Hydrogel/bioactive glass composites for bone regeneration applications: Synthesis and characterisation John A. Killion a,1 , Sharon Kehoe c,2 , Luke M. Geever a,3 , Declan M. Devine a,1 , Eoin Sheehan b,4 , Daniel Boyd c,2 , Clement L. Higginbotham a, ⁎ a Materials Research Institute, Athlone Institute of Technology, Dublin Rd, Athlone, Co. Westmeath, Ireland b Department of Trauma & Orthopaedics, MRHT, Tullamore, Co. Offaly, Ireland c Department of Applied Oral Sciences, Dalhousie University, Halifax, NS B3H 34R2, Canada abstract article info Article history: Received 18 October 2012 Received in revised form 4 March 2013 Accepted 10 June 2013 Available online 24 June 2013 Keywords: Hydrogels Bioactive glasses Mechanical properties Biomineralisation Due to the deficiencies of current commercially available biological bone grafts, alternative bone graft substitutes have come to the forefront of tissue engineering in recent times. The main challenge for scientists in manufactur- ing bone graft substitutes is to obtain a scaffold that has sufficient mechanical strength and bioactive properties to promote formation of new tissue. The ability to synthesise hydrogel based composite scaffolds using photopolymerisation has been demonstrated in this study. The prepared hydrogel based composites were characterised using techniques including Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray spectrometry (EDX), rheological studies and compression testing. In addition, gel fraction, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), porosity and swelling studies of the composites were carried out. It was found that these novel hydrogel bioglass composite formulations did not display the inherent brittleness that is typically associated with bioactive glass based bone graft materials and exhibited enhanced biomechanical properties compared to the polyethylene glycol hydrogel scaffolds along. Together, the combination of enhanced mechanical properties and the deposition of apatite on the surface of these hydrogel based composites make them an ideal candidate as bone graft substitutes in cancellous bone defects or low load bearing applications. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Bone is a complex and highly specialised form of connective tissue with exceptional mechanical and biological properties [1]. Bone be- haves as a dynamic tissue as it has the distinctive capability to regen- erate and remodel through the action of osteoblasts, osteoclasts and osteocytes. However, in the case of critical size defects, the defect be- comes too large for the aforementioned cells to repair the damaged tissue [2]. Bone defects remain a major problem in orthopaedic sur- gery where defects may arise from trauma [3], tumour resection [4–6] and osteomyelitis [7]. The treatments of choice for these types of defects are bone grafting procedures. Currently, the most common type is biological grafts and they include autografts, allografts and xe- nografts. However, each biological graft has its own limitations: auto- grafts for example require an extra surgery and increase the risk of morbidity and may involve blood loss, sepsis and pain [8,9]. On the other hand, allografts (both freeze dried and fresh frozen) as well as xenografts carry histocompatibility antigens different from the host and therefore, increase risk of rejection [10]. They are also expensive and require stringent handling protocols. Nevertheless, it has been estimated that 2.2 million bone grafting procedures are performed worldwide each year to stimulate bone healing [11]. The market for European bone grafts and bone cements was worth $692.1 million in 2009 and is expected to almost double to $1248.0 million by 2016 [12]. Due to the anticipated increase in the mar- ket size and the current issues with biological grafts, synthetic bone graft substitutes are expected to play a vital role in bone regeneration. Hydrogels are 3-D networks formed from hydrophilic polymers which are crosslinked to form insoluble polymer matrices [13]. Hydrogels have excellent biological properties due to their ability to mimic extracellular matrix [14]. Their aqueous environment allows transportation of sub- stances such as nutrients and by-products from cell metabolism. Their properties are reliant on type of crosslinking and crosslink density [15]. One particular material that has been comprehensively studied for tissue engineering applications is polyethylene glycol hydrogels (PEGs) [16–18]. PEG is biocompatible and has the ability to form in situ [19,20], however, PEG hydrogels generally lack the mechanical properties to replicate in vivo conditions for load bearing systems such as encountered in bone Materials Science and Engineering C 33 (2013) 4203–4212 ⁎ Corresponding author. Tel.: +353 90 6468050; fax: +353 90 6424493. E-mail addresses: jkillion@research.ait.ie (J.A. Killion), sh625116@dal.ca (S. Kehoe), lgeever@ait.ie (L.M. Geever), ddevine@ait.ie (D.M. Devine), eoinsheehan@aol.com (E. Sheehan), d.boyd@dal.ca (D. Boyd), chigginbotham@ait.ie (C.L. Higginbotham). 1 Tel.: +353 90 6468059; fax: +353 90 6424493. 2 Tel.: +1 9024946347. 3 Tel.: +353 90 6468054; fax: +353 90 6424493. 4 Tel.: +353 579358776. 0928-4931/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2013.06.013 Contents lists available at ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec