Applied Surface Science 311 (2014) 292–299 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Configurational effects of collagen/ALP coatings on enzyme immobilization and surface mineralization R. Bosco, S.C.G. Leeuwenburgh, J.A. Jansen, J.J.J.P. van den Beucken ∗ Department of Biomaterials (309), Radboud University Medical Center, Nijmegen, The Netherlands a r t i c l e i n f o Article history: Received 13 January 2014 Received in revised form 22 April 2014 Accepted 11 May 2014 Available online 19 May 2014 Keywords: Coating Electrospray ALP Collagen Organic Mineralization a b s t r a c t The ultimate goal for surface modifications in bone implants is to achieve biologically active surface able to control and trigger specific tissue response. In this study was evaluated the effects of organic compound, derived from extracellular matrix, involved in tissue mineralization. Alkaline phosphatase (ALP) plays a fundamental role in bone mineralization concurrently with collagen, the main organic components of bones. Electrospray deposition (ESD) was used to coat titanium disks with ALP and collagen at room temperature. To verify the synergistic role of ALP and collagen different conformations of coatings (mixed and layered) were obtained and their mineralization capacity was tested in vitro. The mineralization tests indicated the fundamental role of collagen to increase ALP coating retention. Analyses indicated that the coating conformation has a role; in fact the mixed group showed improved ALP retention, enzymatic activity and unique mineralized surface morphology. ESD demonstrated to be a successful method to deposit organic molecules preserving their properties as indicated by the in vitro results. These findings proved the synergistic effect of ALP and collagen in inducing mineralization offering an intriguing coating constituent for medical device that aim to trigger surface mineralization such as bone implants. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The primary scope of surface modifications for bone implants is to enhance bone integration to obtain early and strong fixa- tion for functional application of the implant even under load bearing conditions. Bone is a connective tissue characterized by a multi-phase structure of collagen (organic) and hydroxyapatite crystals (inorganic). The inorganic phase is responsible for mechan- ical properties, such as hardness and compression resistance and the organic phase confers flexibility, resilience and fatigue resis- tance to the tissue [1,2]. For decades, titanium has proved to be the most successful material for bone implants due to its suitable mechanical properties and biocompatibility. However, although the bulk properties of titanium are optimal for load bearing appli- cations, the relative passive surface properties are a limitation for rapid integration into bone tissue [3]. ∗ Corresponding author at: Department of Biomaterials (309), Radboudumc, Ph v Leijdenlaan 25, 6525 EX Nijmegen, The Netherlands. Tel.: +31 (0)24 3667305; fax: +31 (0)24 3614657. E-mail address: jeroen.vandenbeucken@radboudumc.nl (J.J.J.P. van den Beucken). URL: http://www.radboudumc.nl/Research/Departments/Dentistry/ biomaterials/Pages/default.aspx (J.J.J.P. van den Beucken). Especially at the interface between implants and bone, a rapid and strong bonding that allows load and stress transfer to stimu- late bone formation defined by the so called Wolff’s law is required [4]. In view of the fundamental role of the interface in integra- tion, the deposition of a thin layer of calcium phosphate onto titanium implant surfaces has been used frequently in the last decades to improve biological responses [5]. Additionally, several bioinspired strategies and compounds have been tested to obtain implant surfaces with a chemical composition similar to the inor- ganic phase of bone tissue. Hydroxyapatite (HA) has been most intensively investigated for bone applications. In vitro experiments demonstrated that HA can increase mesenchymal stem cell [6] and primary human osteoblast cell [7] proliferation and differentiation. Surface modifications based on HA-coatings have proven effects on the in vitro and in vivo performance compared to non-coated titanium controls [8]. A wide range of in vivo and clinical investiga- tions have indicated an improved fixation of HA-coated implants compared to non-coated controls [9–15]. A relatively unexplored area for bioinspired surface engineer- ing is the use of organic moieties. As the organic phase plays an important role during the biological mineralization process [16], particularly collagen fibers and alkaline phosphatase (ALP) are appealing proteins for surface engineering approaches. In fact, the mineralization of bone tissue is a biphasic process in which the first phase is characterized by enzymatic interactions that increase http://dx.doi.org/10.1016/j.apsusc.2014.05.057 0169-4332/© 2014 Elsevier B.V. All rights reserved.