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Since their first description nearly 20 years ago, dense collagen hydrogels obtained by plastic compression have become popular scaffolds in tissue engineering. In particular, when seeded with dental pulp stem cells, they have demonstrated a great in vivo potential in cranial bone repair. Here, we investigated how physico-chemical and cell-seeding conditions could influence the formation and in vitro mineralization of these cellularized scaffolds. A qualitative assessment demonstrated that the gel stability before and after compression was highly sensitive to the conditions of fibrillogenesis, especially initial acid acetic and buffer concentrations. Gels with similar rheological properties but different fibrillar structures that exhibited different stabilities when used for the 3D culture of Stem cells from Human Exfoliated Deciduous teeth (SHEDs) could be prepared. Finally, in our optimal physico-chemical conditions, mineralization could be achieved only using human dental pulp stem cells (hDPSCs) at a high cell density. These results highlight the key role of fibrillogenic conditions and cell type/density on the bone repair potential of cell-laden plastically compressed collagen hydrogels. [ABSTRACT FROM AUTHOR]

Dense collagen hydrogels are promising biomaterials for several tissue-engineering applications. They exhibit high mechanical properties, similar to physiological extracellular matrices, and do not shrink under cellular activity. However, they suffer from several drawbacks, such as weak nutrient and O2 diffusion, impacting cell survival. Here, we report a novel strategy to create a perfusion system within dense and thick collagen hydrogels to promote cell viability. The 3D printing of a thermoplastic filament (high-impact polystyrene, HIPS) with a three-wave shape is used to produce an appropriate sacrificial matrix. The HIPS thermoplastic polymer allows for good shape fidelity of the filament and does not collapse under the mechanical load of the collagen solution. After the collagen gels around the filament and dissolves, a channel is generated, allowing for adequate and rapid hydrogel perfusion. The dissolution process does not alter the collagen hydrogel's physical or chemical properties, and the perfusion is associated with an increased fibroblast survival. Here, we report the novel utilization of thermoplastics to generate a perfusion network within biomimetic collagen hydrogels. [ABSTRACT FROM AUTHOR]

Associating collagen with biodegradable hydrophobic polyesters constitutes a promising method for the design of medicated biomaterials. Current collagen‐polyester composite hydrogels consisting of pre‐formed polymeric particles encapsulated within a low concentrated collagen hydrogel suffer from poor physical properties and low drug loading. Herein, an amphiphilic composite platform associating dense collagen hydrogels and up to 50 wt% polyesters with different hydrophobicity and chain length is developed. An original method of fabrication is disclosed based on in situ nanoprecipitation of polyesters impregnated in a pre‐formed 3D dense collagen network. Composites made of poly(lactic‐co‐glycolic acid) (PLGA) and poly(lactic acid) (PLA) but not polycaprolactone (PCL) exhibit improved mechanical properties compared to those of pure collagen dense hydrogels while keeping a high degree of hydration. Release kinetics of spironolactone, a lipophilic steroid used as a drug model, can be tuned over one month. No cytotoxicity of the composites is observed on fibroblasts and keratinocytes. Unlike the incorporation of pre‐formed particles, the new process allows for both improved physical properties of collagen hydrogels and controlled drug delivery. The ease of fabrication, wide range of accessible compositions, and positive preliminary safety evaluations of these collagen‐polyesters will favor their translation into clinics in wide areas such as drug delivery and tissue engineering. [ABSTRACT FROM AUTHOR]

Diabetic foot ulcers (DFUs) are characterized by a chronic inflammation state which prevents cutaneous wound healing, and DFUs eventually lead to infection and leg amputation. Macrophages located in DFUs are locked in an pro-inflammatory phenotype. In this study, the effect of hyperglycemia and hypoxia on the macrophage phenotype was analyzed. For this purpose, a microarray was performed to study the gene expression profile of macrophages cultivated in a high glucose concentration. Hyperglycemia upregulated the expression of pro-inflammatory cytokines such as TNF-α, IL-1, IL-6, chemokines and downregulated the expression of two receptors involved in phagocytosis (CD 36 and Class B scavenger type I receptors). In addition, eleven anti-apoptotic factors were upregulated whereas three pro-apoptotic genes were downregulated. Subsequently, the contribution of hypoxia and hyperglycemia to chronic inflammation and their potential synergistic effect was evaluated on activated THP-1 derived macrophages. A long term post activation effect (17 hours) was only observed on the upregulation of pro-inflammatory cytokines when hypoxia was combined with a high glucose concentration. In contrast, hyperglycemia and hypoxia did not have any effect on wound healing molecules such as TGF-β1. Taken together, the results show that hyperglycemia acts in synergy with hypoxia to maintain a chronic inflammation state in macrophages. [ABSTRACT FROM AUTHOR]

