Screening Of The Optical Clearing Agents Among Alcohols For Skin

Tissue optical clearing technique, which can effectively enhance the penetration of light in turbid tissue, brings a chance for the clinical application of biomedical optics in diagnosis and therapy. Among various investigations, the research on skin optical clearing is a hot topic. However, current researches are mainly limited in the comparison of optical clearing effect, with a lack of the investigation on the feasibility of its clinical application. This study is to set up a complete method of screening optical clearing agents (OCAs), especially, facing clinical application.Firstly, screening of the effective optical agents or the drug delivery methods was performed on in vitro porcine skin. Two diffusion chambers were set up to simulate the in vivo drug delivery. One chamber near the epidermis was filled with OCAs, and the other one was filled with isotonic saline. The dynamic changes in transmittance and the skin thickness were monitored after the application of six saturated alcohols to in vitro skin samples. From the observed results at 60 minutes, the optical clearing effects of six OCAs, i.e., glycerol, polyethylene glycol 400 (PEG400), polyethylene glycol 200 (PEG200), 1, 3-propylene glycol, 1, 4-butanediol and 1-butanol, showed in the descending order. Further analysis indicated that the optical clearing effects of skin causeded by alcohols were related to the number of hydroxyl groups, but not to the refractive index or molecular weight of OCAs. In order to improve the efficency of transdermal drug delivery, we used a new penetration enhancer, thiazone, mixted with PEG400, and acted onto the epidermis. The results indicated that this method could improve the optical clearing effect on in vitro skins. Moreover, removing the stratum corneum could further increase the effect.Based on the results of in vitro experiments, we carried out further screening of the optimal concentration of glycerol on in vivo skin. Glycerol solutions with different concentrations were injected into the dermis of rat. The results demonstrated glycerol with lower concentration did not induce obvious optical clearing effect; whereas that with higher concentration induced seriously pathologic damage to skins. Hence, 30% glycerol solution, could not only induce ideal optical clearing effect, but also minimize the side effects. Finally, the feasibility of tissue optical clearing technique in clinical application was investigated by considering the biocompatibility and non-invasive drug delivery method of OCAs. Blood circulation function and morphological changes in skins were observed after the application of 30% glycerol solution on the dermis directly. The results showed that there was no obvious pathologic damage to the local skin and blood vessels. Hence, 30% glycerol is biocompatible as an effective OCA in skin optical clearing. Furthermore, a convenient drug delivery method on rat skin in vivo was developed by using of physical and chemical methods. It was found that the combination of removing the stratum coraeum and adding the penetration enhancer, thiazone, could not only enhance the optical clearing effect on skins in vivo, but can also increase the SNR which can be used to acquire the deep blood flow information noninvasively.To sum up, 30% glycerol can obtain good optical clearing effect and biocompatibility by dermal injection; while the combination of physical and chemical method, topical application of OCA on skin epidermis can not only achieve optical transparency non-invasively, but also has maneuverability in clinic. In this thesis, we has selected the OCAs and drug delivery methods for clinical application, and set up a method of OCA screening, which is equally applicable to other biological tissues in optical clearing research. Hence, this research is of important scientific significance and application prospects.