Tag Archives: W. Mark Saltzman

Living skin with blood vessels can be 3D printed

This is a big step forward but it’s not for the faint at heart. Scientists have successfully 3D printed human skin with blood vessels and grafted them onto mice. Rensselaer Polytechnic Institute and Yale University researchers worked together on this tissue engineering project. This video features Renseellaer’s Pankaj Kraande discussing the research,

Here’s a November 1, 2019 Rensselaer Polytechnic news release (also received via email and it’s on EurekAlert) describing the work in detail,

Researchers at Rensselaer Polytechnic Institute have developed a way to 3D print living skin, complete with blood vessels. The advancement, published online today [Nov. 1, 2019] in Tissue Engineering Part A, [the paper is behind a pywall] is a significant step toward creating grafts that are more like the skin our bodies produce naturally.

“Right now, whatever is available as a clinical product is more like a fancy Band-Aid,” said Pankaj Karande, an associate professor of chemical and biological engineering and member of the Center for Biotechnology and Interdisciplinary Studies (CBIS), who led this research at Rensselaer. “It provides some accelerated wound healing, but eventually it just falls off; it never really integrates with the host cells.”

A significant barrier to that integration has been the absence of a functioning vascular system in the skin grafts.

Karande has been working on this challenge for several years, previously publishing one of the first papers showing that researchers could take two types of living human cells, make them into “bio-inks,” and print them into a skin-like structure. Since then, he and his team have been working with researchers from Yale School of Medicine to incorporate vasculature.

In this paper, the researchers show that if they add key elements — including human endothelial cells, which line the inside of blood vessels, and human pericyte cells, which wrap around the endothelial cells — with animal collagen and other structural cells typically found in a skin graft, the cells start communicating and forming a biologically relevant vascular structure within the span of a few weeks. …

“As engineers working to recreate biology, we’ve always appreciated and been aware of the fact that biology is far more complex than the simple systems we make in the lab,” Karande said. “We were pleasantly surprised to find that, once we start approaching that complexity, biology takes over and starts getting closer and closer to what exists in nature.”

Once the Yale team grafted it onto a special type of mouse, the vessels from the skin printed by the Rensselaer team began to communicate and connect with the mouse’s own vessels.

“That’s extremely important, because we know there is actually a transfer of blood and nutrients to the graft which is keeping the graft alive,” Karande said.

In order to make this usable at a clinical level, researchers need to be able to edit the donor cells using something like the CRISPR technology, so that the vessels can integrate and be accepted by the patient’s body.

We are still not at that step, but we are one step closer,” Karande said.

“This significant development highlights the vast potential of 3D bioprinting in precision medicine, where solutions can be tailored to specific situations and eventually to individuals,” said Deepak Vashishth, the director CBIS. “This is a perfect example of how engineers at Rensselaer are solving challenges related to human health.”

Karande said more work will need to be done to address the challenges associated with burn patients, which include the loss of nerve and vascular endings. But the grafts his team has created bring researchers closer to helping people with more discrete issues, like diabetic or pressure ulcers.

“For those patients, these would be perfect, because ulcers usually appear at distinct locations on the body and can be addressed with smaller pieces of skin,” Karande said. “Wound healing typically takes longer in diabetic patients, and this could also help to accelerate that process.”

Very unusually, I cannot find the full title for this paper. Here’s what I found,

Three Dimensional Bioprinting of a Vascularized and Perfusable Skin Graft Using Human Keratinocytes, Fibroblasts, Pericytes, and Endothelial Cells by Dr. Tânia Baltazar, Dr. Jonathan Merola, Miss Carolina Motter Catarino, Miss Catherine Bingchan Xie, Dr. Nancy Kirkiles-Smith, Dr. Vivian Lee, Miss Stéphanie Yuki Kolbeck Hotta, Dr. Guohao Dai, Dr. Xiaowei Xu, Dr. Frederico Castelo Ferreira, Dr. W Mark Saltzman, Dr. Jordan S Pober, and Prof. Pankaj Karande. Tissue Engineering Part A DOI: https://doi.org/10.1089/ten.TEA.2019.0201 Published Online: 1 Nov 2019

As noted earlier, this is behind a paywall.

Finding a way to prevent sunscreens from penetrating the skin

While nanosunscreens have been singled out for their possible impact on our health, the fact is many sunscreens contain dangerous ingredients penetrating the skin. A Dec. 14, 2015 news item on ScienceDaily describes some research into getting sunscreens to stay on the skin surface avoiding penetration,

A new sunscreen has been developed that encapsulates the UV-blocking compounds inside bio-adhesive nanoparticles, which adhere to the skin well, but do not penetrate beyond the skin’s surface. These properties resulted in highly effective UV protection in a mouse model, without the adverse effects observed with commercial sunscreens, including penetration into the bloodstream and generation of reactive oxygen species, which can damage DNA and lead to cancer.

