Synthesis and characterization of stimuli-responsive thin films by initiated chemical vapor deposition method

In this study, it was aimed to synthesize a hydrogel poly (hydroxy propyl methacrylate) (pHPMA) homopolymer and its copolymers obtained with different monomers by initiated chemical vapor deposition (iCVD) method and to investigate its stimuli-responsive properties. Polymeric thin films of pHPMA, poly (hydroxy propyl methacrylate-co-ethylene glycol dimethacrylate) p(HPMA-EGDMA), and poly(N-isopropyl methacrylate-co hydroxy propyl methacrylate) p(NIPAAm-HPMA) were successfully deposited on different substrates. In the deposited films obtained by the iCVD method, the effects of alterations in many parameters such as the flow rate of initiator and monomers into the reactor, filament temperature, substrate temperature, and pressure on the deposition rate and structure of the coatings were investigated. It has been shown that PHPMA thin films can be deposited by iCVD from a reactive mixture of monomer HPMA and initiator TBPO. No deposition was observed without the initiator, but high growth rates could be achieved in the presence of the initiator (~83 nm/min). In the kinetic studies performed at different substrate temperatures, a direct relationship was observed between the deposition rate and the substrate temperature, indicating a surface-kinetics limited regime. During the iCVD studies of pHPMA films, it was observed that the deposition continued for a while after the filament power supply was turned off, and the thickness measurement analysis confirmed this. Thus, a new method has been tried and shown that pulsed-iCVD can deposit polymeric thin films with desired functionalities in the presence of a suitable monomer and an initiator. Up to 70% higher deposition rates can be achieved under pulsed- iCVD conditions compared to the deposition rates observed in conventional continuous power iCVD. Also, the structure of the deposited films was not much affected by pulsed power. Besides the deposition rate, the film morphology was also affected by the duty cycle (DC), which changed the wettability of the film. Chemical structures of iCVD pHPMA films were investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyzes and it was observed that functional groups were retention after the deposition. Atomic force microscopy (AFM) analysis was used to investigate the surface morphologies of the films, and the results were corroborated by contact angle analysis. In order to investigate the responsive of HPMA hydrogel, crosslinker EGDMA and p(HPMA-EGDMA) copolymer were deposited on glass substrates loaded with the chemotherapeutic Carboplatin drug (CAR). The effect of the flow rate of crosslinker on drug release was investigated with three different studies performed by changing the EGDMA flow rate. It was observed that the highest value of carboplatin release (72 ng/g) was reached at the end of 48th hour in the deposition with the highest EGDMA flow rate at pH 1.8. Considering the acidic nature of breast cancer cells, obtaining high release at low pH is an important result. According to cytotoxicity studies, when the effects of p(HPMA-EGDMA) hydrogels against MCF12A healthy breast cell line at 24 and 48 hours were examined, it was concluded that the coatings did not have significant cytotoxicity against healthy cells. According to the results obtained, CAR killed 50% of the cancer cells in the control group when the dose was adjusted and given to kill 50% of the cells. The rate of killing cancer cells in the copolymer-coated drug with high flow rate of EGDMA was up to 82%. When the same parameters were examined in healthy cells, it was observed that CAR directly damaged 76% of healthy cells, while in the coated smart drug system, the toxic effect in healthy MCF12A cell lines decreased to 43% in the coating with high EGDMA. The responsive of p(NIPAAm-HPMA) hydrogel thin films with different HPMA flow rates was investigated by depositing copolymer films on antibiotic-loaded discs. Contact angle analysis from the silicon substrate surface was used to determine the low critical solution temperature (LCST) of the copolymer. According to the results of the analysis, the LCST values of the p(NIPAAm-HPMA) hydrogel films were found to be between 19 and 23 degrees. This value is significantly lower than the PNIPAAM LCST value reported in the literature. According to the results of pH-dependent controlled drug release tests, while more release occurred for Chloramphenicol at pH 1.8, Ampicillin showed higher release at both pH 1.8 and pH 7. The highest release amount for chloramphenicol was reached after 48 hours at pH 1.8 (92 ng/g). The highest release amount for ampicillin was reached at pH 7 (99 ng/g).According to the results of cytotoxicity test performed on MCF 7A human cancer breast cells, it was concluded that p(NIPAAm-HPMA) copolymer hydrogels had no toxic effect on MCF 7A cancer cells.