Portable Seawater Desalination System for Generating Drinkable Water in Remote Locations

Abstract

A portable seawater desalination system would be highly desirable to solve water challenges in rural areas and disaster situations

While many reverse osmosis-based portable desalination systems are already available commercially, they are not adequate for providing reliable drinking water in remote locations due to the requirement of high-pressure pumping and repeated maintenance. We demonstrate a field-deployable desalination system with multistage electromembrane processes, composed of two-stage ion concentration polarization and one-stage electrodialysis, to convert brackish water and seawater to drinkable water. A data-driven predictive model is used to optimize the multistage configuration, and the model predictions show good agreement with the experimental results.

The user-friendly unit, which weighs less than 10 kilograms and does not require the use of filters, can be powered by a small, portable solar panel. Credit: M. Scott Brauer

Researchers build a portable desalination unit that generates clear, clean drinking water without the need for filters or high-pressure pumps

MIT researchers have developed a portable desalination unit, weighing less than 10 kilograms (22 pounds), that can remove particles and salts to generate fresh drinking water.

The device, which is about the size of a suitcase, needs less power to operate than a cell phone charger. It can also be driven by a small, portable solar panel, which can be purchased online for around $50. It automatically generates drinking water that exceeds World Health Organization (WHO) quality standards. The technology is packaged into a user-friendly device that runs with the push of a single button.

Unlike other portable desalination devices that require water to pass through filters, this unit utilizes electrical power to remove particles from drinking water. Eliminating the need for replacement filters significantly reduces the long-term maintenance requirements.

The setup includes a two-stage ion concentration polarization (ICP) process, with water flowing through six modules in the first stage then through three in the second stage, followed by a single electrodialysis process Credit: M. Scott Brauer

This could enable the unit to be deployed in remote and severely resource-limited areas, such as communities on small islands or aboard seafaring cargo ships. It could also be used to aid refugees fleeing natural disasters or by soldiers carrying out long-term military operations.

“This is really the culmination of a 10-year journey that I and my group have been on. We worked for years on the physics behind individual desalination processes, but pushing all those advances into a box, building a system, and demonstrating it in the ocean, that was a really meaningful and rewarding experience for me,” says senior author Jongyoon Han, a professor of electrical engineering and computer science and of biological engineering, and a member of the Research Laboratory of Electronics (RLE).

Joining Han on the paper are first author Junghyo Yoon, a research scientist in RLE; Hyukjin J. Kwon, a former postdoc; SungKu Kang, a postdoc at Northeastern University; and Eric Brack of the U.S. Army Combat Capabilities Development Command (DEVCOM). The research has been published online in the journal Environmental Science and Technology.

Filter-free technology

Commercially available portable desalination units typically require high-pressure pumps to push water through filters, which are very difficult to miniaturize without compromising the energy-efficiency of the device, explains Yoon.

Instead, their unit relies on a technique called ion concentration polarization (ICP), which was pioneered by Han’s group more than 10 years ago. Rather than filtering water, the ICP process applies an electrical field to membranes placed above and below a channel of water. The membranes repel positively or negatively charged particles — including salt molecules, bacteria, and viruses — as they flow past. The charged particles are funneled into a second stream of water that is eventually discharged.

The process removes both dissolved and suspended solids, allowing clean water to pass through the channel. Since it only requires a low-pressure pump, ICP uses less energy than other techniques.

The portable device does not require any replacement filters, which greatly reduces the long-term maintenance requirements. Credit: M. Scott Brauer

But ICP does not always remove all the salts floating in the middle of the channel. So the researchers incorporated a second process, known as electrodialysis, to remove remaining salt ions.

Yoon and Kang used machine learning to find the ideal combination of ICP and electrodialysis modules. The optimal setup includes a two-stage ICP process, with water flowing through six modules in the first stage then through three in the second stage, followed by a single electrodialysis process. This minimized energy usage while ensuring the process remains self-cleaning.

“While it is true that some charged particles could be captured on the ion exchange membrane, if they get trapped, we just reverse the polarity of the electric field and the charged particles can be easily removed,” Yoon explains

They shrunk and stacked the ICP and electrodialysis modules to improve their energy efficiency and enable them to fit inside a portable device. The researchers designed the device for nonexperts, with just one button to launch the automatic desalination and purification process. Once the salinity level and the number of particles decrease to specific thresholds, the device notifies the user that the water is drinkable.

The researchers also created a smartphone app that can control the unit wirelessly and report real-time data on power consumption and water salinity.

Beach tests

After running lab experiments using water with different salinity and turbidity (cloudiness) levels, they field-tested the device at Boston’s Carson Beach.

Yoon and Kwon set the box near the shore and tossed the feed tube into the water. In about half an hour, the device had filled a plastic drinking cup with clear, drinkable water.

“It was successful even in its first run, which was quite exciting and surprising. But I think the main reason we were successful is the accumulation of all these little advances that we made along the way,” Han says.

