Passive and active strategies for transdermal drug delivery with nanotechnology and temporal pressure

• Main Author: Lio, Daniel Chin Shiuan
• Other Authors: Xu Chenjie
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Science::Medicine::Biomedical engineering; Engineering::Nanotechnology
• Online Access: https://hdl.handle.net/10356/136603
• Institution: Nanyang Technological University

The field of transdermal drug delivery (TDD) has made an important contribution to the medical practice because of its avoidance of first-pass effect of the liver and to achieve a more localized drug delivery. However, TDD has yet to achieve its potential as an alternative to oral delivery and hypodermic injections due to the strong skin barrier to substances over 500Da in size. Over the years, many studies have been strategically performed to enhance TDD efficacy while preserving the skin barrier integrity. These strategies can be categorized into passive and active methods. Passive strategies for TDD taps on the hydrophobic properties and surface charge of the skin to modify the drug formulations to achieve modification of the stratum corneum for enhance penetration. However, these strategies face potential skin irritation. Active strategies on the other hand utilize external forces to achieve a stronger disruption of the stratum corneum for improved penetration of drugs of size bigger than 500 Da. However, these technologies are usually bulky, and administrations are mostly performed by healthcare professionals. In the first half of this thesis, nanotechnology is proposed as a compatible and excellent carrier to achieve passive delivery of genetic materials for non-invasive detection and regulation of skin biomarkers. Specifically, the nanoparticles were fabricated by incorporating molecular beacons (MB), oligonucleotide-based hairpin probes with specific target gene recognition ability, onto metal nanoparticles (gold nanorods, AuNR). Tagged on the surface of the AuNR through gold-thiol bonds, these structures can be effectively internalized by human keratinocyte cells. Subsequently, the fluorescence signal of the MB was compared in different in vitro conditions against RT-PCR and Western-Blot to confirm its specificity. Last but not least, these nanosensors were topically applied on the skin for effective penetration into the epidermis tissue to achieve non-invasive detection of skin biomarker. In addition, mesoporous silica nanoparticles (MSNPs) is also proposed in this thesis as a versatile and highly compatible polymeric nanocarrier for MB delivery across the skin. Specifically, MBs were incorporated into the pores of MSNPs, followed by a coating of positively charged poly-l-lysine to improve the cellular uptake (MSNPs-MB-PLL). The uptake efficiency of MSNPs-MB-PLL, specificity and functionality of released MB were tested in human skin squamous carcinoma cells (SCC) with promising results. Subsequently, we topically delivered MSNPs-PLL with Cy5 into SCC xenograft model and observed good penetration of NPs through the trans-follicular route into the SCC tumor. Finally, topically applied MSNPs-siRNA-PLL demonstrated 2-fold suppression of TGFβR-1 gene in SCC. Studies have shown that the size of NPs is the limiting factor to the extent of TDD. Therefore, active strategy will be explored in the second half of the thesis. For the first time, temporal pressure is proposed as a promising alternative to hypodermic injection. The temporal pressure was achieved with the use of magnets and tested in vivo. Optimization was performed with different pressure forces to achieve effective TDD while protecting the skin integrity (0.28MPa for 1- or 5-mins application). Subsequently, temporal pressure demonstrated delivery of molecules up to 200 kDa and nanoparticles up to 500 nm. To prove the translatability, temporal pressure was applied to deliver insulin as a proof of concept in normal and diabetic mice. Effective delivery of insulin was achieved with 80% reduction in blood glucose in just 30 mins, for a period of 6 hrs. In conclusion, nanotechnology and temporal pressure-based strategies are introduced in this thesis for the field of transdermal drug delivery. Especially for delivery of genetic therapy, nanotechnology can facilitate the transdermal delivery of various therapeutic approaches. On the other hand, temporal pressure serves as an attractive alternative to hypodermic injection, achieving effective transdermal delivery similar to microneedles.