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Stimuli Responsive Polymer Nanotubes by Initiated Chemical Vapor Deposition

Final Report Summary - SRPNICVD (Stimuli Responsive Polymer Nanotubes by Initiated Chemical Vapor Deposition)

Nanocarriers, with characteristic dimensions in the nanometer scale, are structures that can hold and transfer specific molecules to target locations. The interest in nanocarriers has been steadily growing for the last several years due to their wide range of application areas including drug delivery, food industry or molecular separation. In addition to their large surface to volume ratios which improve the delivery capacity of the nanocarriers, functionalizing the carrier surface enables the specific binding of molecules and recognition of the target sites for delivery. For example, for many life-threatening diseases, the extensive use of drugs which lack target site-specificity leads to damage to healthy organs. In targeted delivery, the drug is carried to the diseased tissue at controlled amounts, minimizing the exposure and the damage of the healthy tissue. The nanocarriers can easily access target sites and deliver the medication.

For molecular separation applications, the nanocarriers should selectively absorb specific molecules and contain them for a duration of time. This can be achieved by functionalizing the nanocarrier surface and tuning the characteristic dimensions according to the target molecules. The usage of nanocarriers in the food industry requires a good control over the release mechanism, for both burst release and delayed release applications.

Polymers are generally materials of choice when synthesizing the nanocarriers, due to their biocompatible and degradable nature, their tunable response mechanism to stimuli and low cost. Ability to control the response of the nanocarriers for improved performance by tuning the polymer properties is one of the main advantages. However, techniques that allow fabrication of polymeric nanocarriers with specific functionalities and dimensions are very limited.

The aim of the SRPNiCVD project is to develop polymeric nanotubes as potential carriers of macromolecules using the initiated chemical vapour deposition (iCVD) technique. iCVD is a vapour phase polymer deposition method performed at low substrate temperatures, enabling coating of delicate substrates with ultra thin polymer films. Conformal nature of the iCVD process, makes fabrication of high aspect ratio nanostructures using templates possible. In this project, iCVD is used to fabricate polymeric nanotubes and to separately control and tune the dimensions and the response of these nanostructures for nanocarrier applications. The loading and release performance of the nanotubes are studied and the dependence of nanotube performance on the polymer compositions is investigated. This enables us to design and fabricate nanotubes with well defined and controlled response mechanism which is the main objective of the SRPNiCVD project.

As a part of the SRPNiCVD project, an iCVD system was set-up which included building a deposition chamber. The chamber is a custom made chamber and the system was built entirely by our group. Literature search on the stimuli responsive polymers was performed and temperature and pH responsive polymers that can be deposited by iCVD technique were chosen. As for the criteria in choosing the monomer to use, high vapor pressures for fast deposition and low cost were used. Thin films of these polymers were synthesized on silicon wafers and chemical characterizations were performed.

As a part of this project temperature and pH responsive polymer thin films were fabricated using iCVD technique and their composition were optimized for improved response rates. These developed polymer systems were then successfully used to fabricate responsive polymer nanotubes. Loading and release rates of model dyes from these nanotubes were systematically studied by changing the pH or temperature of the medium. Release rates as high as 50% and 45% could be achieved with the pH and temperature responsive nanotubes, respectively. Although these rates are below the release rates of conventional nanospherical delivery devices, the nanotubular shapes have advantages in terms of controlled diffusion of the nanocarriers. The release rates of these nanocarriers could also be improved further by optimizing the chemical composition. The PI plans to continue working on this topic in the future.

The release mechanisms from the nanotubes could further be controlled by developing coaxial nanotubes with hydrogel inner layers that absorb and release the model dye molecules at different rates than the outer layers. While the stimuli responsive outer layers generally demonstrated burst release, including the hydrogel inner layer in the structure reduced the release rates for delayed release applications.

At the end of the SRPNiCVD project, we could achieve significant expertise on fabrication of stimuli responsive polymeric nanotubes with well controlled release mechanisms. We created a library of process parameters for nanocarrier synthesis that can be used in the future for different applications. The nanocarriers developed in this project with their controllable response behaviour and biocompatible nature, have the potential to be developed further as drug delivery devices.

Furthermore, SRPNiCVD project helped Dr. Gozde Ince establish her research group and set-up her laboratory as part of her reintegration to ERA. The outcomes of the SRPNiCVD project were presented in several international conferences and published as a journal paper. The main socio-economic impact of this project is the transfer of the polymer CVD technology to Turkey, which was carried out successfully. With the help of the seminars the PI gave, the techniques gained recognition and the PI could establish new collaborations. Furthermore, the project enabled the PI to train graduate students who will join the work force in the related fields near future.