The resulting water exceeded World Health Organization quality guidelines, and the unit reduced the amount of suspended solids by at least a factor of 10. Their prototype generates drinking water at a rate of 0.3 liters per hour, and requires only 20 watts of power per liter.

“Right now, we are pushing our research to scale up that production rate,” Yoon says.

One of the biggest challenges of designing the portable system was engineering an intuitive device that could be used by anyone, Han says. Yoon hopes to make the device more user-friendly and improve its energy efficiency and production rate through a startup he plans to launch to commercialize the technology.

In the lab, Han wants to apply the lessons he’s learned over the past decade to water-quality issues that go beyond desalination, such as rapidly detecting contaminants in drinking water.

“This is definitely an exciting project, and I am proud of the progress we have made so far, but there is still a lot of work to do,” he says.

For example, while the “development of portable systems using electro-membrane processes is an original and exciting direction in off-grid, small-scale desalination,” the effects of fouling, especially if the water has high turbidity, could significantly increase maintenance requirements and energy costs, notes Nidal Hilal, professor of engineering and director of the New York University Abu Dhabi Water research center, who was not involved with this research.

“Another limitation is the use of expensive materials,” he adds. “It would be interesting to see similar systems with low-cost materials in place.”

Reference: “Portable Seawater Desalination System for Generating Drinkable Water in Remote Locations” by Junghyo Yoon, Hyukjin J. Kwon, SungKu Kang, Eric Brack and Jongyoon Han, 14 April 2022, Environmental Science and Technology. DOI: 10.1021/acs.est.1c08466

The research was funded, in part, by the DEVCOM Soldier Center, the Abdul Latif Jameel Water and Food Systems Lab (J-WAFS), the Experimental AI Postdoc Fellowship Program of Northeastern University, and the Roux AI Institute.

Continuous cuffless monitoring of arterial blood pressure via graphene bioimpedance tattoos

Abstract

Continuous monitoring of arterial blood pressure (BP) in non-clinical (ambulatory) settings is essential for understanding numerous health conditions, including cardiovascular diseases. Besides their importance in medical diagnosis, ambulatory BP monitoring platforms can advance disease correlation with individual behaviour, daily habits and lifestyle, potentially enabling analysis of root causes, prognosis and disease prevention. Although conventional ambulatory BP devices exist, they are uncomfortable, bulky and intrusive. Here we introduce a wearable continuous BP monitoring platform that is based on electrical bioimpedance and leverages atomically thin, self-adhesive, lightweight and unobtrusive graphene electronic tattoos as human bioelectronic interfaces. The graphene electronic tattoos are used to monitor arterial BP for >300 min, a period tenfold longer than reported in previous studies. The BP is recorded continuously and non-invasively, with an accuracy of 0.2 ± 4.5 mm Hg for diastolic pressures and 0.2 ± 5.8 mm Hg for systolic pressures, a performance equivalent to Grade A classification.

A new electronic tattoo that can be worn comfortably on the wrist for hours delivers continuous blood pressure measurements at an accuracy level exceeding nearly all available options on the market today. Credit: University of Texas at Austin

Blood pressure is one of the most important indicators of heart health, but it’s tough to frequently and reliably measure outside of a clinical setting. For decades, cuff-based devices that constrict around the arm to give a reading have been the gold standard. But now, researchers at The University of Texas at Austin and Texas A&M University have developed an electronic tattoo that can be worn comfortably on the wrist for hours and deliver continuous blood pressure measurements at an accuracy level exceeding nearly all available options on the market today.

“Blood pressure is the most important vital sign you can measure, but the methods to do it outside of the clinic passively, without a cuff, are very limited,” said Deji Akinwande, a professor in the Department of Electrical and Computer Engineering at UT Austin and one of the co-leaders of the project, which is documented in a new paper published on June 20, 2022, in Nature Nanotechnology.

High blood pressure can lead to serious heart conditions if left untreated. It can be hard to capture with a traditional blood pressure check because that only measures a moment in time, a single data point.

“Taking infrequent blood pressure measurements has many limitations, and it does not provide insight into exactly how our body is functioning,” said Roozbeh Jafari, a professor of biomedical engineering, computer science, and electrical engineering at Texas A&M and the other co-leader of the project.

E-tattoos are a good choice for mobile blood pressure monitoring because they reside in a sticky, stretchy material encasing the sensors that is comfortable to wear for long periods and does not slide around. Credit: University of Texas at Austin

The continuous monitoring of the e-tattoo allows for blood pressure measurements in all kinds of situations: at times of high stress, while sleeping, exercising, etc. It can deliver thousands of measurements more than any device thus far.

Mobile health monitoring has taken major leaps in recent years, primarily due to technology such as smartwatches. These devices use metallic sensors that get readings based on LED light sources shined through the skin.

However, leading smartwatches are not yet ready for blood pressure monitoring. That’s because the watches slide around on the wrist and might be far from arteries, making it hard to deliver accurate readings. And the light-based measurements can falter in people with darker skin tones and/or larger wrists.

