Skin grafting (my current topic) is a cornerstone of reconstructive surgery. Over 160,000 skin grafts are performed annually for patients after burns, trauma or vascular disease (Serebrakian, et al. Plast Reconstr Surg Glob Open, 2018). Despite various FDA-approved dressings, up to half of skin grafts are rejected. Repeated skin grafting requires multiple surgeries, which increases risk of morbidity and mortality. Although a variety of cadaveric and synthetic alternatives exist, they are limited by allogeneic responses, dysregulated inflammatory reactions, worse scarring, poor functional outcome, and just overall lower quality of life. My research aims to improve the outcome of soft tissue reconstruction through the development of hydrogel biomaterials that can coordinate the interactions of immune cells to improve tolerance in the wound bed of allotransplantation.

If working on a biomaterials-based approach to promote tolerance in soft tissue transplants is of interest to you, contact us and add in the message that you’re interested in my project! #holly #culturingtolerance

Extending the window for cellular change

We’ve explored this approach the most. During the latter stages of wound healing, the microenvironment is in a state of endogenous plasticity, which means the tissue is still undergoing changes as it heals. The goal here is to place materials into wounds that extend the plastic time period by recruiting progenitor cells and other important factors. We primarily do this by designing materials that promote blood vessel formation. Blood vessels are a key component in tissue repair – they deliver important nutrients, regulate the immune response, and guide cell migration and tissue deposition. By maintaining and controlling the process of vessel formation with our materials, we’re thinking we can extend the window of plasticity and promote tissue regeneration. You can learn more about our approaches to promote vessel formation by reading the articles on Our Publications page that deal with therapeutic angiogenic material (filter by Topic: angiogenesis)!

Another way we’re extending endogenous plasticity is by designing materials that allow for rapid cellular infiltration while maintaining structural support. We do this by forming a microscopic scaffold made of packed hydrogel microparticles that are stuck together, which forms pockets of void space that are large enough for cells to fit. Alright, you guessed it – we’re describing MAP… you might as well read about it here.

I am interested in understanding how glycosylation changes with aging and after a stroke, and I want to understand if part of the success of our previous materials are because of changes in the glycosylation profile. My ultimate goal is to design novel glycan-decorated materials to promote recovery after stroke.

If you’re a student who agrees that glycans > proteins and nucleic acids and you’re interested in their impact on stroke recovery, contact us and add in the message that you’re interested in my project! #juhi #sweetbrain

Microporous annealed particles (MAP) scaffolds

The magic of MAP comes from interlinking the HMPs in a granular scaffold so that the particles get stuck in place. There are many, many different techniques for doing this, but the very first MAP scaffold was designed to naturally crosslink in the body. This was great because it meant we could load a syringe with HMPs, inject into the body to form a granular scaffold, then wait for the body’s natural clotting factor to chemically link the particles together. Since then, we’ve also become fond of interlinking using UV light. The benefit of interlinking (or annealing) HMPs is that we create a stable structure that sticks around for longer and makes cells extra happy. We’ve seen MAP scaffolds promote aspects of wound healing in disease models like stroke, myocardial infarction, skin wounds, and spinal cord injury. And once the MAP scaffold has completed its job, it naturally gets degraded by the body.

Inter-subunit descriptors

We have 7 descriptors that measure features of the scaffold that do not refer to the subunits of the space – hence the term ‘inter-subunit’ because they exist between or across multiple subunits. (Recall that subunits are the pockets of empty space throughout the scaffold.) For example, we study pathways that can be traveled by cells inside the scaffold. The measurements taken for each pathway give rise to inter-subunit descriptors.

Return descriptor data

LOVAMAP does some powerful computing to generate an ever-growing list of descriptors that quantitatively characterize the MAP scaffold. These measurements describe features of the void space between the particles, the pathways throughout the scaffold, integrin-binding hotspots, and more. By quantifying the microarchitecture of our scaffolds, researchers can study how scaffold geometry affects other measurable properties, like infiltrating cell behavior and material mechanics. Ultimately, these types of analyses will help us optimize our material for the best possible therapeutic effect.

Generate images and GIFs

Coming soon!

Global descriptors

LOVAMAP computes 12 global descriptors for each scaffold. ‘Global’ refers to the fact that a single value is reported for the descriptor, which captures information spanning the entire scaffold. For example, the most common global descriptor reported in the literature for granular biomaterials is Void-Volume Fraction, where the top of the fraction is the volume of scaffold that’s occupied by empty space and the bottom of the fraction is the total volume of the scaffold.

Subunit descriptors

Coming soon!

Outer porosity

Coming soon!

