www.MaterialsViews.com 1479 © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.small-journal.com Biomimetic Concealing of PLGA Microspheres in a 3D Scaffold to Prevent Macrophage Uptake Silvia Minardi, Bruna Corradetti, Francesca Taraballi, Monica Sandri, Jonathan O. Martinez, Sebastian T. Powell, Anna Tampieri, Bradley K. Weiner, and Ennio Tasciotti* 1. Introduction Biomaterials mimicking the structure and composition of the extracellular matrix (ECM) are capable of acting as induc- tive templates for the formation of site-specific functional tissues. [1] The reciprocal interaction between cells and ECM is key for tissue regeneration and the consequent tissue homeostasis. [2] With respect to synthetic materials, hosts favorably respond to collagenous materials, promoting mate- rial integration. [3,4] Collagen, the most abundant structural protein in the ECM of connective tissues, plays a prominent role in maintaining the integrity of tissue architecture and has been successfully used in several tissue engineering applica- tions. [5–7] Collagen is a highly dynamic component, providing essential information for cell attachment, [8] migration, [9] and organization. [10] However, collagen alone lacks the ability to recapitulate the complexity of tissues’ milieu, therefore bio- active factors are necessary additions to address any specific DOI: 10.1002/smll.201503484 Scaffolds functionalized with delivery systems for the release of growth factors is a robust strategy to enhance tissue regeneration. However, after implantation, macrophages infiltrate the scaffold, eventually initiating the degradation and clearance of the delivery systems. Herein, it is hypothesized that fully embedding the poly( D,L-lactide-co-glycolide acid) microspheres (MS) in a highly structured collagen-based scaffold (concealing) can prevent their detection, preserving the integrity of the payload. Confocal laser microscopy reveals that non-embedded MS are easily internalized; when concealed, J774 and bone marrow-derived macrophages (BMDM) cannot detect them. This is further demonstrated by flow cytometry, as a tenfold decrease is found in the number of MS engulfed by the cells, suggesting that collagen can cloak the MS. This correlates with the amount of nitric oxide and tumor necrosis factor-α produced by J774 and BMDM in response to the concealed MS, comparable to that found for non-functionalized collagen scaffolds. Finally, the release kinetics of a reporter protein is preserved in the presence of macrophages, only when MS are concealed. The data provide detailed strategies for fabricating three dimensional (3D) biomimetic scaffolds able to conceal delivery systems and preserve the therapeutic molecules for release. Tissue Engineering Dr. S. Minardi, Dr. B. Corradetti, Dr. F. Taraballi, Dr. J. O. Martinez, S. T. Powell, Dr. B. K. Weiner, Dr. E. Tasciotti Department of Regenerative Medicine Houston Methodist Research Institute (HMRI) 6670 Bertner Ave., Houston, TX 77030, USA E-mail: etasciotti@HoustonMethodist.org Dr. S. Minardi, Dr. M. Sandri, Dr. A. Tampieri Institute of Science and Technology for Ceramics-CNR (ISTEC-CNR) Via Granarolo 64, 48018 Faenza, RA, Italy Dr. B. Corradetti Department of Life and Environmental Sciences Università Politecnica delle Marche 60131 Ancona, Italy Dr. B. K. Weiner Department of Orthopedic Surgery Houston Methodist Hospital 6550 Fannin St., Houston, TX 77030, USA small 2016, 12, No. 11, 1479–1488