Graphene is one of the strongest and thinnest materials in existence, and it is a key ingredient in the e-tattoo. It is similar to graphite found in pencils, but the atoms are precisely arranged into thin layers.

E-tattoos make sense as a vehicle for mobile blood pressure monitoring because they reside in a sticky, stretchy material encasing the sensors that is comfortable to wear for long periods and does not slide around.

“The sensor for the tattoo is weightless and unobtrusive. You place it there. You don’t even see it, and it doesn’t move,” Jafari said. “You need the sensor to stay in the same place because if you happen to move it around, the measurements are going to be different.”

The device takes its measurements by shooting an electrical current into the skin and then analyzing the body’s response, which is known as bioimpedance. There is a correlation between bioimpedance and changes in blood pressure that has to do with blood volume changes. However, the correlation is not particularly obvious, so the team had to create a machine learning model to analyze the connection to get accurate blood pressure readings.

In medicine, cuff-less blood pressure monitoring is the “holy grail,” Jafari said, but there isn’t a viable solution on the market yet. It’s part of a larger push in medicine to use technology to untether patients from machines while collecting more data wherever they are, allowing them to go from room to room, clinic to clinic, and still get personalized care.

“All this data can help create a digital twin to model the human body, to predict and show how it might react and respond to treatments over time,” Akinwande said.

Reference: “Continuous cuffless monitoring of arterial blood pressure via graphene bioimpedance tattoos” by Dmitry Kireev, Kaan Sel, Bassem Ibrahim, Neelotpala Kumar, Ali Akbari, Roozbeh Jafari and Deji Akinwande, 20 June 2022, Nature Nanotechnology. DOI: 10.1038/s41565-022-01145-w

Team members on the project include Dmitry Kireev and Neelotpala Kumar of the Department of Electrical and Computer Engineering at UT Austin; Kaan Sel and Bassem Ibrahim of the Department of Electrical and Computer Engineering at Texas A&M; and Ali Akbari of the Department of Biomedical Engineering at Texas A&M. The research was supported by grants from the Office of Naval Research, National Science Foundation and National Institutes of Health.

Creating renewable biocement entirely out of waste material

Cement is a binder, a substance used in construction that hardens, sets, and adheres to other materials to bind them together. When sand and gravel are combined with cement, concrete is produced. Cement is classified as hydraulic or non-hydraulic, with non-hydraulic cement not setting when water is present, while hydraulic cement needs a chemical reaction between dry materials and water.

Cement is one of the most widely used materials on the planet. Cement consumption in the United States was estimated to be 109 million metric tons in 2021.

Cement manufacturing has an impact on the environment at every level of the process. Some examples include airborne pollutants in the form of dust, fumes, noise, and vibration while running equipment and blasting at quarries, as well as damage to the landscape caused by quarrying.

Scientists at Nanyang Technological University, Singapore (NTU Singapore) have discovered a method to produce biocement from waste, making the alternative to traditional cement greener and more sustainable.

Biocement is a kind of renewable cement that uses bacteria to create a hardening reaction that binds soil into a solid block.

The NTU scientists have now created biocement from two common waste materials: industrial carbide sludge and urea (from mammalian urine).

They devised a method for forming a hard solid, or precipitate, from the interaction of urea with calcium ions in industrial carbide sludge. When this reaction occurs in soil, the precipitate binds soil particles together and fills gaps between them, resulting in a compact mass of soil. This produces a biocement block that is strong, durable, and less permeable.

The research team, led by Professor Chu Jian, Chair of the School of Civil and Environmental Engineering, showed in a proof-of-concept research paper published on February 22nd, 2022 in the Journal of Environmental Chemical Engineering that their biocement could potentially become a sustainable and cost-effective method for soil improvement, such as strengthening the ground for use in construction or excavation, controlling beach erosion, reducing dust or wind erosion in the desert, or building freshwater reservoirs on beaches or in the desert.

Wu Shifan Chu Jian (from left to right) Dr. Wu Shifan, Senior Research Fellow, Centre for Urban Solutions, School of Civil and Environmental Engineering, NTU, and Professor Chu Jian, Chair of the School of Civil and Environmental Engineering, NTU holding up blocks of biocement made from urea and carbide sludge. Credit: Nanyang Technological University, Singapore

It can also be used as biogrout to seal cracks in rock for seepage control and even to touch up and repair monuments like rock carvings and statues.

“Biocement is a sustainable and renewable alternative to traditional cement and has great potential to be used for construction projects that require the ground to be treated,” said Prof Chu, who is also the Director of NTU’s Centre for Urban Solutions. “Our research makes biocement even more sustainable by using two types of waste material as its raw materials. In the long run, it will not only make it cheaper to manufacture biocement, but also reduce the cost involved for waste disposal.”

The NTU scientists’ research supports the NTU 2025 strategic plan which aims to address some of humanity’s grand challenges, including mitigating human impact on the environment through advancing research and development in sustainability

Urine, bacteria, and calcium: A simple recipe for biocement

The biocement-making process requires less energy and generates fewer carbon emissions compared to traditional cement production methods.

