Contents lists available at ScienceDirect Journal of the European Ceramic Society journal homepage: www.elsevier.com/locate/jeurceramsoc Original Article GrainboundarycorrosioninTiO 2 bonescafoldsdopedwithgroupIIcations Anne Klemm a , Manuel Gomez-Florit b,c , Patricia Almeida Carvalho d , Mattis Wachendörfer a,e , Manuela E. Gomes b,c , Håvard J. Haugen a , Hanna Tiainen a, ⁎ a University of Oslo, Department of Biomaterials, Institute of Clinical Dentistry, P.O. Box 1109 Blindern, 0317, Oslo, Norway b 3B's Research Group, I3Bs – Research Institute on Biomaterials, Biodegradables and Biomimetics, University of Minho, Headquarters of the European Institute of Excellence on Tissue Engineering and Regenerative Medicine, AvePark, Parque de Ciência e Tecnologia, Zona Industrial da Gandra, 4805-017, Barco, Guimarães, Portugal c ICVS/3B’s–PT Government Associate Laboratory, Braga, Guimarães, Portugal d SINTEF Materials and Chemistry, PB 124, Blindern, NO-0314, Oslo, Norway e Helmholtz-Institute for Biomedical Engineering, Chair of Medical Engineering, RWTH Aachen University, Pauwelsstraße 20, 52074, Aachen, Germany ARTICLEINFO Keywords: Doped TiO 2 Corrosion Grain boundary SrTiO 3 Osteogenic diferentiation ABSTRACT A pH drop during the infammatory phase during bone regeneration can cause corrosion in TiO 2 bone scafolds and the loss of compressive strength. Corrosion as ion leaching and dissolution is confned to grain boundaries. Cationic doping of TiO 2 showed to increase the compressive strength but increased the amount of impurities in grainboundariesaswell.Therefore,thisstudyshowedthediferentgrainboundary formationforCa,SrandMg doped scafolds and their corrosion behavior. After corrosion, the amorphous phase in grain boundaries was dissolvedinalldopedscafolds.Diferencesoccurredduetothe formationofanadditionalcrystallinephaseinSr doped scafolds. The presence of an amorphous and crystalline phase led to an inhomogeneous dissolution in grain boundaries and a signifcant decrease in compressive strength already after 4h in contact with an acidic environment. Released ions did not show any cytotoxic efect on hASCs. Mg doped TiO 2 scafolds led to sig- nifcant increased osteogenic diferentiation. 1. Introduction The potential for highly porous TiO 2 scafolds as bone scafolds is well-known [1–3]. Due to a sufcient pore size, interconnectivity and large surface-to-volume ratio, these scafolds allow cell ingrowth, vas- cularization and cell adhesion [2,3]. Furthermore, TiO 2 scafolds pro- ducedbythepolymerspongereplicationmethodcombinehighporosity with high compressive strength [4]. This property of bone scafolds is crucial for the support of bone cells during bone regeneration process and should be stable during the infammatory phase. To reach a compressive strength similar to that of natural bone (2–12MPa), diferent strategies have been proposed to increase the strength of TiO 2 scafolds. One possible strategy is the so-called double coating,wherethefnalsinteredscafoldsarecoatedwithalowviscous slurry to densify the strut architecture. Using this strategy, the com- pressivestrengthofTiO 2 scafoldscanbeincreased fromapprox.1MPa up to 1.6MPa for a porosity of approx. 90% [4]. We have also shown that cationic doping of TiO 2 slurries leads to a similar signifcant in- creaseincompressivestrength.Theadvantageofthisstrategyisthatno additionalstep,includinglowviscousslurryandsinteringprocedure,is necessary. By adding diferent ions to the slurry, two mechanisms lead to higher compressive strength. First, the slurry viscosity is increased, which was shown to afect the fnal strength. Second, the sintering behavior of TiO 2 is changed and the presence of a liquid phase during sintering was proposed as reason for the improved strut densifcation and a high compressive strength of 1.64MPa [5]. Corrosion resistance of the TiO2 scafolds is an important property to ensure a high compressive strength during infammatory phase. Duringinfammatoryphase,alargeamountofmacrophagesarepresent whichcanacidifytheirmicroenvironmenttoapHlevelof3.6–3.7[6]. Ceramics in general show corrosion in acidic environments due to ion leachinganddissolution[7].Theseefectstendtoconcentrateonareas where crystal lattice defects are dominant, such as grain boundaries. Mülleretal.foundreleasedSiandAlfromTiO 2 grain boundaries after storingtheTiO 2 bonescafolds for8weeksin1mMHClsolution(pH3). Furthermore, the study showed signifcant decrease in compressive strength after corrosion [8]. In the present study, TiO 2 scafolds doped with divalent Ca, Sr and Mgcationsshowedadiferentandnewimpurityrich formationingrain boundaries. Considering that corrosion is likely to occur in these areas, the new formation has to be investigated with focus on corrosion be- havior. TEM was used to investigate the grain boundary formation in https://doi.org/10.1016/j.jeurceramsoc.2018.12.055 Received 24 October 2018; Received in revised form 16 December 2018; Accepted 22 December 2018 ⁎ Corresponding author. E-mail address: Hanna.tiainen@odont.uio.no (H. Tiainen). Journal of the European Ceramic Society xxx (xxxx) xxx–xxx 0955-2219/ © 2018 Elsevier Ltd. All rights reserved. Please cite this article as: Klemm, A., Journal of the European Ceramic Society, https://doi.org/10.1016/j.jeurceramsoc.2018.12.055