile biomaterials having various potential biomedical applications, such as membranes for extra corporal devices or matrixes for guided skin reconstruction. The surface properties (e.g. hydrophilicity or charges) of such materials can be tailored over a wide range by variation of molecular parameters such as different co-monomers or their sequence structure. Some of these materials show interesting biofunctionalities such as capability for selective cell cultivation. So far, the majority of AN-based copolymers, which were investigated in physiological environments, were processed from the solution (e.g. membranes), as these materials are thermo-sensitive and might degrade when heated. In this work we aimed at the synthesis of hydrophobic, melt-processable AN-based copolymers with adjustable elastic properties for preparation of model scaffolds with controlled pore geometry and size. For this purpose a series of copolymers from acrylonitrile and n-butyl acrylate (nBA) was synthesized via free radical copolymerisation technique. The content of nBA in the copolymer varied from 45 wt% to 70 wt%, which was confirmed by 1H-NMR spectroscopy. The glass transition temperatures (Tg) of the P(AN-co-nBA) copolymers determined by differential scanning calorimetry (DSC) decreased from 58 degrees C to 20 degrees C with increasing nBA-content, which was in excellent agreement with the prediction of the Gordon-Taylor equation based on the Tgs of the homopolymers. The Young's modulus obtained in tensile tests was found to decrease significantly with rising nBA-content from 1062 MPa to 1.2 MPa. All copolymers could be successfully processed from the melt with processing temperatures ranging from 50 degrees C to 170 degrees C, whereby thermally induced decomposition was only observed at temperatures higher than 320 degrees C in thermal gravimetric analysis (TGA). Finally, the melt processed P(AN-co-nBA) biomaterials were sterilized with ethylene oxide and tested for cytotoxicity in direct contact tests with L929 cells according to the EN DIN ISO standard 10993-5. All tested samples exhibited non-toxic effects on the functional integrity of the cell membrane and the mitochondrial activity. However, the morphology of the cells on the samples was different from that observed on polystyrene as control, indicating slightly cytotoxic effects according to the evaluation guide of the US Pharmacopeial Convention. Thus, the melt-processable, hydrophobic P(AN-co-nBA) copolymers with adjustable mechanical properties are promising candidates for in vitro investigations of tissue growth kinetics.
Clinical hemorheology and microcirculation 01/2010; 45(2-4):401-11. · 3.40 Impact Factor
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ABSTRACT: Multiblock copolymers with shape-memory capability attracted tremendous interest as promising candidate materials for smart, degradable implants. In the present study the hen's egg-chorioallantoic membrane test (HET-CAM test) was used to investigate the angiogenic properties of a thermoplastic, biodegradable multiblock copolymer PDC composed of poly(p-dioxanone) hard segments (PPDO) and crystallizable poly(ε-caprolactone) switching segments (PCL), whereby PPDO and PCL homopolymers were investigated as controls. According to our HET-CAM test data, only PDC induced significant microvessel attraction and formation in the contact area of the test specimen after 48 hours of incubation showing newly formed blood vessels along the outer edge of the material. In contrast, no newly formed blood vessels were observed around the PPDO or PCL specimen after the same incubation period. These in vivo results indicate that the multiblock copolymer PDC possibly possesses an angiogenic effect and it can induce blood vessel formation in its direct vicinity when it is implanted in vivo.
Clinical hemorheology and microcirculation 01/2010; 46(2-3):233-8. · 3.40 Impact Factor
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ABSTRACT: The degradation behavior and the effect on angiogenesis of multiblock copolymers based on poly(p-dioxanone)- and poly(epsilon-caprolactone)-segments (PDC) were studied in vivo. PDC is a multifunctional biomaterial combining degradability and shape-memory capabilities. The "in vivo" degradation of PDC is characterized by a fragmentation occurring at the material tissue interface. This observation is consistent with the enzyme supported degradation behaviour, which was determined "in vitro". PDC revealed to induce the formation of blood micro-vessels nearby in the periimplantary tissues. Both might explain the good PDC integration into tissues in terms of a strong connection between the implant and the periimplantary tissue. Micro blood-vessels might be involved in the clearance of the small particles, which appear in the periimplantary tissue when PDC degrades.
Clinical hemorheology and microcirculation 01/2010; 45(2-4):117-22. · 3.40 Impact Factor
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ABSTRACT: Shape-memory polymers are smart materials with an high application potential as intelligent implant material e.g. as self adjusting orthodontic wires or selectively pliable tools for small scale surgical procedures. Typically heat or light are used to initiate the shape-memory effect. By incorporating magnetic nanomaterials into shape-memory polymers a non-contact triggering of shape-memory polymers can be realized when the nanocomposite is exposed to an alternating magnetic field. Here we report controlled actuation of shape-memory polymer networks by application of an alternating magnetic field. Shape-memory nanocomposites were prepared by crosslinking of oligo(c-caprolactone)dimethacrylate in the presence of silica coated nanosized magnetite nanomaterials. Effects of magnetite nanomaterials on the thermal and mechanical properties of the composite have been investigated by means of differential scanning calorimetry (DSC), dynamic mechanical analysis at varied temperature (DMTA) as well as by tensile tests and cyclic thermomechanical experiments. The influence of the nanomaterials on the shape-memory and elastic properties of the nanocomposite are discussed. Finally, the macroscopic shape-memory effect by inductive heating of the nanocomposite samples in an alternating magnetic field (f= 258 kHz; H=17 kA/m) was explored.
Materials Research Society Symposia Proceedings. 01/2009; 1140:185-190.
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Material Research Society Proceeding Articles. 01/2009; 1190:55-61.
