Elaboration and evaluation of alginate foam scaffolds for soft tissue engineering.

Controlling microarchitecture in polymer scaffolds is a priority in material design for soft tissue applications. This paper reports for the first time the elaboration of alginate foam-based scaffolds for mesenchymal stem cell (MSC) delivery and a comparative study of various surfactants on the final device performance. The use of surfactants permitted to obtain highly interconnected porous scaffolds with tunable pore size on surface and in cross-section. Their mechanical properties in compression appeared to be adapted to soft tissue engineering. Scaffold structures could sustain MSC proliferation over 14 days. Paracrine activity of scaffold-seeded MSCs varied with the scaffold structure and growth factors release was globally improved in comparison with control alginate scaffolds. Our results provide evidence that exploiting different surfactant types for alginate foam preparation could be an original method to obtain biocompatible scaffolds with tunable architecture for soft tissue engineering.

Optimization of Injectable Thermosensitive Scaffolds with Enhanced Mechanical Properties for Cell Therapy.

Strong injectable chitosan thermosensitive hydrogels can be created, without chemical modification, by combining sodium hydrogen carbonate with another weak base, namely, beta-glycerophosphate (BGP) or phosphate buffer (PB). Here the influence of gelling agent concentration on the mechanical properties, gelation kinetics, osmolality, swelling, and compatibility for cell encapsulation, is studied in order to find the most optimal formulations and demonstrate their potential for cell therapy and tissue engineering. The new formulations present up to a 50-fold increase of the Young's modulus after gelation compared with conventional chitosan-BGP hydrogels, while reducing the ionic strength to the level of iso-osmolality. Increasing PB concentration accelerates gelation but reduces the mechanical properties. Increasing BGP also has this effect, but to a lesser extent. Cells can be easily encapsulated by mixing the cell suspension within the hydrogel solution at room temperature, prior to rapid gelation at body temperature. After encapsulation, L929 mouse fibroblasts are homogeneously distributed within scaffolds and present a strongly increased viability and growth, when compared with conventional chitosan-BGP hydrogels. Two particularly promising formulations are evaluated with human mesenchymal stem cells. Their viability and metabolic activity are maintained over 7 d in vitro.

Validation and application of a nondestructive and contactless method for rheological evaluation of biomaterials.

Hydrogels are extensively used for tissue engineering, cell therapy or controlled release of bioactive factors. Nondestructive techniques that can follow their viscoelastic properties during polymerization, remodeling, and degradation are needed, since these properties are determinant for their in vivo efficiency. In this work, we proposed the viscoelastic testing of bilayered materials (VeTBiM) as a new method for nondestructive and contact-less mechanical characterization of soft materials. The VeTBiM method measures the dynamic displacement response of a material, to a low amplitude vibration in order to characterize its viscoelastic properties. We validated VeTBiM by comparing data obtained on various agar and chitosan hydrogels with data from rotational rheometry, and compression tests. We then investigated its potential to follow the mechanical properties of chitosan hydrogels during gelation and in the presence of papain and lysozyme that induce fast or slow enzymatic degradation. Due to this nondestructive and contactless approach, samples can be removed from the instrument and stored in different conditions between measurements. VeTBiM is well adapted to follow biomaterials alone or with cells, over long periods of time. This new method will help in the fine tuning of the mechanical properties of biomaterials used for cell therapy and tissue engineering. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2565-2573, 2017.

Chitosan thermogels for local expansion and delivery of tumor-specific T lymphocytes towards enhanced cancer immunotherapies.

The success of promising anti-cancer adoptive cell therapies relies on the abilities of the perfused CD8(+) T lymphocytes to gain access to and persist within the tumor microenvironment to carry out their cytotoxic functions. We propose a new method for their local delivery as a living concentrate, which may not only reduce the numbers of cells required for treatment but also enhance their site-specific mobilization. Using combinations of sodium hydrogen carbonate and phosphate buffer as gelling agents, novel injectable chitosan-based biocompatible thermogels (CTGels) having excellent mechanical properties and cytocompatibility have been developed. Three thermogel formulations with acceptable physicochemical properties, such as physiological pH and osmolality, macroporosity, and gelation rates were compared. The CTGel2 formulation outperformed the others by providing an environment suitable for the encapsulation of viable CD8(+) T lymphocytes, supporting their proliferation and gradual release. In addition, the encapsulated T cell phenotypes were influenced by surrounding conditions and by tumor cells, while maintaining their capacity to kill tumor cells. This strongly suggests that cells encapsulated in this formulation retain their anti-cancer functions, and that this locally injectable hydrogel may be further developed to complement a wide variety of existing immunotherapies.

Evaluation of polyelectrolyte complex-based scaffolds for mesenchymal stem cell therapy in cardiac ischemia treatment.

Three-dimensional (3D) scaffolds hold great potential for stem cell-based therapies. Indeed, recent results have shown that biomimetic scaffolds may enhance cell survival and promote an increase in the concentration of therapeutic cells at the injury site. The aim of this work was to engineer an original polymeric scaffold based on the respective beneficial effects of alginate and chitosan. Formulations were made from various alginate/chitosan ratios to form opposite-charge polyelectrolyte complexes (PECs). After freeze-drying, the resultant matrices presented a highly interconnected porous microstructure and mechanical properties suitable for cell culture. In vitro evaluation demonstrated their compatibility with mesenchymal stell cell (MSC) proliferation and their ability to maintain paracrine activity. Finally, the in vivo performance of seeded 3D PEC scaffolds with a polymeric ratio of 40/60 was evaluated after an acute myocardial infarction provoked in a rat model. Evaluation of cardiac function showed a significant increase in the ejection fraction, improved neovascularization, attenuated fibrosis as well as less left ventricular dilatation as compared to an animal control group. These results provide evidence that 3D PEC scaffolds prepared from alginate and chitosan offer an efficient environment for 3D culturing of MSCs and represent an innovative solution for tissue engineering.

Alginate scaffolds for mesenchymal stem cell cardiac therapy: influence of alginate composition.

Despite the success of alginate scaffolds and mesenchymal stem cells (MSCs) therapy in cardiac failure treatment, the impact of the physicochemical environment provided by alginate matrices on cell behavior has never been investigated. The purpose of this work was double: to determine the alginate composition influence on (1) encapsulated rat MSC viability, paracrine activity, and phenotype in vitro and (2) cardiac implantability and in vivo biocompatibility of patch shape scaffolds. Two alginates, differing in composition and thus presenting different mechanical properties when hydrogels, were characterized. In both cases, encapsulated MSC viability was maintained at around 75%, and their secretion characteristics were retained 28 days postencapsulation. In vivo study revealed a high cardiac compatibility of the tested alginates: cardiac parameters were maintained, and rats did not present any sign of infection. Moreover, explanted hydrogels appeared surrounded by a vascularized tissue. However, scaffold implantability was highly dependent on alginate composition. G-type alginate patches, presenting higher elastic and Young moduli than M-type alginate patches, showed a better implantation easiness and were the only ones that maintained their shape and morphology in vivo. As a consequence of alginate chemical composition and resulting hydrogel structuration, G-type alginate hydrogels appear to be more adapted for cardiac implantation.