Background
Multifunctional titanium surfaces with high osteogenic activity and antibacterial properties is substantially desired in implant dentistry. Recently, the benefits of strontium (Sr) loaded titanium surfaces on promoting both osteoblast activity and bone formation were reported in vitro and in vivo, respectively. On the other hand, little is known about the influence of physico-chemical properties of Sr-loaded titanium surfaces on bacterial adhesion.      
Aim/Hypothesis
This study aimed to evaluate the physico-chemical properties of Sr-loaded titanium specimens, and its influence on Staphylococcus aureus (S. aureus; ATCC #33591) adhesion and osteoblast (MC3T3-E1) cell activity.  
Material and Methods
Commercially pure titanium discs were polished with SiC sandpapers (up to grit #2500) and equally divided into three groups: 1) machined surface (MS), 2) alkaline etched surface (AES), and 3) Sr-loaded to AES (Sr-AES). The AES group was obtained by fully immersing part of the MS discs into 5 M NaOH at 60 °C, for 24 hours. Part of the AES discs was submitted to alkali-hydrothermal treatment with 60 mM Sr(OH)2 ∙ 8H2O solution, in steel autoclave, to generate Sr-AES group. The surface physico-chemical properties were determined by means of field-emission gun scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometry (EDX), contact angle with deionized water and diiodomethane (surface free energy), and surface roughness (Ra and Rz value). The response of MC3T3-E1 cells activity was assessed by AlamarBlue assay, whereas S. aureus cells adhesion was measured by couting colony forming units per milliliter (c.f.u./mL). Cells morphologies were determined by FE-SEM analysis.    
Results
FE-SEM analysis showed a polished-like surface in MS group, whereas AES specimens presented a fine network nanostructured surface. The Sr-AES group exhibited the same nanostructured pattern surface as AES group, with embbeded particles of Sr. The EDX spectra confirmed amounts of Sr in the Sr-AES group. A well-structured cubic-shape of calcium was detected on AES and Sr-AES specimens. From contact angle measurements, the treatments performed on AES and Sr-AES groups increased both wettability with water and the surface free energy, compared to MS group. In addition, Sr-AES group presented an amphiphilic characteristic. No diferences were observed from surface roughness analysis. The AlamarBlue assay showed that Sr-AES group increased MC3T3-E1 activity at day 14. No diferences were observed on S. aureus adhesion to the different substrates. FE-SEM images showed that osteoblastic cell monolayers and S. aureus aggregate were present on all especimens. 
Conclusions and Clinical Implications
Our preliminary results indicate that Sr incorporation to a fine network nanostructured titanium surface has potential to enhance osteoblast cell activity at day 14. The nanostructured roughness observed on AES and Sr-AES groups had not effect on S. aureus cell adhesion. Sr-AES is a low-cost treatment and may be a promising option to improve implants osseointegration.

Sr-loaded titanium surface enhance MC3T3-E1 osteoblastic activity- a preliminary in vitro study