Grafting Polymer Brushes by ATRP from Functionalized Poly(ether ether ketone) Microparticles

Abstract

Poly(ether ether ketone) (PEEK) is a semi-crystalline thermoplastic with excellent mechanical and chemical properties. PEEK exhibits a high degree of resistance to thermal, chemical, and bio-degradation. PEEK is used as biomaterial in the field of orthopaedic and dental implants; however, due to its intrinsic hydrophobicity and inert surface, PEEK does not effectively support bone growth. Therefore, new methods to modify PEEK's surface to improve osseointegration are key to next generation polymer implant materials. Unfortunately, PEEK is a challenging material to both modify and subsequently characterize thus stymieing efforts to improve PEEK osseointegration. In this manuscript, we demonstrate how surface-initiated atom transfer radical polymerization (SI-ATRP) can be used to modify novel PEEK microparticles (PMP). The hard core-soft shell microparticles were synthesized and characterized by DLS, ATR-IR, XPS and TEM, indicating the grafted materials increased solubility and stability in a range of solvents. The discovered surface grafted PMP can be used as compatibilizers for the polymer-tissue interface.

Figure 1.

Overlay of ATR-IR spectroscopy of PMP-iBBr (black) and PMP-g-PDMAEMA (red).

Figure 2.

a) TGA of PMP-g-PDMAEMA and b) XPS analysis of PMP, PMP-iBBr, and PMP-g-PDMAEMA samples. (C1s scan)

Figure 3:

a) Procedure of redissolving PMP-g-PDMAEMA in methanol; b)The TEM images of PMP-g-PDMAEMA samples prepared by drop-casting a methanol dispersion of PEEK particles onto a Cu-based TEM grid. The grid was dried in air before loaded to the sample chamber of TEM. c) DLS measurements for 0.67±0.02 mg/mL PMP-g-PDMAEMA in methanol at 25 °C

Figure 4:

In vitro studies of polymer-grafted PEEK microparticles. a) Biocompatibility assays illustrating the effect of 72 h treatment of HEK293 cells with 10 mg/ml polymer-grafted PEEK microparticles normalized to no treatment control. Data presented is the average of three replicates, ns: not significant vs no treatment control. b)Osteoinductive properties of polymer-grafted PEEK microparticles evaluated in the presence of BMP2 using C2C12 cells. Quantification of ALP expression on different treatments, bars indicate % Mean ± SEM (n=3), ns: not significant vs control. c) Microscopy images of C2C12 cells stained for ALP after 72 hours in cell culture in presence of 10 mg/ml PEEK microparticles and ±100 ng/ml BMP2. Intensity of blue color correlates with intracellular ALP expression, scale bar = 200 μm.

Scheme 1.

Micro-precipitation process of PEEK microparticles (PMP)

Scheme 2.

Modification of PMP surface with ATRP initiator and grafting polymers via SI-ATRP