Tissue mimetic hyaluronan bioink containing collagen fibers with controlled orientation modulating cell migration and alignment.

Biofabrication is providing scientists and clinicians the ability to produce engineered tissues with desired shapes and gradients of composition and biological cues. Typical resolutions achieved with extrusion-based bioprinting are at the macroscopic level. However, for capturing the fibrillar nature of the extracellular matrix (ECM), it is necessary to arrange ECM components at smaller scales, down to the micron and the molecular level. Herein, we introduce a bioink containing the tyramine derivative of hyaluronan (HA; henceforth known as THA) and collagen (Col) type 1. In this bioink, similar to connective tissues, Col is present in the fibrillar form, and HA functions as a viscoelastic space filler. THA was enzymatically cross-linked under mild conditions allowing simultaneous Col fibrillogenesis, thus achieving a homogeneous distribution of Col fibrils within the viscoelastic HA-based matrix. The THA-Col composite displayed synergistic properties in terms of storage modulus and shear thinning, translating into good printability. Shear-induced alignment of the Col fibrils along the printing direction was achieved and quantified via immunofluorescence and second-harmonic generation. Cell-free and cell-laden constructs were printed and characterized, analyzing the influence of the controlled microscopic anisotropy on human bone marrow-derived mesenchymal stromal cell (hMSC) migration. Anisotropic HA-Col showed cell-instructive properties modulating hMSC adhesion, morphology, and migration from micropellets stimulated by the presence and the orientation of Col fibers. Actin filament staining showed that hMSCs embedded in aligned constructs displayed increased cytoskeleton alignment along the fibril direction. Based on gene expression of cartilage/bone markers and ECM production, hMSCs embedded in the isotropic bioink displayed chondrogenic differentiation comparable with standard pellet culture by means of proteoglycan production (safranin O staining and proteoglycan quantification). The possibility of printing matrix components with control over microscopic alignment brings biofabrication one step closer to capturing the complexity of native tissues.

Photoinduced chitosan-PEG hydrogels with long-term antibacterial properties.

Photochemical processes offer the possibility of preparing functional hydrogels under green conditions that are compatible with both synthetic and natural polymers. In this study, chitosan-based poly(ethylene) glycol (PEG) were successfully synthesized under light irradiation in aqueous medium. Kinetic studies under irradiation showed that less than 2 min were necessary to obtain fully cross-linked networks. Thermomechanical analyses and swelling experiments indicated that introduction of chitosan overall weakens the hydrogel network but can create domains of higher thermal stability than the PEG-alone structure. The resulting chitosan-PEG hydrogels demonstrated a tremendous inhibition (100%) of bacterial growth (Escherichia coli and Staphylococcus aureus). After 6 months' ageing, one of the hydrogels preserved a high antifouling activity against Escherichia coli. This interesting result, which could be correlated with the network features, demonstrates the strong potential of these photochemical methods to obtain robust bio-functional materials.

Eosin-mediated synthesis of polymer coatings combining photodynamic inactivation and antimicrobial properties.

Polymer coatings exhibiting photodynamic bacterial inactivation properties have been successfully engineered. Such coatings were obtained by photoinduced crosslinking of a PEG-diacrylate monomer associated with the eosin Y dye which was used as both a radical photoinitiator and an antibacterial agent. A dual curing process was followed by combining compatible and solvent-free polymerization mechanisms, i.e. Aza-Michael reaction and free-radical polymerization in the presence of amines. The kinetics evolution of the photopolymerization process was followed using in situ Fourier transform infrared spectroscopy, allowing for the elucidation of the underlying mechanistic pathways. The influence of eosin Y and amines on the thermal and mechanical properties of the films was evidenced and discussed in terms of crosslinking chemistry. The antibacterial properties of the coatings against two different strains (Escherichia coli and Staphylococcus aureus) were evaluated on short and long terms, revealing that eosin confers both photodynamic inactivation and antimicrobial properties to the films. These coatings are therefore particularly promising for disposable medical devices.

Dense fibrillar collagen matrices to analyse extracellular matrix receptor function.

AIM: The goal of this study was to understand whether dense fibrillar collagen matrices, with a hierarchical structure resembling native collagen matrices, could be useful to study collagen receptor function, in a more physiological context. The receptor analysed here was integrin α11ß1, already shown to be involved in cell attachment and migration on collagen-coated plastic, and also in contraction of loose fibrillar collagen hydrogels. MATERIALS AND METHODS: Collagen matrices prepared here corresponded to dense fibrillar hydrogels concentrated at 5mg/ml. The behaviour of α11ß1 deficient fibroblasts seeded on these concentrated matrices was assessed in terms of adhesion, morphology and migration, then compared to that observed on classical hydrogels at 1mg/ml, corresponding to loose collagen matrices. RESULTS: Short-term attachment assays showed disturbed interactions between α11ß1 deficient cells and collagen matrices in a concentration-dependent manner. Long-term assays revealed reduced cell spreading of alpha 11(-/-) cells on the dense collagen matrices, associated with a disturbed cytoskeleton network. Moreover, anoikis was observed when alpha 11(-/-) cells were seeded on 5mg/ml matrices, and not on looser 1mg/ml matrices. In scratch wound in vitro assays, carried out with cells on 5mg/ml fibrillar collagen matrices, alpha 11(-/-) cells migrated much better than their wild-type counterparts. In contrast, no significant difference was observed between wild and knock-out cells seeded on plastic. CONCLUSIONS: The present study demonstrates the validity of in vivo-like dense fibrillar collagen matrices to evaluate cell receptor functions more significantly than with 2D cell cultures or loose hydrogels.

[Importance of the post-prandial glycemia in the management of type 2 diabetes]. / Importance de la glycémie postprandiale dans la prise en charge du diabète de type 2.

Cardiovascular disease is the main cause of mortality in diabetic patients. The risk of cardiovascular disease occurs at a lower glycemic level compared to microvascular complications. Post-prandial hyperglycemia seems to play a major role in the development of atherosclerotic lesions. In this article we review the evidence regarding the prognostic value of post-challenge hyperglycaemia relative to the risk of cardiovascular disease, explore the physio-pathologic mechanisms responsible for the negative effects of post-prandial hyperglycaemia and detail the benefits of treatment aimed at controlling post-prandial glycaemia.

A specific beta 3-adrenoceptor agonist induces increased pancreatic islet blood flow and insulin secretion in rats.

In order to study the role of beta 3-adrenoceptor stimulation on insulin secretion in rats, plasma insulin level and islet blood flow were measured during treatment with CL 316243 which is chemically named disodium (R,R)-5-[2-[[2,3-(3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]-1, 3-benzodioxole-2,2-dicarboxylate, a specific beta 3-adrenoceptor agonist. CL 316243 induced a marked increase in both islet blood flow and plasma insulin concentration without changes in whole pancreatic blood flow. This increase was totally prevented when the rats were pretreated with bupranolol, a beta 1, beta 2, beta 3-adrenoceptor antagonist, but not with nadolol, a beta 1, beta 2-adrenoceptor antagonist. We conclude that beta 3-adrenoceptor stimulation provokes a marked vasodilatation of microvessels in the islets of Langerhans, which in turn could contribute to the increase in insulin secretion.