Tag Archives: TiO2 nanoparticles

Metal nanoparticles and gut microbiomes

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What happens when you eat or drink nanoparticles, metallic or otherwise? No one really knows. Part of the problem with doing research now is there are no benchmarks for the quantity we’ve been ingesting over the centuries. Nanoparticles do occur naturally, as well, people who’ve eaten with utensils made of or coated with silver or gold have ingested silver or gold nanoparticles that were shed by those very utensils. In short, we’ve been ingesting any number of nanoparticles through our food, drink, and utensils in addition to the engineered nanoparticles that are found in consumer products. So, part of what researchers need to determine is the point at which we need to be concerned about nanoparticles. That’s trickier than it might seem since we ingest our nanoparticles and recycle them into the environment (air, water, soil) to reingest (inhale, drink, eat, etc.) them at a later date. The endeavour to understand what impact engineered nanoparticles in particular will have on us as more are used in our products is akin to assembling a puzzle.

There’s a May 5, 2015 news item on Azonano which describes research into the effects that metallic nanoparticles have on the micriobiome (bacteria) in our guts,

Exposure of a model human colon to metal oxide nanoparticles, at levels that could be present in foods, consumer goods, or treated drinking water, led to multiple, measurable differences in the normal microbial community that inhabits the human gut. The changes observed in microbial metabolism and the gut microenvironment with exposure to nanoparticles could have implications for overall human health, as discussed in an article published in Environmental Engineering Science, a peer-reviewed journal from Mary Ann Liebert, Inc., publishers. The article is available free on the Environmental Engineering Science website until June 1, 2015.

A May 4, 2015 Mary Ann Liebert publisher news release on EurekAlert, which originated the news item, describes the research in more detail (Note: A link has been removed),

Alicia Taylor, Ian Marcus, Risa Guysi, and Sharon Walker, University of California, Riverside, individually introduced three different nanoparticles–zinc oxide, cerium dioxide, and titanium dioxide–commonly used in products such as toothpastes, cosmetics, sunscreens, coatings, and paints, into a model of the human colon. The model colon mimics the normal gut environment and contains the microorganisms typically present in the human microbiome.

In the article “Metal Oxide Nanoparticles Induce Minimal Phenotypic Changes in a Model Colon Gut Microbiota” the researchers described changes in both specific characteristics of the microbial community and of the gut microenvironment after exposure to the nanoparticles.

Here’s a link to and a citation for the paper,

Metal Oxide Nanoparticles Induce Minimal Phenotypic Changes in a Model Colon Gut Microbiota by Alicia A. Taylor, Ian M. Marcus Ian, Risa L., Guysi, and Sharon L. Walker. Environmental Engineering Science. DOI:10.1089/ees.2014.0518 Online Ahead of Print: April 24, 2015

I’ve taken a quick look at the research while it’s still open access (till June 1, 2015) to highlight the bits I consider interesting. There’s this about the nanoparticle (NP) quantities used in the study (Note: Links have been removed),

Environmentally relevant NP concentrations were chosen to emulate human exposures to NPs through ingestion of both food and drinking water at 0.01 μg/L ZnO NP, 0.01 μg/L CeO2 NP, and 3 mg/L TiO2 NP (Gottschalk et al., 2009; Kiser et al., 2009, 2013; Weir et al., 2012; Keller and Lazareva, 2013). Recent work has also indicated that adults in the USA ingest 5 mg TiO2 per day, half of which is in the nano-size range (Lomer et al., 2000; Powell et al., 2010). Exposure routes and reliable dosing information of NPs that are embedded in solid matrices are difficult to predict, and this is often a limitation of analytical techniques (Nowack et al., 2012; Yang and Westerhoff, 2014). The exposure levels used in this study were predominately selected from literature values that give predictions on amount of NPs in water and food sources (Gottschalk et al., 2009; Kiser et al., 2009; Weir et al., 2012; Keller and Lazareva, 2013; Keller et al., 2013).

For anyone unfamiliar with chemical notations, ZnO NP is zinc oxide nanoparticle, 0.01 μg/L is one/one hundredth of a microgram per litre,  CeO2 is cesisum dioxide NP, and TiO2 is titanium dioxide NP while 3 mg/L, is 3 milligrams per litre.

After assuring the quantities used in the study are the same as they expect humans to be ingesting on a regular basis, the researchers describe some of the factors which may affect the interaction between the tested nanoparticles and the bacteria (Note: Links have been removed),

It is essential to note that interactions between NPs and bacteria in the intestines may be dependent on numerous factors: the surface charge of the NPs and bacteria, the chemical composition and surface charge of the digested food, and variability in diet. These factors may ultimately correlate to effects seen in humans on an individual basis. In fact, similar work has demonstrated that exposing common NPs found in food to stomach-like conditions will change their surface chemistry from negative to neutral or positive, causing the NPs to interact with negatively charged mucus proteins in the gastrointestinal tract and, in turn, affecting the transport of NPs within the intestine (McCracken et al., 2013). The purpose of this work was to measure responses of the microbial community during the NP exposures. Based on previous research, it is anticipated that the NPs altered by stomach-like conditions would also cause changes in the gut environment (McCracken et al., 2013).

Here’s some of what they discovered,

Our initial hypothesis, that NPs induce phenotypic changes in a gut microbial community, was affirmed through significant measurable effects seen in the data. Tests that supported that NPs caused changes in the phenotype included hydrophobicity, EPM, sugar content of the EPS, cell size, conductivity, and SFCA (specifically butyric acid) production. Data for cell concentration and the protein content of the EPS demonstrated no significant results. Data were inconclusive for pH. With such a complex biological system, it is very likely that the phenotypic and biochemical changes observed are combinations of responses happening in parallel. The effects seen may be attributed to both changes induced by the NPs and natural phenomena associated with microbial community activity and other metabolic processes in a multifaceted environment such as the gut. Some examples of natural processes that could also influence the phenotypic and biochemical parameters are osmolarity, active metabolites, and electrolyte concentrations (Miller and Wood, 1996; Record et al., 1998).

