Page 90 - Clinical relevance of current materials for cranial implants

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Chapter 4
Specimen preparation
The fractured cranioplasty was compared to fresh specimens of CMW-3 (PMMA). Following the manufacturer’s instructions, the PMMA particles (40.0 g) were mixed with MMA liquid (17.9 g) in a vacuum holder. The malleable CMW-3 was put into a nylon 3D printed cranial mold. One specimen was cured for 30 minutes at atmospheric pressure, another was cured for 30 minutes at a pressure of 2.2 bar.
Gel permeation chromatography
The average molecular weights and their distributions were assessed by gel permeation chromatography. Four small samples were collected from the edge of the fractured implant. To compare, 2 fresh samples of CMW-3 were retrieved. In total 6 samples were analyzed using GPC to determine the relative molecular weights. The samples of the fractured implant were washed with demi-water to remove as many blood stains as possible, and all samples were measured in duplo.
Suspensions were formed by mixing each sample in tetrahydrofuran (THF) while stirring and heating, resulting in sample concentrations of around 2 mg/mL. These suspensions were filtered to remove the present non-soluble salts and additives, and injected into the GPC column (300 x 7.5 mm, 3 μm particles, Mixed-C and Mixed-D columns connected in series (Polymer Labs, currently Agilent Technologies, Santa Clara, California, USA)). The mobile phase consisted of tetrahydrofuran at 1 mL/min and 40 °C. Ultraviolet/visible photodiode array (UV/Vis-PDA) and refractive index (RI) detectors were used to analyze the samples and were compared to polystyrene standards.
Porosity and density
The porosity was determined by measuring the density and using 3D μCT. The density of the specimens was measured using a Mettler Toledo AT261 (Greifensee, Switzerland) analytical balance. Micro-CT data were acquired using a SKYSCAN 1272 (Bruker, Kontich, Belgium) with the following settings: voltage = 100 kV, current = 100 μA, exposure time = 31.2 s, pixel size = 6.7 μm, and 1200 projection angles. The porosity was determined with CTAn software (v1.7.17; Bruker, Kontich, Belgium).