###### Abstract  
Porosity and roughened surfaces of implant materials have been shown to lead to improved cellular attachment and enhanced osseointegration. These topography changes in the surface also aid in the mechanical interlocking of the material to the bone. Polyetheretherketone (PEEK) has emerged as a popular alternative to titanium-based implants due to its lack of stress-shielding effect, radiolucency, and high chemical resistance. However, PEEK is bioinert, thus requiring surface modifications to elicit appropriate cellular responses that lead to successful osteointegration of the material in vivo. Sulfonation is a process used to modify the surface of PEEK, which can be controlled by varying parameters such as soak time and soak temperature, thereby fabricating a porous surface on the material. This work aimed to ensure the repeatability of a previously optimized sulfonated and hydrothermally treated PEEK surface and subsequently observe the mechanical properties, bacterial attachment, and cellular response of pre-osteoblast MC3T3-E1 cells on the surface. This study found that while all PEEK surfaces had similar cell and _Staphylococcus aureus_ attachment, the sulfonated and hydrothermally treated PEEK (peak mean load of 605 N, \(p\leq 0.0001\)) and the sulfonated only PEEK (peak mean load of 495 N, \(p=0.0240\)) had a higher level of performance in expulsion testing than smooth PEEK due to its mechanical interlocking ability. Imaging and contact angle analysis confirm that a surface with repeatable porosity can be achieved. polyetheretherketone (PEEK); sulfonation; expulsion; surface modification 2020 May  
bone [17; 18; 19]. In comparison, titanium has a Young's elastic modulus of 80-110 GPa, which can cause a situation known as stress shielding to occur and lead to failure when used as an implant material [8; 12; 17; 18; 19; 20]. PEEK has a similar modulus to bone, eliminating the stress-shielding effect seen in the metallic implant systems. X-rays are utilized in the surgery to examine the implant placement and subsequent bone healing. Metallic implants scatter the X-rays and make it more challenging to see the bone-implant contact area, showing the degree of osseointegration, which determines when the dentist can remove the temporary implant and place the permanent implant. PEEK is a radiolucent material and does not interfere with the X-rays, making for a clear image for the surgeon to examine. Metallic implants are known to have poor esthetic quality, with some of the implant bodies being visible in the gumline. Sulfonated PEEK has a near-bone appearance and will blend well with the patient's bone, leading to a more pleasing esthetic look. Metallic ion release from dental implants is a concern for patients who have a metal allergy, and PEEK will not have this concern. One of the main reasons why implants fail is due to poor osseointegration. Therefore, materials used in orthopedic and dental applications must enhance osseointegration at the implant interface to achieve long-term clinical success [4; 6; 9; 10; 11; 13; 14]. Ossoeintegration is defined as the direct connection between living bone and an implant surface and is most influenced by surface porosity, surface topography, surface chemistry, and wettability [8; 12; 15; 16; 19]. A disadvantage of utilizing PEEK as an implant is that it is bioinert, thus requiring some surface modification to elicit the desirable cellular responses in vivo and enhance osseointegration [5; 7; 17; 18; 20]. Many chemical and physical surface modification techniques have been employed to improve the bioactivity of PEEK, including sandblasting, laser microfabrication patterning, plasma spraying, ultraviolet irradiation, diazonium chemistry reactions, hydroxylation, microwave-assisted deposition, sputtering, aerosol deposition, and biological functionalization [1; 2; 18; 20; 21; 22; 23; 24; 25; 26; 27; 28]. However, these methods can require expensive equipment, be challenging to reproduce, leave behind unstable coatings, and cannot be used on complex shapes [2; 29].