In the field of dental implantology, the choice of material for implant components is critical for ensuring long-term success and patient satisfaction [1]. The establishment of an effective biological interface between restorative biomaterials and the surrounding tissues is essential for maintaining long-term oral health [2]. For optimal tissue integration, the ideal material surface should possess dual functions: it should provide a surface that is conducive to cell spreading and adhesion for tissue healing, while also inhibiting bacterial colonization [3]. Traditionally, titanium has been the material of choice for most dental implants due to its well-established biocompatibility and mechanical properties [4]. However, its metallic appearance, potential for allergic reactions, and risk of peri-implantitis have led to increased interest in alternative materials that can better meet both functional and aesthetic demands [5].

Polyetheretherketone (PEEK) is a high-performance polymer that is widely used in maxillofacial and orthopedic applications and has emerged as a promising alternative to titanium in dental applications [6], [7]. PEEK offers several advantages including excellent mechanical properties, radiolucency, chemical stability, and a color more similar to natural teeth, making it an aesthetically attractive option in dental implant components [8], [9]. Despite these benefits, one of the major limitations of PEEK is its bio-inertness and hydrophobic surface, which hinders soft tissue integration and reduce its potential for long-term success in oral implants [10], [11]. Therefore, surface modification strategies aimed at improving the bioactivity and antimicrobial performance of PEEK are essential for its wider adoption in clinical practice. To address the limitations of PEEK surfaces, plasma treatment has been extensively studied as a surface modification technique for enhancing hydrophilicity and introducing functional groups that facilitate further modifications [11], [12], [13]. Following this initial treatment, bioactive coatings can be applied to the activated surfaces, creating a dual-functional interface that supports both enhanced soft tissue integration and infection prevention [14].

One promising approach involves the use of dopamine (DA), a molecule inspired by the adhesive proteins in mussel foot, which can form a stable polymeric coating on a variety of surfaces, including PEEK [13], [15], [16]. Through self-polymerization under mild conditions, polydopamine (PDA) can form adherent coatings on various surfaces, and its abundant functional groups (catechol, amine, and imine) enable further modification with various bioactive molecules [15]. Chlorhexidine (CHX) is a cationic biguanide antiseptic, which has been widely recognized as the gold standard antimicrobial agent in dentistry due to its broad-spectrum antimicrobial activity and substantivity [17]. The PDA coating enables effective immobilization of the antibacterial agent CHX on the PEEK surface. However, free CHX molecules were prone to rapid clearance by physiological fluids, leading to suboptimal long-term efficacy. The combination of PDA and CHX represents a strategic approach to address this limitation along with the surface biocompatibility and infection control challenges associated with PEEK material [18], [19].

In this study, we proposed a novel surface modification strategy for PEEK that combines plasma treatment with a dopamine-crosslinked chlorhexidine. The physicochemical properties of the modified surfaces were comprehensively characterized by multiple analytical techniques. The biological response was evaluated through in vitro studies with human gingival fibroblasts (HGFs), examining their adhesion, morphological characteristics, and proliferation dynamics on the functionalized PEEK surfaces. Furthermore, the antimicrobial performance evaluation primarily focused on Streptococcus mutans (S. mutans), an early colonizer in oral biofilm formation that serves as an established model organism for assessing dental material surfaces. To complement this analysis and evaluate broad-spectrum efficacy, we conducted additional experiments with Escherichia coli as a representative Gram-negative bacterium. Based on these research objectives, two null hypotheses were tested: the P-PDA-CHX modified PEEK surface shows no enhancement in cell adhesion and proliferation of HGFs compared to unmodified PEEK surface (H0–1), and the P-PDA-CHX modified PEEK surface demonstrates no improvement in antibacterial activity against S. mutans compared to unmodified PEEK surface (H0–2).