Silicon revisited – From dust to high-tech nanomaterial

David Wang Auditorium, 3rd floor Dalia Maydan Bldg
Prof. Vesa-Pekka Lehto, PhD. Candidate

Prof. Vesa-Pekka Lehto, PhD. Candidate

(Guangdong Campus) professorship in Materials Physics at University of Eastern Finland where he started in 2008

Silicon is typically considered as the basic material for semiconducting industry. However, silicon can have several features beneficial for various applications like nanotheranostics and Li-ion batteries as well. Those features are commonly related to high surface area, mesoporosity and surface chemistry of silicon. Regarding biomedical applications and especially theranostics, the applied biomaterial need to be nontoxic and bioresorbable. In targeted drug delivery, the nanovector (carrier of the drug), need to bypass several biological barriers carrying a high amount of the payload and protecting the payload from the surroundings and premature release. Thus, the nanovector should be integrated with appropriate functionalities. As the physicochemical properties of silicon can easily be varied and its structure can be made porous, it is one of the best choices to fulfill the criteria mentioned above. Porous silicon (PSi) also possesses properties beneficial for combination therapy. When prepared as a black material, PSi absorbs infrared light extremely well. With a temperature responsive polymer coating, infrared light can be utilized to externally trigger the drug release from the vector and simultaneously realize photothermal therapy based on local hyperthermia. Beside these effects, PSi could also stimulate immune response against cancer. The intravenously administrated vectors are radiolabeled for SPECT/CT imaging, or iron oxide nanocrystals are precipitated into the pores for MRI. Upon systemic administration, it is essential that the vectors circulate in blood stream long enough to utilize effectively the enhanced permeation and retention (EPR) effect to realize passive targeting of the vectors into solid tumors. Passive targeting is also a prerequisite for ligand-based active targeting. However, the vectors are covered with proteins (opsonins) adsorbed from plasma activating the reticuloendothelial system (RES), thus hampering both passive and active targeting. One option to circumvent this challenge is to cover the vectors with natural bilayers obtained from cells or exosomes secreted by the cells. Silicon is considered as a superior anode material for Li-ion batteries due to its ten times higher capacity than that for the present graphite anodes. The obstacle in utilizing silicon in Li-ion battery applications has been its tendency to pulverize during the charge-discharge cycles which leads to poor cycle life. The concept ‘full silicon anode’ addresses this issue in case of microbatteries. In the concept, ion-conducting polymer is electrodeposited into the pores of the mesoporous PSi film that has been prelithiated to LixSiy. The pores in Si accommodate the volume expansion due to lithiation, the solid electrolyte brings the mechanical strength and stabilize the solid-electrolyte-interface, and prelithiation addresses the issue related to the loss of coulombic efficiency during the initial cycling

Prof. Eizenberg Moshe