A Combination of the Natural Molecules Gallic Acid and Carvacrol Eradicates P. aeruginosa and S. aureus Mature Biofilms.

Wound infection, especially the development of bacterial biofilms, delays wound healing and is a major public health concern. Bacteria in biofilms are more tolerant to antimicrobial agents, and new treatments to eradicate mature biofilms are needed. Combining antimicrobial molecules with different mechanisms of action is an attractive strategy to tackle the heterogeneous nature of microbial communities in biofilms. This study focused on three molecules of natural origin: gallic acid (G), carvacrol (K) and curcumin (Q). Their abilities, individually or in combination, to eradicate biofilms were quantified on mono- and dual-species mature biofilms of Pseudomonas aeruginosa and Staphylococcus aureus, the strains most commonly found in infected wounds. G presented biofilm eradicating activity on P. aeruginosa, whereas K had biofilm eradicating activity on S. aureus and P. aeruginosa. Q had no potent biofilm eradicating activity. The combination of G and K increased the effects previously observed on P. aeruginosa biofilm and led to complete eradication of S. aureus biofilm. This combination was also efficient in eradicating a dual-species biofilm of S. aureus and P. aeruginosa. This work demonstrates that K and G used in combination have a strong and synergistic eradicating activity on both mono- and dual-species mature biofilms of S. aureus and P. aeruginosa and may therefore represent an efficient alternative for the treatment of biofilms in wounds.

An Alginate-Based Hydrogel with a High Angiogenic Capacity and a High Osteogenic Potential.

In bone tissue engineering, autologous cells are combined with osteoconductive scaffolds and implanted into bone defects. The major challenge is the lack of post-implantation vascular growth into biomaterial. The objective of the present study was to develop a new alginate-based hydrogel that enhances the regeneration of bone defects after surgery. The viability of human bone marrow-derived mesenchymal stem cells (BM-MSCs) or human endothelial cells (ECs) cultured alone or together on the hydrogel was analyzed for 24 and 96 h. After seeding, the cells self-assembled and aggregated to form clusters. For functional validation, empty or cellularized hydrogel matrices were implanted ectopically at subcutaneous sites in nude mice. After 2 months, the matrices were explanted. Transplanted human cells were present, and we observed vessels expressing human von Willebrand factor (resulting from the incorporation of transplanted ECs into neovessels and/or the differentiation of BM-MSCs into ECs). The addition of BM-MSCs improved host vascularization and neovessel formation from human cells, relative to ECs alone. Although we did not observe bone formation, the transplanted BM-MSCs were able to differentiate into osteoblasts. This new biomaterial provided an appropriate three-dimensional environment for transplanted cells and has a high angiogenic capacity and an osteogenic potential.

Functional Validation of a New Alginate-based Hydrogel Scaffold Combined with Mesenchymal Stem Cells in a Rat Hard Palate Cleft Model.

BACKGROUND: One of the major difficulties in cleft palate repair is the requirement for several surgical procedures and autologous bone grafting to form a bony bridge across the cleft defect. Engineered tissue, composed of a biomaterial scaffold and multipotent stem cells, may be a useful alternative for minimizing the non-negligible risk of donor site morbidity. The present study was designed to confirm the healing and osteogenic properties of a novel alginate-based hydrogel in palate repair. METHODS: Matrix constructs, seeded with allogeneic bone marrow-derived mesenchymal stem cells (BM-MSCs) or not, were incorporated into a surgically created, critical-sized cleft palate defect in the rat. Control with no scaffold was also tested. Bone formation was assessed using microcomputed tomography at weeks 2, 4, 8, and 12 and a histologic analysis at week 12. RESULTS: At 12 weeks, the proportion of bone filling associated with the use of hydrogel scaffold alone did not differ significantly from the values observed in the scaffold-free experiment (61.01% ± 5.288% versus 36.91% ± 5.132%; p = 0.1620). The addition of BM-MSCs stimulated bone formation not only at the margin of the defect but also in the center of the implant. CONCLUSIONS: In a relevant in vivo model of cleft palate in the rat, we confirmed the alginate-based hydrogel's biocompatibility and real advantages for tissue healing. Addition of BM-MSCs stimulated bone formation in the center of the implant, demonstrating the new biomaterial's potential for use as a bone substitute grafting material for cleft palate repair.

Processing and antibacterial properties of chitosan-coated alginate fibers.

The preparation of chitosan-coated alginate fibers by a wet spin process is presented and the characterization of the antibacterial activities of these fibers is discussed. Preformed calcium alginate fibers were passed in chitosan acetate solutions. The coagulation method of the coating consisted in the immersion of fibers in a bath of calcium dihydroxide solution (0.1 M). The antibacterial evaluation was achieved by a CFU (Colony-Forming Units) counting method after 6 h of incubation at 37 °C. The incorporation of chitosan on calcium alginate fibers brings antibacterial activities against Staphylococcus epidermidis, Escherichia coli and various Staphylococcus aureus strains namely MSSA (Methicillin Sensitive Staphylococcus aureus), CA-MRSA (Community Associated Methicillin Resistant Staphylococcus aureus) and HA-MRSA (Healthcare Associated Methicillin Resistant Staphylococcus aureus) which make these chitosan-coated fibers potential candidates for wound dressing materials. Developing a wound dressing with the haemostatic and healing properties of alginate combined with antibacterial properties of chitosan is envisioned for fighting against the infections and more particularly nosocomial diseases.

Characterization of insoluble calcium alginates by solid-state NMR.

Three series of 9 insoluble calcium alginate powders with different average calcium contents (1.5, 3.5 and 8%, w/w) are investigated by means of 13C solid-state NMR spectroscopy. The effect of the increased calcium content on the determination of the mannuronate (M) to guluronate (G) ratio from spectral deconvolution of the 13C CP/MAS spectra is discussed, and the variations observed are commented in function of possible structural modifications related to the interaction with the divalent cations. The possibility of using solid-state NMR spectroscopy for the quantification of the calcium content in unknown alginate samples is explored performing principal component analysis (PCA) of the spectra. The results obtained show that a clear separation of alginates with slightly different calcium content is possible. The proposed method relies on the sole use of the chemical shifts of the signals corresponding to pyranose carbons, suggesting that PCA of solid-state NMR data holds promises as a rapid and undestructive method for screening the calcium content of alginate-based materials with biomedical uses.

High-resolution nuclear magnetic resonance spectroscopy studies of polysaccharides crosslinked by sodium trimetaphosphate: a proposal for the reaction mechanism.

An NMR spectroscopy study ((31)P, (1)H, (13)C) of the postulated crosslinking mechanism of sodium trimetaphosphate (STMP) on polysaccharides is reported using methyl alpha-D-glucopyranoside as a model. In a first step, reaction of STMP with Glc-OMe gives grafted sodium tripolyphosphate (STPP(g)). On the one hand, STTP(g) can react with a second alcohol functionality to give a crosslinked monophosphate. On the other hand, a monophosphate (grafted phosphate) could be obtained by alkaline degradation of STPP(g). NMR spectroscopy allows to detect the various species formed and to obtain the crosslinking density of STMP-polysaccharides hydrogels.