Thermoresponsive polymers in controlled drug delivery and gene delivery
Appears in the following Collection
- Farmasøytisk institutt 
AbstractIn this thesis, emphasis is given to the study of temperature-responsive systems and their use in drug and gene delivery applications.
Studies on polymer-surfactant systems were conducted, using amino acid-based surfactants. In these studies, ethyl (hydroxyethyl) cellulose (EHEC) was the investigated polymer, while the interactions with six different surfactants were analyzed. Three of these were anionic and lysine-based, having a gemini-like structure and different alkyl chain length. In addition, three cationic arginine-based surfactants were investigated. Of these, two had a gemini structure, while the third was monomeric.
The polymer-surfactant systems were characterized in terms of their rheological properties, i.e. complex viscosity, gel points, gel properties and thermodynamic features in form of cloud points. It was shown that the mixtures were generally low viscous at room temperature, and that the viscosity increased at higher temperatures, in agreement with the formation of a polymer network stabilized by hydrophobic associations and electrostatic repulsions. Sol-gel transitions were also observed, suggesting that the gels could be employed as pharmaceutical formulations undergoing gelation in situ, once injected.
Importantly, surfactants with long alkyl chains and gemini-like structure were the most efficient, which implies that very low amounts are needed in order to induce the sol-gel transition at elevated temperatures.
The biocompatibility of the EHEC-surfactant systems was evaluated by performing in vitro experiments on a human cell line (HeLa cells). These studies revealed that the higher toxicity of the long-chain/gemini-like surfactants was significantly compensated by their superior efficiency at low concentrations.
Experiments were further carried out with the intention of developing a microparticulate system for controlled drug delivery. An emulsification-solvent evaporation method was employed according to a planned experimental design that aimed at evaluating the process parameters on the size properties of the microparticles. Chitosan, a hydrophobicallymodified chitosan derivative (HM-chitosan) and poly lactic-co-glycolic acid (PLGA) were investigated as the polymeric matrix. The blank microparticles were characterized in terms of size and size distribution. Following the multivariate analysis, specific parameters were chosen to produce the drug-loaded microparticles. Naltrexone, an opioid antagonist, was used as the model drug. The microparticles were evaluated in terms of their morphological properties (scanning electron microscopy), and the drug encapsulation efficiency and loading capacity were determined. In vitro drug release experiments were carried out. The results from this study showed that HM-chitosan microparticles were recovered in a high yield and that the encapsulation efficiency was higher as compared to the use of the other polymers. Importantly, this polymer also demonstrated the higher capacity to retain the drug, which was slowly released for at least 50 days.
Finally, four cationic temperature-responsive block copolymers were evaluated as gene carriers. These polymers had a structure based on poly (N-isopropylacrylamide)-blockpoly(( 3-acrylamidopropyl) trimethylammonium chloride) (PNIPAAM-b-PAMPTMA(+)), and were distinct in terms of the length of the blocks. Complexes between polymer and plasmid DNA were prepared at different polymer/DNA ratios, and used to transfect HeLa cells. Because the plasmid DNA coded for green fluorescent protein (GFP), the expression of this protein was followed by flow cytometry. Cell viability studies were simultaneously carried out in order to evaluate the cytotoxic effects of the complexes. The results showed that polymers with longer PNIPAAM or shorter PAMPTMA(+) were the most effective carriers. A series of physicochemical experiments were carried out (dynamic light scattering, zeta potential and turbidity), so as to gain insights into copolymer structureactivity relationships. It was shown that the most effective carriers had a compact PNIPAAM core that collapsed at 37 °C surrounded by a positively charged corona.
List of papers. Papers I - III and V are removed from the thesis due to publisher restrictions.
Paper I: Maria Teresa Calejo, Anna-Lena Kjøniksen, Eduardo F. Marques, Maria J. Araújo, Sverre Arne Sande, Bo Nyström (2012), Interactions between ethyl(hydroxyethyl) cellulose and lysine-based surfactants in aqueous media. European Polymer Journal, 48(9), 1622-1631. doi:10.1016/j.eurpolymj.2012.06.009
Paper II: Maria Teresa Calejo, Ana Maria S. Cardoso, Eduardo F. Marques, Maria J. Araújo, Anna- Lena Kjøniksen, Sverre Arne Sande, Maria C. Pedroso de Lima, Amália S. Jurado, Bo Nyström (2013), In vitro cytotoxicity of a thermoresponsive gel system combining ethyl(hydroxyethyl) cellulose and lysine-based surfactants. Colloids and Surfaces B: Biointerfaces, 102, 682-686. doi:10.1016/j.colsurfb.2012.09.033
Paper III: Maria Teresa Calejo, Anna-Lena Kjøniksen, Aurora Pinazo, Lourdes Pérez, Ana Maria S. Cardoso, Maria C. Pedroso de Lima, Amália S. Jurado, Sverre Arne Sande, Bo Nyström (2012), Thermoresponsive hydrogels with low toxicity from mixtures of ethyl(hydroxyethyl) cellulose and arginine-based surfactants. International Journal of Pharmaceutics, 436, 454-462. doi:10.1016/j.ijpharm.2012.07.018
Paper IV: Maria Teresa Calejo, Anna-Lena Kjøniksen, Atoosa Maleki, Bo Nyström, Sverre Arne Sande (2013), Microparticles based on hydrophobically modified chitosan as drug carriers. Submitted version, published in: J. Appl. Polym. Article first published online: 29 OCT 2013. doi:10.1002/APP.40055
Paper V: Maria Teresa Calejo, Ana Maria Cardoso, Anna-Lena Kjøniksen, Aurora Pinazo, Kaizheng Zhu, Catarina M. Morais, Sverre Arne Sande, Ana Luísa Cardoso, Maria C. Pedroso de Lima, Amália Jurado, Bo Nyström (2012), Temperature-responsive cationic block copolymers as nanocarriers for gene delivery, International Journal of Pharmaceutics, 448, 105-114. doi:10.1016/j.ijpharm.2013.03.028