Contents lists available at ScienceDirect Materials Science & Engineering C journal homepage: www.elsevier.com/locate/msec Effect of crystalline phases of titania nanotube arrays on adipose derived stem cell adhesion and proliferation Marcela Ferreira Dias-Netipanyj a , Kari Cowden b , Luciane Sopchenski c , Sheron Campos Cogo d , Selene Elifio-Esposito a , Ketul C. Popat b,e , Paulo Soares c, ⁎ a Graduate Program in Health Science, School of Medicine, Pontifícia Universidade Católica do Paraná, Curitiba, Paraná, Brazil b Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, USA c Department of Mechanical Engineering, Polytechnic School, Pontifícia Universidade Católica do Paraná, Curitiba, Paraná, Brazil d Department of Biological Sciences, School of Health and Biosciences, Pontifícia Universidade Católica do Paraná, Curitiba, Paraná, Brazil e School of Biomedical Engineering, Colorado State University, Fort Collins, CO, USA ARTICLE INFO Keywords: Titania nanotube arrays Anatase Rutile Adipose derived stem cells Cell proliferation ABSTRACT The aim of this work was to evaluate the cellular response to titanium nanotube arrays with variable crystalline structure. Cytotoxicity, viability and the ability of the titania nanotube arrays to stimulate adhesion and pro- liferation of adipose derived stem cells (ADSCs) was evaluated. Titania nanotube arrays were fabricated by electrochemical anodization of titanium in diethyleneglycol/hydrofluoric acid electrolyte at 60 V for 6 h, then annealed at 300, 530 and 630 °C for 5 h. The nanotube arrays were characterized using scanning electron mi- croscopy (SEM), contact angle goniometry, x-ray diffraction (XRD) and protein adsorption. ADSCs were cultured on titania nanotube arrays at a density of 1 × 10 4 cells/ml. The cells were allowed to adhere and to proliferate for 1, 4 and 7 days. Cell viability was characterized by the CellTiter-Blue® Cell Viability Assay; and cell mor- phology was characterized by SEM. Cell adhesion, proliferation and morphology were characterized using fluorescence microscopy by staining the cells with DAPI and rhodamine/phalloidin. The results from this study showed that the annealing at 300 and 530 °C formed anatase phase, and annealing at 630 °C formed anatase/ rutile phase. The results indicated that the modification of the crystalline structure (i.e. anatase/rutile phase) of titania nanotube arrays influenced the ADSC adhesion and proliferation. Future studies are now directed towards evaluating differentiation of this cellular model in osteoblasts. 1. Introduction Biomaterials have been used as implants in the human body to perform certain biological functions, such as replace or repair of dif- ferent tissues like bone, cartilage or ligaments, tendons, etc. [1]. His- torically, the use of metal alloys started in 1923 with the emergence of cobalt‑chromium alloy, in 1942 was introduced the stainless steel and in 1951 was introduced the titanium alloy [2]. Recently, increasing research in metallic biomaterials has been invested in application of the nonconventional reconstructive surgery of hard tissues/organs, as well as to development of new alloys for bone tissue engineering and re- generation [3,4]. Metallic materials have been widely used in tem- porary orthopedic implants such as bone plates, pins and screws, as well as permanent orthopedic implants such as total joint replacements [5]. Globally, at least 2.2 million bone grafting procedures are performed annually and approximately 500,000 of such procedures are done in the United States alone [6]. In addition, metals such as titanium (Ti), tan- talum (Ta); and alloys such as Ti-Al-Va, Co-Cr-Mb, Fe-Cr-Ni are also used in dental implants [7]. Recent data show that about 100,000 to 300,000 dental implants are carried out per year, which approximately similar to the numbers of artificial hip and knee joints combined [8]. Despite the development and use of these biomaterials, there is still a significant increase in revision surgery of implants each year. The total number of hip revision surgery is expected to increase by 137% and knee revision surgery by 607% until 2030 [9]. These data revealed that there might be greater efforts for the development of biomaterials with improved properties. Titanium and its alloys are widely used in orthopedic and dental devices and components due to their excellent properties such as low elastic modulus, good fatigue resistance, better corrosion resistance, https://doi.org/10.1016/j.msec.2019.109850 ⁎ Corresponding author at: Pontifical Universidade Católica do Paraná, Department of Mechanical Engineering - Polytechnic School R. Imaculada Conceição, 1155, Curitiba, PR – 80215-901, Brazil E-mail addresses: ketul.popat@colostate.edu (K.C. Popat), pa.soares@pucpr.br (P. Soares). Materials Science & Engineering C 103 (2019) 109850 Available online 03 June 2019 0928-4931/ © 2019 Published by Elsevier B.V. T