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      Freeze-Casting of Porous Biomaterials: Structure, Properties and Opportunities

      review-article
      Materials
      Molecular Diversity Preservation International
      freeze-casting, porous ceramics, composites, biomaterials

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          Abstract

          The freeze-casting of porous materials has received a great deal of attention during the past few years. This simple process, where a material suspension is simply frozen and then sublimated, provides materials with unique porous architectures, where the porosity is almost a direct replica of the frozen solvent crystals. This review focuses on the recent results on the process and the derived porous structures with regards to the biomaterials applications. Of particular interest is the architecture of the materials and the versatility of the process, which can be readily controlled and applied to biomaterials applications. A careful control of the starting formulation and processing conditions is required to control the integrity of the structure and resulting properties. Further in vitro and in vivo investigations are required to validate the potential of this new class of porous materials.

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          Most cited references72

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          Porous chitosan scaffolds for tissue engineering.

          The wide array of tissue engineering applications exacerbates the need for biodegradable materials with broad potential. Chitosan, the partially deacetylated derivative of chitin, may be one such material. In this study, we examined the use of chitosan for formation of porous scaffolds of controlled microstructure in several tissue-relevant geometries. Porous chitosan materials were prepared by controlled freezing and lyophilization of chitosan solutions and gels. The materials were characterized via light and scanning electron microscopy as well as tensile testing. The scaffolds formed included porous membranes, blocks, tubes and beads. Mean pore diameters could be controlled within the range 1-250 microm, by varying the freezing conditions. Freshly lyophilized chitosan scaffolds could be treated with glycosaminoglycans to form ionic complex materials which retained the original pore structure. Chitosan scaffolds could be rehydrated via an ethanol series to avoid the stiffening caused by rehydration in basic solutions. Hydrated porous chitosan membranes were at least twice as extensible as non-porous chitosan membranes, but their elastic moduli and tensile strengths were about tenfold lower than non-porous controls. The methods and structures described here provide a starting point for the design and fabrication of a family of polysaccharide based scaffold materials with potentially broad applicability.
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            Collagen/chitosan porous scaffolds with improved biostability for skin tissue engineering.

            L. Ma (2003)
            Porous scaffolds for skin tissue engineering were fabricated by freeze-drying the mixture of collagen and chitosan solutions. Glutaraldehyde (GA) was used to treat the scaffolds to improve their biostability. Confocal laser scanning microscopy observation confirmed the even distribution of these two constituent materials in the scaffold. The GA concentrations have a slight effect on the cross-section morphology and the swelling ratios of the cross-linked scaffolds. The collagenase digestion test proved that the presence of chitosan can obviously improve the biostability of the collagen/chitosan scaffold under the GA treatment, where chitosan might function as a cross-linking bridge. A detail investigation found that a steady increase of the biostability of the collagen/chitosan scaffold was achieved when GA concentration was lower than 0.1%, then was less influenced at a still higher GA concentration up to 0.25%. In vitro culture of human dermal fibroblasts proved that the GA-treated scaffold could retain the original good cytocompatibility of collagen to effectively accelerate cell infiltration and proliferation. In vivo animal tests further revealed that the scaffold could sufficiently support and accelerate the fibroblasts infiltration from the surrounding tissue. Immunohistochemistry analysis of the scaffold embedded for 28 days indicated that the biodegradation of the 0.25% GA-treated scaffold is a long-term process. All these results suggest that collagen/chitosan scaffold cross-linked by GA is a potential candidate for dermal equivalent with enhanced biostability and good biocompatibility.
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              Freezing as a path to build complex composites

              Materials that are strong, ultra-light weight and tough are in demand for a range of applications, requiring architectures and components carefully designed from the micrometer down to nanometer scales. Nacre-a structure found in many molluscan shells-and bone are frequently used as examples for how nature achieves this through hybrid organic-inorganic composites. Unfortunately, it has proven extremely difficult to transcribe nacre-like clever designs into synthetic materials, partly because their intricate structures need to be replicated at several length scales. We demonstrate how the physics of ice formation can be used to develop sophisticated porous and layered-hybrid materials, including artificial bone, ceramic/metal composites, and porous scaffolds for osseous tissue regeneration with strengths up to four times higher than those currently used for implantation.
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                Author and article information

                Journal
                Materials (Basel)
                Materials (Basel)
                materials
                Materials
                Molecular Diversity Preservation International
                1996-1944
                17 March 2010
                March 2010
                : 3
                : 3
                : 1913-1927
                Affiliations
                Laboratoire de Synthèse et Fonctionnalisation des Céramiques, UMR 3080, CNRS/Saint-Gobain CREE, Cavaillon, France; E-Mail: sylvain.deville@ 123456saint-gobain.com ; Tel.: +4-32-50-06-59; Fax: +4-32-50-09-04
                Article
                materials-03-01913
                10.3390/ma3031913
                5445887
                ad770749-fc5e-4ca5-b103-a02a6fca68df
                © 2010 by the authors;

                licensee Molecular Diversity Preservation International, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/3.0/).

                History
                : 05 February 2010
                : 24 February 2010
                : 16 March 2010
                Categories
                Review

                freeze-casting,porous ceramics,composites,biomaterials
                freeze-casting, porous ceramics, composites, biomaterials

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