Hybrid Titanium/Biodegradable Polymer Implants with an Hierarchical Pore Structure as a Means to Control Selective Cell Movement

UNLABELLED: In order to improve implant success rate, it is important to enhance their responsiveness to the prevailing conditions following implantation. Uncontrolled movement of inflammatory cells and fibroblasts is one of these in vivo problems and the porosity properties of the implant have a strong effect on these. Here, we describe a hybrid system composed of a macroporous titanium structure filled with a microporous biodegradable polymer. This polymer matrix has a distinct porosity gradient to accommodate different cell types (fibroblasts and epithelial cells). The main clinical application of this system will be the prevention of restenosis due to excessive fibroblast migration and proliferation in the case of tracheal implants. METHODOLOGY/PRINCIPAL FINDINGS: A microbead-based titanium template was filled with a porous Poly (L-lactic acid) (PLLA) body by freeze-extraction method. A distinct porosity difference was obtained between the inner and outer surfaces of the implant as characterized by image analysis and Mercury porosimetry (9.8±2.2 µm vs. 36.7±11.4 µm, p≤0.05). On top, a thin PLLA film was added to optimize the growth of epithelial cells, which was confirmed by using human respiratory epithelial cells. To check the control of fibroblast movement, PKH26 labeled fibroblasts were seeded onto Titanium and Titanium/PLLA implants. The cell movement was quantified by confocal microscopy: in one week cells moved deeper in Ti samples compared to Ti/PLLA. CONCLUSIONS: In vitro experiments showed that this new implant is effective for guiding different kind of cells it will contact upon implantation. Overall, this system would enable spatial and temporal control over cell migration by a gradient ranging from macroporosity to nanoporosity within a tracheal implant. Moreover, mechanical properties will be dependent mainly on the titanium frame. This will make it possible to create a polymeric environment which is suitable for cells without the need to meet mechanical requirements with the polymeric structure

Labour Relations, Flexibility, and Management Intensity in Dutch Firms: An Investigation Using the OSA/SCP Labour Panel Database

'High road' Human Resource Management practices (often associated with rigid labour markets) differ from 'low road' practices (flexible labour markets) in terms of employment protection, earnings differentials among employees and amount of direct employees' supervision. Firms employing 'low road' practices tend to rely heavily on supervision, as a consequence of the lack of trust among employees, hence leading to higher management intensity. In earlier research, this phenomenon was observed at country-level. However, the evidence was based on highly aggregated data. The focus of this study is therefore to explore whether the same observation exists at firm level. The 'low road' HRM practice is represented by an external flexibility measure i.e. the intensity of the use of flexible workers. Besides the labour flexibility variable, the influences of various factors associated with firms' internal and external environment are also investigated. The analysis is done using multiple regression analyses on the OSA/SCP database for year 2007-2008. Shares of workers hired from manpower agency are shown to have a small, yet positively significant impact on levels of management intensity in the firm. Firm size, on the other hand, has a significantly negative impact on management intensity. Extent of research and innovation activities in the firm is also found to exert significant influence on management intensity. Firms that are more research intensive and innovative tend to have higher management intensity as compared to non-innovating firms. Lastly, substantial sectoral variations are also observed, which might be explained by firm-level factor such as firm size and level of technical complexity.Economics of InnovationManagement of TechnologyTechnology, Policy and Managemen