The NTU team’s biocement is created from two types of waste material: industrial carbide sludge – the waste material from the production of acetylene gas, sourced from Singapore factories – and urea found in urine.

Firstly, the team treats carbide sludge with an acid to produce soluble calcium. Urea is then added to the soluble calcium to form a cementation solution. The team then adds a bacterial culture to this cementation solution. The bacteria from the culture then break down the urea in the solution to form carbonate ions.

These ions react with the soluble calcium ions in a process called microbially induced calcite precipitation (MICP). This reaction forms calcium carbonate – a hard, solid material that is naturally found in chalk, limestone, and marble.

Biocement Test Specimen

The test specimen of a Buddha hand was provided by Dazu Rock Carvings, a UNESCO World Heritage Site in China. Repair work using biocement was done at Chongqing University, China, by Dr. Yang Yang. The biocement solution is colorless, allowing restoration works to maintain the carving’s original color. Credit: Nanyang Technological University, Singapore

When this reaction occurs in soil or sand, the resulting calcium carbonate generated bonds soil or sand particles together to increase their strength and fills the pores between them to reduce water seepage through the material. The same process can also be used on rock joints, which allows for the repair of rock carvings and statues.

The soil reinforced with biocement has an unconfined compression strength of up to 1.7 megapascals (MPa), which is higher than that of the same soil treated using an equivalent amount of cement.

This makes the team’s biocement suitable for use in soil improvement projects such as strengthening the ground or reducing water seepage for use in construction or excavation or controlling beach erosion along coastlines.

Paper first author Dr. Yang Yang, a former NTU Ph.D. student and research associate at the Centre for Urban Solutions who is currently a postdoctorate fellow at Chongqing University, China, said: “The calcium carbonate precipitation at various cementation levels strengthens the soil or sand by gradually filling out the pores among the particles. The biocement could also be used to seal cracks in soil or rock to reduce water seepage.”

A sustainable alternative to cement

Biocement production is greener and more sustainable than the methods used to produce traditional cement.

“One part of the cement-making process is the burning of raw materials at very high temperatures over 1,000 degrees Celsius to form clinkers – the binding agent for cement. This process produces a lot of carbon dioxide,” said Prof Chu. “However, our biocement is produced at room temperature without burning anything, and thus it is a greener, less energy demanding, and carbon-neutral process.”

Dr. Yang Yang said: “In Singapore, carbide sludge is seen as waste material. However, it is a good raw material for the production of biocement. By extracting calcium from carbide sludge, we make the production more sustainable as we do not need to use materials like limestone which has to be mined from a mountain.”

Prof Chu added: “Limestone is a finite resource – once it’s gone, it’s gone. The mining of limestone affects our natural environment and ecosystem too.”

The research team says that if biocement production could be scaled to the levels of traditional cement-making, the overall cost of its production compared to that of conventional cement would be lower, which would make biocement both greener and cheaper alternative to cement.

Restoring monuments and strengthening shorelines

Another advantage of the NTU team’s method in formulating biocement is that both the bacterial culture and cementation solution are colorless. When applied to soil, sand, or rock, their original color is preserved.

This makes it useful for restoring old rock monuments and artifacts. For example, Dr. Yang Yang has used the biocement to repair old Buddha monuments in China. The biocement can be used to seal gaps in cracked monuments and has been used to restore broken-off pieces, such as the fingers of a Buddha’s hands. As the solution is colorless, the monuments retain their original color, keeping the restoration work true to history.

In collaboration with relevant national agencies in Singapore, the team is currently trialing their new biocement at East Coast Park, where it is being used to strengthen the sand on the beach. By spraying the biocement solutions on top of the sand, a hard crust is formed, preventing sand from being washed out to sea.

The team is also exploring further large-scale applications of their biocement in Singapore, such as road repair by sealing cracks on roads, sealing gaps in underground tunnels to prevent water seepage, or even as cultivation grounds for coral reefs as carol larvae like to grow on calcium carbonate.

Reference: “Utilization of carbide sludge and urine for sustainable biocement production” by Yang Yang, Jian Chu, Liang Cheng, Hanlong Liu, 22 February 2022, Journal of Environmental Chemical Engineering. DOI: 10.1016/j.jece.2022.107443

In world-first, Tel Aviv University researchers engineer human spinal cord implants for treating paralysis.

Abstract

Cell therapy using induced pluripotent stem cell-derived neurons is considered a promising approach to regenerate the injured spinal cord (SC). However, the scar formed at the chronic phase is not a permissive microenvironment for cell or biomaterial engraftment or for tissue assembly. Engineering of a functional human neuronal network is now reported by mimicking the embryonic development of the SC in a 3D dynamic biomaterial-based microenvironment. Throughout the in vitro cultivation stage, the system's components have a synergistic effect, providing appropriate cues for SC neurogenesis. While the initial biomaterial supported efficient cell differentiation in 3D, the cells remodeled it to provide an inductive microenvironment for the assembly of functional SC implants. The engineered tissues are characterized for morphology and function, and their therapeutic potential is investigated, revealing improved structural and functional outcomes after acute and chronic SC injuries. Such technology is envisioned to be translated to the clinic to rewire human injured SC.

