Mineralized collagen plywood contributes to bone autograft performance.

Autologous bone (AB) is the gold standard for bone-replacement surgeries, despite its limited availability and the need for an extra surgical site. Traditionally, competitive biomaterials for bone repair have focused on mimicking the mineral aspect of bone, as evidenced by the widespread clinical use of bioactive ceramics. However, AB also exhibits hierarchical organic structures that might substantially affect bone regeneration.

Collagen Suprafibrillar Confinement Drives the Activity of Acidic Calcium-Binding Polymers on Apatite Mineralization.

Bone collagenous extracellular matrix provides a confined environment into which apatite crystals form. This biomineralization process is related to a cascade of events partly controlled by noncollagenous proteins. Although overlooked in bone models, concentration and physical environment influence their activities.

Origin of transparency in scattering biomimetic collagen materials.

Living tissues, heterogeneous at the microscale, usually scatter light. Strong scattering is responsible for the whiteness of bones, teeth, and brain and is known to limit severely the performances of biomedical optical imaging. Transparency is also found within collagen-based extracellular tissues such as decalcified ivory, fish scales, or cornea.

Self-Assembled Collagen Microparticles by Aerosol as a Versatile Platform for Injectable Anisotropic Materials.

Extracellular matrices (ECM) rich in type I collagen exhibit characteristic anisotropic ultrastructures. Nevertheless, working in vitro with this biomacromolecule remains challenging. When processed, denaturation of the collagen molecule is easily induced in vitro avoiding proper fibril self-assembly and further hierarchical order.

Involvement of 3D osteoblast migration and bone apatite during in vitro early osteocytogenesis.

The transition from osteoblast to osteocyte is described to occur through passive entrapment mechanism (self-buried, or embedded by neighboring cells). Here, we provide evidence of a new pathway where osteoblasts are "more" active than generally assumed. We demonstrate that osteoblasts possess the ability to migrate and differentiate into early osteocytes inside dense collagen matrices.

Evaluation of dense collagen matrices as medicated wound dressing for the treatment of cutaneous chronic wounds.

Cutaneous chronic wounds are characterized by an impaired wound healing which may lead to infection and amputation. When current treatments are not effective enough, the application of wound dressings is required. To date, no ideal biomaterial is available.

Water-mediated structuring of bone apatite.

It is well known that organic molecules from the vertebrate extracellular matrix of calcifying tissues are essential in structuring the apatite mineral. Here, we show that water also plays a structuring role. By using solid-state nuclear magnetic resonance, wide-angle X-ray scattering and cryogenic transmission electron microscopy to characterize the structure and organization of crystalline and biomimetic apatite nanoparticles as well as intact bone samples, we demonstrate that water orients apatite crystals through an amorphous calcium phosphate-like layer that coats the crystalline core of bone apatite.

Collagen osteoid-like model allows kinetic gene expression studies of non-collagenous proteins in relation with mineral development to understand bone biomineralization.

Among persisting questions on bone calcification, a major one is the link between protein expression and mineral deposition. A cell culture system is here proposed opening new integrative studies on biomineralization, improving our knowledge on the role played by non-collagenous proteins in bone. This experimental in vitro model consisted in human primary osteoblasts cultured for 60 days at the surface of a 3D collagen scaffold mimicking an osteoid matrix.

The predominant role of collagen in the nucleation, growth, structure and orientation of bone apatite.

The involvement of collagen in bone biomineralization is commonly admitted, yet its role remains unclear. Here we show that type I collagen in vitro can initiate and orientate the growth of carbonated apatite mineral in the absence of any other vertebrate extracellular matrix molecules of calcifying tissues. We also show that the collagen matrix influences the structural characteristics on the atomic scale, and controls the size and the three-dimensional distribution of apatite at larger length scales.

Fibroblasts within concentrated collagen hydrogels favour chronic skin wound healing.

Apligraf(®), a skin substitute currently used in skin chronic wound treatment, acts as a source of macromolecules and cytokines to promote wound healing. Normal collagen hydrogel (NCH), obtained from collagen at low concentration (0.66 mg/ml), is the base of the dermal layer.

In vitro studies and preliminary in vivo evaluation of silicified concentrated collagen hydrogels.

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.

Dense fibrillar collagen matrices sustain osteoblast phenotype in vitro and promote bone formation in rat calvaria defect.

Two pure collagen materials were prepared from acidic collagen solutions at 5 and 40 mg/mL. Benefits of collagen concentration on bone repair were evaluated in vitro with human calvaria cells and in vivo in a rat cranial defect. Both materials exhibited specific structures, 5 mg/mL was soft with an open porous network of fibrils; 40 mg/mL was stiffer with a plugged surface and bundles of collagen fibrils.

Dense fibrillar collagen matrices for tissue repair.