Silica nanoparticles appear as promising drug carriers for intracellular delivery. However, the mechanisms by which they are degraded within cells remain largely unknown. In this context, we have prepared three types of PEGylated fluorescent silica nanoparticles with various internal structures (core-shell biocomposite, multilayered, and hollow mesoporous) and studied their degradation in a buffer, in a culture medium, and in contact with human dermal fibroblasts. All particles were prone to dissolve in solution, leading to an increase of porosity and/or the precipitation of new colloids and eventually fragmentation, with a faster rate in the medium compared to that in the buffer. All particles were also uptaken by the cells without significant cytotoxic effect. Their intracellular degradation occurred faster than in suspension, but following almost similar dissolution mechanisms. These results strongly suggest that in these conditions, silica nanoparticles must be primarily considered as hydrolytically degraded and not biodegraded, a point of importance for their future applications in drug delivery. [ABSTRACT FROM AUTHOR]

Silica-collagen type I nanocomposite hydrogels are evaluated as medicated dressings to prevent infection in chronic wounds. Two antibiotics, gentamicin and rifamycin, are encapsulated in a single step within plain silica nanoparticles. Their antimicrobial efficiency against Pseudomonas aeruginosa and Staphylococcus aureus is assessed. Gentamycin-loaded 500 nm particles can be immobilized at high silica dose in concentrated collagen hydrogels without modifying their fibrillar structure or impacting on their rheological behavior and increases their proteolytic stability. Gentamicin release from the nanocomposites is sustained over 7 days, offering an unparalleled prolonged antibacterial activity. Particle immobilization also decreases their cytotoxicity towards surface-seeded fibroblast cells. Rifamycin-loaded 100 nm particles significantly alter the collagen hydrogel structure at high silica doses. The thus-obtained nanocomposites show no antibacterial efficiency, due to strong adsorption of rifamycin on collagen fibers. The complex interplay of interactions between drugs, silica and collagen is a key factor regulating the properties of these composite hydrogels as antibiotic-delivering biological dressings and must be taken into account for future extension to other wound healing agents. [ABSTRACT FROM AUTHOR]

Although silicon is a widespread constituent in dental materials, its possible influence on the formation and repair of teeth remains largely unexplored. Here, we studied the effect of two silicic acid-releasing nanomaterials, silica and bioglass, on a living model of pulp consisting of dental pulp stem cells seeded in dense type I collagen hydrogels. Silica nanoparticles and released silicic acid had little effect on cell viability and mineralization efficiency but impacted metabolic activity, delayed matrix remodeling, and led to heterogeneous cell distribution. Bioglass improved cell metabolic activity and led to a homogeneous dispersion of cells and mineral deposits within the hydrogel. These results suggest that the presence of calcium ions in bioglass is not only favorable to cell proliferation but can also counterbalance the negative effects of silicon. Both chemical and biological processes should therefore be considered when investigating the effects of silicon-containing materials on dental tissues.

Multifunctional nanomaterials combining diagnosis and therapeutic properties have attracted a considerable attention in cancer research. Yet some important challenges are still to be faced, including an optimal coupling between these two types of properties that would be effective within complex biological tissues. To address these points, we have prepared novel nanoplatforms associating controlled drug delivery of doxorubicin and Magnetic Resonance Imaging (MRI) contrast-enhancement that exhibit high specificity towards cancer cells compared to normal cells and evaluated them both in 2D cultures and within 3D tissue-like biomimetic matrices., Methods: Nanoplatforms were prepared from hollow silica nanoparticles coated with MnO 2 nanosheets and conjugated with the AS1411 aptamer as a targeting agent. They were fully characterized from a chemical and structural point of view as well as for drug release and MRI signal enhancement. Standard two-dimensional monolayer cultures were performed using HeLa and Normal Human Dermal Fibroblasts (NHDF) cells to testify targeting and cytotoxicity. Cellularized type I collagen-based hydrogels were also used to study nanoparticles behavior in 3D biomimetic environments., Results: The as-established nanoplatforms can enter HeLa cells, leading to the dissociation of the MnO 2 nanosheets into Mn 2+ that enhanced T 1 magnetic resonance signals and concomitantly release doxorubicin, both effects being markedly more significant than in the presence of NHDFs. Moreover, particles functionality and specificity were preserved when the cells were immobilized within type I collagen-based fibrillar hydrogels., Conclusion: The use of MnO 2 nanosheets as glutathione-sensitive coatings of drug loaded nanoparticles together with surface conjugation with a targeting aptamer offers an effective strategy to obtain efficient and specific nanotheranostic systems for cancer research, both in 2D and 3D. The here-described tissue-like models should be easy to implement and could constitute an interesting intermediate validation step for newly-developed theranostic nanoparticles before in vivo evaluation., Competing Interests: Competing Interests: The authors have declared that no competing interest exists.

