Applications of zero-valent silicon nanostructures in biomedicine

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

Bio-hybrid electronic and photonic devices

Bio-hybrid devices, combining electronic and photonic components with cells, tissues, and organs, hold potential for advancing our understanding of biology, physiology, and pathologies and for treating a wide range of conditions and diseases. In this review, I describe the devices, materials, and technologies that enable bio-hybrid devices and provide examples of their utilization at multiple biological scales ranging from the subcellular to whole organs. Finally, I describe the outcomes of a National Science Foundation (NSF)-funded workshop envisioning potential applications of these technologies to improve health outcomes and quality of life.

Green Synthesis of Silver Nanoparticles Using Pomegranate and Orange Peel Extracts and Their Antifungal Activity against Alternaria solani, the Causal Agent of Early Blight Disease of Tomato

This study aimed to synthesize silver nanoparticles (AgNPs) by pomegranate and orange peel extracts using a low concentration of AgNO₃ solution to controlearly blight of tomato caused by Alternaria solani. The pathogen was isolated from infected tomato plants growing in different areas of Saudi Arabia. The isolates of this pathogen were morphologically and molecularly identified. Extracts from peels of pomegranate and orange fruits effectively developed a simple, quick, eco-friendly and economical method through a synthesis of AgNPs as antifungal agents against A. solani. Phenolic content in the pomegranate peel extract was greater than orange peel extract. Phenolic compounds showed a variation of both peel extracts as identified and quantified by High-Performance Liquid Chromatography. The phenolic composition displayed variability as the pomegranate peel extract exhibited an exorbitant amount of Quercitrin (23.62 mg/g DW), while orange peel extract recorded a high amount of Chlorogenic acid (5.92 mg/g DW). Biosynthesized AgNPs were characterized using UV- visible spectroscopy which recorded an average wavelength of 437 nm and 450 nm for pomegranate and orange peels, respectively. Fourier-transform infrared spectroscopy exhibited 32x73.24, 2223.71, 2047.29 and 1972.46 cm^-1, and 3260.70, 1634.62, 1376.62 and 1243.76 cm^-1 for pomegranate and orange peels, respectively. Transmission electron microscopy showed spherical shape of nanoparticles. Zetasizer analysis presented negative charge values; -16.9 and -19.5 mV with average particle sizes 8 and 14 nm fin case of pomegranate and orange peels, respectively. In vitro, antifungal assay was done to estimate the possibility of biosynthesized AgNPs and crude extracts of fruit peels to reduce the mycelial growth of A. solani. AgNPs displayed more fungal mycelial inhibition than crude extracts of two peels and AgNO₃. We recommend the use of AgNPs synthesized from fruit peels for controlling fungal plant pathogens and may be applied broadly and safely in place by using the chemical fungicides, which display high toxicity for humans.

Macrophage reprogramming into a pro-healing phenotype by siRNA delivered with LBL assembled nanocomplexes for wound healing applications

Excessive inflammatory responses in wounds are characterized by the presence of high levels of pro-inflammatory M1 macrophages rather than pro-healing M2 macrophages, which leads to delayed wound healing. Macrophage reprogramming from the M1 to M2 phenotype through knockdown of interferon regulatory factor 5 (irf5) has emerged as a possible therapeutic strategy. While downregulation of irf5 could be achieved by siRNA, it very much depends on successful intracellular delivery by suitable siRNA carriers. Here, we report on highly stable selenium-based layer-by-layer (LBL) nanocomplexes (NCs) for siRNA delivery with polyethyleneimine (PEI-LBL-NCs) as the final polymer layer. PEI-LBL-NCs showed good protection of siRNA with only 40% siRNA release in a buffer of pH = 8.5 after 72 h or in simulated wound fluid after 4 h. PEI-LBL-NCs also proved to be able to transfect RAW 264.7 cells with irf5-siRNA, resulting in successful reprogramming to the M2 phenotype as evidenced by a 3.4 and 2.6 times decrease in NOS-2 and TNF-α mRNA expression levels, respectively. Moreover, irf5-siRNA transfected cells exhibited a 2.5 times increase of the healing mediator Arg-1 and a 64% increase in expression of the M2 cell surface marker CD206⁺. Incubation of fibroblast cells with conditioned medium isolated from irf5-siRNA transfected RAW 264.7 cells resulted in accelerated wound healing in an in vitro scratch assay. These results show that irf5-siRNA loaded PEI-LBL-NCs are a promising therapeutic approach to tune macrophage polarization for improved wound healing.

