A novel absorbable scaffold composed of chitosan and gelatin was fabricated by freezing and lyophilizing methods, resulting in an asymmetric structure. This bilaminar texture is suitable for preparing a bilayer skin substitute. The methods employed to confirm the applicability of this chitosan-gelatin scaffold as an ideal skin substitute were a water uptake ability test, in vitro fibroblast proliferation, and scaffold tests in which fibroblasts were co-cultured with keratinocytes. The chitosan-gelatin scaffolds were more wettable and adsorbed more water than did chitosan alone. In static cell culture the thinner scaffold is better than the thicker one, and because of diffusion limitations in the scaffold, culture time must be within 3 weeks before transplantation to living tissues. Keratinocytes were co-cultured with fibroblasts in chitosan-gelatin scaffolds to construct an artificial bilayer skin in vitro. The artificial skin obtained was flexible and had good mechanical properties. Moreover, there was no contraction observed in the in vitro cell culture tests. The data from this study suggest that chitosan-gelatin scaffolds are suitable for skin tissue engineering goals.

Purpose This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy laser beam without the use of binders. Design/methodology/approach Selective laser sintering or melting (SLS/SLM) techniques are first introduced, followed by analysis of results from silica (SiO2), zirconia (ZrO2) and ceramic-reinforced metal matrix composites processed by direct laser sintering and melting. Findings At the current state of technology, it is still a challenge to fabricate dense ceramic components directly using SLS/SLM. Critical challenges encountered during direct laser melting of ceramic will be discussed, including deposition of ceramic powder layer, interaction between laser and powder particles, dynamic melting and consolidation mechanism of the process and the presence of residual stresses in ceramics processed via SLS/SLM. Originality/value Despite the challenges, SLS/SLM still has the potential in fabrication of ceramics. Additional research is needed to understand and establish the optimal interaction between the laser beam and ceramic powder bed for full density part fabrication. Looking into the future, other melting-based techniques for ceramic and composites are presented, along with their potential applications.

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Background: Significant amount of research, both experimental and numerical, has been conducted to study the mechanical behaviour of biodegradable polymer PL(L)A due to its wide range of applications. However, mechanical brittleness or poor elongation of PL(L)A has limited its applications considerably, particularly in the biomedical field. This study aims to study the potential in improving the ductility of PLA by blending with PBS in varied weight ratios. Methods: The preparation of PLA and PBS blends, with various weight ratios, was achieved by melting and mixing technique at high temperature using HAAKE™ Rheomix OS Mixer. Differential Scanning Calorimetry (DSC) was applied to investigate the melting behaviour, crystallization and miscibility of the blends. Small dog-bone specimens, produced by compression moulding, were used to test mechanical properties under uniaxial tension. Moreover, an advanced viscoplastic model with nonlinear hardening variables was applied to simulate ratedependent plastic deformation of PLA/PBS blends, with model parameters calibrated simultaneously against the tensile test data. Results: Optical Microscopy showed that PBS composition aid with the crystallization of PLA. The elongation of PLA/PBS blends increased with the increase of PBS content, but with a compromise of tensile modulus and strength. An increase of strain rate led to enhanced stress response, demonstrating the time-dependent deformation nature of the material. Model simulations of time-dependent plastic deformation for PLA/PBS blends compared well with experimental results. Conclusions: The crystallinity of PLA/PBS blends increased with the addition of PBS content. The brittleness of pure PLA can be improved by blending with ductile PBS using mechanical mixing technique, but with a loss of stiffness and strength. The tensile tests at different strain rates confirmed the time-dependent plastic deformation nature of the blends, i.e., viscoplasticity, which can be simulated by the Chaboche viscoplastic model with nonlinear hardening variables.

How to cite this article: Schiavone A, Qiu TY, Zhao LG. Crimping and deployment of metallic and polymeric stents --finite element modelling. Vessel Plus 2017;1:12-21.Aim: This paper aims to compare the mechanical performance of metallic (Xience) and bioresorbable polymeric (Elixir) stents during the process of crimping and deployment. Methods: Finite element software ABAQUS was used to create the geometrical models and meshes for the balloon, stent and diseased artery. To simulate the crimping of stents, 12 rigid plates were generated around the stent and subjected to radially enforced displacement. The deployment of both stents was simulated by applying internal pressure to the balloon, where hard contacts were defined between balloon, stent and diseased artery. Results: Elixir stent exhibited a lower expansion rate than Xience stent during deployment. The stent diameter achieved after balloon deflation was found smaller for Elixir stent due to higher recoiling. Lower level of stresses was found in the plaque and artery when expanded by Elixir stent. Reduced expansion, increased dogboning and decreased vessel stresses were obtained when considering the crimping-generated residual stresses in the simulations. Conclusion: There is a challenge for polymeric stents to match the mechanical performance of metallic stents. However, polymeric stents impose lower stresses to the artery system due to less property mismatch between polymers and arterial tissues, which could be clinically beneficial. Key words:Polymeric stents, metallic stents, finite element, crimping, deployment ABSTRACTArticle history:

A key feature contributing to the rapid economic development of China is the deregulation of the labour market and the dramatic growth in the use of informal employment. This paper reviews recent developments of informal employment in China and the role of institutional actors. It also examines the role of government policy and regulation in improving or worsening, directly and indirectly, the terms and conditions of those engaged in informal employment. The study contributes to the understanding of the situation of informal employment in China as one of the countries that contains the largest number and proportion, in relation to formal employment, of informal workers, not only in the semi-and manual skilled segment, but also increasingly extended to include highly educated workers, notably university graduates. It has implications for employment relations and social policy for foreign firms wishing to enter or already operating in China in terms of their human resource acquisition and management. The paper concludes that strong state intervention is necessary to uplift the employment prospect of workers in informal employment, particular in labour markets where workers hold weak bargaining power and are largely unorganised.

Extant studies of HRM and industrial relations in multinational corporations (MNCs) have focused primarily on MNCs from developed economies. Few studies have examined the investment strategy and labour management practices of MNCs from emerging economies, such as China, in developing countries like Vietnam. Adopting a combined theoretical framework for analysis, this study fills the research gap by examining the investment motives, business strategy and management practices of three case study firms in the construction and light manufacturing industries. It compares and contrasts the institutional supports for and barriers to these state-owned and privately owned firms from both home and host countries. The paper argues that the role of institutional actors differs across ownership forms and industrial sectors and that a multi-theoretical perspective, including in particular the political economy perspective, is needed to study Chinese MNCs' HRM practices in order to more fully understand how the practices are shaped and perceived. Key points1 Chinese multinational firms need political, cultural and social capital as well as other organizational resources to develop their operations overseas. 2 Actors in the global value chain and national governments play an important role in shaping Chinese firms' operational environment and management practices.