Polyol-based soft hydrogels for biorecognition and tissue engineering applications

The need for new designs of biomaterials for existing challenges in biomedical applications has led to the fabrication of three different polymeric hydrogels using dendritic polyglycerol and polyethylene glycol. These polymers were used for their bio-inertness, the possibility of a large varieties of functionalization and the ability to adapt the mechanical properties of the resulting material to the desired applications. In the first project, the aim was to build a bioactive material specific for antibody detection where specific peptides were immobilized in the matrix as capture ligands. The challenge was to immobilize these molecules of recognition without altering their biological functions, without any change of conformation nor denaturation and without any leaching out of the system overtime. The easy and fast crosslinking biorthogonal approach to build the hydrogels was therefore well suited for the biosensing applications since they were also customizable to the desired application. The main reason for the use of hydrogels was to enhance the capability of 3D structures to improve biosensing strategies in terms of sensitivity, high loading capacity, and stability of the biomolecules, which prevents errors in the sensing method. Another aspect was the possibility of miniaturization of the system by using, for example, microarrays. All these aspects lack in existing 2D systems, which are however used in current biosensors. The strategy was thus to improve these existing 2D systems by using the advantages offered by a 3D hydrogel approach. To predict the biosensing ability of our systems, we first characterized in depth the hydrogels in nano- and micro-scales, varying the molecular weights of the linkers. The linkers would influence the mechanical properties and morphology of the hydrogel networks. Regarding the physical properties of the networks, a remarkable swelling of the hydrogels (up to 100 their dry weight) was reached with an increasing swelling as a function of the molecular weights of the linkers. For the biosensing characterization, we obtained a specific and selective detection. Besides, a higher loading capacity was obtained with seven times higher than the one of 2D arrays. The sensitivity increased by 20% compared to the 2D detection method, the obtained limit of detection being 27 pg/mL. In the second project, we proposed a patterned soft nanocomposite hydrogel as a soft cell culture scaffold. Directing stem cells to a specific lineage and keeping their pluripotency is challenging. And yet, in soft tissue engineering, soft tissue reconstruction to restore deficient tissues underneath the skin remains a hard endeavor. Recent studies have shown that culturing hMSCs on typical TCPS or glass (hard substrates) has damaged the intrinsic function of these cells which has led to loss of stemness as the number of passages increased. In addition, they lost their adipogenesis differentiation potential. Stemness is defined as the mechano-sensing ability, immunophenotyping, and differentiation potential of a cell. To retain these properties of the stem cell, we produced a tissue mimicking cell responsive platform by tuning the mechanical, biological, and morphological characteristics of the nanocomposite fabricated in a biorthogonal click strategy and Au-S chemistry. We obtained nanocomposites with stiffness in the range of liver tissues (elastic moduli < 2 kPa). To correctly predict the effect of the matrix on hMSCs, we studied their mechanical properties as a function of two different molecular weights of PEG linkers. The locomotion of hMSCs was first investigated on two different surfaces with patterns (wrinkles or creases) and the strong attachment of the cells on the nanocomposites was assessed. Stemness and differentiation potential were observed with an influence of the mechanical characteristics and the presence of adhesive peptides (RGD) and their spatial organization. We hypothesized that such system would influence the cells’ behavior and morphology. In addition, they would keep their stemness compared to on bare TCPS or glass (hard surfaces). The studies have shown that a cell culture on these hydrogels preserved the immunophenotyping and mechano-sensibility of the hMSCs but lost on hard surfaces. This suggested that these polymeric networks had a positive influence on the hMSCs’ fate by keeping their pluripotency. Finally, the soft substrates allowed exclusively the differentiation into a specific lineage, yielding adipocytes. In the third project, a hybrid hydrogel has been established using both inorganic and organic materials to produce a nanocomposite. The hydrogel was virus responsive giving a double response, both an optical and a mechanical response to Influenza virus. We combined the use of gold nanoparticles for their optical properties, polysaccharides (sialic acid) for their specificity to Influenza virus and polyols for their ability to produce a highly swellable hydrogel. Besides the unique optical properties of gold nanoparticles displaying a color change visible by naked eyes, they also offer the possibility to anchor multiple molecules and biomolecules preventing at the same time any leaching out of the network and a better stability. The polyols (polyethylene glycol and dendritic polyglycerol) produced a bio-orthogonal hydrogel by strain-promoted azide-alkyne cycloaddition, which represents a suitable environment for biospecies by preventing their denaturation and any unspecific interaction. In addition, to enhance the specificity of the system, we used a bioimprinting procedure and used the virus as a template to create specific recognition sites. Specific recognition of macro-biomolecules such as virus represents a challenge and a responsive system giving a double response to viruses is unique to this date. We present here a proof-of-principle that any virus and more generally any multivalent molecule can be recognized in a responsive polymer network by responding with a color change and shrinkage detectable by eyes. Given the specific molecules and imprint technique, these hydrogel features make it a customizable network for the desired application

Interaction of human mesenchymal stem cells with soft nanocomposite hydrogels based on polyethylene glycol and dendritic polyglycerol

Keeping the stemness of human mesenchymal stem cells (hMSCs) and their adipocyte differentiation potential is critical for clinical use. However, these features are lost on traditional substrates. hMSCs have often been studied on stiff materials whereas culturing hMSCs in their native niche increases their potential. Herein, a patterned hydrogel nanocomposite with the stiffness of liver tissues is obtained without any molding process. To investigate hMSCs' mechanoresponse to the material, the RGD spacing units and the stiffness of the hydrogels are dually tuned via the linker length. This work suggests that hMSCs' locomotion is influenced by the nature of the hydrogel layer (bulk or thin film). Contrary to on bulk surfaces, cell traction occurs during cell spreading on thin films. In addition, hMSCs' spreading behavior varies from shorter to longer linker‐based hydrogels, where on both surfaces hMSCs maintains their stemness as well as their adipogenic differentiation potential with a higher number of adipocytes for nanocomposites with a longer polymer linker. Overall, this work addresses the need for a new alternative for hMSCs culture allowing the cells to differentiate exclusively into adipocytes. This material represents a cell‐responsive platform with a tissue‐mimicking architecture given by the mechanical and morphological properties of the hydrogel