Conformationally Switchable Silylone: Electron Redistribution Accompanied by Ligand Reorientation around a Monatomic Silicon

Complexes that could be switched between two electronic states by external stimuli have attracted much attention for their potential application in molecular devices. However, a realization of such a phenomenon with low-valent main-group element-centered complexes remains challenging. Herein, we report the synthesis of cyclic (alkyl)(amino)silylene (CAASi)-ligated monatomic silicon(0) complexes (silylones). The bis(CAASi)-ligated silylone adopts a π-localized ylidene structure (greenish-black color) in the solid state and a π-delocalized ylidene structure (dark-purple color) in solution that could be reversibly switched upon phase transfer (ylidene [L: → :Si = L ↔ L = Si: ← :L]). The observed remarkable difference in the physical properties of the two isomers is attributed to the balanced steric demand and redox noninnocent character of the CAASi ligand which are altered by the orientation of the two terminal ligands with respect to the Si-Si-Si plane: twisted structure (π-localized ylidene) and planar structure (π-delocalized ylidene). Conversely, the CAASi/CDASi-ligated heteroleptic silylone (CDASi = cyclic dialkylsilylene) only exhibited the twisted π-localized ylidene structure regardless of the phase. The synthesized silylones also proved themselves as monatomic silicon surrogates. Thermolysis of the silylones in the presence of an ethane-1,2-diimine afforded the corresponding diaminosilylenes. Analyses of the products suggested a stepwise mechanism that proceeds via a disilavinylidene intermediate.

Antibody-Functionalized Gold Nanostar-Mediated On-Resonance Picosecond Laser Optoporation for Targeted Delivery of RNA Therapeutics

The rapid advances of genetic and genomic technology indicate promising therapeutic potential of genetic materials for regulating abnormal gene expressions causing diseases and disorders. However, targeted intracellular delivery of RNA therapeutics still remains a major challenge hindering the clinical translation. In this study, an elaborated plasmonic optoporation approach is proposed to efficiently and selectively transfect specific cells. The site-specific optoporation is obtained by tuning the spectral range of a supercontinuum pulsed picosecond laser in order for each individual cell binding gold nanostar with their unique resonance peak to magnify the local field strength in the near-infrared region and facilitate a selective delivery of small interfering RNA, messenger RNA, and Cas9-ribonucleoprotein into human retinal pigment epithelial cells. Numerical simulations indicate that optoporation is not due to a plasma-mediated process but rather due to a highly localized temperature rise both in time (few nanoseconds) and space (few nanometers). Taking advantage of the numerical simulation and fine-tuning of the optical strategy, the perforated lipid bilayer of targeted cells undergoes a membrane recovery process, important to retain their viability. The results signify the prospects of antibody functionalized nanostar-mediated optoporation as a simple and realistic gene delivery approach for future clinical practices.

Insights into Theranostic Properties of Titanium Dioxide for Nanomedicine

Titanium dioxide (TiO2) nanostructures exhibit a broad range of theranostic properties that make them attractive for biomedical applications. TiO2 nanostructures promise to improve current theranostic strategies by leveraging the enhanced quantum confinement, thermal conversion, specific surface area, and surface activity. This review highlights certain important aspects of fabrication strategies, which are employed to generate multifunctional TiO2 nanostructures, while outlining post-fabrication techniques with an emphasis on their suitability for nanomedicine. The biodistribution, toxicity, biocompatibility, cellular adhesion, and endocytosis of these nanostructures, when exposed to biological microenvironments, are examined in regard to their geometry, size, and surface chemistry. The final section focuses on recent biomedical applications of TiO2 nanostructures, specifically evaluating therapeutic delivery, photodynamic and sonodynamic therapy, bioimaging, biosensing, tissue regeneration, as well as chronic wound healing.

