Dynamic Mineralization: Low‐Temperature, Rapid, and Multidirectional Process to Encapsulate Polyether‐Ether‐Ketone with Carbonate‐Rich Hydroxyapatite for Osseointegration

Abstract

Polyether‐ether‐ketone (PEEK) is one of the key materials used to fabricate intervertebral spacers due to its mechanical similarity to bone and non‐interference with imaging. However, its surface chemistry limits osseointegration, while its chemical unreactivity and low glass transition/melting temperature poses technical challenges to the application of coatings conducive to bone growth. The present work applies nature‐inspired interfacial and surface chemistry processes to encapsulate PEEK with nanocrystalline carbonate‐rich hydroxyapatite (C‐Ap), a bioactive mineral valued for its chemical/structural similarity to bone mineral and its bioresorbability. This technique is distinguished from previous work by the combined features of low‐temperature, multidirectional/rapid application, and additive‐free processing. The resultant nanocrystalline C‐Ap coating encapsulates PEEK, indicating suitability with standard and state‐of‐the‐art spacers, made by additive/subtractive techniques. A precursor CaCO3 layer is deposited on PEEK by nacre‐inspired convective self‐assembly, followed by a travertine‐inspired rapid (10 min) cold‐sintering treatment. The CaCO3 layer is converted to C‐Ap in phosphate buffered saline through dissolution‐recrystallization processes inspired by the hydrated layer of bone. The coatings exhibit contact pressures that are an order of magnitude higher than coatings deposited by the biomimetic method. There is potential for application to other orthopaedic materials and incorporation of biologics throughout the coating structure for sustained release.

Microfluidic device with a carbonate‐rich hydroxyapatite micro‐coating

“…The thickness of the microcoating is driven by the low-temperature deposition process, where a precursor CaCO 3 -NP microcoating is deposited onto an exposed area of a glass slide by the CSA technique and subsequently converted to carbonate-rich hydroxyapatite through dissolution-recrystallization processes in PBS. [18] The CSA technique induces the self-assembly of CaCO 3 -NPs toward the triple contact line of liquid (CaCO 3 -NP suspension), solid (glass), and vapor phase (air) due to capillary forces at the meniscus when the suspension evaporates. [24,25] The contact angle is a key determinant of deposition thickness [18,24,25] and previous studies that used a similar low-temperature deposition method to deposit a contiguous microfilm of carbonate-rich hydroxyapatite on polyether-ether-ketone (PEEK) reported a film thickness of <3 µm.…”

“…[18] The CSA technique induces the self-assembly of CaCO 3 -NPs toward the triple contact line of liquid (CaCO 3 -NP suspension), solid (glass), and vapor phase (air) due to capillary forces at the meniscus when the suspension evaporates. [24,25] The contact angle is a key determinant of deposition thickness [18,24,25] and previous studies that used a similar low-temperature deposition method to deposit a contiguous microfilm of carbonate-rich hydroxyapatite on polyether-ether-ketone (PEEK) reported a film thickness of <3 µm. [18] In addition to substrate type (PEEK vs. glass), other factors that may have contributed to the differences in thickness include temperature (130 • C vs. 80 • C), angle at which the sample was placed in the suspension, and the presence of the polypropylene-based tape that surrounds the exposed area of the glass slide.…”

“…A suitable low-temperature technique to deposit a carbonate-rich hydroxyapatite microcoating onto exposed areas of a glass slide has been described by Lui et al [18,19] Briefly, CaCO 3 nanoparticles (CaCO 3 -NP) can be deposited on the exposed area of a glass slide by convective self-assembly (CSA) [18] (Figure 1). The precursor CaCO 3 then can be converted to carbonaterich hydroxyapatite by dissolution-recrystallization in a F I G U R E 1 Schematic diagram of the low-temperature deposition method to form a microcoating of carbonate-rich hydroxyapatite and incorporate it within the microchannels of a microfluidic device.…”

“…Low-temperature deposition: A glass slide is covered/masked with polypropylene-based tape and CaCO 3 nanoparticles (CaCO 3 -NP) are deposited on exposed areas by convective . [18] The precursor CaCO 3 is converted to carbonate-rich hydroxyapatite by dissolution-recrystallization in phosphate-buffered saline (PBS). [19] Device fabrication: The tape is removed; in a separate process, PDMS is poured on a silicon wafer with the microfluidic design to form a mould of the device layout.…”

Surface Modification of Carbon Fiber-Polyetheretherketone Composite to Impart Bioactivity by Using Apatite Nuclei

“…For solving this problem, many methods to impart bioactivity to the PEEK have been reported [10]. For example, titanium oxide (TiO 2 ) coating by the sol-gel process [11,12], sulfuric acid (H 2 SO 4 ) treatment [13], H 2 SO 4 and calcium chloride (CaCl 2 ) treatment [14], and carbonate-rich hydroxyapatite coating by dynamic mineralization [15] have been reported. In addition, Prochor et al reported that PEEK reinforced with 30% glass fiber showed hydroxyapatite formation [16].…”