The preparation of dense fibrillar collagen matrices, through a sol/gel transition at variable concentrations, offers routes to produce a range of simple, non toxic materials. Concentrated hydrogels entrapping cells show enhanced properties in terms of reduced contraction and enhanced cell proliferation . Dense fibrillar matrices attain tissue like mechanical properties and show ultrastructures described in connective tissues, namely liquid crystalline cholesteric geometries.

Synthesis and in vivo integration of improved concentrated collagen hydrogels.

Normal collagen hydrogels, currently used as the dermal layer of skin substitute Apligraf®, are obtained by encapsulating dermal fibroblasts in a collagen hydrogel at low concentration (0.66 mg/ml). However they suffer from extensive contraction by cells and weak resistance against degradation, which limits their use as permanent graft.

Silica-collagen bionanocomposites as three-dimensional scaffolds for fibroblast immobilization.

Silica-collagen bionanocomposite hydrogels were obtained by addition of silica nanoparticles to a protein suspension followed by neutralization. Electron microscopy studies indicated that larger silica nanoparticles (80 nm) do not interact strongly with collagen, whereas smaller ones (12 nm) form rosaries along the protein fibers. However, the composite network structurally evolved with time due to the contraction of the cells and the dissolution of the silica nanoparticles.

Collagen supramolecular and suprafibrillar organizations on osteoblasts long-term behavior: benefits for bone healing materials.

This study compares the behavior of osteoblastic cells seeded on three structurally distinct collagen-based materials. Adhesion and long-term behavior were evaluated in vitro in regard to collagen scaffolds forming loose or dense fibrillar networks or exempt of fibrils. In this purpose collagen solutions at concentrations of 5 and 40 mg/mL were processed by freeze-drying or by sol/gel fibrillogenesis to form either sponges or hydrogels.

Concentrated collagen hydrogels as dermal substitutes.

Collagen hydrogels first appeared promising for skin repair. Unfortunately, their extensive contraction and their poor mechanical properties constituted major disadvantages toward their utilization as permanent graft. The present study has investigated a way to correct these drawbacks by increasing the collagen concentration in controlled conditions.

Dense fibrillar collagen matrices: a model to study myofibroblast behaviour during wound healing.

Fibroblastic cells play an important part in wound healing. Human dermal fibroblasts seeded onto three-dimensional fibrillar collagen matrices migrate into the collagen network and differentiate into myofibroblasts. In order to evaluate the use of collagen matrices as model systems for studying myofibroblast phenotype during wound healing, myofibroblast behaviour migrating into dense or loose matrices was compared.

Dense tissue-like collagen matrices formed in cell-free conditions.

A new protocol was developed to produce dense organized collagen matrices hierarchically ordered on a large scale. It consists of a two stage process: (1) the organization of a collagen solution and (2) the stabilization of the organizations by a sol-gel transition that leads to the formation of collagen fibrils. This new protocol relies on the continuous injection of an acid-soluble collagen solution into glass microchambers.

Type I collagen, a versatile liquid crystal biological template for silica structuration from nano- to microscopic scales.

Type I collagen is a suitable and versatile template for the structuration of silica at different length scales.

Biomimetism and bioinspiration as tools for the design of innovative materials and systems.

Materials found in nature combine many inspiring properties such as sophistication, miniaturization, hierarchical organizations, hybridation, resistance and adaptability. Elucidating the basic components and building principles selected by evolution to propose more reliable, efficient and environment-respecting materials requires a multidisciplinary approach.

Fibroblast populated dense collagen matrices: cell migration, cell density and metalloproteinases expression.

Dense collagen matrices obtained by using the property of type I collagen to form liquid crystals at high concentrations, were shown to be colonized by human dermal fibroblasts (Biomaterials 23 (2002) 27). In order to evaluate them as possible tissue substitutes, we investigated in this study the mechanism of cell colonization. Fibroblasts were seeded at the surface of collagen matrices at concentrations of 5 and 40 b mg/ml.

Liquid crystalline assemblies of collagen in bone and in vitro systems.

Precise descriptions of the three-dimensional arrangements of collagen in bone are essential to understand the mechanical properties of this complex tissue. Transmission electron microscopy (TEM) analysis of decalcified human compact bone in section reveals characteristic patterns forming regular series of nested arcs. Such patterns are a direct consequence of an organization described as a twisted plywood and relate the distribution of collagen fibrils in osteons with that of molecules in cholesteric liquid crystals.

Production of ordered collagen matrices for three-dimensional cell culture.

The aim of this study was to produce collagen gels with controlled fibrillar order as matrices for cell culture. Their structural characterization and colonization by human dermal fibroblasts arc presently reported. Ordered matrices are obtained by using the property of type I collagen monomers to self-assemble in liquid crystalline arrays by slow evaporation of acidic solutions at high concentrations.