• The researchers from Sagol Center for Regenerative Biotechnology engineered functional human spinal cord tissues, from human materials and cells, and implanted them in lab models that featured chronic paralysis, successfully restoring walking abilities in 80% of tests.
• The technology behind the breakthrough uses patient tissue samples, transforming it into a functioning spinal cord implant via a process that mimics the development of the spinal cord in human embryos.
• The researchers: “Our goal for the next few years is to engineer personalized spinal cord implants to repair tissue damaged from injury without the risk of implant rejection.”

For the first time in the world, researchers from Sagol Center for Regenerative Biotechnology at Tel Aviv University have engineered 3D human spinal cord tissues and implanted them in lab model with long-term chronic paralysis. The results were highly encouraging: an approximately 80% success rate in restoring walking abilities. Now the researchers are preparing for the next stage of the study: clinical trials in human patients. They hope that within a few years the engineered tissues will be implanted in paralyzed individuals enabling them to stand up and walk again.

The groundbreaking study was led Prof. Tal Dvir’s research team at the Sagol Center for Regenerative Biotechnology, the Shmunis School of Biomedicine and Cancer Research, and the Department of Biomedical Engineering at Tel Aviv University. The team at Prof. Dvir’s lab includes PhD student Lior Wertheim, Dr. Reuven Edri, and Dr. Yona Goldshmit. Other contributors included Prof. Irit Gat-Viks from the Shmunis School of Biomedicine and Cancer Research, Prof. Yaniv Assaf from the Sagol School of Neuroscience, and Dr. Angela Ruban from the Steyer School of Health Professions, all at Tel Aviv University. The results of the study were published in the prestigious scientific journalAdvanced Science.

Prof. Dvir explains: “Our technology is based on taking a small biopsy of belly fat tissue from the patient. This tissue, like all tissues in our body, consists of cells together with an extracellular matrix (comprising substances like collagens and sugars). After separating the cells from the extracellular matrix we used genetic engineering to reprogram the cells, reverting them to a state that resembles embryonic stem cells – namely cells capable of becoming any type of cell in the body. From the extracellular matrix we produced a personalized hydrogel, that would evoke no immune response or rejection after implantation. We then encapsulated the stem cells in the hydrogel and in a process that mimics the embryonic development of the spinal cord we turned the cells into 3D implants of neuronal networks containing motor neurons.”

The human spinal cord implants were then implanted in lab models, divided into two groups: those who had only recently been paralyzed (the acute model) and those who had been paralyzed for a long time – equivalent to a year in human terms (the chronic model). Following the implantation, 100% of the lab models with acute paralysis and 80% of those with chronic paralysis regained their ability to walk.

Prof. Dvir: “The model animals underwent a rapid rehabilitation process, at the end of which they could walk quite well. This is the first instance in the world in which implanted engineered human tissues have generated recovery in an animal model for long-term chronic paralysis – which is the most relevant model for paralysis treatments in humans. There are millions of people around the world who are paralyzed due to spinal injury, and there is still no effective treatment for their condition. Individuals injured at a very young age are destined to sit in a wheelchair for the rest of their lives, bearing all the social, financial, and health-related costs of paralysis. Our goal is to produce personalized spinal cord implants for every paralyzed person, enabling regeneration of the damaged tissue with no risk of rejection.

Based on the revolutionary organ engineering technology developed at Prof. Dvir’s lab, he teamed up with industry partners to establish Matricelf (matricelf.com) in 2019. The company applies Prof. Dvir’s approach in the aims of making spinal cord implant treatments commercially available for persons suffering from paralysis.

Prof. Dvir, head of Sagol Center for Regenerative Biotechnology,concludes: “We hope to reach the stage of clinical trials in humans within the next few years, and ultimately get these patients back on their feet. The company’s preclinical program has already been discussed with the FDA. Since we are proposing an advanced technology in regenerative medicine, and since at present there is no alternative for paralyzed patients, we have good reason to expect relatively rapid approval of our technology.”

