Investigation on the swelling mechanics of hydrogel tissue expanders using a skin-mimicking apparatus

Thesis

The concept of self-expanding hydrogel tissue expanders has opened a new pathway to the treatment of soft tissue defects. Traditionally designed to expand the skin, modifications to the swelling behaviour of these devices may lead to various new-found applications. Properties of poly(vinylpyrrolidone) /poly(methyl-methacrylate) (VP/MMA) hydrogel system such as the degree, rate, force generation, and anisotropic behaviour of swelling were investigated in this study as part of a preliminary understanding of the hydrogel material.

The swelling of hydrogel network is the balance between two main driving forces: 1) the relaxation of the gel network and 2) the osmotic diffusion of solvent via gel hydrophilicity. A direct relationship between the elastic modulus and the swelling pressure was found by measuring the swelling force over the hydration period. Despite reduction in the overall swelling ratio, gels with a larger modulus were observed to have a larger corresponding force generation. This is due to the straining of gels with higher cross-linking density. The results showed a maximum stress of 64.0 ± 3.2 kPa and 30.8 ± 1.5 kPa for 90:10 wt% and 99:1 wt% VP/MMA, respectively.

Specially modified anisotropic swelling gels were shown to have larger stress generation along the axis of directional swelling (~70-80 kPa). Limitation factors to the anisotropic modification are materialistic and geometrical. Shape-memory characteristics were found to be reduced at high compression ratio as a result of plastic deformation. Gels with slenderness ratio above 2.5 were evaluated to be susceptible to device slippage/buckling. These results provide useful design limitations for self-expanding tissue expanders.

The overall goal in creating a new testing system for self-swelling tissue expanders was achieved.A skin-mimicking apparatus was specially built to highlight the amount of skin expansion and simulate surface topography. Strain contours along the expanded skin were also plotted to represent skin tension. Prior to this study,these measurements were only possible under in vivo animal testing. The advantage in having this device is to support the prevention of related animal testing.

Authors: Maneepairoj, P

• Publication date: 2014
• DOI: 10.5287/ora-az2pa17br
• Type of award: MPhil
• Level of award: Masters
• Awarding institution: University of Oxford
• Language: English
• Keywords: soft tissue; swelling; implants; dermal tissue; tissue expander; hydrogels
• Subjects: Plastic and reconstructive surgery; Materials engineering; Biomedical engineering