Clinical Hemorheology and Microcirculation - Volume 60, issue 1

Authors: Lendlein, Andreas | Neffe, Axel T. | Jérôme, Christine

Article Type: Editorial

DOI: 10.3233/CH-151941

Citation: Clinical Hemorheology and Microcirculation, vol. 60, no. 1, pp. 1-2, 2015

Authors: Geven, Mike A. | Barbieri, Davide | Yuan, Huipin | de Bruijn, Joost D. | Grijpma, Dirk W.

Article Type: Research Article

Abstract: Composite materials of photo-crosslinked poly(trimethylene carbonate) and nanoscale hydroxyapatite were prepared and their mechanical characteristics for application as orbital floor implants were assessed. The composites were prepared by solvent casting poly(trimethylene carbonate) macromers with varying amounts of nano-hydroxyapatite and subsequent photo-crosslinking. The incorporation of the nano-hydroxyapatite into the composites was examined by thermogravimetric analysis, scanning electron microscopy and gel content measurements. The mechanical properties were investigated by tensile testing and trouser tearing experiments. Our results show that nano-hydroxyapatite particles can readily be incorporated into photo-crosslinked poly(trimethylene carbonate) networks. Compared to the networks without nano-hydroxyapatite, incorporation of 36.3 wt.% of the apatite …resulted in an increase of the E modulus, yield strength and tensile strength from 2.2 MPa to 51 MPa, 0.5 to 1.4 N/mm2 and from 1.3 to 3.9 N/mm2 , respectively. We found that composites containing 12.4 wt.% nano-hydroxyapatite had the highest values of strain at break, toughness and average tear propagation strength (376% , 777 N/mm2 and 3.1 N/mm2 , respectively). Show more

Keywords: Composites, photo-crosslinked poly(trimethylene carbonate), nano-hydroxyapatite, orbital floor repair

DOI: 10.3233/CH-151936

Citation: Clinical Hemorheology and Microcirculation, vol. 60, no. 1, pp. 3-11, 2015

Authors: Julich-Gruner, Konstanze K. | Roch, Toralf | Ma, Nan | Neffe, Axel T. | Lendlein, Andreas

Article Type: Research Article

Abstract: Desamino tyrosine (DAT) and desamino tyrosyl tyrosine (DATT) can be used to functionalize the end groups of water soluble polymers. The phenolic groups may enable physical interactions by π – π interaction and hydrogen bonds, which might lead to the formation of a hydrogel by physical crosslinking. However, using star-shaped oligo(ethylene glycols) (sOEG) with a molecular weight of 5 kDa for functionalization with DAT or DATT resulted in the formation of surfactants and not in hydrogels. As the molecular weight of the sOEG polymer chain can have an influence on forming physical cross links, DAT(T)-fuctionalization of sOEGs with …higher molecular weight was investigated, the polymers were structurally characterized and for their mechanical properties were evaluated by rheological measurements. Aqueous solutions of DAT(T)-sOEGs with 10 and 20 kDa showed lower storage and loss moduli compared to unfunctionalized sOEGs indicating also the formation of surfactants. Cell-based assays showed that all sOEG solutions did not impair cell viability and were free of endotoxins, which could otherwise induce uncontrolled immune responses. Conclusively, our data suggested that the sOEG solutions have surface active properties without inducing unwanted cellular responses, which is required e.g. in pharmaceutical applications to solubilize hydophobic substances. Show more

Keywords: Oligo(ethylene glycol), star polymers, self-organization, surfactant, biocompatibility

DOI: 10.3233/CH-151938

Citation: Clinical Hemorheology and Microcirculation, vol. 60, no. 1, pp. 13-23, 2015

Authors: Seelbach, Ryan J. | D’Este, Matteo | Alini, Mauro | Mata, Alvaro | Eglin, David

Article Type: Research Article

Abstract: BACKGROUND: Poly(N -isopropylacrylamide) conjugated hyaluronan (HA-pN), a brush-like copolymer system which serves as a polymer vehicle for cellular and drug delivery, has been previously synthesized via the copper catalyzed azide-alkyne reaction (CuAAC) using a combination of copper sulfate and ascorbic acid (CuAsc) as the catalytic system of choice. Bromotris(triphenylphosphine) copper(I) (CuBr(PPh3 )3 ) is an alternative catalytic compound containing a phosphorous ligand which stabilizes copper in the +1 oxidative state in aqueous solvents and can be employed at true catalyst concentrations. OBJECTIVE: CuAsc and CuBr(PPh3 )3 were compared for their efficiency; 1) in the …synthesis of HA-pN via CuAAC; 2) in producing thermoresponsive compositions and 3) in being extracted from the polymeric compositions. METHODS: The synthesis of the brush copolymer was carried out under strict Schlenk conditions, then characterized by ATR-FTIR, 1 H NMR, ICP-SFMS, and rheological measurements. RESULTS: CuBr(PPh3 )3 catalyzed CuAAC leads to better grafting in water, at a true catalyst concentration, compared to CuAsc. Polymeric solutions exhibited similar traits of increasing mechanical stiffness with rising temperature. Despite purification via chelation and/or dialysis, residual copper was present in similar concentrations in the final polymers. CONCLUSIONS: In the CuAAC driven copolymer synthesis of the HA-pN, CuBr(PPh3 )3 is a better catalyst than CuAsc. Show more

Keywords: Hyaluronan, copper catalyzed azide-alkyne cycloaddition, poly(N-isopropylacrylamide), bromotris (triphenylphosphine) copper(I)

DOI: 10.3233/CH-151933

Citation: Clinical Hemorheology and Microcirculation, vol. 60, no. 1, pp. 25-37, 2015

Authors: Aqil, A. | Tchemtchoua, V.T. | Colige, A. | Atanasova, G. | Poumay, Y. | Jérôme, C.

