Fabrication of hierarchical multilayer poly(glycerol sebacate urethane) scaffolds based on ice-templating

In this study, it was demonstrated that ice-templating via freeze drying with custom-made moulds, in combination with air brushing, allows for the fabrication of poly(glycerol sebacate urethane) (PGSU) scaffolds with hierarchical multilayer microstructures to replicate various native soft tissues. The PGSU scaffolds were either monolayered but exhibited an anisotropic microstructure, or bilayered and trilayered, with each layer showing different microstructures. By using freeze drying with custom-made moulds, the ice crystals of the solvent were grown unidirectionally, and after freeze-drying, the scaffolds had an anisotropic microstructure, mimicking tissues such as tendon and skeletal muscle. The anisotropic PGSU scaffolds were also examined for their tensile strength, and a range of mechanical properties were obtained by altering the reactants’ molar ratio and polymer concentration. This is of importance, since soft tissues exhibit different mechanical properties depending on their native location and functionality. By combining freeze drying with airbrushing, scaffolds were fabricated with a thin, non-porous layer on top of the porous layers to allow three-dimensional cell co-culture for tissues such as skin and oral mucosa. These results show that fabrication techniques can be combined to produce PGSU scaffolds with tailored hierarchical microstructures and mechanical properties for multiple tissue engineering applications

Molecular DNA identity of the mouflon of Cyprus (Ovis orientalis ophion, Bovidae): Near Eastern origin and divergence from Western Mediterranean conspecific populations

The mouflon population of Cyprus (Ovis orientalis ophion) comprises historically preserved feral descendants of sheep domesticated during the Neolithic. We determined genetic identity of this taxon in order to elucidate its systematic placement and enforce its protection. We used 12 loci of microsatellite DNA to infer genetic relationships between the Cypriot mouflon and either long-time isolated (Corsica, Sardinia) or recently introduced (central Italy) European mouflons (O. o. musimon). We also sequenced the mitochondrial DNA (mtDNA) Cytochrome-b gene to infer the origin of the Cypriot mouflon including many National Centre for Biotechnology Information (NCBI) entries of European and Near Eastern conspecifics. Microsatellites disclosed net divergence between Western Mediterranean and Cypriot mouflon. The latter was included in the highly heterogeneous Near Eastern O. orientalis mtDNA group, Iran representing the most credited region as the source for its ancient introduction to Cyprus. Both international and national legislation protect the mouflon of Cyprus as a wild taxon (O. o. ophion). However, the IUCN Red List of Threatened Species and NCBI include the Cypriot mouflon as subspecies of its respective domestic species, the sheep (O. aries). Unfortunately, people charged with crime against protected mouflon may benefit from such taxonomic inconsistency between legislation and databases, as the latter can frustrate molecular DNA forensic outcomes. Until a definitive light can be shed on Near Eastern O. orientalis systematics, we suggest that the Cypriot mouflon should be unvaryingly referred to as O. o. ophion in order not to impair conservation in the country where it resides

Measuring bank efficiency: DEA application

The paper aims to improve the methodology of measuring efficiency of Latvian banks. Efficiency scores were calculated with application of non-parametric frontier technique Data Envelopment Analysis (DEA). Input-oriented DEA model under Variable Returns to Scale (VRS) assumption was used. Potential model variables were selected based on the intermediation and profitability approach. Fourteen alternative models with different inputs-outputs combinations were developed for the research purposes. To substantiate the variables selection for DEA model the received data was processed, using such methods, as correlation analysis, linear regression analysis, analysis of mean values, and two-samples Kolmogorov-Smirnov test. The research results assisted the authors in providing general recommendations about the variables selection for DEA application in the Latvian banking sector. The present research contributes to the existing analytical data on bank performance in Latvia. The empirical findings provide a background for further studies, in particular, the efficiency of Latvian banks could be analysed in the extended time period

General flow characteristics in a compliant model of a carotid bifurcation

The flow dynamic characteristics of a compliant model of a human carotid bifurcation were investigated and compared with a rigid model of similar geometry [1,2]. Using Laser Doppler Velocimetry the flowfield was interrogated in two orthogonal planes at different locations along the axis of the internal carotid. The wall motion under physiologic pulsatile conditions was also simultaneously monitored. Complicated flow features such as helical structures and regions of reversed flow were analyzed. Negative velocity regions at the proximal axial locations were augmented temporally and spatially for the compliant model. Helical structures had different temporal characteristics and appeared more spread towards the centerline in the presence of a compliant wall