Reference: “Regenerating the injured spinal cord at the chronic phase by engineered iPSCsderived 3D neuronal networks” by Lior Wertheim,Reuven Edri, Yona Goldshmit, Tomer Kagan, Nadav Noor, Angela Ruban, Assaf Shapira, Irit Gat-Viks, Yaniv Assaf and Tal Dvir, 7 February 2022, Advanced Science. DOI: 10.1002/advs.202105694

Regenerating the Injured Spinal Cord at the Chronic Phase by Engineered iPSCs-Derived 3D Neuronal Networks

A new MIT-designed surgical sticky tape can be applied quickly and easily, like duct tape to a pipe, to repair leaks and tears in the gastrointestinal tract and other tissues and organs. Credit: Courtesy of the researchers

Abstract

Surgical sealing and repair of injured and resected gastrointestinal (GI) organs are critical requirements for successful treatment and tissue healing. Despite being the standard of care, hand-sewn closure of GI defects using sutures faces limitations and challenges. In this work, we introduce an off-the-shelf bioadhesive GI patch capable of atraumatic, rapid, robust, and sutureless repair of GI defects. The GI patch integrates a nonadhesive top layer and a dry, bioadhesive bottom layer, resulting in a thin, flexible, transparent, and ready-to-use patch with tissue-matching mechanical properties. The rapid, robust, and sutureless sealing capability of the GI patch is systematically characterized using ex vivo porcine GI organ models. In vitro and in vivo rat models are used to evaluate the biocompatibility and degradability of the GI patch in comparison to commercially available tissue adhesives (Coseal and Histoacryl). To validate the GI patch’s efficacy, we demonstrate successful sutureless in vivo sealing and healing of GI defects in rat colon, stomach, and small intestine as well as in porcine colon injury models. The proposed GI patch provides a promising alternative to suture for repair of GI defects and offers potential clinical opportunities for the repair of other organs.

The sticky patch could be quickly applied to repair gut leaks and tears.

A staple on any engineer’s workbench, duct tape is a quick and dependable fix for cracks and tears in many structural materials. MIT engineers have now developed a kind of surgical duct tape — a strong, flexible, and biocompatible sticky patch that can be easily and quickly applied to biological tissues and organs to help seal tears and wounds.

Like duct tape, the new patch is sticky on one side and smooth on the other. In its current formulation, the adhesive is targeted to seal defects in the gastrointestinal tract, which the engineers describe as the body’s own biological ductwork.

In numerous experiments, the team has shown the patch can be quickly stuck to large tears and punctures in the colon, stomach, and intestines of various animal models. The adhesive binds strongly to tissues within several seconds and holds for over a month. It is also flexible, able to expand and contract with a functioning organ as it heals. Once an injury is fully healed, the patch gradually degrades without causing inflammation or sticking to surrounding tissues.

The team envisions the surgical sticky patch could one day be stocked in operating rooms and used as a fast and safe alternative or reinforcement to hand-sewn sutures to repair leaks and tears in the gut and other biological tissues.

“We think this surgical tape is a good base technology to be made into an actual, off-the-shelf product,” says Hyunwoo Yuk, a research scientist in MIT’s Department of Mechanical Engineering. “Surgeons could use it as they use duct tape in the nonsurgical world. It doesn’t need any preparation or prior step. Just take it out, open, and use.”

Yuk, the study’s co-lead and co-corresponding author, and his colleagues published their results on February 2, 2022, in the journal Science Translational Medicine. Other co-authors include MIT postdoc and lead author Jingjing Wu; project supervisor and co-corresponding author Xuanhe Zhao, who is a professor of mechanical engineering and of civil and environmental engineering at MIT; and collaborators from the Mayo Clinic and the Southern University of Science and Technology.

A gut instinct

The new surgical duct tape builds on the team’s 2019 design for a double-sided tape. That early iteration comprised a single layer that was sticky on both sides and designed to join two wet surfaces together.

The adhesive was made from polyacrylic acid, an absorbent material found in diapers, which starts out dry and absorbs moisture when in contact with a wet surface or tissue, temporarily sticking to the tissue in the process. The researchers mixed into the material NHS esters, chemical compounds that can bind with proteins in the tissue to form stronger bonds. Finally, they reinforced the adhesive with gelatin or chitosan — natural ingredients that kept the tape’s shape.

The researchers found the double-sided tape strongly bonded different tissues together. But when consulting with surgeons, they realized that a single-sided version might make a more practical impact.

“In practical situations, it’s not common to have to stick two tissues together —organs need to be separate from each other,” Wu says. “One suggestion was to use this sticky element to repair leaks and defects in the gut.”

Surgeons typically repair leaks and tears in the gastrointestinal tract with surgical sutures. But sewing the stitches requires precision and training, and following surgery the sutures can trigger scarring around the injury. The tissue between stitches could also tear, causing secondary leakages that could lead to sepsis.

“We thought, maybe we could turn our sticky element into a product to repair gut leaks, similar to sealing pipes with duct tape,” Wu says. “That pushed us toward something more like single-sided tape.”

Same tape, new tricks

The researchers first tuned their adhesive recipe, replacing gelatin and chitosan with a longer-lasting hydrogel — in this case, polyvinyl alcohol. This swap kept the adhesive physically stable for over a month, long enough for a typical gut injury to heal. They also added a second, nonsticky top layer to keep the patch from sticking to surrounding tissue. This layer was made from a biodegradable polyurethane that has about the same stretch and stiffness of natural gut tissue.

“We don’t want the patch to be weaker than tissue because otherwise it would risk bursting,” Yuk says. “We also don’t want it to be stiffer because it would restrict the peristaltic movement in guts that is essential for digestion.”