Here’s the concluding sentence from the abstract,

Overall, the NPs caused nonlethal, significant changes to the microbial community’s phenotype, which may be related to overall health effects. [emphasis mine]

This research like the work I featured in a June 27, 2013 posting points to some issues with researching the impact that nanoparticles may have on our bodies. There was no cause for immediate alarm in 2013 and it appears that is still the case in 2015. However, that assumes quantities being ingested don’t increase significantly.

Sandia National Laboratories looking for commercial partners to bring titanium dioxide nanoparticles (5 nm in diameter) to market

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Sandia National Laboratories (Sandia Labs) doesn’t  ask directly but I think the call for partners is more than heavily implied. Let’s start with a June 17, 2014 news item on ScienceDaily,

Sandia National Laboratories has come up with an inexpensive way to synthesize titanium-dioxide nanoparticles and is seeking partners who can demonstrate the process at industrial scale for everything from solar cells to light-emitting diodes (LEDs).

Titanium-dioxide (TiO2) nanoparticles show great promise as fillers to tune the refractive index of anti-reflective coatings on signs and optical encapsulants for LEDs, solar cells and other optical devices. Optical encapsulants are coverings or coatings, usually made of silicone, that protect a device.

Industry has largely shunned TiO2 nanoparticles because they’ve been difficult and expensive to make, and current methods produce particles that are too large.

Sandia became interested in TiO2 for optical encapsulants because of its work on LED materials for solid-state lighting.

Current production methods for TiO2 often require high-temperature processing or costly surfactants — molecules that bind to something to make it soluble in another material, like dish soap does with fat.
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Those methods produce less-than-ideal nanoparticles that are very expensive, can vary widely in size and show significant particle clumping, called agglomeration.

Sandia’s technique, on the other hand, uses readily available, low-cost materials and results in nanoparticles that are small, roughly uniform in size and don’t clump.

“We wanted something that was low cost and scalable, and that made particles that were very small,” said researcher Todd Monson, who along with principal investigator Dale Huber patented the process in mid-2011 as “High-yield synthesis of brookite TiO2 nanoparticles.” [emphases mine]

A June 17, 2014 Sandia Labs news release, which originated the news item, goes on to describe the technology (Note: Links have been removed),

Their (Monson and Huber) method produces nanoparticles roughly 5 nanometers in diameter, approximately 100 times smaller than the wavelength of visible light, so there’s little light scattering, Monson said.

“That’s the advantage of nanoparticles — not just nanoparticles, but small nanoparticles,” he said.

Scattering decreases the amount of light transmission. Less scattering also can help extract more light, in the case of an LED, or capture more light, in the case of a solar cell.

TiO2 can increase the refractive index of materials, such as silicone in lenses or optical encapsulants. Refractive index is the ability of material to bend light. Eyeglass lenses, for example, have a high refractive index.

Practical nanoparticles must be able to handle different surfactants so they’re soluble in a wide range of solvents. Different applications require different solvents for processing.

…

“If someone wants to use TiO2 nanoparticles in a range of different polymers and applications, it’s convenient to have your particles be suspension-stable in a wide range of solvents as well,” Monson said. “Some biological applications may require stability in aqueous-based solvents, so it could be very useful to have surfactants available that can make the particles stable in water.”

The researchers came up with their synthesis technique by pooling their backgrounds — Huber’s expertise in nanoparticle synthesis and polymer chemistry and Monson’s knowledge of materials physics. The work was done under a Laboratory Directed Research and Development project Huber began in 2005.

“The original project goals were to investigate the basic science of nanoparticle dispersions, but when this synthesis was developed near the end of the project, the commercial applications were obvious,” Huber said. The researchers subsequently refined the process to make particles easier to manufacture.

Existing synthesis methods for TiO2 particles were too costly and difficult to scale up production. In addition, chemical suppliers ship titanium-dioxide nanoparticles dried and without surfactants, so particles clump together and are impossible to break up. “Then you no longer have the properties you want,” Monson said.

The researchers tried various types of alcohol as an inexpensive solvent to see if they could get a common titanium source, titanium isopropoxide, to react with water and alcohol.

The biggest challenge, Monson said, was figuring out how to control the reaction, since adding water to titanium isopropoxide most often results in a fast reaction that produces large chunks of TiO2, rather than nanoparticles. “So the trick was to control the reaction by controlling the addition of water to that reaction,” he said.

…

Some textbooks dismissed the titanium isopropoxide-water-alcohol method as a way of making TiO2 nanoparticles. Huber and Monson, however, persisted until they discovered how to add water very slowly by putting it into a dilute solution of alcohol. “As we tweaked the synthesis conditions, we were able to synthesize nanoparticles,” Monson said.

Whoever wrote the news release now makes the plea which isn’t quite a plea (Note: A link has been removed),

The next step is to demonstrate synthesis at an industrial scale, which will require a commercial partner. Monson, who presented the work at Sandia’s fall Science and Technology Showcase, said Sandia has received inquiries from companies interested in commercializing the technology.

“Here at Sandia we’re not set up to produce the particles on a commercial scale,” he said. “We want them to pick it up and run with it and start producing these on a wide enough scale to sell to the end user.”

Sandia would synthesize a small number of particles, then work with a partner company to form composites and evaluate them to see if they can be used as better encapsulants for LEDs, flexible high-index refraction composites for lenses or solar concentrators. “I think it can meet quite a few needs,” Monson said.

I wish them good luck.