Laser based functionalization for graded immobilization of biomolecules on biocompatible polymer surfaces

Surface modification is a powerful tool for the development of cell guiding structures for tissue engineering as well as for the development of in vitro assays for molecular screening. In both applications the biomolecule concentration linked to the surface is an important functionalization property. While cell guiding structures need continuous linear gradients of either increasing or decreasing signaling molecule concentration, assays for molecular screening need distinct areas of functionalization for testing of various molecule concentrations. Therefore a laser based method for local surface activation is under investigation. Laser irradiation is a powerful tool, which provides a high temporal and spatial resolution for the generation of structures in the micrometer range. In the current research we investigated the influence of UV-Laser irradiation with the wavelengths of 193nm and 248nm on the activation of poly(methyl metacrylate) (PMMA) and poly-ε-caprolactone (PCL). We demonstrate that PMMA and PCL can be locally activated. In a subsequent wet chemical step the activated groups can be functionalized with amine groups. These amines can be used for immobilization of bioactive compounds like RGD (Arginine- Glycine-Aspartate)-peptides or lactose. RGD-peptides will serve as cell recognition domain and enhance cell adhesion, while lactose serves as a model molecule for further surface modification. We found out that by defined pulse accumulation the activation dose can be increased. This leads to an increase of the surface activation and therefore the increase of the functionalization density. The successful activation and amination of the surfaces was shown by staining with an amino-specific fluorescent dye and XPS-analysis. The process window for PMMA and PCL activation with irradiation of 193nm differ, but the increasing fluorescence signal corresponds to the increasing irradiation dose. Activation with irradiation of 248nm leads to a weak surface activation The RGD-peptide functionalized surfaces have been seeded with neuronal B35-cells which differentiate under serum deprived conditions. We could successfully demonstrate that cells favor areas with higher concentration of RGD-peptides. Finally we showed that lactose can be successfully linked to the amines. The specific binding of lactose could be demonstrated by staining with a FITC labeled Erythrina cristagally Lectin

Evaluation of electrical impedance tomography for determination of urinary bladder volume : comparison with standard ultrasound methods in healthy volunteers

Abstract Background Continuous non-invasive urinary bladder volume measurement (cystovolumetry) would allow better management of urinary tract disease. Electrical impedance tomography (EIT) represents a promising method to overcome the limitations of non-continuous ultrasound measurements. The aim of this study was to compare the measurement accuracy of EIT to standard ultrasound in healthy volunteers. Methods For EIT of the bladder a commercial device (Goe MF II) was used with 4 different configurations of 16 standard ECG electrodes attached to the lower abdomen of healthy participants. To estimate maximum bladder capacity (BCmax) and residual urine (RU) two ultrasound methods (US-Ellipsoid and US-L × W × H) and a bedside bladder scanner (BS), were performed at the point of urgency and after voiding. For volume reference, BCmax and RU were validated by urine collection in a weight measuring pitcher. The global impedance method was used offline to estimate BCmax and RU from EIT. Results The mean error of US-Ellipsoid (37 ± 17%) and US-L × W × H (36 ± 15%) and EIT (32 ± 18%) showed no significant differences in the estimation of BCmax (mean 743 ± 200 ml) normalized to pitcher volumetry. BS showed significantly worse accuracy (55 ± 9%). Volumetry of RU (mean 152.1 ± 64 ml) revealed comparable higher errors for both EIT (72 ± 58%) and BS (63 ± 24%) compared to US-Ellipsoid (54 ± 25%). In case of RU, EIT accuracy is dependent on electrode configuration, as the Stripes (41 ± 25%) and Matrix (38 ± 27%) configurations revealed significantly superior accuracy to the 1 × 16 (116 ± 62%) configuration. Conclusions EIT-cystovolumetry compares well with ultrasound techniques. For estimation of RU, the selection of the EIT electrode configuration is important. Also, the development of an algorithm should consider the impact of movement artefacts. Finally, the accuracy of non-invasive ultrasound accepted as gold standard of cystovolumetry should be reconsidered