In initial tests, the patch did stick to tissues, but it also swelled, just as a fully wet, hydrogel-based diaper would. This swelling stretched the tape and the underlying tear it was intended to seal.

“It was almost an impossible problem because hydrogel naturally swells,” Yuk says. “But we did a simple trick: We prestretched the adhesive layer a bit, then introduced the nonadhesive layer, so that when applied to a tissue, that prestretching cancels out the swelling.”

The team then carried out experiments to test the patch’s properties and performance. When the patch was placed in a culture with human epithelial cells, the cells continued to grow, showing that the patch is biocompatible. When implanted under the skin of rats, the patch biodegraded after about 12 weeks, with no toxic effects.

The researchers also applied the patch to defects in the animals’ colons and stomachs, and found it maintained a strong bond as the injuries fully healed. It also produced minimal scarring and inflammation compared with repairs made with conventional sutures.

Finally, the team applied the patch over colon defects in pigs, and observed that the animals continued to feed normally, with no fever, lethargy, or other adverse health effects. After four weeks, the defects fully healed, with no sign of secondary leakage

Taken together, the experiments suggest that the surgical patch could potentially safely repair gastrointestinal injuries, and could be applied just as easily as commercial duct tape. Yuk and Zhao are further developing the adhesive through a new startup and hope to pursue FDA approval to test the patch in medical settings.

“We are studying a fundamental mechanics problem, adhesion, in an extremely challenging environment, inside the body. There are millions of surgeries worldwide a year to repair gastrointestinal defects, and the leakage rate is up to 20 percent in high-risk patients,” Zhao says. “This tape could solve that problem, and potentially save thousands of lives.”

Reference: “An off-the-shelf bioadhesive patch for sutureless repair of gastrointestinal defects” by Jingjing Wu, Hyunwoo Yuk, Tiffany L. Sarrafian, Chuan Fei Guo, Leigh G. Griffiths, Christoph S. Nabzdyk and Xuanhe Zhao, 2 February 2022, Science Translational Medicine. DOI: 10.1126/scitranslmed.abh2857

This work was supported by the MIT Deshpande Center and the Centers for Mechanical Engineering Research and Education at MIT, and SUSTechs

An off-the-shelf bioadhesive patch for sutureless repair of gastrointestinal defects

Clearing up marine plastic pollution is energy-intensive – but ships could convert the plastic they collect into fuel and create a self-sustaining clean-up operation.

Specially-equipped ships could filter plastic from the ocean and convert it into a fuel that would provide power not only for the conversion, but also to drive the ship, creating a self-sustaining clean-up operation.

As much as 12.7 million tonnes of plastic enter the oceans each year and it is eventually ground into tiny particles that can get into the food chain. Present clear-up efforts use ships that collect and store plastic before returning to port, often thousands of kilometers away, to unload the waste and refuel. This is time-intensive and uses a lot of fossil fuel.

But Michael Timko at Worcester Polytechnic Institute, Massachusetts, and his colleagues believe this plastic can be converted into fuel on a ship while at sea using hydrothermal liquefaction. This involves the material being broken down into constituent polymers at temperatures of up to 550°C and pressures of 27,500 kPa.

They believe enough fuel could be created from plastic to sustain the conversion process, power the ship, and even store excess.

Timko says that his team’s modeling suggests that large booms placed in the Great Pacific Garbage Patch (GPGP), an area believed to cover 1.6 million square kilometers where waste naturally collects, could gather enough plastic so that a single ship could convert 11,500 tonnes each year.

Timko adds that data about the density of plastic in the GPGP is scarce. However, at all but the very lowest density estimates a ship could be entirely self-sufficient while harvesting plastic from a boom and even generate enough excess fuel to travel between booms and eventually back to port.

Burning the created fuel would generate carbon emissions, but they would be significantly less than the emissions associated with a traditional ship collecting plastic and ferrying it back to port for recycling.

“This is not a silver bullet,” says Timko. “We think it’s an interesting way to add to [the technological solutions] already out there.”

Significance

Plastic waste accumulating in the world's oceans forms massive “plastic islands” in the oceanic gyres. Removing plastic offers an opportunity to restore our oceans to a more pristine state. To clean the gyres, ships must collect and store the plastic before transporting it to port, often thousands of kilometers away. Instead, ocean plastic waste can be converted into fuel shipboard, for example, using hydrothermal liquefaction (HTL), which depolymerizes plastics at high temperatures (300 °C to 550 °C) and high pressure (250 bar to 300 bar). The resulting depolymerization products, termed “blue diesel,” have the potential for self-powered clean-up. The objective of this work is to evaluate the thermodynamic feasibility of this scheme and its implications on clean-up.

