Applied Surface Science 270 (2013) 473–479 Contents lists available at SciVerse ScienceDirect Applied Surface Science j our nal ho me p age: www.elsevier.com/loc ate/apsusc Surface chemical functionalities affect the behavior of human adipose-derived stem cells in vitro Xujie Liu a , Qingling Feng a,∗ , Akash Bachhuka b , Krasimir Vasilev b,c a State key laboratory of new ceramics and fine processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China b Mawson Institute, University of South Australia, Mawson Lakes 5095, Australia c School of Advanced Manufacturing, University of South Australia, Mawson Lakes 5095, Australia a r t i c l e i n f o Article history: Received 25 July 2012 Received in revised form 21 December 2012 Accepted 9 January 2013 Available online 17 January 2013 Keywords: Adipose-derived stem cell Plasma polymerization Surface modification Hydroxyapatite Differentiation a b s t r a c t This study examines the effect of surface chemical functionalities on the behavior of human adipose- derived stem cells (hASCs) in vitro. Plasma polymerized films rich in amine ( NH 2 ), carboxyl ( COOH) and methyl ( CH 3 ), were generated on hydroxyapatite (HAp) substrates. The surface chemical function- alities were characterized by X-ray photoelectron spectroscopy (XPS). The ability of different substrates to absorb proteins was evaluated. The results showed that substrates modified with hydrophilic func- tional group ( COOH and NH 2 ) can absorb more proteins than these modified with more hydrophobic functional group ( CH 3 ). The behavior of human adipose-derived stem cells (hASCs) cultured on differ- ent substrates was investigated in vitro: cell counting kit-8 (CCK-8) analysis was used to characterize cell proliferation, scanning electronic microscopy (SEM) analysis was used to characterize cell morphology and alkaline phosphatase (ALP) activity analysis was used to account for differentiation. The results of this study demonstrated that the NH 2 modified surfaces encourage osteogenic differentiation; the COOH modified surfaces promote cell adhesion and spreading and the CH 3 modified surfaces have the lowest ability to induce osteogenic differentiation. These findings confirmed that the surface chemical states of biomaterials can affect the behavior of hASCs in vitro. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In tissue engineering and regenerative medicine, as in many other areas, material plays a cornerstone and an important role not only as inert mechanical supports or cell and drug delivery vehicles but also to direct and guide the interaction at the tis- sue or cell–material interface [1]. Materials can provide cues that control cell adhesion, proliferation, differentiation and migration. These cues include the material physical and chemical properties such as surface topography [2–4], mechanical properties [5,6], sur- face chemical states [7–9], etc. Understanding these interactions is important for the future materials design that will facilitate and promote tissue repair and regeneration [10]. Stem cells based therapies have generated significant inter- est and are regarded as the future of various medical procedures and treatments. Human adipose-derived stem cell (hASC) is a type of mesenchymal stem cell which has the potential to undergo multilineage differentiation: adipogenesis [11], osteogenesis [12], chondrogenesis [13], neurogenesis [14], angiogenesis [15] and so on. Compared with other sources of mesenchymal stem cells such ∗ Corresponding author. Tel.: +86 10 62782770; fax: +86 10 62771160. E-mail address: biomater@mail.tsinghua.edu.cn (Q. Feng). as bone marrow, the most commonly used in tissue engineer- ing, adipose tissue is available in relatively large quantities using liposuction procedures which the patients are ready to accept [16]. Accordingly, over the last 10 years, an increasing number of researchers have started using hASCs as seeding cells for bone tissue engineering instead of human bone marrow-derived mesenchymal stem cells (hMSCs) [17–19]. In the context of stem cell based thereapies, it is important to understand how material surface properties influence the dif- ferentiation of hASC cells. Hydroxyapatite (HAp), which is the inorganic constituent of human bones and widely used in bone tis- sue engineering because of its good biocompatibility, was selected as the substrates. It is very interesting to know if the surface modification can affect the biocompatibility and osteoinduction of HAp. Plasma polymerization is usually employed as a surface modification method. Compared with other methods, for example, silanization or self-assembling, plasma polymerization can effec- tively provide a pinhole free film with high retention of functional groups and good surface coverage with relatively low cost [20]. In this study, a range of surfaces of engineered surface func- tionalities were prepared to explore how the surface chemical states influence hASC morphology, proliferation and differentiation in vitro. Amine ( NH 2 ), carboxyl ( COOH) and methyl ( CH 3 ) were generated on HAp substrates by plasma polymerization. These 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.01.063