In vitro screening of biocompatibility of modified polyetheretherketone as an implant material: Cytotoxicity and cell adhesion

Introduction. In modern medical practice, bone implants are in demand as an effective solution for restoring bone tissue, including for the rehabilitation of patients with wounds sustained in combat. Polyetheretherketone (PEEK) is considered a promising polymer material for surgical implant production due to a number of properties that closely mimic bone tissue. However, the use of unmodified PEEK in implantology is limited by its biological inertness and poor osseointegration. Modification of this material, including through structural changes to the surface, can increase its biological activity, osteoconductivity, and antibacterial properties.

Objective. To evaluate the cytotoxicity and surface adhesion properties of PEEK modified via various methods.

Materials and methods. PEEK powder was synthesized via polycondensation under nucleophilic substitution conditions by reacting hydroquinone with 4,4’-difluorobenzophenone; for further studies, disk-shaped specimens were fabricated via milling. PEEK surface was modified using one of three methods: sulfonation with concentrated sulfuric acid, treatment with piranha solution followed by functionalization with glycine, or high-temperature fusion with NaCl followed by leaching. The structure of the obtained materials was studied using IR spectrometry and scanning electron microscopy. Cytotoxicity was assessed using the MTT test. The adhesive properties of PEEK materials were evaluated by culturing human dermal fibroblasts on their surface, followed by fluorescence visualization using Calcein AM and Hoechst 33342 fluorochromes. Analysis of adhesion and morphology of attached cells was performed using an inverted Leica DMI 3000 B microscope.

Results. It was shown that PEEK obtained via polycondensation of hydroquinone and 4,4’-difluorobenzophenone does not exhibit a cytotoxic effect on anchorage-dependent cells. Under the influence of the 1-day extract of PEEK and its dilutions, relative cell viability ranged from 96 to 126%, while for the 7-day extract, it varied from 132 to 141% (vs. 100% for the control); stimulation of proliferative activity of cells by PEEK extract was demonstrated. It was found that modification of the specimens does not lead to increased cell adhesion. The porous PEEK specimen obtained by pressing with NaCl followed by its leaching was characterized by uneven adhesion and impaired viability of most cells on the specimen surface. Treatment of PEEK with glycine led to decreased adhesion, impaired viability, and altered morphological characteristics of a large proportion of cells on the specimen surface. On the surface of sulfonated PEEK, the cells remained viable; however, the morphology of the attached cells differed significantly from the typical pattern. Specifically, instead of a subconfluent monolayer of flattened cells characteristic of successful adhesion, cell conglomerates of various sizes, formed by rounded and, less frequently, spindle-shaped cells, were unevenly distributed across the surface.

Conclusions. When modifying PEEK via sulfonation with concentrated H₂SO₄, treatment with glycine, or high-temperature fusion with NaCl, no improvement in the biocompatibility of the material was detected; on the contrary, impairments in the viability and morphology of anchorage-dependent cells adhered to the surface of the modified PEEK were observed. These findings highlight the need to continue searching for PEEK modification methods to overcome the limitations of the material and expand its areas of application in solving urgent interdisciplinary biomedical problems.

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