Polyurethane nanocomposites as potential drug delivery systems

Polymer nanocomposites (NCs) are materials with remarkable potential in the field of controlled drug delivery. There are a range of factors proposed to perturb the release mechanisms in polymer NCs, but little focus has been directed towards the understanding of interactions between the drug and NC which can also affect the drug release behaviour. The objective of this research was to examine the potential of polyurethane nanocomposites (PUNCs) as controlled drug delivery systems. Specifically, the aims were to investigate the impact of adding a drug on the silicate dispersion and release behaviour of PUNCs, as well as to assess the impact of fabrication method on the biological interactions of PUNCs and the activity of released drugs. Organically modified silicates (OMS) were prepared using OMs with varying alkyl chain length. The resulting OMS were incorporated at various loadings into PU matrices and solvent cast to form PUNCs. Findings revealed that the optimum dispersion was achieved from samples with lower clay loadings and longer alkyl chains. A better dispersed sample also conferred an increase in strain while maintaining the Young's modulus and tensile strength of the material. The drug release behaviour of PUNCs was significantly impacted by the properties of the added drug. Results showed that drug release was restricted by the size of the drug. For cases using lower molecular weight drugs that can be released, release of hydrophobic drugs was more sustained than for hydrophilic drugs. However, where strong attractive interactions existed with the host polymer, hydrophilic drugs also showed sustained release. The subsequent introduction of silicates modulated drug release based on the charge and polarity of the drug. Positively charged drugs had a tendency to interact with clay to a greater degree and release was significantly reduced by the introduction of clay, while anionic and neutral drugs were modulated to a lesser extent. If the charge of the added drug had a repulsive nature with clay, then increasing clay loading promoted the release. PUNCs fabricated both as films and as coatings demonstrated good cell viability and low cell growth inhibition. Biological assays to assess drug activity showed that drugs remained active after release. PUNCs show promise as drug delivery systems, where the drug release profile and mechanical properties can be modulated through changes in modifiers, clay loading and understanding of component interactions