Article Type: Research Article

Abstract: Composite Crosslinked nanofibrous membranes of chitosan, ethylene glycol diglycidyl ether (EGDE) and polyethylene oxide was successfully prepared with bead free morphology via electrospinning technique followed by heat mediated chemical crosslinking. Architectural stability of nanofiber mat in aqueous medium was achieved by chemical crosslinking of only 1% EGDE, and tensile strength tests revealed that increasing EGDE content has considerably enhance the elastic modulus of nanofibers. The structure, morphology and mechanical properties of nanofibers were characterized by Attenuated Total Reflection-Fourier Transform Infrared spectroscopy (ATR–FTIR), scanning electron microscopy (SEM) and Instron machine, respectively. Skin fibroblasts and endothelial cells showed good attachment, proliferation and …viability on crosslinked electrospun membranes. The results indicate a good biocompatibility and non-toxic nature of the resulted membrane. Show more

Keywords: Chitosan, electrospinning, crosslinking, mechanical properties, tissue engineering, cytotoxicity

DOI: 10.3233/CH-151930

Citation: Clinical Hemorheology and Microcirculation, vol. 60, no. 1, pp. 39-50, 2015

Authors: Roch, Toralf | Ma, Nan | Kratz, Karl | Lendlein, Andreas

Article Type: Research Article

Abstract: A major challenge in biomaterial synthesis and functionalization is the prevention of microbial contaminations such as endotoxins (lipopolysaccharides (LPS)). In addition to LPS, which are exclusively expressed by Gram negative bacteria, also other microbial products derived from fungi or Gram positive bacteria can be found as contaminations in research laboratories. Typically, the Limulus amebocyte lysate (LAL)-test is used to determine the endotoxin levels of medical devices. However, this test fails to detect material-bound LPS and other microbial contaminations and, as demonstrated in this study, detects LPS from various bacterial species with different sensitivities. In this work, a cell-based …assay using genetically engineered RAW macrophages, which detect not only soluble but also material-bound microbial contaminations is introduced. The sensitivity of this cell-line towards different LPS species and different heat-inactivated microbes was investigated. As proof of principle a soft hydrophobic poly(n -butyl acrylate) network (cPn BA), which may due to adhesive properties strongly bind microbes, was deliberately contaminated with heat-inactivated bacteria. While the LAL-test failed to detect the microbial contamination, the cell-based assay clearly detected material-bound microbial contaminations. Our data demonstrate that a cell-based detection system should routinely be used as supplement to the LAL-test to determine microbial contaminations of biomaterials. Show more

Keywords: Biomaterials, polymers, endotoxins, microbial contaminations, immuno-compatibility

DOI: 10.3233/CH-151939

Citation: Clinical Hemorheology and Microcirculation, vol. 60, no. 1, pp. 51-63, 2015

Authors: Riva, Raphaël | Schmeits, Stéphanie | Croisier, Florence | Lecomte, Philippe | Jérôme, Christine

Article Type: Research Article

Abstract: In previous works, poly(D,L-lactide-co -ɛ CL-poly(ethylene glycol) (poly(D,L-La-co -α PEGɛ CL) amphiphilic graft-copolymers were successfully synthesized according to a copper azide-alkyne cycloaddition (CuAAC) strategy. This paper aims at reporting on the behavior of this amphiphilic copolymer in water, which was not studied in the previous paper. Moreover, the ability of the copolymer to stabilize a PLA nanoparticles aqueous suspension is presented. For this purpose, dynamic light scattering (DLS) and transmission electron microscopy (TEM) are proposed to characterize the nanoparticles in solution. Otherwise, the strategy developed for the synthesis of the amphiphilic copolymers was adapted and extended to the synthesis of …PLA-based degradable hydrogel, potentially applicable as drug-loaded degradable polymer implant. Show more

Keywords: Amphiphilic copolymers, aliphatic polyesters, degradable hydrogel, drug delivery

DOI: 10.3233/CH-151932

Citation: Clinical Hemorheology and Microcirculation, vol. 60, no. 1, pp. 65-75, 2015

