| 1. |
- Ohrlander, M., et al.
(author)
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The effect of electron beam irradiation on PCL and PDXO-X monitored by luminescence and electron spin resonance measurements
- 2000
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In: Polymer. - 0032-3861 .- 1873-2291. ; 41:4, s. 1277-1286
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Journal article (peer-reviewed)abstract
- The effect of electron beam irradiation in air or argon was studied on two hydrolysable aliphatic polyesters, poly(e-caprolactone) (PCL) and chemically cross-linked poly(1,5-dioxepan-2-one) (PDXO-X). A secondary alkylether radical and a tertiary alkyl radical were identified by ESR in PCL and PDXO-X after irradiation in both air and argon. For the samples irradiated in air, peroxy radicals were detected in PCL but not in PDXO-X. For irradiated PCL, the intensities in the luminescence measurements seemed to be dose-dependent. Large amounts of oxidation products were found present in the PDXO-X irradiated in air and the luminescence intensities seemed to be dose-dependent.The effect of electron beam irradiation in air or argon was studied on two hydrolysable aliphatic polyesters, poly(e-caprolactone) (PCL) and chemically cross-linked poly(1,5-dioxepan-2-one) (PDXO-X). A secondary alkylether radical and tertiary alkyl radical were identified by ESR in PCL and PDXO-X after irradiation in both air and argon. For the samples irradiated in air, peroxy radicals were detected in PCL but not in PDXO-X. For irradiated PCL, the intensities in the luminescence measurements seemed to be dose-dependent. Large amounts of oxidation products were found present in the PDXO-X irradiated in air and the luminescence intensities seemed to be dose-dependent.
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| 2. |
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| 3. |
- Lindberg, T., et al.
(author)
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Graft polymerisation of acrylamide onto PCL film by electron beam pre-irradiation in air or argon. Morphology in the final grafted state
- 2000
-
In: Polymer. - 0032-3861 .- 1873-2291. ; 41:11, s. 4099-4111
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Journal article (peer-reviewed)abstract
- Poly(epsilon-caprolactone) has been graft polymerised to final graft yields with acrylamide (AAm) as monomer in an aqueous solution by the pre-irradiation method. The synthesis of the samples obtained, pre-irradiated in air or argon atmosphere, was controlled by dose and concentration of inhibitor, provided as Mohr's salt, in the ranges from 2.5 to 10 Mrad and from 0.005 to 0.500 wt%, respectively. Final graft yields and lateral dimensions in swollen condition ranged from 70 to 3400 wt%, and from 23 x 30 to 89 x 94 mm(2), respectively, as atmosphere during irradiation, dose and concentration of inhibitor were altered. These properties gave values in crystallinity extending from 4 to 57 wt%. Samples pre-irradiated in air and subsequently graft polymerised yielded higher values of crystallinity in the entire range of dose and concentration of inhibitor. At low concentration of inhibitor, final graft yield and lateral dimension for samples pre-irradiated in air had considerably larger values while the final graft yield and lateral dimension of samples pre-irradiated in argon had slightly larger values at high concentration of inhibitor. The initial biaxial morphology of the PCL film was continuously transformed into a uniform morphology, which was reached at a final graft yield of approximately 800 wt%.
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| 4. |
- Olander, B., et al.
(author)
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Argon microwave plasma treatment and subsequent hydrosilylation grafting as a way to obtain silicone biomaterials with well-defined surface structures
- 2002
-
In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 3:3, s. 505-510
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Journal article (peer-reviewed)abstract
- A method of grafting well-defined and hydrolytically stable surface structures onto cross-linked poly(dimethylsiloxane) (PDMS) has been developed. In the first step, argon microwave plasma was used to introduce Si-H groups onto the surface. In the second step, allyltetrafluoroethyl ether was grafted to these Si-H groups using a platinum-catalyzed hydrosilylation reaction. The influences of the plasma parameters of power, pressure, and treatment time on the surface composition, both before and after the hydrosilylation step, were investigated by X-ray photoelectron spectroscopy and contact angle measurements. It was found that the pressure had little influence on the results, whereas the power and treatment time determined the rate of change in surface composition during the plasma treatment. The graft yield reached a plateau value corresponding to about 5% grafted molecules in the analyzed surface region. Hydrosilylation grafting of PDMS is a promising method to obtain biomaterials with hydrolytically stable structures covalently bound to the surface.
