1 3 Injectable and porous PLGA microspheres that form highly porous 4 scaffolds at body temperature 5 6 7 Omar Qutachi a Q1 , Jolanda R. Vetsch b , Daniel Gill c , Helen Cox c , David J. Scurr a , Sandra Hofmann b , 8 Ralph Müller b , Robin A. Quirk c , Kevin M. Shakesheff a , Cheryl V. Rahman a,⇑ 9 a School of Pharmacy, University of Nottingham, University Park, Nottingham NG7 2RD, UK 10 b Institute for Biomechanics, ETH Zurich, Vladimir-Prelog-Weg 3, 8093 Zurich, Switzerland 11 c RegenTec Ltd, Biocity Nottingham, Pennyfoot Street, Nottingham NG1 1GF, UK 12 13 15 article info 16 Article history: 17 Received 21 February 2014 18 Received in revised form 19 July 2014 19 Accepted 15 August 2014 20 Available online xxxx 21 Keywords: 22 PLGA 23 Microsphere 24 Scaffold 25 Porosity 26 Cell delivery 27 28 abstract 29 Injectable scaffolds are of interest in the field of regenerative medicine because of their minimally inva- 30 sive mode of delivery. For tissue repair applications, it is essential that such scaffolds have the mechanical 31 properties, porosity and pore diameter to support the formation of new tissue. In the current study, por- 32 ous poly(DL-lactic acid-co-glycolic acid) (PLGA) microspheres were fabricated with an average size of 33 84 ± 24 lm for use as injectable cell carriers. Treatment with ethanolic sodium hydroxide for 2 min 34 was observed to increase surface porosity without causing the microsphere structure to disintegrate. This 35 surface treatment also enabled the microspheres to fuse together at 37 °C to form scaffold structures. The 36 average compressive strength of the scaffolds after 24 h at 37 °C was 0.9 ± 0.1 MPa, and the average 37 Young’s modulus was 9.4 ± 1.2 MPa. Scaffold porosity levels were 81.6% on average, with a mean pore 38 diameter of 54 ± 38 lm. This study demonstrates a method for fabricating porous PLGA microspheres 39 that form solid porous scaffolds at body temperature, creating an injectable system capable of supporting 40 NIH-3T3 cell attachment and proliferation in vitro. 41 Ó 2014 Acta Materialia Inc. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND 42 license (http://creativecommons.org/licenses/by-nc-nd/3.0/). 43 44 45 1. Introduction 46 The use of polymer scaffolds to deliver cells for regenerative 47 medicine applications can potentially overcome poor cell engraft- 48 ment and improve cell survival [1]. In particular, injectable scaffolds 49 show promise for this application, as cells can be mixed homoge- 50 neously with the scaffold formulation prior to injection. The ability 51 to deliver injectable scaffolds in a minimally invasive manner to a 52 cavity of any size or shape renders them especially attractive for 53 clinical use in tissue repair. A number of synthetic polymers have 54 been investigated for this application to date, including the biode- 55 gradable polymer poly(DL-lactic acid-co-glycolic acid) (PLGA). PLGA 56 is frequently used in regenerative medicine applications, as the deg- 57 radation rate of the polymer can be controlled and it has FDA 58 approval for certain clinical applications [2,3]. PLGA-based scaffold 59 systems have been reported extensively to support cell attachment 60 and proliferation, deliver growth factors in a controlled manner, and 61 support bone regeneration in vivo [4–8]. 62 In order to maintain, induce and restore biological functions, 63 scaffolds for tissue repair require suitable physical properties. Ide- 64 ally, the scaffold should be strong enough to retain its structure 65 without exhibiting stiffness that may affect the surrounding tissue 66 [2]. The microstructural properties of the scaffold also play a vital 67 role in successful tissue repair, as porosity levels and pore diam- 68 eter influence cell attachment, proliferation and migration in 69 addition to nutrient delivery and waste removal [9,10]. Studies 70 have indicated that scaffolds should possess multi-scale porosity 71 involving both micro-porosity and macro-porosity, with pore 72 diameters ranging from <20 lm to >100 lm [9]. The versatility 73 of chemically synthesized polymers such as PLGA is an advantage 74 in this respect, as it enables the fabrication of scaffolds with dif- 75 ferent porosities and mechanical properties. However, a delicate 76 balance is required in terms of these properties, as increasing 77 the porosity of a scaffold causes a subsequent decrease in 78 mechanical properties such as compressive strength. Attaining 79 suitable porosity and strength in an injectable formulation is 80 therefore a considerable challenge. 81 One type of injectable scaffold for tissue engineering applications 82 involves the use of discreet polymer microspheres. Microspheres 83 can be fabricated using a variety of different biodegradable polymers http://dx.doi.org/10.1016/j.actbio.2014.08.015 1742-7061/Ó 2014 Acta Materialia Inc. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). ⇑ Corresponding author. E-mail address: cheryl.rahman@nottingham.ac.uk (C.V. Rahman). Acta Biomaterialia xxx (2014) xxx–xxx Contents lists available at ScienceDirect Acta Biomaterialia journal homepage: www.elsevier.com/locate/actabiomat ACTBIO 3344 No. of Pages 9, Model 5G 30 August 2014 Please cite this article in press as: Qutachi O et al. Injectable and porous PLGA microspheres that form highly porous scaffolds at body temperature. Acta Biomater (2014), http://dx.doi.org/10.1016/j.actbio.2014.08.015