An in vitro experimental model to predict the mechanical behaviour of macroporous scaffolds implanted in articular cartilage

A model is proposed to assess mechanical behaviour of tissue engineering scaffolds and predict their performance in vivo during tissue regeneration. To simulate the growth of tissue inside the pores of the scaffold, the scaffold is swollen with a Poly (Vinyl alcohol) solution and subjected to repeated freezing and thawing cycles. In this way the Poly (Vinyl alcohol) becomes a gel whose stiffness increases with the number of freezing and thawing cycles. Mechanical properties of the construct immersed in water are shown to be determined, in large extent, by the water mobility constraints imposed by the gel filling the pores. This is similar to the way that water mobility determines mechanical properties of highly hydrated tissues, such as articular cartilage. As a consequence, the apparent elastic modulus of the scaffold in compression tests is much higher than those of the empty scaffold or the gel. Thus this experimental model allows assessing fatigue behaviour of the scaffolds under long-term dynamic loading in a realistic way, without recourse to animal experimentation.The UPV group acknowledges the support of the Spanish MICINN through project MAT2010-21611-C03-01. CIBER-BBN is an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program. CIBER Actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund. The authors thank the microscopy service of Universitat Politecnica de Valencia for useful help and advice and Ricardo Perez Feito for technical assistance in the experimental set up.Vikingsson, LKA.; Gallego Ferrer, G.; Gómez-Tejedor, JA.; Gómez Ribelles, JL. (2014). An in vitro experimental model to predict the mechanical behaviour of macroporous scaffolds implanted in articular cartilage. Journal of the Mechanical Behavior of Biomedical Materials. 32:125-131. https://doi.org/10.1016/j.jmbbm.2013.12.024S1251313

cAMP-Signalling Regulates Gametocyte-Infected Erythrocyte Deformability Required for Malaria Parasite Transmission.

Blocking Plasmodium falciparum transmission to mosquitoes has been designated a strategic objective in the global agenda of malaria elimination. Transmission is ensured by gametocyte-infected erythrocytes (GIE) that sequester in the bone marrow and at maturation are released into peripheral blood from where they are taken up during a mosquito blood meal. Release into the blood circulation is accompanied by an increase in GIE deformability that allows them to pass through the spleen. Here, we used a microsphere matrix to mimic splenic filtration and investigated the role of cAMP-signalling in regulating GIE deformability. We demonstrated that mature GIE deformability is dependent on reduced cAMP-signalling and on increased phosphodiesterase expression in stage V gametocytes, and that parasite cAMP-dependent kinase activity contributes to the stiffness of immature gametocytes. Importantly, pharmacological agents that raise cAMP levels in transmissible stage V gametocytes render them less deformable and hence less likely to circulate through the spleen. Therefore, phosphodiesterase inhibitors that raise cAMP levels in P. falciparum infected erythrocytes, such as sildenafil, represent new candidate drugs to block transmission of malaria parasites

Prediction of the in vivo mechanical behavior of biointegrable acrylic macroporous scaffolds

[EN] This study examines a biocompatible scaffold series of random copolymer networks P(EA-HEA) made of Ethyl Acrylate, EA, and 2-Hydroxyl Ethyl Acrylate, HEA. The P(EA-HEA) scaffolds have been synthesized with varying crosslinking density and filled with a Poly(Vinyl Alcohol), PVA, to mimic the growing cartilaginous tissue during tissue repair. In cartilage regeneration the scaffold needs to have sufficient mechanical properties to sustain the compression in the joint and, at the same time, transmit mechanical signals to the cells for chondrogenic differentiation. Mechanical tests show that the elastic modulus increases with increasing crosslinking density of P(EA-HEA) scaffolds. The water plays an important role in the mechanical behavior of the scaffold, but highly depends on the crosslinking density of the proper polymer. Furthermore, when the scaffold with hydrogel is tested it can be seen that the modulus increases with increasing hydrogel density. Even so, the mechanical properties are inferior than those of the scaffolds with water filling the pores. The hydrogel inside the pores of the scaffolds facilitates the expulsion of water during compression and lowers the mechanical modulus of the scaffold. The P(EA-HEA) with PVA shows to be a good artificial cartilage model with mechanical properties close to native articular cartilage.This work was funded by the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2013-46467-C4-1-R (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 are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund. The authors acknowledge the assistance and advice of Electron Microscopy Service of the UPV.Vikingsson, L.; Antolinos Turpín, CM.; Gómez-Tejedor, JA.; Gallego Ferrer, G.; Gómez Ribelles, JL. (2016). Prediction of the in vivo mechanical behavior of biointegrable acrylic macroporous scaffolds. Materials Science and Engineering: C. 61:651-658. https://doi.org/10.1016/j.msec.2015.12.068S6516586