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| 5. |
- Olander, B., et al.
(author)
-
Silicone elastiomer surface functionalized with primary amines and subsequently coupled with heparin
- 2003
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 4:1, s. 145-148
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Journal article (peer-reviewed)abstract
- Primary amines covalently bonded to the surface of poly(dimethylsiloxane) were obtained by hydrosilylation grafting of aminopropyl vinyl ether to Si-H groups formed during argon plasma treatment. The amine groups were derivatized using pentafluorobenzaldehyde and characterized by X-ray photoelectron spectroscopy. The graft yield was about 3% grafted molecules within the depth of the analysis. The terminal aldehyde groups of diazotized heparin was also coupled to the primary amines. This led to a silicone elastomer with covalently bonded heparin which was expected to be hydrolytically stable. This method of bonding primary amines to the surface of silicone elastomers and the subsequent coupling of aldehyde-containing molecules is a promising way of obtaining novel biomaterials.
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| 6. |
- Olander, B., et al.
(author)
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Silicone elastomers with controlled surface composition using argon or hydrogen plasma treatment
- 2003
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In: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 90:5, s. 1378-1383
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Journal article (peer-reviewed)abstract
- Plasma treatment of poly(dimethyl siloxane) (PDMS) leads to changes in the surface composition that can be followed by X-ray photoelectron spectroscopy (XPS). Prolonged plasma treatment in argon or hydrogen leads to an increase in oxygen, a decrease in carbon, and only minor changes in the silicon content. The extent of the change in elemental composition is dependent on the plasma conditions (e.g., the power and pressure during the treatment). We have determined how these parameters influence the surface composition of PDMS exposed to argon and hydrogen microwave plasma as a function of treatment time. A model has been developed describing the extent of change in surface composition under different plasma conditions. The power had a large impact on the rate of change in elemental surface composition, whereas the pressure had only a minor influence. We show that the rate of change in elemental composition can be described by one factor common for all treatments and one factor specific for each plasma condition of power, pressure, and gas. Using this model we can determine the plasma parameters and treatment time to obtain any desired extent of surface modification.
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| 7. |
- Qu, X., et al.
(author)
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Effect of lactic/glycolic acid side chains on the thermal degradation kinetics of chitosan derivatives
- 2000
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In: Polymer. - 0032-3861 .- 1873-2291. ; 41:13, s. 4841-4847
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Journal article (peer-reviewed)abstract
- The thermal degradation properties of chitosan and lactic and/or glycolic acid grafted chitosan have been studied by differential scanning calorimetry (DSC) and thermogravimetric analyses (TG) in the range of 25-500 degrees C. Both DSC and dynamic TG results show that the samples are thermal degraded easily after grafting the lactic and/or glycolic acid. From the isothermal TG experiments, the initial activation energy and the activation energy at different stages is obtained. The initial activation energy of all grafted samples is much lower than that of chitosan, especially for the sample GA/CS = 2 and it varies with degree of conversion. The FT-IR spectra of thermally degraded residues give an indication of the chitosan polyscaccharide ring degradation after 30 min in 280 degrees C, while sample GA/CS = 2 will degrade only after 15 min.
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| 8. |
- Qu, X., et al.
(author)
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Novel pH-sensitive chitosan hydrogels : swelling behavior and states of water
- 2000
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In: Polymer. - 0032-3861 .- 1873-2291. ; 41:12, s. 4589-4598
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Journal article (peer-reviewed)abstract
- Physically crosslinked chitosan hydrogels were synthesized by grafting D,L-lactic acid (LA) and/or glycolic acid (GA) with different feed ratios. The physical crosslinking was formed due to the hydrophobic side chains aggregation and intermolecular interactions through hydrogen bonds between side and main chains. The crystallinity of original chitosan decreased by grafting LA and GA. The structural change of the hydrogels in different pH buffers was characterized by FT-IR method and the results were interpreted. Differential scanning calorimetry (DSC) was used to probe the states of water in the chitosan hydrogels. Three types of water were found in the samples, i.e. freezing water (namely free water), non-freezing water (namely bound water), and freezing bound water, while there are variations in the amount of bound water for different hydrogels. The effect of hydrophobic side chains on water state and swelling behavior were discussed.