Shear stress at a compliant model of the human carotid bifurcation

To investigate the role of a compliant wall to the near wall hemodynamic flowfield, two models of the carotid bifurcation were constructed. Both were of identical internal geometries, however, one was made of compliant material which produced approximately the same degree of wall motion as that occurring in vivo while the other one was rigid. The inner geometries were formed from the same mold so that the configurations are directly comparable. Each model was placed in a pulsatile flow system that produced a physiologic flow waveform. Velocity was measured with a single component Laser system and wall shear rate was estimated from near wall data. Wall motion in the compliant model was measured by a wall motion transducer and the maximum diameter change varied between 4-7 percent in the model with the greatest change at the axis intersection. The mean shear stress in the compliant model was observed to be smaller by about 30 percent at most locations. The variation in peak shear stress was greater and occasionally reached as much as 100 percent with the compliant model consistently having smaller positive and negative peaks. The separation point was seen to move further upstream in the compliant cast. The modified flowfield in the presence of a compliant wall can then be important in the hemodynamic theory of atherogenesis. To investigate the role of a compliant wall to the near wall hemodynamic flowfield, two models of the carotid bifurcation were constructed. Both were of identical internal geometries, however, one was made of compliant materials which produced approximately the same degree of wall motion as that occurring in vivo while the other one was rigid. The inner geometries were formed from the same mold so that the configurations are directly comparable. Each model was placed in a pulsatile flow system that produced a physiologic flow waveform. Velocity was measured with a single component Laser system and wall shear rate was estimated from near wall data. Wall motion in the compliant model was measured by a wall motion transducer and the maximum diameter change varied between 4-7 percent in the model with the greatest change at the axis intersection. The mean shear stress in the compliant model was observed to be smaller by about 30 percent at most locations. The variation in peak shear stress was greater and occasionally reached as much as 100 percent with the compliant model consistently having smaller positive and negative peaks. The separation point was seen to move further upstream in the compliant cast. The modified flow field in the presence of a compliant wall can the be important in the hemodynamic theory of atherogenesis

A flow visualization study of an anatomic coronary artery anastomosis model with an implant

Flow Streamlining Devices is a new tool in Coronary Artery Bypass Grafting (CABG). They aim in: a) Performing a sutureless anastomosis to reduce thrombosis at the veno-arterial junction, and b) Providing a hemodynamically efficient scaffolding to reduce secondary flow disturbances. Thrombosis and flow disturbances are factors that have been reported as contributing factors to the development of intimal hyperplasia (IH) and failure of the graft. By reducing thrombosis and flow disturbances, it is expected that IH will be inhibited and the lifetime of the graft extended. To evaluate the hemodynamic benefits of such an implant, two models were designed and fabricated. One simulated the geometry of the conventional anastomosis without an implant, and the other simulated an anastomosis with a flow streamlining implant. Identical flow conditions relevant to a coronary anastomosis were imposed on both models and flow visualization was performed with dye injection and a digital camera. Results showed reduction of disturbances in the presence of the implant. This reduction seems to be favorable to hemodynamic streamlining which may create conditions that may inhibit the initialization of IH. However, the compliance and geometric mismatch between the anastomosis and the implant created a disturbance at the rigid compliant wall interface, which should be eliminated prior to clinical applications

Effects of arterial wall distensibility on the near wall flowfield in a model of a human carotid bifurcation

Arterial wall distensibility is believed to be of secondary importance to the general flowfield of the human carotid artery. However, it has been reported that it may have greater influence on the near wall flow variables such as shear stress and separation zones. To further investigate this factor two models of the carotid bifurcation were constructed. One was rigid and one was made of a compliant material and produced approximately the same degree of wall motion as that occurring in vivo. Each model was placed in a pulsatile flow system and velocities and shear stresses were measured with a single component laser system along the diameter at different axial locations. Wall motion was also measured and the maximum diameter change varied between 4-7% around the model. Lower shear stresses were observed at the locations of measurement in the compliant model. The separation zone during systole was observed to be more extensive radially and axially, upstream of the mid-sinus for the compliant model. In addition, the separation zone was found to be more extensive in time during the pulsatile cycle. These observations in comparison with previously reported data at these locations may be important in a hemodynamic theory of atherogenesis

Fluid dynamics at the carotid bifurcation

Arterial wall distensibility is believed to be of secondary importance to the general flowfield of the human carotid artery. However, it has been reported that it may have greater influence on the near wall flow variables such as shear stress and separation zones (Liepsch et al. 1983, Duncan et al. 1990) To further investigate this factor two models of the carotid bifurcation were constructed. One was rigid and one was made of a compliant material and produced approximately the same degree of wall motion as that occurring in vivo. Each model was placed in a pulsatile flow system and velocities and shear stresses were measured with a single component laser system along the diameter at different axial locations. Wall motion was also measured and the maximum diameter change varied between 4-7% around the model Lower shear stresses were observed at the locations of measurement in the compliant model. The separation zone during systole was observed to be more extensive radially and axially, upstream of the mid-sinus for the compliant model. In addition, the separation zone was found to be more extensive in time during the pulsatile cycle. These observations in comparison with previously reported data (Zarins et al. 1983, Ku et al. 1985) at these locations may be important in a hemodynamic theory of atherogenesis