Cell supports based on electroactive materials, that generate electrical signal variations as a response to mechanical deformations and vice-versa, are gaining increasing attention for tissue engineering applications. In particular, poly(vinylidene fluoride), PVDF, has been proven to be suitable for these applications in the form of films and two-dimensional membranes. In this work, several strategies have been implemented in order to develop PVDF three-dimensional scaffolds. Three processing methods, including solvent casting with particulate leaching and three-dimensional nylon, and freeze extraction with poly(vinyl alcohol) templates are presented in order to obtain three-dimensional scaffolds with different architectures and interconnected porosity. Further, it is shown that the scaffolds are in the electroactive β-phase and show a crystallinity degree of ~ 45%. Finally, quasi-static mechanical measurements showed that an increase of the porous size within the scaffold leads to a tensile strengths and the Young's modulus decrease, allowing tuning scaffold properties for specific tissues.

ElsevierVikingsson, LKA.; Claessens, B.; Gómez Tejedor, JA.; Gallego Ferrer, G.; Gómez Ribelles, JL. (2015). Relationship between micro-porosity, water permeability and mechanical behavior in scaffolds for cartilage engineering. that the stress response of the scaffold/hydrogel construct is a synergic effect from the performance of each of the components. This is interesting since it predicts that the in vivo outcome of the scaffold is not only depending on the material architecture but also the growing tissue inside the scaffolds pores. On the other hand, the confined compression results show that the compliance of the scaffold is mainly controlled by the micro porosity of the scaffold and less by the hydrogel density in the scaffold pores. These conclusions bring together valuable information for customizing the optimal scaffold and to predict the in vivo mechanical behavior.

ElsevierVallés Lluch, A.; Arnal Pastor, MP.; Martínez Ramos, C.; Vilariño Feltrer, G.; Vikingsson, L.; Castells Sala, C.; Semino, CE.... (2013). Combining self-assembling peptide gels with three-dimensional elastomer scaffolds. Acta Biomaterialia. 9 (12) Abstract: Some of the problems raised by the combination of porous scaffolds and self-assembling peptide (SAP) gels as constructs for tissue engineering applications are for the first time addressed. Scaffolds of poly(ethyl acrylate) and the SAP gel RAD16-I were employed. The in situ gelation of the SAP gel inside the pores of the scaffolds was studied. The scaffold-cum-gel constructs were characterized morphologically, physico-chemically and mechanically. The possibility of incorporating an active molecule (bovine serum albumin, taken here as a model molecule for others) in the gel within the scaffold's pores was assessed, and the kinetics of its release in PBS was followed. Cell seeding and colonization of these constructs was preliminary studied with L929 fibroblasts and checked afterwards with sheep adipose-tissue derived stem cells (ASCs) intended for further preclinical studies. Static (conventional) and dynamically assisted seedings were compared for bare scaffolds and the scaffoldcum-gel constructs. The SAP gel inside the pores of the scaffold significantly improved the uniformity and density of cell colonization of the 3D structure. These constructs could be of use in different advanced tissue engineering applications where, apart from a cell-friendly ECM-like aqueous environment, a larger-scale three-dimensional structure able to keep the cells in a specific place, give mechanical support and/or conduct spatially the tissue growth could be required. COMBINING SELF-ASSEMBLING PEPTIDE GELS WITH 3D ELASTOMER SCAFFOLDSA. AbstractSome of the problems raised by the combination of porous scaffolds and selfassembling peptide (SAP) gels as constructs for tissue engineering applications are for the first time addressed. Scaffolds of poly(ethyl acrylate) and the SAP gel RAD16-I were employed. The in situ gelation of the SAP gel inside the pores of the scaffolds was studied. The scaffold-cum-gel constructs were characterized morphologically, physicochemically and mechanically. The possibility of incorporating an active molecule (bovine serum albumin, taken here as a model molecule for others) in the gel within the scaffold's pores was assessed, and the kinetics of its release in PBS was followed. Cell intended for further preclinical studies. Static (conventional) and dynamically assisted seedings were compared for bare scaffolds and the scaffold-cum-gel constructs. The SAP gel inside the pores of the scaffold significantly improved the uniformity and density of cell colonization of the 3D structure. These constructs could be of use in different advanced tissue engineering applications where, apart from a cell-friendly ECM-like aqueous environment, a larger-scale three-dimensional structure able to keep the cells in a specific place, give mechanical support and/o...

Tissue engineering applications rely on scaffolds that during its service life, either for in-vivo or in vitro applications, are under mechanical solicitations. The variation of the mechanical condition of the scaffold is strongly relevant for cell culture and has been scarcely addressed.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.

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. L. Vikingsson, et al., J Mech Behav Biomed 32 (2014) 125-131 2

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.

press-fit technique in a cartilage defect after microfracture surgery in the femoral condyle of the knee joint of the sheep and histologic and mechanical evaluation was done 4.5 months later. The first group consists of a biodegradable Polycaprolactone, PCL, scaffold with double porosity. The second test group consists of a PCL scaffold attached to a Poly(L-lactic acid), PLLA, pin anchored to the subchondral bone. Results: For both groups most of the defects (75%) exhibited the articular surface completely or almost completely repaired with a neotissue. Nevertheless, the surface had a rougher appearance than controls and the repair tissue was immature. In the trials with solely scaffold implantation, severe subchondral bone alterations were seen with many large nodular formations. These alterations were ameliorated when implanting the scaffold with a subchondral bone anchoring pin. Discussion: The results show that tissue repair is improved by implanting a PCL scaffold compared to solely microfracture surgery, and most importantly, that subchondral bone alterations, normally seen after microfracture surgery, were partially prevented when implanting the PCL scaffold with a fixation system to the subchondral bone.

In vitro mechanical fatigue behavior of poly-ɛ-caprolactone macroporous scaffolds for cartilage tissue engineering: Influence of pore filling by a poly(vinyl alcohol) gel AbstractPolymeric scaffolds used in regenerative therapies are implanted in the damaged tissue and submitted 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 behavior 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. AbstractPolymeric scaffolds used in regenerative therapies are implanted in the damaged tissue and submitted 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 2 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.