Anodic Titanium Dioxide Nanotubes for Magnetically Guided Therapeutic Delivery

Hollow titanium dioxide (TiO₂) nanotubes offer substantially higher drug loading capacity and slower drug release kinetics compared to solid drug nanocarriers of comparable size. In this report, we load TiO₂ nanotubes with iron oxide nanoparticles to facilitate site-specific magnetic guidance and drug delivery. We generate magnetic TiO₂ nanotubes (TiO₂NTs) by incorporating a ferrofluid containing Ø ≈ 10 nm iron oxide nanoparticles in planar sheets of weakly connected TiO₂ nanotubes. After thermal annealing, the magnetic tubular arrays are loaded with therapeutic drugs and then sonicated to separate the nanotubes. We demonstrate that magnetic TiO₂NTs are non-toxic for HeLa cells at therapeutic concentrations (≤200 µg/mL). Adhesion and endocytosis of magnetic nanotubes to a layer of HeLa cells are increased in the presence of a magnetic gradient field. As a proof-of-concept, we load the nanotubes with the topoisomerase inhibitor camptothecin and achieve a 90% killing efficiency. We also load the nanotubes with oligonucleotides for cell transfection and achieve 100% cellular uptake efficiency. Our results demonstrate the potential of magnetic TiO₂NTs for a wide range of biomedical applications, including site-specific delivery of therapeutic drugs.

Intracellular Drug Delivery with Anodic Titanium Dioxide Nanotubes and Nanocylinders

Titanium dioxide (TiO₂) holds remarkable promises for developing current theranostic strategies. Anodic TiO₂ nanostructures as a porous scaffold have offered a broad range of useful theranostic properties; however, previous attempts to generate single and uniform TiO₂ one-dimensional nanocarriers from anodic nanotube arrays have resulted in a broad cluster size distribution of arbitrarily broken tubes that are unsuitable for therapeutic delivery systems due to poor biodistribution and the risk of introducing tissue inflammation. Here, we achieve well-separated, uniformly shaped anodic TiO₂ nanotubes and nanocylinders through a time-varying electrochemical anodization protocol that leads to the generation of planar sheets of weakly connected nanotubes with a defined fracture point near the base. Subsequent sonication cleanly detaches the nanotubes from the base. Depending on the position of the fracture point, we can fabricate single-anodic nanocylinders that are open on both ends and nanotubes that are closed on one end. We proceed to show that anodic nanotubes and nanocylinders are nontoxic at therapeutic concentrations. When conjugated with the anticancer drug doxorubicin using a pH-responsive linker, they are readily internalized by cells and subsequently release their drug cargo into acidic intracellular compartments. Our results demonstrate that uniformly sized anodic TiO₂ nanotubes and nanocylinders are suitable for subcellular delivery of therapeutic agents in cancer therapy.

Manipulating human dendritic cell phenotype and function with targeted porous silicon nanoparticles

Dendritic cells (DC) are the most potent antigen-presenting cells and are fundamental for the establishment of transplant tolerance. The Dendritic Cell-Specific Intracellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN; CD209) receptor provides a target for dendritic cell therapy. Biodegradable and high-surface area porous silicon (pSi) nanoparticles displaying anti-DC-SIGN antibodies and loaded with the immunosuppressant rapamycin (Sirolimus) serve as a fit-for-purpose platform to target and modify DC. Here, we describe the fabrication of rapamycin-loaded DC-SIGN displaying pSi nanoparticles, the uptake efficiency into DC and the extent of nanoparticle-induced modulation of phenotype and function. DC-SIGN antibody displaying pSi nanoparticles favourably targeted and were phagocytosed by monocyte-derived and myeloid DC in whole human blood in a time- and dose-dependent manner. DC preconditioning with rapamycin-loaded nanoparticles, resulted in a maturation resistant phenotype and significantly suppressed allogeneic T-cell proliferation.

Antibacterial properties of nitric oxide-releasing porous silicon nanoparticles

In this study, the antibacterial efficacy of NO-releasing porous silicon nanoparticles (pSiNPs) is reported. NO-releasing pSiNPs were produced via the conjugation of S-nitrosothiol (SNO) and S-nitrosoglutathione (GSNO) donors to the nanoparticle surfaces. The release of the conjugated NO caused by the decomposition of the conjugated SNO and GSNO was boosted in the presence of ascorbic acid. The released NO was bactericidal to Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli), and eliminated bacterial growth within 2 h of incubation without compromising the viability of mammalian cells. These results demonstrate the advantages of NO-releasing pSiNPs for antibacterial applications, for example, in chronic wound treatment.