Silicon dioxide nanoparticles, also known as silica nanoparticles or nanosilica, are the basis for a great deal of biomedical research due to their stability, low toxicity and ability to be functionalized with a range of molecules and polymers.
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Nanosilica particles are divided into P-type and S-type according to their structure. The P-type particles are characterized by numerous nanopores, which have a pore rate of 0.61 ml/g and exhibit a higher ultraviolet reflectivity compared to the S-type; the latter also has a comparatively smaller surface area.
Nanosilica are the second most produced nanomaterial globally. Due to this, several research papers in recent decades have focused on the potential applications of nanosilica in multiple industries and their potential toxicity.
Chemical Properties of Nanosilica
Chemical Data
|
| Chemical symbol |
SiO2 |
| CAS No |
7631-86-9 |
| Group |
Silicon 14
Oxygen 16 |
| Electronic configuration |
Silicon [Ne] 3s2 3p2
Oxygen [He] 2s2 2p4 |
Chemical Composition
|
Element
|
Content (%)
|
| Silicon |
46.83 |
| Oxygen |
53.33 |
Physical Properties of Nanosilica
Nanosilica appears in the form of a white powder. The table below provides the physical properties of these nanoparticles.
Properties
|
Metric
|
Imperial
|
| Density |
2.4 g/cm3 |
0.086 lb/in3 |
| Molar Mass |
59.96 g/mol |
- |
Thermal Properties of Nanosilica
| Properties |
Metric |
Imperial |
| Melting Point |
1600°C |
2912°F |
| Boling Point |
2230°C |
4046°F |
Applications of Nanosilica
The chief applications of nanosilica are as an additive for the manufacture of rubber and plastics; as a strengthening filler for concrete and other construction composites; and as a stable, non-toxic platform for biomedical applications such as drug delivery and theranostics.
Nanosilica for Biomedical Applications
Nanosilica are an emerging technology in the biomedical field due to their favorable biocompatibility, large surface area, and controllable particle size. These beneficial properties also make SiO2 nanoparticles useful materials in the food industry.
Several economical and convenient strategies have been developed to manufacture nanosilica based on common synthesis methods. While many successful studies have demonstrated the efficaciousness of SiO2 nanoparticles for treating various cancers and diagnosing diseases, challenges persist.
One of the main challenges associated with using nanosilica in biomedical applications is to do with their toxicity and toxicity mechanisms. This is still a poorly understood area of research, with in vitro and in vivo studies in their infancy.
Nonporous Nanosilica: Biomedical Applications and Synthesis
Nonporous nanosilica, also termed N-SiNPs, are particularly useful for biomedical applications such as drug delivery and disease diagnosis due to their excellent biocompatibility. These nanoparticles are irregular and amorphous, having no standard structural shape.
N-SiNPs are widely used in biomedical applications such as medical imaging, as stabilizing agents for therapeutics, and enzyme encapsulation. There are two main routes for synthesizing these nanoparticles: thermal methods and wet methods. Wet preparation approaches include precipitation and chemical sol-gel methods.
Mesoporous Nanosilica: Biomedical Applications and Synthesis
M-SiNPs (mesoporous silica nanoparticles) have a more regular shape than their nonporous counterparts. These types of nanosilica have beneficial physiochemical properties such as controllable porosity, good biocompatibility, large surface area, and high thermal stability.
Due to these beneficial properties, M-SiNPs are widely employed by biomedical scientists for applications such as catalysis, bioimaging, and drug delivery. Aside from this, M-SiNPs have been employed as platforms for preparing other nanomaterials.
M-SiNPs are commonly prepared using a number of methods. These include improved Stöber synthesis methods, evaporation-induced self-assembly, and the use of liquid crystal templates (template synthesis) and one-pot synthesis.
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Nanosilica as Drug Delivery Systems
As mentioned above, one of the main biomedical applications for nanosilica is as carriers for drug delivery, delivered via eye drops, intravenous injections, oral tablets, or pulmonary inhalation routes.
Research has been conducted into the use of nanosilica to deliver drugs to target various cancers such as liver cancer, lung cancer, glioblastoma, and colon cancer. They have been employed to treat viral infections, myocardial infarction, colitis, and neurodegenerative diseases as well as various cancers.
Medical Imaging
Functionalized nanosilica has been used in MRI, light imaging, dual-mode imaging, radio-labeled imaging, and ultrasound imaging.
Toxicity
Patients can be easily exposed to nanoparticles through eating, breathing, and touching them. Their small size, high surface-to-volume ratios, and enhanced surface reactivity make them a concern for scientists, making studies on their toxicity a crucial endeavor in the biomedical and food industries.
For this reason, and the fact that they are widely employed in medical imaging and drug delivery, the in vitro and in vivo toxicity of nanosilica has been extensively studied.
Research into potential toxicity in respiratory systems has indicated potential oxidative stress in human lung fibroblast cells related to the cytotoxicity of nanosilica. Other studies have indicated a relationship between nanosilica and elevated transcription of chemokines, which are pro-inflammatory.
Furthermore, due to their small size, silicon dioxide nanoparticles can cross the blood brain barrier, with concerns being raised in research about their potential link to neurodegenerative disorders such as Alzheimer's disease. Nanosilica can also potentially cause mitochondrial dysfunction, leading to corneal damage in the eye.
Research has also indicated potential nanosilica-linked toxicity in the gastrointestinal, digestive, and circulatory systems. Clearly, more research is needed into the potential toxicity of silicon dioxide nanoparticles, especially as they are becoming more commonly employed in the biomedical field.
References and Further Reading
Huang, Y et al. (2022) Silica nanoparticles: Biomedical applications and toxicity Biomedicine & Pharmacotherapy 151, 113053 [online] sciencedirect.com. Available at: https://doi.org/10.1016/j.biopha.2022.113053
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