A US National Institute of Biomedical Imaging and Bioengineering (NIBIB) Dec. 14, 2015 news release, which originated the news item, expands on the theme (Note: Links have been removed),

Commercial sunscreens use compounds that effectively filter out damaging UV light. However, there is concern that these agents have a variety of harmful effects due to penetration past the surface skin. For example, these products have been found in human breast tissue and urine and are known to disrupt the normal function of some hormones. Also, the exposure of the UV filters to light can produce toxic reactive oxygen species that are destructive to cells and tissues and can cause tumors through DNA damage.

“This work applies a novel bioengineering idea to a little known but significant health problem, adds Jessica Tucker, Ph.D., Director of the NIBIB Program in Delivery Systems and Devices for Drugs and Biologics. “While we are all familiar with the benefits of sunscreen, the potential toxicities from sunscreen due to penetration into the body and creation of DNA-damaging agents are not well known. Bioengineering sunscreen to inhibit penetration and keep any DNA-damaging compounds isolated in the nanoparticle and away from the skin is a great example of how a sophisticated technology can be used to solve a problem affecting the health of millions of people.”

Bioengineers and dermatologists at Yale University in New Haven, Connecticut combined their expertise in nanoparticle-based drug delivery and the molecular and cellular characteristics of the skin to address these potential health hazards of current commercial sunscreens.

The news release then goes on to provide some technical details,

The group encapsulated a commonly used sunscreen, padimate O (PO), inside a nanoparticle (a very small molecule often used to transport drugs and other agents into the body). PO is related to the better-known sunscreen PABA.

The bioadhesive nanoparticle containing the sunscreen PO was tested on pigs for penetration into the skin. A control group of pigs received the PO alone, not encapsulated in a nanoparticle. The PO penetrated beyond the surface layers of skin where it could potentially enter the bloodstream through blood vessels that are in the deeper skin layers. However, the PO inside the nanoparticle remained on the surface of the skin and did not penetrate into deeper layers.

Because the bioadhesive nanoparticles, or BNPs are larger than skin pores it was somewhat expected that they could not enter the body by that route. However, skin is full of hair follicles that are larger than BNPs and so could be a way for migration into the body. Surprisingly, BNPs did not pass through the hair follicle openings either. Tests indicated that the adhesive properties of the BNPs caused them to stick to the skin surface, unable to move through the hair follicles.

Further testing showed that the BNPs were water resistant and remained on the skin for a day or more, yet were easily removed by towel wiping. They also disappeared in several days through natural exfoliation of the surface skin.

BNPs enhance the effect of sunscreen

An important test was whether the BNP-encapsulated sunscreen retained its UV filtering properties. The researchers used a mouse model to test whether PO blocked sunburn when encapsulated in the BNPs. The BNP formulation successfully provided the same amount of UV protection as the commercial products applied directly to the skin of the hairless mouse model. Surprisingly, this was achieved even though the BNPs carried only a fraction (5%) of the amount of commercial sunblock applied to the mice.

Finally, the encapsulated sunscreen was tested for the formation of damaging oxygen-carrying molecules known as reactive oxygen species, (ROS) when exposed to UV light. The researchers hypothesized that any ROS created by the sunscreen’s interaction with UV would stay contained inside the BNP, unable to damage surrounding tissue. Following exposure to UV light, no damaging ROS were detected outside of the nanoparticle, indicating that any harmful agents that were formed remained inside of the nanoparticle, unable to make contact with the skin.

“We are extremely pleased with the properties and performance of our BNP formulation,” says senior author Mark Saltzman, Ph.D., Yale School of Engineering and Applied Science. “The sunscreen loaded BNPs combine the best properties of an effective sunscreen with a safety profile that alleviates the potential toxicities of the actual sunscreen product because it is encapsulated and literally never touches the skin.” Adds co-senior author, Michael Girardi, M.D. “Our nanoparticles performed as expected, however, these are preclinical findings. We are now in a position to assess the effects on human skin.”

So, all of this work has been done on animal models, which means that human clinical trials are the likely next step. As we wait, here’s a link to and a citation for this group’s paper,

A sunblock based on bioadhesive nanoparticles by Yang Deng, Asiri Ediriwickrema, Fan Yang, Julia Lewis, Michael Girardi, & W. Mark Saltzman. Nature Materials 14, 1278–1285 (2015) doi:10.1038/nmat4422 Published online 28 September 2015

This paper is behind a paywall.

Safer sunblock and bioadhesive nanoparticles from Yale University

The skin has a lot of protective barriers but it’s always possible to make something better so a sunblock that doesn’t penetrate the* skin at all seems like it might be a good thing. Interestingly, this new sunblock or sunscreen is enabled by nanoparticles but not the metallic nanoparticles found in what are sometimes called nanosunscreens. From a Sept. 29, 2015 news item on Nanowerk,

Researchers at Yale have developed a sunscreen that doesn’t penetrate the skin, eliminating serious health concerns associated with commercial sunscreens.

Most commercial sunblocks are good at preventing sunburn, but they can go below the skin’s surface and enter the bloodstream. As a result, they pose possible hormonal side effects and could even be promoting the kind of skin cancers they’re designed to prevent.

But researchers at Yale have developed a new sunblock, made with bioadhesive nanoparticles, that stays on the surface of the skin.