Abstract

Collecting and removing ocean plastics can mitigate their environmental impacts; however, ocean clean-up will be a complex and energy-intensive operation that has not been fully evaluated. This work examines the thermodynamic feasibility and subsequent implications of hydrothermally converting this waste into a fuel to enable self-powered clean-up. A comprehensive probabilistic exergy analysis demonstrates that hydrothermal liquefaction has the potential to generate sufficient energy to power both the process and the ship performing the clean-up. Self-powered clean-up reduces the number of roundtrips to the port of a waste-laden ship, eliminating the need for fossil fuel use for most plastic concentrations. Several clean-up scenarios are modelled for the Great Pacific Garbage Patch (GPGP), corresponding to 230 t to 11,500 t of plastic removed yearly; the range corresponds to uncertainty in the surface concentration of plastics in the GPGP. Estimated clean-up times depend mainly on the number of booms that can be deployed in the GPGP without sacrificing collection efficiency. Self-powered clean-up may be a viable approach for the removal of plastics from the ocean, and gaps in our understanding of GPGP characteristics should be addressed to reduce uncertainty.

An estimated 4.8 million to 12.7 million tons of plastic enter the ocean each year, distributing widely across the ocean’s surface and water column, settling into sediments, and accumulating in marine life. Numerous studies have shown that plastics contribute to significant damages to marine life and birds, therefore motivating the introduction of effective mitigation and removal measures. Reducing or eliminating the amount of plastic waste generated is critically important, especially when the current loading may persist for years to even decades.

As a highly visible part of an integrated approach for removing plastics from the environment, efforts are underway to collect oceanic plastic from accumulation zones in gyres formed by ocean currents. Present approaches to remove plastic from the open ocean utilize a ship that must store plastic on board until it returns to port, often thousands of kilometers away, to unload the plastic, refuel, and resupply.

Optimistic evaluation of clean-up time using the harvest–return approach indicates that at least 50 y will be required for full plastic removal, with an annual cost of $36.2 million; more conservative estimates suggest that partial removal will require more than 130 y. Clean-up times of decades mean that environmental degradation may have already reduced the existing plastics to microscopic and smaller forms that can no longer be harvested before clean-up is completed. These considerations underscore the massive challenge of removing plastics from the ocean and naturally raise the following question: Can any approach remove plastics from the ocean faster than they degrade?

Some current plastic removal strategies involve accumulation via a system of booms, consisting of semi-circular buoys fit with a fine mesh extending below the ocean surface. These booms are positioned so that prevailing currents bring plastic to the boom, where it then accumulates. The currently envisioned approach is for a ship to steam to the boom system, collect plastic, and then return to port to offload and refuel before resuming collection activities.

The time required for recovering plastics could be reduced if return trips to refuel and unload plastic were eliminated. Indeed, the harvested plastic has an energy density similar to hydrocarbon fuels; harnessing this energy to power the ship could thereby eliminate the need to refuel or unload plastic from the ship, reducing fossil fuel usage and potentially clean up times.

Self-powered harvesting may provide a way to accomplish clean-up using the passive boom collection approach at timescales less than environmental degradation. Unfortunately, clean-up itself is a moving target, as technology improves and especially as plastic continues to accumulate. What is required, therefore, is a framework to evaluate the impact of self-powered harvesting on clean-up time and fuel usage. The framework can then be updated as more data becomes available.

To be valuable, the clean-up framework must be reducible to practice using actual technology. A viable technology for converting plastics into usable fuel is hydrothermal liquefaction (HTL), which utilizes high temperature (300 °C to 550 °C) and high pressure (250 bar to 300 bar) to transform plastics into monomers and other small molecules suitable as fuels. Oil yields from HTL are typical>90% even in the absence of catalysts and, unlike pyrolysis, yields of solid by-products—which would need to be stored or burned in a special combustor—are less than 5%, thus conferring certain comparative advantages to HTL. Ideally, a vessel equipped with an HTL-based plastic conversion system could fuel itself, creating its fuel from recovered materials. The result could be termed “blue diesel,” to reference its marine origin and in contrast with both traditional marine diesel and “green diesel,” derived from land-based renewable resources.

To make the HTL approach feasible, the work produced from the plastic must exceed that required by the process and, ideally, the ship’s engines so that fuel can be stockpiled during collection for later use. Exergy analysis provides a framework to determine the maximum amount of work that a complex process is capable of producing without violating the fundamental laws of thermodynamics. The reliability of an exergy analysis depends on the reliability of the data it uses as inputs, and key parameters describing HTL performance and ocean surface plastic concentration are currently not known with certainty. A rigorous and statistically meaningful analysis of shipboard plastic processing must therefore integrate uncertainty. Here, the Monte Carlo (MC) simulation method, which has proven its usefulness for similar types of analyses, is an appropriate tool for handling the uncertainties inherent in the current application and allows for the integration of new information and data as further study of oceanic surface plastic is completed.

Accordingly, the thermodynamic performance of a shipboard HTL process was evaluated to determine whether (and when) the process could provide sufficient energy to power itself plus the ship. A framework was then developed to evaluate the implications of shipboard plastic conversion on fuel use and cleanup times. The results provide valuable insight into the potential use of shipboard conversion technologies for accelerating the removal of plastics from the ocean, and the framework should prove useful for guiding future work in this area.