Med-Tech Innovation Materials
those produced using chemical crosslinking. In the experimental phase, four hydrogel concentrations were prepared using varying quantities of PVOH and PAA combined with a dimethyl sulphoxide (DMSO)/distilled water solution. The production method for each of four concentrations (see Table I) was as follows: • The polymer was dissolved at 80°C while the distilled water/DMSO mixture was added gradually and combined using magnetic agitation.
• Samples were placed in an ultrasonic bath for one hour to remove bubbles.
• Samples were subjected to repeated cryo-cycles by freezing in liquid nitrogen for twenty minutes followed by thawing. Prepared samples were characterised using two techniques: differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The first of these techniques was performed on dried samples using a TA DSC Q2000 within the temperature range of 20 to 230°C. Results are shown in Figure 1.
Results of characterisation Endothermic transitions were found to occur in samples 3 and 4. This is attributable to the formation of crystals at what is known as crystallisation temperature (Tc), measured as 152.93°C and 153.58°C for samples 3 and 4, respectively.
Crystallisation temperature for samples 1 and 2 could not be ascertained because no distinct crystalline melting endotherms were found to occur, which suggests a lower degree of crystallisation in these samples. It can be inferred that DMSO plays a role in increasing crystallinity in the hydrogel compositions, an effect noted in prior literature.5
The second characterisation technique, DMA, was conducted using a TA DMA Q800, which permits analysis in compression mode or tensile mode. Only compression mode analysis was used here because the samples were found to be too delicate to withstand tensile mode testing. Samples were characterised in their swollen state, with approximate thicknesses of 12 mm and
Figure 1: DSC plot
7 mm, and coated in silicone vacuum grease to conserve water content. Results were compared against published measurements for human blood vessels (Figure 2).
Key findings
The study found that • Increasing the DMSO content led to increased mechanical strength of the material composition.
• Using higher molecular weight polymer resulted in specimens with increased material strength.
• The addition of DMSO was found to have a significant effect on the storage modulus of the samples. This result concurs with findings of prior research.6
• Figures obtained using DMA are similar to published values for veins, but arteries are substantially higher. This may be due to the use of compression testing
Figure 2: DMA results compared with reported blood vessel results
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