Effect of additive particles on mechanical, thermal, and cell functioning properties of poly(methyl methacrylate) cement

Abstract

The most common bone cement material used clinically today for orthopedic surgery is poly(methyl methacrylate) (PMMA). Conventional PMMA bone cement has several mechanical, thermal, and biological disadvantages. To overcome these problems, researchers have investigated combinations of PMMA bone cement and several bioactive particles (micrometers to nanometers in size), such as magnesium oxide, hydroxyapatite, chitosan, barium sulfate, and silica. A study comparing the effect of these individual additives on the mechanical, thermal, and cell functional properties of PMMA would be important to enable selection of suitable additives and design improved PMMA cement for orthopedic applications. Therefore, the goal of this study was to determine the effect of inclusion of magnesium oxide, hydroxyapatite, chitosan, barium sulfate, and silica additives in PMMA on the mechanical, thermal, and cell functional performance of PMMA. American Society for Testing and Materials standard three-point bend flexural and fracture tests were conducted to determine the flexural strength, flexural modulus, and fracture toughness of the different PMMA samples. A custom-made temperature measurement system was used to determine maximum curing temperature and the time needed for each PMMA sample to reach its maximum curing temperature. Osteoblast adhesion and proliferation experiments were performed to determine cell viability using the different PMMA cements. We found that flexural strength and fracture toughness were significantly greater for PMMA specimens that incorporated silica than for the other specimens. All additives prolonged the time taken to reach maximum curing temperature and significantly improved cell adhesion of the PMMA samples. The results of this study could be useful for improving the union of implant-PMMA or bone-PMMA interfaces by incorporating nanoparticles into PMMA cement for orthopedic and orthodontic applications.

Keywords: barium sulfate; cell viability; chitosan; curing temperature; flexural strength; fracture toughness; hydroxyapatite; magnesium oxide; poly(methyl methacrylate); silica.

Figure 1

(A) Evex mechanical test system (Evex Analytical Instruments Inc., Princeton, NJ, USA) used for the three-point flexural and fracture tests in the different PMMA samples. (B) Fabricated indenter and support fixtures for flexural tests. (C) Alignment of a notched specimen during fracture tests. During the tests, two lines perpendicular to each other were drawn to align the center of the notch with the center of the roller on the indenter using a Nikon stereomicroscope and NIS BR software (Nikon, Tokyo, Japan). Abbreviation: PMMA, poly(methyl methacrylate).

Figure 2

(A) Schematic view of the experimental setup for measurement of exothermic temperature of PMMA cement. (B) Fabricated setup for measurement of exothermic temperature of PMMA cement. Note: InstruNet: Omega Engineering, Inc., Stamford, CT, USA. Abbreviation: PMMA, poly(methyl methacrylate).

Figure 3

Cell culture protocols for cell adhesion tests on PMMA, including (A) a DAPI-stained image showing osteocyte nuclei and (B) a custom-made well plate for culturing cells on PMMA cements. Abbreviations: DAPI, 4′,6-diamidino-2-phenylindole; PMMA, poly(methyl methacrylate).

Figure 4

(A) Stress versus strain plots of PMMA samples tested during this study. (B) Bar diagram of the variation in flexural strength of PMMA samples due to variation of additives to PMMA. Notes: Data are presented as the mean ± standard error of mean; n=3 for PMMA-CS; n=4 for the rest of the samples. *P<0.05 (compared with PMMA). Abbreviations: CS, chitosan; HAp, hydroxyapatite; MgO, magnesium oxide; PMMA, poly(methyl methacrylate); BaSO₄, barium sulfate; SiO₂, silica.

Figure 5

Bar diagram of the variation in fracture toughness of PMMA samples due to variation in additives to PMMA. Notes: Data are presented as the mean ± standard error of the mean; n=4 for PMMA-HAp and PMMA-SiO₂; n=3 for the rest of the samples. *P,0.05 (compared with PMMA). Abbreviations: CS, chitosan; HAp, hydroxyapatite; MgO, magnesium oxide; PMMA, poly(methyl methacrylate); BaSO₄, barium sulfate; SiO₂, silica.

Figure 6

Time versus temperature graphs of different PMMA sample specimens. Abbreviations: CS, chitosan; HAp, hydroxyapatite; MgO, magnesium oxide; PMMA, poly(methyl methacrylate); BaSO₄, barium sulfate; SiO₂, silica.

Figure 7

Bar diagram of the variation in cell density with PMMA samples due to variation in additives to PMMA. Notes: Data are presented as the mean ± standard error of the mean; n=8. *P<0.05 versus PMMA. Abbreviations: CS, chitosan; HAp, hydroxyapatite; MgO, magnesium oxide; PMMA, poly(methyl methacrylate); BaSO₄, barium sulfate; SiO₂, silica.

Figure 8

Fluorescent microscope images of different kinds of bone cements used during cell proliferation tests. (A) PMMA, (B) PMMA with MgO, (C) PMMA with HAp, (D) PMMA with CS, (E) PMMA with BaSO₄, and (F) PMMA with SiO₂. Abbreviations: CS, chitosan; HAp, hydroxyapatite; MgO, magnesium oxide; PMMA, poly(methyl methacrylate); BaSO₄, barium sulfate; SiO₂, silica.

Figure 9

Scanning electron micrographs of the different types of bone cement used in cell function tests (30,000×, scale bar 3 μm). (A) PMMA, (B) PMMA with MgO, (C) PMMA with HAp, (D) PMMA with CS, (E) PMMA with BaSO₄, and (F) PMMA with SiO₂. Abbreviations: CS, chitosan; HAp, hydroxyapatite; MgO, magnesium oxide; PMMA, poly(methyl methacrylate); BaSO₄, barium sulfate; SiO₂, silica.

Figure 10

Atomic force micrographs of amplitude (A–F) and height (G–L) of PMMA, PMMA with MgO, PMMA with HAp, PMMA with CS, PMMA with BaSO₄, and PMMA with SiO₂. Abbreviations: CS, chitosan; HAp, hydroxyapatite; MgO, magnesium oxide; PMMA, poly(methyl methacrylate); BaSO₄, barium sulfate; SiO₂, silica.