Water Absorption of Poly(methyl methacrylate) Measured by Vertical Interference Microscopy

Abstract

PMMA (poly(methyl methacrylate)) is widely used to prepare orthopedic cements. They are in direct contact with cells and body fluids. PMMA, despite its hydrophobic nature, can absorb ~2% w/w water. We have evaluated by vertical interference microscopy if water absorption can produce a significant swelling in different types of PMMA blocks: pure, with a plasticizer, with a cross-linker, and in two types of commercial bone cements. Graphite rods which do not swell in water were used as internal standard. Hardness, indentation modulus, plastic, and elastic works were determined by nanoindentation under a 25mN fixed force. Vertical interference microscopy was used to image the polymer in the dry state and hydrated states (after 24 h in distilled water). On the surface of the polished polymers (before and after hydration), we measured roughness by the fractal dimension, the swelling in the vertical and the lateral directions. For each polymer block, four images were obtained and values were averaged. Comparison and standardization of the images in the dry and hydrated states were done with Matlab software. The average value measured on the graphite rod between the two images (dried and hydrated) was used for standardization of the images which were visualized in 3D. After grinding, a small retraction was noticeable between the surface of the rod and the polymers. A retraction ring was also visible around the graphite rod. After hydration, only the pure PMMA and bone cements had a significant swelling in the vertical direction. The presence of polymer beads in the cements limited the swelling in the lateral direction. Swelling parameters correlated with the nanoindentation data. PMMA can swell by absorbing a small amount of water and this induces a swelling that varies with the polymer composition and particle inclusions.

Study of the water structure in poly(methyl methacrylate-block-2-hydroxyethyl methacrylate) and its relationship to platelet adhesion on the copolymer surface

“…It is well known that hydrophobic polyMMA can contain approximately 2 wt% of water. [34] Our result was consistent with this value, and the water could only be classified as non-freezing water. Based on this value, 2 wt%, the number of non-freezing water molecules governed by the MMA unit is estimated to be 0.11.…”

“…Thus, the temperature of the sample increased during each XRD scan. [34] The intensities of the crystalline peaks at 2θ = 22.9°, 24.4°, and 26.1°in the diffraction patterns for each scan were summed, and the changes in the intensities (crystallinity) as a function of the temperature were investigated.…”

A stable lead halide perovskite nanocrystals protected by PMMA

“…4c, d). The top surface of composite film changed from smooth (Stage I) to coarse porous (Stage II), due to water diffusion, swelling of PMMA into pores [42]. Meanwhile, the crystal structures of the two stages were detected by XRD.…”

Effects of Different pH-Values on the Nanomechanical Surface Properties of PEEK and CFR-PEEK Compared to Dental Resin-Based Materials

“…This result is consistent with the study of Assuncao et al [37], who reported that storage in saliva could significantly reduce the hardness of the PMMA resin after 15, 30, and 60 days’ treatment. Moreover, it is reported that after 24 h immersion in the water, the PMMA matrix can significantly swell in the lateral and vertical directions [38], indicating that the solvent molecules penetrate into the PMMA matrix and break the intermolecular bonding between polymer networks. Once the matrix network is broken, the properties of PMMA will get worse inevitably.…”