A Sept. 28, 2015 Yale University news release by William Weir, whch originated the news item, describes the research in more detail,

“We found that when we apply the sunblock to the skin, it doesn’t come off, and more importantly, it doesn’t penetrate any further into the skin,” said the paper’s senior author, Mark Saltzman, the Goizueta Foundation Professor of Biomedical Engineering. “Nanoparticles are large enough to keep from going through the skin’s surface, and our nanoparticles are so adhesive that they don’t even go into hair follicles, which are relatively open.”

Using mouse models, the researchers tested their sunblock against direct ultraviolet rays and their ability to cause sunburn. In this regard, even though it used a significantly smaller amount of the active ingredient than commercial sunscreens, the researchers’ formulation protected equally well against sunburn.

They also looked at an indirect — and much less studied — effect of UV light. When the active ingredients of sunscreen absorb UV light, a chemical change triggers the generation of oxygen-carrying molecules known as reactive oxygen species (ROS). If a sunscreen’s agents penetrate the skin, this chemical change could cause cellular damage, and potentially facilitate skin cancer.

“Commercial chemical sunblock is protective against the direct hazards of ultraviolet damage of DNA, but might not be against the indirect ones,” said co-author Michael Girardi, a professor of dermatology at Yale Medical School. “In fact, the indirect damage was worse when we used the commercial sunblock.”

Girardi, who specializes in skin cancer development and progression, said little research has been done on the ultimate effects of sunblock usage and the generation of ROS, “but obviously, there’s concern there.”

Previous studies have found traces of commercial sunscreen chemicals in users’ bloodstreams, urine, and breast milk. There is evidence that these chemicals cause disruptions with the endocrine system, such as blocking sex hormone receptors.

To test penetration levels, the researchers applied strips of adhesive tape to skin previously treated with sunscreen. The tape was then removed rapidly, along with a thin layer of skin. Repeating this procedure allowed the researchers to remove the majority of the outer skin layer, and measure how deep the chemicals had penetrated into the skin. Traces of the sunscreen chemical administered in a conventional way were found to have soaked deep within the skin. The Yale team’s sunblock came off entirely with the initial tape strips.

Tests also showed that a substantial amount of the Yale team’s sunscreen remained on the skin’s surface for days, even after exposure to water. When wiped repeatedly with a towel, the new sunblock was entirely removed. [emphasis mine]

To make the sunblock, the researchers developed a nanoparticle with a surface coating rich in aldehyde groups, which stick tenaciously to the outer skin layer. The nanoparticle’s hydrophilic layer essentially locks in the active ingredient, a hydrophobic chemical called padimate O.

Some sunscreen solutions that use larger particles of inorganic compounds, such as titanium dioxide or zinc oxide, also don’t penetrate the skin. For aesthetic reasons, though, these opaque sunscreen products aren’t very popular. By using a nanoparticle to encase padimate O, an organic chemical used in many commercial sunscreens, the Yale team’s sunblock is both transparent and stays out of the skin cells and bloodstream.

This seems a little confusing to me and I think clarification may be helpful. My understanding is that the metallic nanoparticles (nano titanium dioxide and nano zinc oxide) engineered for use in commercial sunscreens are also (in addition to the macroscale titanium dioxide and zinc oxide referred to in the Yale news release) too large to pass through the skin. At least that was the understanding in 2010 and I haven’t stumbled across any information that is contradictory. Here’s an excerpt from a July 20, 2010 posting where I featured portions of a debate between Georgia Miller (at that time representing Friends of the Earth) and Dr. Andrew Maynard (at that time director of the University of Michigan Risk Science Center and a longtime participant in the nanotechnology risk discussions),

Three of the scientists whose work was cited by FoE as proof that nanosunscreens are dangerous either posted directly or asked Andrew to post comments which clarified the situation with exquisite care,

Despite FoE’s implications that nanoparticles in sunscreens might cause cancer because they are photoactive, Peter Dobson points out that there are nanomaterials used in sunscreens that are designed not to be photoactive. Brian Gulson, who’s work on zinc skin penetration was cited by FoE, points out that his studies only show conclusively that zinc atoms or ions can pass through the skin, not that nanoparticles can pass through. He also notes that the amount of zinc penetration from zinc-based sunscreens is very much lower than the level of zinc people have in their body in the first place. Tilman Butz, who led one of the largest projects on nanoparticle penetration through skin to date, points out that – based on current understanding – the nanoparticles used in sunscreens are too large to penetrate through the skin.

However, there may be other ingredients which do pass through into the bloodstream and are concerning.

One other thing I’d like to note. Not being able to remove the sunscreen easily ( “When wiped repeatedly with a towel, the new sunblock was entirely removed.”) may prove to be a problem as we need Vitamin D, which is for the most part obtainable by sun exposure.

In any event, here’s a link to and a citation for the paper,

A sunblock based on bioadhesive nanoparticles by Yang Deng, Asiri Ediriwickrema, Fan Yang, Julia Lewis, Michael Girardi, & W. Mark Saltzman. Nature Materials (2015) doi:10.1038/nmat4422 Published online 28 September 2015

This paper is behind a paywall.

*’teh’ changed to ‘the’ on June 6, 2016.