The effect of vibrations on Marangoni convection and melt mixing during crystal growing by the Czochralski method

Vibrational melt flows in Czochralski crystal growth are investigated numerically on the basis of unsteady Navier-Stokes-Boussinesq formulation for incompressible fluid. The finite element code ASTRA is used for calculations. It is found that the vibrations provide much more effective mixing of the melt flow compared to the rotation of the crystal and the crucible. Numerical modeling indicates the existence of standing vibrational waves on the free melt surface. It is demonstrated that the vibrations can be used to weaken and to compensate the influence of the thermo-capillary Marangoni convection for normal and microgravity environments.Comment: 14 pages, 7 figures, 10 referencie

In vitro mechanical fatigue behavior of poly-ε-caprolactone macroporous scaffolds for cartilage tissue engineering: Influence of pore filling by a poly(vinyl alcohol) gel

Polymeric scaffolds used in regenerative therapies are implanted in the damaged tissue and subjected to repeated loading cycles. In the case of articular cartilage engineering, an implanted scaffold is typically subjected to long term dynamic compression. The evolution of the mechanical properties of the scaffold during bioresorption has been deeply studied in the past, but the possibility of failure due to mechanical fatigue has not been properly addressed. Nevertheless, the macroporous scaffold is susceptible to failure after repeated loading-unloading cycles. In this work fatigue studies of polycaprolactone scaffolds were carried by subjecting the scaffold to repeated compression cycles in conditions simulating the scaffold implanted in the articular cartilage. The behaviour of the polycaprolactone sponge with the pores filled with a poly(vinyl alcohol) gel simulating the new formed tissue within the pores was compared with that of the material immersed in water. Results were analyzed with Morrow’s criteria for failure and accurate fittings are obtained just up to 200 loading cycles. It is also shown that the presence of poly(vinyl alcohol) increases the elastic modulus of the scaffolds, the effect being more pronounced with increasing the number of freeze/thawing cycles.This work is funded by FEDER funds through the "Programa Operacional Fatores de Competitividade – COMPETE" and by national funds arranged by FCT- Fundação para a Ciência e a Tecnologia, project reference PEST-C/FIS/UI607/2011. The authors also thank funding from Matepro –Optimizing Materials and Processes”, ref. NORTE-07-0124-FEDER000037”, co-funded by the “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte), under the “Quadro de Referência Estratégico Nacional” (QREN), through the “Fundo Europeu de Desenvolvimento Regional” (FEDER). The authors also thank support from the COST Action MP1206 “Electrospun Nano-fibres for bio inspired composite materials and innovative industrial applications” and MP1301 “New Generation Biomimetic and Customized Implants for Bone Engineering”. JAP and VS thank the FCT for the SFRH/BD/64586/2009 and SFRH/BPD/63148/2009 grants, respectively. JLGR acknowledge the support of the Spanish Ministry of Science and Innovation through project No. MAT2010-21611-C03-01 (including the FEDER financial support). CIBER-BBN is an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions and financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund

Fatigue prediction in fibrin poly-ε-caprolactone macroporous scaffolds

Tissue engineering applications rely on scaffolds that during its service life, either for in-vivo or in vitro applications, are under loading. The variation of the mechanical condition of the scaffold is strongly relevant for cell culture and has scarcely been addressed. The fatigue life cycle of poly-ε-caprolactone, PCL, scaffolds with and without fibrin as filler of the pore structure were characterized both dry and immersed in liquid water. It is observed that the there is a strong increase from 100 to 500 in the number of loading cycles before collapse in the samples tested in immersed conditions due to the more uniform stress distributions within the samples, the fibrin loading playing a minor role in the mechanical performance of the scaffolds.This work is funded by FEDER funds through the "Programa Operacional Factores de Competitividade – COMPETE" and by national funds arranged by FCT- Fundação para a Ciência e Tecnologia, project references NANO/NMed-SD/0156/2007, PTDC/CTM-NAN/112574/2009 and PEST-C/FIS/UI607/2011. The authors also thank funding from Matepro –Optimizing Materials and Processes”, ref. NORTE-07-0124-FEDER-000037”, co-funded by the “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte), under the “Quadro de Referência Estratégico Nacional” (QREN), through the “Fundo Europeu de Desenvolvimento Regional” (FEDER). JAP and VS thank the FCT for the SFRH/BD/64586/2009/ and SFRH/BPD/63148/2009 grants, respectively. JLGR acknowledge the support of the Spanish Ministry of Science and Innovation through project No. MAT2010-21611-C03-01 (including the FEDER financial support). CIBER-BBN is an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions and financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund