PCL microspheres based functional scaffolds by bottom-up approach with predefined microstructural properties and release profiles Alessia Luciani a, c , Valentina Coccoli a, c , Silvia Orsi a, c , Luigi Ambrosio b , Paolo A. Netti a, c, * a Interdisciplinary Research Centre on Biomaterials (CRIB), University of Naples Federico II, Piazzale Tecchio 80, 80125 Naples, Italy b Institute of Composites and Biomedical Materials, IMCB-CNR, National Research Council, Piazzale Tecchio 80, 80125 Naples, Italy c Italian Institute of Technology, IIT, via Morego 30,16163 Genova, Italy article info Article history: Received 3 July 2008 Accepted 5 September 2008 Available online 1 October 2008 Keywords: Scaffold Controlled drug release Microsphere Sintering Bioactivity abstract Advanced tissue engineering approaches rely upon the employment of biomaterials that integrate biodegradable scaffolds with growth factor delivery devices to better guide cellular activities and enhance tissue neogenesis. Along these lines, here we proposed a bottom-up approach for the realization of bioactive scaffolds with controllable pore size and interconnection, combined with protein-loaded polymeric microcarriers acting as local chrono-programmed point source generation of bioactive signals. Bioactive scaffolds are obtained through the thermal assembly of protein activated poly(3-caprolactone) (PCL) microspheres prepared by double emulsion and larger protein free PCL microspheres obtained by single emulsion. It is shown that the pore dimension, interconnectivity and mechanical properties in compression of the scaffold could be predefined by an appropriate choice of the size of the protein-free microparticles and process conditions. Protein-loaded microparticles were successfully included within the scaffold and provided a sustained delivery of a model protein (BSA). These matrices offer the possibility to concurrently modulate and control the size and extension of the porosity, mechanical properties and the spatial-temporal distribution of multiple bioactive signals. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Tissue engineering (TE) aims at the repairing and restoring damaged tissue function employing three fundamental ‘‘tools’’, namely cells, scaffolds and growth factors [1–7], which, however are not always simultaneously used. On the other hand, summoning recent experimental and clinical evidences indicates that the success of any TE approach mainly relies on the delicate and dynamic interplay among these three components and that functional tissue integration and regeneration depend upon their sapient integration [5]. Therefore, biomaterial scaffolds have to provide biological signals able to guide and direct cell function through a combination of matricellular cues exposition and growth factors sequestration and delivery [8]. An ideal scaffold for bone tissue repair should have a three-dimensional porous structure with a highly interconnected pore network, being biocompatible and bioresorbable at a controllable degradation and resorption, as well as possess mechanical properties similar to those of the tissues at the site of implantation [9]. Moreover, a scaffold should promote and guide cell-induced tissue regeneration through a control of local microenvironment by exposing the appropriate signals at the desired site, with sufficient local dose for the required time frame. To this end, recent approaches to scaffold design have been pursued by integrating fundamental concepts of drug delivery to enhance the ability to trigger biological signals favourable for complex tissue morphogenesis [10,11]. These include direct interspersion of growth factors within the scaffold [5–7] or their encapsulation in micro-depots interspersed in the scaffold structure [12]. However, these approaches do not allow an independent control of pore size and degree of interconnection and the release of bioactive agents. A number of synthetic polymers have been employed for bone tissue engineering applications, among these poly(3-caprolactone) (PCL) is one of the most widely investigated polymers. PCL is a bioresorbable polymer with potential applications for bone and cartilage repair and has certain advantages compared to other polymers such as PLA (poly lactic acid): (a) it is more stable in ambient conditions; (b) it is significantly less expensive and, (c) it is readily available in large quantities [13]. Several technologies have been used to make PCL porous such as gas foaming [14], salt leaching [15], solvent casting [15] and their combination [16]. However, beside their well-known limitations regarding the control of porosity and interconnectivity along with poor * Corresponding author. Interdisciplinary Research Centre on Biomaterials (CRIB), University of Naples Federico II, Piazzale Tecchio 80, 80125 Naples, Italy. Tel.: þ39 081 768 2408; fax: þ39 081 768 2404. E-mail address: nettipa@unina.it (P.A. Netti). Contents lists available at ScienceDirect Biomaterials journal homepage: www.elsevier.com/locate/biomaterials 0142-9612/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2008.09.007 Biomaterials 29 (2008) 4800–4807