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| 9. |
- Qu, X., et al.
(author)
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Surface modification of high density polyethylene tubes by coating chitosan, chitosan hydrogel and heparin
- 2001
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In: Polymer Bulletin. - : Springer Science and Business Media LLC. - 0170-0839 .- 1436-2449. ; 46:03-feb, s. 223-229
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Journal article (peer-reviewed)abstract
- Chitosan and chitosan hydrogel were immobilized on both the inside and outside surfaces of high density polyethylene (HDPE) tubes with 2.5x4 mm diameters. First, acrylic acid was grafted on the surfaces of HDPE by electron beam (2.5 Mrad) preirradiation method. Then chitosan/HCl and chitosan/lactic acid solutions were coated on the modified hydrophilic HDPE surfaces, the latter could form a pH-sensitive hydrogel layer on the surfaces. The tube surfaces were further modified with heparin by surface interpenetrating method to improve blood compatibility. ATR-FTIR and ESCA methods were used to characterize the coated surfaces. The morphology changes were monitored by Scanning Electron Microscope (SEM).
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| 10. |
- Wirsen, A, et al.
(author)
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Neuropsychological performance differs between type 1 diabetic and normal men during insulin-induced hypoglycaemia
- 1992
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In: Diabetic Medicine. - 1464-5491. ; 9:2, s. 156-165
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Journal article (peer-reviewed)abstract
- Cerebral function was measured with a neuropsychological test battery before, during, and after insulin-induced hypoglycaemia (blood glucose approximately 2.0 mmol l-1) in 10 male Type 1 diabetic patients (age 20-43 years, duration of diabetes 14 (2-30) years) and in 12 normal men. There were no group differences in neuropsychological results at normal glucose levels. Significant effects of hypoglycaemia were found in reaction-time measures (p less than 0.001) and in other tests requiring speed and attention (p less than 0.001), in verbal fluency (p less than 0.05), and short-term memory (p less than 0.001). Significant group effects and interactions (p less than 0.05) revealed that the diabetic patients were generally more affected by hypoglycaemia than the normal subjects. This might have been partly due to the larger absolute decrease in blood glucose level in the diabetic patients, although the rate of glucose decrease was not related to performance in either group. Thus, the diabetic brain might be more vulnerable to hypoglycaemia, perhaps through the persistent impact of repeated hypoglycaemic episodes, although no neuropsychological deficit is demonstrable at normal blood glucose levels.
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| 11. |
- Wirsen, A., et al.
(author)
-
Quantified EEG and cortical evoked responses in patients with chronic traumatic frontal lesions
- 1992
-
In: Electroencephalography and Clinical Neurophysiology / Evoked Potentials Section. - 0168-5597 .- 1872-6224. ; 84:2, s. 127-138
-
Journal article (peer-reviewed)abstract
- Eighteen frontal trauma patients and 17 age-matched control subjects had quantified EEGs and measurements of sensory (SEP) and auditory evoked potentials (P300) using a Biologic Brain Atlas III system. The findings were compared to the conventional paper EEG, and to the frontal lesion volumes, severity of head injury, and outcome variables. The quantified EEG confirmed the pathological findings detected by visual inspection, but some regional abnormalities were more easily detected by topographic mapping. The regional distribution of pathological slowing corresponded well with the morphological lesions in most patients. The modal frequency of EEG correlated both with lesion volume and injury severity and with the outcome variables. There were no pathological findings in the SEPs, and all but one patient had clearly distinguishable P300 responses. There was a significant reduction in P300 amplitude in the frontal patients at the anterior, but not at the posterior electrodes. The topographical distribution of the P300 changes corresponded well with the morphological lesions. Our findings indicate that the P300 potential is, in part, dependent upon the prefrontal cortical areas. The present study thus supports P300 investigations which have shown amplitude reduction in other disorders (e.g., schizophrenia) with a presumed prefrontal dysfunction.
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| 12. |
- Wirsen, A., et al.
