Review Article A review of bioactive glasses: Their structure, properties, fabrication, and apatite formation Gurbinder Kaur, 1 Om P. Pandey, 2 Kulvir Singh, 2 Dan Homa, 1 Brian Scott, 1 Gary Pickrell 1 1 Department of Material Science and Engineering, Holden Hall, Virginia Tech, Blacksburg-24060, Virginia, USA 2 School of Physics and Materials Science, Thapar University, Patiala-147004, Punjab, India Received 14 December 2012; revised 14 February 2013; accepted 20 February 2013 Published online 6 March 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jbm.a.34690 Abstract: Bioactive glass and glass–ceramics are used in bone repair applications and are being developed for tissue engineering applications. Bioactive glasses/bioglass are very attractive materials for producing scaffolds devoted to bone regeneration due to their versatile properties, which can be properly designed depending on their composition. An im- portant feature of bioactive glasses, which enables them to work for applications in bone tissue engineering, is their abil- ity to enhance revascularization, osteoblast adhesion, enzyme activity and differentiation of mesenchymal stem cells as well as osteoprogenitor cells. An extensive amount of research work has been carried out to develop silicate, borate/borosili- cate bioactive glasses and phosphate glasses. Along with this, some metallic glasses have also been investigated for biomedical and technological applications in tissue engineer- ing. Many trace elements have also been incorporated in the glass network to obtain the desired properties, which have beneficial effects on bone remodeling and/or associated angiogenesis. The motivation of this review is to provide an overview of the general requirements, composition, struc- ture-property relationship with hydroxyapatite formation and future perspectives of bioglasses. Attention has also been given to developments of metallic glasses and doped bio- glasses along with the techniques used for their fabrication. V C 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 254– 274, 2014. Key Words: glass, glass ceramics, bioactivity, biodegradable, hydroxyapatite How to cite this article: Kaur G, Pandey OP, Singh K, Homa D, Scott B, Pickrell G. 2014. A review of bioactive glasses: Their structure, properties, fabrication, and apatite formation. J Biomed Mater Res Part A 2014:102A:254–274. INTRODUCTION The natural or man-made materials, which are used to replace or supplement the functions of living tissues, are known as biomaterials. 1 The imperative terminology for the study of biological performance of materials includes: bio- compatibility and biomaterials. The biomaterials should be biocompatible that is in vivo harmony of biomaterial and vice versa. 2 In addition to this, biomaterials must possess features like bioinert behavior, bioactivity, biostability, and biodegradibilty. 3 Biomaterials are generally categorized as (a) natural or synthetic polymers, (b) metals, (c) compo- sites, and (d) ceramics (bioglasses) as shown in Figure 1. Although the composition flexibility for polymers pro- vides them with their unique characteristics, but their low mechanical strength cannot withstand the stresses required in many applications. Metals have high wear resistance, strength and ductility. However, their high corrosion rate and low biocompatibility are undesirable for living tissues, and the high diffusion of metal ions may lead to allergic reactions. 4 Some composites have cross-linked elastomers which give them high elastic moduli which in turn are bene- ficial for biocompatibility. Ceramics generally posses good biocompatibility along with resistance to corrosion and compression. Unfortunately these materials are brittle and maintain small resilience, high density and low fracture strength. The use of biodegradable polymer scaffolds for the regeneration of bones is limited and challenging. These polymers lack a mechanically biocompatible hydroxyapatite (HA) inorganic phase. 5-8 The scaffolds which are fabricated from calcium phosphate-based inorganic materials or bio- ceramics such as bioactive glass usually provide a higher mechanical strength. Bioactive glass and glass–ceramics are also used in bone repair applications and are being developed for tissue engi- neering applications. 9 Bioactive glasses/bioglasses are very attractive materials for producing scaffolds devoted to bone regeneration due to their versatile properties, which can be properly designed depending on their composition. 10 The Correspondence to: G. Kaur; e-mail: gkaur82@vt.edu 254 V C 2013 WILEY PERIODICALS, INC.