Penn Engineering’s Blinking Eye-on-a-Chip Used for Disease Modeling and Drug Testing

By Lauren Salig

Rachel Young, a graduate student in Huh’s lab, holds up the new eye-on-a-chip device. The latest iteration of the lab’s eye-on-a-chip has a mechanical eyelid to simulate blinking, and was used to test an experimental drug for dry eye disease. By incorporating human cells into an engineered scaffolding, the eye-on-a-chip has many of the benefits of testing on living subjects, while minimizing risks and ethical concerns.

People who spend eight or more hours a day staring at a computer screen may notice their eyes becoming tired or dry, and, if those conditions are severe enough, they may eventually develop dry eye disease (DED). DED is a common disease with shockingly few FDA-approved drug options, partially because of the difficulties of modeling the complex pathophysiology in human eyes. Enter the blinking eye-on-a-chip: an artificial human eye replica constructed in the laboratory of Penn Engineering researchers.

This eye-on-a-chip, complete with a blinking eyelid, is helping scientists and drug developers to improve their understanding and treatment of DED, among other potential uses. The research, published in Nature Medicine, outlines the accuracy of the eye-on-a-chip as an organ stand-in and demonstrates its utility as a drug testing platform.

Dan Huh and Jeongyun Seo

The study was led by Dan Huh, associate professor in the Department of Bioengineering, and graduate student Jeongyun Seo.

They collaborated with Vivian Lee, Vatinee Bunya and Mina Massaro-Giordano from the Department of Ophthalmology in Penn’s Perelman School of Medicine, as well as with Vivek Shenoy, Eduardo D. Glandt President’s Distinguished Professor in Penn Engineering’s Department of Materials Science and Engineering. Other collaborators included Woo Byun, Andrei Georgescu and Yoon-suk Yi, members of Huh’s lab, and Farid Alisafaei, a member of Shenoy’s lab.

Huh’s lab specializes in creating organs-on-a-chip that provide microengineered in vitro platforms to mimic their in vivo counterparts, including lung and bone marrow proxies launched into space this May to study astronaut illness. The lab has spent years fine-tuning its eye-on-a-chip, which earned them the 2018 Lush Prize for its promise in animal-free testing of drugs, chemicals, and cosmetics.

In this study, Huh and Seo focused on engineering an eye model that could imitate a healthy eye and an eye with DED, allowing them to test an experimental drug without risk of human harm.

The Huh lab’s eye-on-a-chip attached to a motorized, gelatin-based eyelid. Blinking spreads tears over the corneal surface, and so was a critical aspect to replicate in the researchers’ model of dry eye disease. cells. The cells of the cornea grow on the inner circle of scaffolding, dyed yellow, and the cells of the conjunctiva grow on the surrounding red circle. Artificial tears are supplied by a tear duct, dyed blue.

To construct their eye-on-a-chip, Huh’s team starts with a porous scaffold engineered with 3D printing, about the size of a dime and the shape of a contact lens, on which they grow human eye cells. The cells of the cornea grow on the inner circle of scaffolding, dyed yellow, and the cells of the conjunctiva, the specialized tissue covering the white part of human eyes, grow on the surrounding red circle. A slab of gelatin acts as the eyelid, mechanically sliding over the eye at the same rate as human blinking. Fed by a tear duct, dyed blue, the eyelid spreads artificial tear secretions over the eye to form what is called a tear film.

“From an engineering standpoint, we found it interesting to think about the possibility of mimicking the dynamic environment of a blinking human eye. Blinking serves to spread tears and generate a thin film that keeps the ocular surface hydrated. It also helps form a smooth refractive surface for light transmission. This was a key feature of the ocular surface that we wanted to recapitulate in our device,” says Huh.

For people with DED, that tear film evaporates faster than it’s replenished, resulting in inflammation and irritation. A common cause of DED is the reduced blinking that occurs during excessive computer usage, but people can develop the disease for other reasons as well. DED affects about 14 percent of the world’s population but has been notably difficult to develop new treatments for, with 200 failed clinical drug trials since 2010 and only two currently available FDA-approved drugs for treatment.

Huh’s lab has been considering the drug-testing potential of organs-on-a-chip since their initial conceptualization, and, because of its surface-level area of impact, DED seemed the perfect place to start putting their eye model to the test. But before they started a drug trial, the team had to ensure their model could really imitate the conditions of DED.