(author)
-
Quantified EEG and cortical evoked responses in patients with chronic traumatic frontal lesions
- 1992
-
In: Electroencephalography and Clinical Neurophysiology / Evoked Potentials Section. - : Elsevier BV. - 0168-5597. ; 84:2, s. 127-138
-
Journal article (peer-reviewed)abstract
- Eighteen frontal trauma patients and 17 age-matched control subjects had quantified EEGs and measurements of sensory (SEP) and auditory evoked potentials (P300) using a Biologic Brain Atlas III system. The findings were compared to the conventional paper EEG, and to the frontal lesion volumes, severity of head injury, and outcome variables. The quantified EEG confirmed the pathological findings detected by visual inspection, but some regional abnormalities were more easily detected by topographic mapping. The regional distribution of pathological slowing corresponded well with the morphological lesions in most patients. The modal frequency of EEG correlated both with lesion volume and injury severity and with the outcome variables. There were no pathological findings in the SEPs, and all but one patient had clearly distinguishable P300 responses. There was a significant reduction in P300 amplitude in the frontal patients at the anterior, but not at the posterior electrodes. The topographical distribution of the P300 changes corresponded well with the morphological lesions. Our findings indicate that the P300 potential is, in part, dependent upon the prefrontal cortical areas. The present study thus supports P300 investigations which have shown amplitude reduction in other disorders (e.g., schizophrenia) with a presumed prefrontal dysfunction.
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| 13. |
- Wirsen, A., et al.
(author)
-
Solvent-free vapor-phase photografting of acrylamide onto poly(ethylene terephthalate)
- 2005
-
In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 6:5, s. 2697-2702
-
Journal article (peer-reviewed)abstract
- Poly(ethylene terphthalate) (PET) films were photografted under reduced pressure in a solvent-free vapor of acrylamide and a co-initiator, benzophenone. Characterization of grafted samples by ESCA and contact angles showed that the grafting increased with grafting time and temperature. The amide groups obtained by the acrylamide grafting were converted into amine groups by the Hofmann rearrangement to be used in coupling reactions. The amine groups were confirmed by reaction with pentafluorobenzoyl chloride, which provides a fluorine label for ESCA. Surface grafting of polymeric substrates in the vapor phase induced by plasma or high energy and UV irradiation is reviewed.
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| 14. |
- Wirsen, A., et al.
(author)
-
Solvent free vapor phase photografting of maleic anhydride onto poly(ethylene terephthalate) and surface coupling of fluorinated probes, PEG, and an RGD-peptide
- 2005
-
In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 6:4, s. 2281-2289
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Journal article (peer-reviewed)abstract
- Poly(ethylene terephthalate) (PET) was photografted in a solvent free vapor of maleic anhydride and benzophenone. After hydrolysis of the initially grafted succinic anhydride groups, the carboxylic PET surfaces were modified by coupling reactions in organic and aqueous solutions. 2,2,2-Trifluoroethylan-fine and diamino PEGs of molecular weight 3400 and 2000 were reacted with acid chloride groups obtained by treating the PET-COOH surface with PCl5. Furthermore, fluoro substituted thiols and a cystein terminated RGD containing peptide were bound to PET-COOH surfaces via a disulfide link by a three step coupling sequence. Coupling yields and surface concentrations of the fluoro substituted ligands were calculated from ESCA data. The RGD-peptide surfaces were evaluated by cultivation with rat smooth muscle cells.
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| 15. |
- Wirsen, A., et al.
(author)
-
Solvent free vapour phase photografting of acrylamide onto poly(methyl methacrylate)
- 2005
-
In: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 46:13, s. 4554-4561
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Journal article (peer-reviewed)abstract
- Poly(methyl methacrylate) (PMMA) sheets were surface grafted with acrylamide under reduced pressure in a solvent free vapour of acrylamide and benzophenone. The grafting was initiated with UV irradiation and no pre-treatment of PMMA by impregnation or sorption of reactants was required. Characterization of grafted samples by ESCA and contact angles showed that the nitrogen content increased with grafting time and temperature. The surface bound amide groups obtained were converted into amine groups by the Hofmann reaction and used in coupling reactions with a p-nitrophenyl carbonate terminated PEG and 4,4,4-trifluoro butyraldehyde.
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