Hydrogel microparticles (HMPs)

The first step is to design the particles that compose our MAP material. Each particle is actually a network of entangled polymers (like a microscopic hairball), and we typically work with hydrogel polymers that swell in water – hence the term HMPs. The process starts with some good ‘ole polymer chemistry, where we customize our material to fit the therapeutic application. Once the polymers are just right, we form them into the desired shape, then lock the shape into place through a process called polymerization. Most of our MAP experiments use spherical HMPs produced through emulsion or microfluidic techniques, but we’ve been experimenting with other shapes as well. (I know we just dropped some technical terms, so if you’re unfamiliar and want to learn more about HMPs, click here, we won’t tell anyone 🤫)

Inner porosity

Coming soon!

Granular scaffolds

The word ‘scaffold’ implies a supporting structure or framework, so at this step, we’re creating a framework using the HMPs as building blocks. The term ‘granular’ has a specific definition as well, but we’ll leave you to read this review for the nitty-gritty details. The take-home point is that granular materials transition from a ‘liquid-like’ state to a ‘solid-like’ state when particle jamming occurs – so to create a solid structure from HMPs, we pack them together. Now we have a granular scaffold with empty space in between the particles to support cell ingrowth. But remember, a granular scaffold is just a collection of particles jammed together, so it’s still a dynamic system where everything can slosh around.

Wound healing

We are inspired by our body’s ability to heal. This occurs through a process called endogenous regeneration, which takes advantage of the activation of ‘plasticity’ upon injury. Plasticity is the ability to transform local cells into tissue factories that produce extracellular matrix and other multicellular structures that got destroyed. The goal of plasticity is to produce brand-spanking-new tissue. As you may have guessed, these pathways are usually dormant and only awaken once the body recognizes that an injury has occurred. So this begs the question – if tissues have the ability to fix themselves back to working order, why do some injuries cause permanent damage? This is because there are two competing forces in healing: plasticity and scarring. Scarring is a pro-survival mechanism that evolved to ensure that we survive an injury. Regenerating tissue takes time and resources – time that we may not have if the injury starts inhibiting important bodily functions or introducing deadly bacterial infections. Thus, at the same time that pro-regenerative pathways are activated to promote functional recovery, there are also pro-survival mechanisms activated that favor a quick-fix. Usually, scarring wins, and scar tissue gets deposited that is not completely functional.

Our main goals are to 1) scale-down scarring so that our tissues have a chance to regrow, and 2) deliver key signals that promote tissue regeneration. Luckily we know that our body actively works to repair itself after injury, so we only have to deliver the pro-healing components that are low or lacking in the wound environment. And the good news is that biomaterials can be designed to do just that – modulate the pathways that are responsible for scarring, while at the same time deliver key therapeutics to promote functional tissue deposition.

Extract spatial landmarks

LOVAMAP relies on accurately identifying key spatial landmarks within the void space of MAP scaffolds. These landmarks are subtypes of the medial axis, which are central locations in space, and they serve as a starting point to orient LOVAMAP to the space. Our custom algorithms are highly effective at locating these landmarks because we takes advantage of information stored within the graphical representation of granular material. Once the information has been stored, we’re ready to start dissecting and analyzing the MAP scaffold.

Heterogeneity

MAP is a collection of tiny particles, but nobody says we have to use the SAME particles throughout our scaffold. In fact, having the option to easily combine different types of particles into one scaffold is a big plus with our material. We can include particles of different shapes, sizes, and stiffnesses…made from different polymers…with different degradation rates…carrying different types of drugs… Really the world is our MAP-oyster! And not only can we precisely choose the proportion of these particle types, but we can also vary where in the scaffold they lie. Do you want everything to be mixed like rainbow Dippin’ Dots? Do you want particle types to be nicely layered like a cake? You choose. This is all to say, the heterogeneity offered by MAP allows for a highly personalized, versatile therapeutic material.

Injectability

In the same way that it would be difficult to fit a sponge into a needle, it’s difficult for a non-granular matrix to be injected. And if something can’t be injected, then getting it to the right place might require some surgery. Luckily MAP is granular, so all of the tiny particles can fit inside a syringe. And – thanks to the concept of particle jamming – after injection, the particles reform into a scaffold that perfectly conforms to the shape of the wound. Once the material has been deposited, the last step is to perform some chemistry magic to interlink the particles so they don’t go anywhere. The injectability of MAP makes it much more convenient for physician’s to use, and patients can avoid undergoing unnecessary surgery – everyone wins!

Aside from sex and age, my work focuses on further development of a dual-function angiogenic biomaterial, CLUVENA, that previous lab members developed (Sean, Shiva, and Lina). When injected intracranially into the stroke cavity, CLUVENA can both restore blood vessel density and decrease inflammation. This material was also able to reduce physical disability in a rodent model of stroke. My goal is to better understand the mechanism of action of CLUVENA in order to design a novel approach that further reduces physical disability. I also want to make sure our materials can be easily manufactured, shipped, and stored.

