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      Bioactive Glasses: From Parent 45S5 Composition to Scaffold-Assisted Tissue-Healing Therapies

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          Abstract

          Nowadays, bioactive glasses (BGs) are mainly used to improve and support the healing process of osseous defects deriving from traumatic events, tumor removal, congenital pathologies, implant revisions, or infections. In the past, several approaches have been proposed in the replacement of extensive bone defects, each one with its own advantages and drawbacks. As a result, the need for synthetic bone grafts is still a remarkable clinical challenge since more than 1 million bone-graft surgical operations are annually performed worldwide. Moreover, recent studies show the effectiveness of BGs in the regeneration of soft tissues, too. Often, surgical criteria do not match the engineering ones and, thus, a compromise is required for getting closer to an ideal outcome in terms of good regeneration, mechanical support, and biocompatibility in contact with living tissues. The aim of the present review is providing a general overview of BGs, with particular reference to their use in clinics over the last decades and the latest synthesis/processing methods. Recent advances in the use of BGs in tissue engineering are outlined, where the use of porous scaffolds is gaining growing importance thanks to the new possibilities given by technological progress extended to both manufacturing processes and functionalization techniques.

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          Most cited references 139

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          Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism

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            Porosity of 3D biomaterial scaffolds and osteogenesis.

            Porosity and pore size of biomaterial scaffolds play a critical role in bone formation in vitro and in vivo. This review explores the state of knowledge regarding the relationship between porosity and pore size of biomaterials used for bone regeneration. The effect of these morphological features on osteogenesis in vitro and in vivo, as well as relationships to mechanical properties of the scaffolds, are addressed. In vitro, lower porosity stimulates osteogenesis by suppressing cell proliferation and forcing cell aggregation. In contrast, in vivo, higher porosity and pore size result in greater bone ingrowth, a conclusion that is supported by the absence of reports that show enhanced osteogenic outcomes for scaffolds with low void volumes. However, this trend results in diminished mechanical properties, thereby setting an upper functional limit for pore size and porosity. Thus, a balance must be reached depending on the repair, rate of remodeling and rate of degradation of the scaffold material. Based on early studies, the minimum requirement for pore size is considered to be approximately 100 microm due to cell size, migration requirements and transport. However, pore sizes >300 microm are recommended, due to enhanced new bone formation and the formation of capillaries. Because of vascularization, pore size has been shown to affect the progression of osteogenesis. Small pores favored hypoxic conditions and induced osteochondral formation before osteogenesis, while large pores, that are well-vascularized, lead to direct osteogenesis (without preceding cartilage formation). Gradients in pore sizes are recommended for future studies focused on the formation of multiple tissues and tissue interfaces. New fabrication techniques, such as solid-free form fabrication, can potentially be used to generate scaffolds with morphological and mechanical properties more selectively designed to meet the specificity of bone-repair needs.
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              Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering.

              Biodegradable polymers and bioactive ceramics are being combined in a variety of composite materials for tissue engineering scaffolds. Materials and fabrication routes for three-dimensional (3D) scaffolds with interconnected high porosities suitable for bone tissue engineering are reviewed. Different polymer and ceramic compositions applied and their impact on biodegradability and bioactivity of the scaffolds are discussed, including in vitro and in vivo assessments. The mechanical properties of today's available porous scaffolds are analyzed in detail, revealing insufficient elastic stiffness and compressive strength compared to human bone. Further challenges in scaffold fabrication for tissue engineering such as biomolecules incorporation, surface functionalization and 3D scaffold characterization are discussed, giving possible solution strategies. Stem cell incorporation into scaffolds as a future trend is addressed shortly, highlighting the immense potential for creating next-generation synthetic/living composite biomaterials that feature high adaptiveness to the biological environment.
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                Author and article information

                Journal
                J Funct Biomater
                J Funct Biomater
                jfb
                Journal of Functional Biomaterials
                MDPI
                2079-4983
                16 March 2018
                March 2018
                : 9
                : 1
                Affiliations
                Institute of Materials Physics and Engineering, Department of Applied Science and Technology, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy; elisa.fiume@ 123456polito.it (E.F.); jacopo.barberi@ 123456studenti.polito.it (J.B.)
                Author notes
                [* ]Correspondence: enrica.verne@ 123456polito.it (E.V.); francesco.baino@ 123456polito.it (F.B.); Tel.: +39-011-090-4717 (E.V.); +39-011-090-4668 (F.B.)
                Article
                jfb-09-00024
                10.3390/jfb9010024
                5872110
                29547544
                © 2018 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

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