The conjugation of polyethylenimine (PEI) to silica nanoparticles has emerged as a useful strategy in gene delivery. Here we investigate the influence of the PEI conjugation mode on the transfection ability of plain silica nanoparticles. Surface functionalization with sulfonate- and chloride-bearing silanes modulates the amount and conformation of PEI and therefore the particles' affinity for the plasmid, without impacting on cytotoxicity. However, transfection efficiency in both immortalized and primary cells is more directly correlated to the nature and strength of the particle-PEI interactions. It suggests that PEI detachment from the particle surface at the stage of endosomal escape is a key event in the plasmid delivery process. These data should provide fruitful guidelines for the fine tuning of colloidal surfaces intended for intracellular delivery of bioactive molecules.

Local delivery of biomolecules from hydrogels is highly challenging because of their rapid diffusion and degradation. Gene therapy represents an alternative that allows for the prolonged production of proteins by transfected cells. In this study, we have developed nanocomposites consisting of DNA-polyethylenimine-silica nanoparticle complexes coencapsulated with fibroblasts within collagen hydrogels. Through the modulation of the particle size and polyethylenimine molecular weight, it was possible to achieve "in-gel" transfection permitting the sustained production of biomolecules from hydrogels over 1 week. Alternative configurations consisting of particle addition to cellularized gels and cell culture in the presence of complex-containing hydrogels were also investigated. These studies demonstrated that particle encapsulation limits DNA and silica dissemination outside the collagen hydrogels. They also show the key role of cell proliferation within collagen hydrogels on the transfection efficiency. Such nanocomposites therefore constitute promising materials for the development of novel gene delivery systems to promote tissue repair.

The sol-gel process provides a robust and versatile technology for the immobilization of biologicals. A wide range of inorganic, composites and hybrid materials can be prepared to encapsulate molecular drugs, proteins, antibodies/antigens, enzymes, nucleic acids, prokaryotic and eukaryotic cells into bulk gels, particles and films. This review describes the applications of sol-gel encapsulation relevant to medicinal chemistry focusing on the recent development of biosensors as well as systems for production, screening and delivery of bioactive compounds and biomaterials.

A model of the fate of colloidal silica in the dermis was designed based on the diffusion of fluorescent silica nanoparticles through collagen hydrogels. The diffusion process was found to depend on particle size (10-200 nm) and surface charge, as well as on collagen concentration (1.5-5 mg mL -1 ). The presence of human dermal fibroblasts within the hydrogels also significantly impacted on the behaviour of the particles. In particular, the simultaneous monitoring of particulate and soluble forms of silica showed that both the hydrogel network and the cellular activity have a strong influence on the solubilization process of the silica particles, through a combination of surface sorption, uptake and intracellular dissolution. Interactions between silica and collagen in 3D environments also lower the cytotoxicity of 10 nm particles compared to traditional 2D cultures. The results emphasize the complexity of silica chemistry in living tissues and specifically indicate the need for further investigations of the in vivo behaviour of its soluble forms.

Hybrid and nanocomposite silica-collagen materials derived from concentrated collagen hydrogels were evaluated in vitro and in vivo to establish their potentialities for biological dressings. Silicification significantly improved the mechanical and thermal stability of the collagen network within the hybrid systems. Nanocomposites were found to favor the metabolic activity of immobilized human dermal fibroblasts while decreasing the hydrogel contraction. Cell adhesion experiments suggested that in vitro cell behavior was dictated by mechanical properties and surface structure of the scaffold. First-to-date in vivo implantation of bulk hydrogels in subcutaneous sites of rats was performed over the vascular inflammatory period. These materials were colonized and vascularized without inducing strong inflammatory response. These data raise reasonable hope for the future application of silica-collagen biomaterials as biological dressings., (© 2011 American Chemical Society)