Authors: Fang, Liang | Wischke, Christian | Kratz, Karl | Lendlein, Andreas

Article Type: Research Article

Abstract: BACKGROUND: In this work, a model approach to investigate changes in crystalline morphology during heating/cooling procedures in the context of programming and induction of the shape-memory effect is presented. OBJECTIVE AND METHOD: Atomic-force microscopy (AFM) was performed to investigate the variations in poly(ɛ -caprolactone) (PCL) crystalline morphology in nm thin films on a silicon substrate and a film with 20 μm thickness, prepared from a copolyesterurethane (named PDLCL) consisting of crystallizable poly(ω -pentadecalactone) (PPDL) hard segments and crystallizable PCL segments forming switching domains. RESULTS: PCL crystals in switching domains melted/recrystallized repeatedly during …heating/cooling cycles between 20 and 70 °C, while no evident variation in PPDL crystals forming hard domains was observed. When film thickness was 20 nm, PCL edge-on lamellae were observed, confined in the phase-separated morphology. Flat-on PCL lamellae, which broke out from the previous phase-separated morphology, were obtained at a film thickness of 170 nm. In contrast, large PCL spherulites were observed in the 20 μm thick film. CONCLUSION: PCL crystalline morphology in PDLCL as well as the competition between crystallization and phase separation can be tailored by the film thickness and the substrate. Such AFM investigations on thin films can be a helpful approach for predicting the crystal morphology in micro-/nanoscaled objects. Show more

Keywords: Crystalline morphology, poly(ɛ-caprolactone), shape-memory polymer

DOI: 10.3233/CH-151934

Citation: Clinical Hemorheology and Microcirculation, vol. 60, no. 1, pp. 77-87, 2015

Authors: ter Boo, G.A. | Grijpma, D.W. | Richards, R.G. | Moriarty, T.F. | Eglin, D.

Article Type: Research Article

Abstract: BACKGROUND: Infection is a common problem in trauma and orthopaedic surgery. Antibiotic-loaded biomaterials are used locally to clear infections as an adjunct to systemic antibiotics. Gentamicin-sulphate (GEN-SULPH) is commonly used in antibiotic-loaded biomaterials, although it displays high water solubility resulting in quick diffusion from the carrier. OBJECTIVE: Preparation of a lipophilic derivative of gentamicin to reduce solubility and obtain a slower release. Subsequently, entrapment of this lipophilic gentamicin within poly(trimethylene carbonate) (PTMC) matrices. METHODS: Hydrophobic ion-pairing was used to prepare lipophilic gentamicin (GEN-AOT). The susceptibility of Staphylococcus aureus NCTC 12973 and …Staphylococcus epidermidis 103.1 for GEN-AOT was tested and the viability of fibroblasts upon exposure to GEN-AOT was assessed. GEN-AOT was then loaded into PTMC films. RESULTS: GEN-AOT was successfully prepared as confirmed by FTIR-spectroscopy. GEN-AOT was bactericidal for S. epidermidis and S. aureus at 0.5 μM and 8.5 μM, respectively. At 1.1 μM GEN-AOT no reduction in fibroblast viability was observed. At 11 μM the reduction was ∼50% . PTMC discs loaded with GEN-AOT were prepared by compression molding. CONCLUSIONS: Lipophilic GEN-AOT was at least as potent as GEN-SULPH. For S. epidermidis it was even more potent than GEN-SULPH. More than 50% fibroblast cell viability was maintained at bactericidal concentration for both bacterial strains. Show more

Keywords: Orthopaedic infection, local infection treatment, gentamicin, antibiotic modification, poly(trimethylene carbonate), drug delivery

DOI: 10.3233/CH-151935

Citation: Clinical Hemorheology and Microcirculation, vol. 60, no. 1, pp. 89-98, 2015

Authors: Narra, Nathaniel | Blanquer, Sébastien B.G. | Haimi, Suvi P. | Grijpma, Dirk W. | Hyttinen, Jari

Article Type: Research Article

Abstract: BACKGROUND: Advances in rapid-prototyping and 3D printing technologies have enhanced the possibilities in preparing designed architectures for tissue engineering applications. A major advantage in custom designing is the ability to create structures with desired mechanical properties. While the behaviour of a designed scaffold can be simulated using bulk material properties, it is important to verify the behaviour of a printed scaffold at the microstructure level. OBJECTIVE: In this study we present an effective method in validating the mechanical behaviour of designed scaffolds using a μCT with an in-situ mechanical deformation device. METHODS: …The scaffolds were prepared from biodegradable poly(trimethylene carbonate) (PTMC) by stereolithography and images obtained using a high-resolution μCT with 12.25μm isometric voxels. The data was processed (filtering, segmentation) and analysed (surface generation, registration) to extract relevant deformation features. RESULTS: The computed local deformation fields, calculated at sub-pore resolutions, displayed expected linear behaviour within the scaffold along the compressions axis. On planes perpendicular to this axis, the deformations varied by 150– 200μm. CONCLUSIONS: μCT based imaging with in-situ deformation provides a vital tool in validating the design parameters of printed scaffolds. Deformation fields obtained from micro-tomographic image volumes can serve to corroborate the simulated ideal design with the realized product. Show more

Keywords: MicroCT, scaffold design, in-situ deformation, 3D-printing, poly(trimethylene carbonate), PTMC

DOI: 10.3233/CH-151931

Citation: Clinical Hemorheology and Microcirculation, vol. 60, no. 1, pp. 99-108, 2015