An experimental fatigue study of a porous scaffold for the regeneration of articular cartilage

The aim of this experimental study is to predict the long-term mechanical behavior of a porous scaffold implanted in a cartilage defect for tissue engineering purpose. Fatigue studies were performed by up to 100,000 unconfined compression cycles in a polycaprolactone (PCL) scaffold with highly interconnected pores architecture. The scaffold compliance, stress strain response and hysteresis energy have been measured after different number of fatigue cycles, while the morphology has been observed by scanning electron microscopy at the same fatigue times. To simulate the growing tissue in the scaffold/tissue construct, the scaffold was filled with an aqueous solution of polyvinyl alcohol (PVA) and subjected to repeating cycles of freezing and thawing that increase the hydrogel stiffness. Fatigue studies show that the mechanical loading provokes failure of the dry scaffold at a smaller number of deformation cycles than when it is immersed in water, and also that 100,000 compressive dynamic cycles do not affect the scaffold/gel construct. This shows the stability of the scaffold implanted in a chondral defect and gives a realistic simulation of the mechanical performance from implantation of the empty scaffold to regeneration of the new tissue inside the scaffold's pores.This work was funded by the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2013-46467-C4-1-R (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. The authors acknowledge the assistance and advice of Electron Microscopy Service of the UPVVikingsson, LKA.; Gómez-Tejedor, JA.; Gallego Ferrer, G.; Gómez Ribelles, JL. (2015). An experimental fatigue study of a porous scaffold for the regeneration of articular cartilage. Journal of Biomechanics. 48(7):1310-1317. https://doi.org/10.1016/j.jbiomech.2015.02.013S1310131748

Computational methodology to determine fluid related parameters on non regular three-dimensional scaffolds

The application of three-dimensional (3D) biomaterials to facilitate the adhesion, proliferation, and differentiation of cells has been widely studied for tissue engineering purposes. The fabrication methods used to improve the mechanical response of the scaffold produce complex and non regular structures. Apart from the mechanical aspect, the fluid behavior in the inner part of the scaffold should also be considered. Parameters such as permeability (k) or wall shear stress (WSS) are important aspects in the provision of nutrients, the removal of metabolic waste products or the mechanically-induced differentiation of cells attached in the trabecular network of the scaffolds. Experimental measurements of these parameters are not available in all labs. However, fluid parameters should be known prior to other types of experiments. The present work compares an experimental study with a computational fluid dynamics (CFD) methodology to determine the related fluid parameters (k and WSS) of complex non regular poly(L-lactic acid) scaffolds based only on the treatment of microphotographic images obtained with a microCT (lCT). The CFD analysis shows similar tendencies and results with low relative difference compared to those of the experimental study, for high flow rates. For low flow rates the accuracy of this prediction reduces. The correlation between the computational and experimental results validates the robustness of the proposed methodology.The authors gratefully acknowledge research support from the Spanish Ministry of Science and Innovation through research project DPI2010-20399-C04-01. The Instituto de Salud Carlos III (ISCIII) through the CIBER initiative and the Platform for Biological Tissue Characterization of the Centro de Investigacion Biomedica en Red en Bioingenieria, Biomateriales y Nanomedicina (CIBER-BBN) are also gratefully acknowledged.Acosta Santamaría, VA.; Malvé, M.; Duizabo, A.; Mena Tobar, A.; Gallego Ferrer, G.; García Aznar, J.; Doblare Castellano, M.... (2013). Computational methodology to determine fluid related parameters on non regular three-dimensional scaffolds. Annals of Biomedical Engineering. 41(11):2367-2380. https://doi.org/10.1007/s10439-013-0849-8S236723804111Acosta Santamaría, V., H. Deplaine, D. Mariggió, A. R. Villanueva-Molines, J. M. García-Aznar, J. L. Gómez Ribelles, M. Doblaré, G. Gallego Ferrer, and I. Ochoa. Influence of the macro and micro-porous structure on the mechanical behavior of poly(l-lactic acid) scaffolds. J. Non-Cryst. Solids 358(23):3141–3149, 2012.Adachi, T., Y. Osako, M. Tanaka, M. Hojo, and S. J. Hollister. 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Improved regeneration of articular cartilage by human mesenchymal stem cells through osteoclasts and BMP2 signaling

Granero-Molto, F.; Ripalda-Cemborain, P.; Izal-Azcarate, I.; Crespo-Cullell, I.; Duart-Vicente, J.; Deplaine, H.; Gómez Ribelles, JL.... (2013). Improved regeneration of articular cartilage by human mesenchymal stem cells through osteoclasts and BMP2 signaling. Osteoarthritis and Cartilage. 21S:116-116. doi:10.1016/j.joca.2013.02.246S11611621