“Initially, we thought modeling DED would be as simple as just keeping the culture environment dry. But as it turns out, it’s an incredibly complex multifactorial disease with a variety of sub-types,” Huh says. “Regardless of type, however, there are two core mechanisms that underlie the development and progression of DED. First, as water evaporates from the tear film, salt concentration increases dramatically, resulting in hyperosmolarity of tears. And second, with increased tear evaporation, the tear film becomes thinner more rapidly and often ruptures prematurely, which is referred to as tear film instability. The question was: Is our model capable of modeling these core mechanisms of dry eye?”

The answer, after much experimentation, was yes. The team evoked DED conditions in their eye-on-a-chip by cutting their device’s artificial blinking in half and carefully creating an enclosed environment that simulated the humidity of real-life conditions. When put to the test against real human eyes, both healthy and with DED, the corresponding eye-on-a-chip models proved their similarity to the actual organ on multiple clinical measures. The eyes-on-a-chip mimicked actual eyes’ performance in a Schirmer strip, which tests liquid production; in an osmolarity test, which looks at tear film salt content; and in a keratography test, which evaluates the time it takes for a tear film to break up.

Having confirmed their eye-on-a-chip’s ability to mirror the performance of a human eye in normal and DED-inducing settings, Huh’s team turned to the pharmaceutical industry to find a promising DED drug candidate to test-drive their model. They landed on an upcoming drug based on lubricin, a protein primarily found in the lubricating fluid that protects joints.

“When people think of DED, they normally treat it as a chronic disease driven by inflammation,” says Huh, “but there’s now increasing evidence suggesting that mechanical forces are important for understanding the pathophysiology of DED. As the tear film becomes thinner and more unstable, friction between the eyelids and the ocular surface increases, and this can damage the epithelial surface and also trigger adverse biological responses such as inflammation. Based on these observations, there is emerging interest in developing ophthalmic lubricants as a topical treatment for dry eye. In our study, we used an lubricin-based drug that is currently undergoing clinical trials. When we tested this drug in our device, we were able to demonstrate its friction-lowering effects, but, more importantly, using this model we discovered its previously unknown capacity to suppress inflammation of the ocular surface.”

By comparing the testing results of their models of a healthy eye, an eye with DED, and an eye with DED plus lubricin, Huh and Seo were able to further scientists’ understanding of how lubricin works and show the drug’s promise as a DED treatment.

Similarly, the process of building a blinking eye-on-a-chip pushed forward scientists’ understanding of the eye itself, providing insights into the role of mechanics in biology. Collaborating with Shenoy, director of the Center for Engineering MechanoBiology, the team’s attention was drawn to how the physical blinking action was affecting the cells they cultivated to engineer an artificial eye on top of their scaffolding.

“Initially, the corneal cells start off as a single layer, but they become stratified and form multiple layers as a result of differentiation, which happens when these cells are cultured at the air-liquid interface. They also form tight cell-cell junctions and express a set of markers during differentiation,” Huh says. “Interestingly, we found out that mechanical forces due to blinking actually help the cells differentiate more rapidly and more efficiently. When the corneal cells were cultured under air in the presence of blinking, the rate and extent of differentiation increased significantly in comparison to static models without blinking. Based on this result, we speculate that blink-induced physiological forces may contribute to differentiation and maintenance of the cornea.”

In other words, human cornea cells growing on the scientists’ scaffold more quickly became specialized and efficient at their particular jobs when the artificial eyelid was blinking on top of them, suggesting that mechanical forces like blinking contribute significantly to how cells function. These types of conceptual advances, coupled with drug discovery applications, highlight the multifaceted value that engineered organs-on-a-chip can contribute to science.

Huh and Seo’s eye-on-a-chip is still just dipping its toes into the field of drug testing, but this first step is a victory that represents years of work refining their artificial eye to reach this level of accuracy and utility.

“Although we have just demonstrated proof-of-concept,” says Seo, “I hope our eye-on-a-chip platform is further advanced and used for a variety of applications besides drug screening, such as testing of contact lenses and eye surgeries in the future.”

“We are particularly proud of the fact that our work offers a great and rare example of interdisciplinary efforts encompassing a broad spectrum of research activities from design and fabrication of novel bioengineering systems to in vitro modeling of complex human disease to drug testing,” says Huh. “I think this is what makes our study unique and representative of innovation that can be brought about by organ-on-a-chip technology.”

This work was supported by the National Institutes of Health through grants 1DP2HL127720–0, R01EY026972 and K08EY025742–01, the National Science Foundation through grants CMMI:15–48571, and Research to Prevent Blindness.

Originally posted on the Penn Engineering Medium blog.

Week in BioE (April 24, 2018)

Pushing the Limits of Imaging

An image showing 7-tesla MRI of the human brain

Since the late 1970s with the advent of computed tomography (CT), medical imaging has grown exponentially. Magnetic resonance imaging (MRI) offers some of the clearest pictures of human anatomy and pathology, particularly as the strength of the magnetic field used (measured in units called Teslas) increases. However, MRI machines are expensive, and the costs increase as one uses a machine with higher field strength to ‘see’ the human more closely. Therefore, it is often more useful (and certainly less expensive) to modify existing MRI technology on hand, rather than acquire a new machine.

A recent example is the work of Tamer Ibrahim, PhD, Associate Professor of Bioengineering at the University of Pittsburgh. Dr. Ibrahim used a series of multiple NIH grants to develop a coil system for Pitt’s 7T-MRI — one of only approximately 60 worldwide — enabling it to more accurately image the brain’s white matter. Dr. Ibrahim is interested in seeing how hyperintensity in the white matter is related to depression, which is one of the highest-burden but least-discussed diseases in the world. Called a “tic-tac-toe” radiofrequency coil setting, the device that Dr. Ibrahim created is a network of antennas fitted to the head that minimize concerns such as coil heating and radiofrequency intensity losses, as well as safety concerns.

Dr. Ibrahim has more NIH funding on the way to continue optimizing his device and apply it in other psychiatric and neurological disorders. Rather than purchasing a new MRI machine with higher field strengths to achieve this image quality, Dr. Ibrahim’s coil design can be used on existing machines. One possible outcome is more clinicians using this new coil to study how changes in the brain’s white matter structure occur in a broad range of brain diseases, leading to both earlier detection anfor ad more effective treatment.

Smart Shunt for Hydrocephalus

Hydrocephalus, once more commonly known as “water on the brain,” is a condition marked by abnormal accumulation of cerebrospinal fluid (CSF) in the skull. If unchecked, the accumulation of fluid will create dangerous pressures in the brain that can result in brain damage. Hydrocephalus occurs in one in every 1,000 births, and nearly 400,000 adults in the US suffered at least on episode of hydrocephalus. For both infants and adults, hydrocephalus is often treated surgically with the installation of a shunt to channel the excess CSF out of the cranium. These shunts are simple but effective devices that operate mechanically. However, since they’re entirely mechanical, they fail over time. Being able to determine that such a failure was imminent could allow patients to receive a replacement shunt before complications arise.

To meet this clinical need, a group of scientists at the University of Southern California (USC)  updated existing shunt systems with microsensing technology, creating a “smart shunt” that can tell clinicians how an installed shunt is functioning and alert the clinician that a replacement is needed. The group, including Ellis Fan-Chuin Meng, PhD, Gabilan Distinguished Professorship in Science and Engineering, Dwight C. and Hildagarde E. Baum Chair, and Professor of Biomedical Engineering and Electrical Engineering-Electrophysics, has created a start-up called Senseer to produce these smart shunts.

The shunt currently measures pressure, flow, and occlusion using miniature microelectronics sensors. If device approval comes, the company hopes to move on to developing smart sensors for other organ systems.

DNA-based Drug Testing

Drug and alcohol testing is a controversial topic, partly because of the balance between individual rights to use legal drugs and potential for societal harm if these drugs are abused or if patients transition into illegal drug use and dependence. Inventing technology to determine when, and how much, a person has been drinking or using drugs (including tobacco) would probably increase, rather than decrease, the controversy involved in the topic.

New technology reported recently adds a new element to this discussion. According to Robert Philibert, MD, PhD, Professor of Psychiatry at the University of Iowa and an adjunct faculty member in the Department of Biomedical Engineering, his company’s tests, which rely on epigenetic markers of substance use, could be used, for example, to inform a primary care physician about the actual history of substance use, rather than relying solely on patients’ self-reported use.

Dr. Philibert’s tests are currently pending approval by the Food and Drug Administration. Marketing for the products will begin in the coming weeks.

People and Places

Recognizing the changing priorities in engineering and the growing role of data sciences, Boston University has decided to adapt its curriculum by adding data science requirements for all majors. According to John White, PhD, Chair of the Department of Biomedical Engineering, “Advances in data sciences and computing technology will allow us to make sense of all these data.”

The Biomedical Science Program at Howard Payne University in Brownwood, Texas, has received a $200,000 grant from  the James A. “Buddy” Davidson Charitable Foundation to endow a scholarship in Davidson’s name, as well as to refurbish the program’s Winebrenner Memorial Hall of Science.

Finally, we offer our congratulations this week to James C. Gee, PhD, Professor of Radiologic Science in Radiology at the University of Pennsylvania’s Perelman School of Medicine and a Graduate Group faculty member in Penn’s Department of Bioengineering.  Dr. Gee was named a fellow of the American Institute for Medical and Biological Engineering.