If you’re a student who wants to work on cutting-edge technology in the stroke recovery space, contact us and add in the message that you are interested in my project! #kevin #stroke

Ninjabyte Computing

If you’ve ever watched a Marvel movie or played a video game like Witcher 3, you know graphics have come a long way. But you may not know how much serious math and research goes into 3D animation. Technologies in simulation and visual effects are incredibly powerful, yet most scientists don’t have access to them because software engineers in animation don’t often chill with scientists. Ninjabyte Computing was founded to connect the science community with high-performance animation tools used in industry.

The company is headed by Peter Cheng, PhD, who offers the perfect blend of expertise in mathematics, computer science, and animation. Ninjabyte Computing uses professional visual effects software, like SideFX Houdini, to generate physically-accurate simulations of randomly packed particles with varying shapes, sizes, stiffness, and textures. These simulations are fantastic mimics of a range of MAP scaffold types, which makes the data perfect to analyze with LOVAMAP in order to study our scaffolds. Ninjabyte Computing also renders beautiful images and videos of our material to help explain our work. One of their images was featured on the cover of Nature Materials!

While our collaboration focuses on MAP simulations, this only scratches the surface of animation technology. We’re happy to share the love for Ninjabyte, and we recommend reaching out to ninjabytecomputing@gmail.com for any inquiries.

Biomaterial scaffold

A biomaterial scaffold is exactly what it sounds like – a structure made from building blocks that provides support. In this case, the building blocks we use are nanoscopically small because our scaffolds interact with tissue at the microscopic level. The scaffolds act as a supplemental extracellular matrix that provides physical support in compromised tissue, and they also serve as a framework to help nearby cells move around and do their job. You can see below that a typical scaffold looks like a little slab of clear Jello.

The scaffold itself can also behave as a drug and influence biological processes in the tissue surrounding it. This is possible because cells in the tissue are mechanoresponsive, which means that they can sense the structural features around them and respond to any changes. We can engineer the structural features of our scaffold to influence cell behavior, which leads to therapeutic action.

When we make scaffolds out of hydrogel microparticles and link these particles together, we create MAP – but you can read more about that here.

Read in formatted data

LOVAMAP is a software designed for analyzing granular material. For this reason, LOVAMAP takes in a specific data format that highlights individual particles – basically each voxel (3D pixel) associated with a particular particle should be labeled with a unique identifying number. This ensures that our software is analyzing exactly what you intended. Alternatively, if you’re simulating spherical particles with a known center and radius, go ahead and input the sphere data – our code can handle it.

Re-opening the window for cellular change

The most difficult wounds to treat are those that are chronic or well-past the phase of endogenous plasticity – when tissue is still being remodeled. For these wounds, we want to re-activate plasticity so that the body has another opportunity to heal itself properly. As you can imagine, this is harder to achieve than when wounds are still fresh in the acute or sub-acute phase. Our strategy is to first identify the molecules that are present in wounds during endogenous plasticity. We will then introduce materials that induce blood vessel formation as a source for replenishing the molecules that are present during plasticity. The goal is to determine the minimum molecular signals needed to re-open the window for cellular change.

Tweaking the immune system

The goal with this approach is to design materials that communicate with our body’s immune system and urge it to generate a lasting pro-regenerative response in the wound. The immune system is most commonly known for helping us fight disease. When external objects enter our body, specialized cells will recognize them as foreign and trigger a specific immune response depending on the type of invader. Viruses, for example, often trigger a danger! danger! response that causes the immune system to produce antibodies against the virus for long-lasting defense. This means you’re protected from getting sick if you get infected with the same virus again. Materials made in lab, however, don’t always elicit the same immune response, which means our materials can be explicitly engineered to tweak the immune system in a certain direction.

LOVAMAP is the name of our current software package that takes in simulated MAP scaffolds and segments the void space into natural pockets of open space. The software then performs numerous computations to characterize the space. This is an ongoing project because we are continually looking for bigger and better metrics to describe local geometry that capture more complicated features like curvature.

The next stage in this computational work will incorporate machine learning techniques to convert microscope images of MAP into formats that can be read by LOVAMAP. We are also simulating more advanced particles shapes, stiffnesses, and textures. In the future, we plan to use mathematical modeling to study fluid flow and cell migration within the void space.

If you’re a student who wants to apply your math and coding skills to questions in wound healing, contact us and add in the message that you’re interested in my project! #lindsay #computational

My lab has worked for over a decade on approaches to deliver genetic material from hydrogel biomaterials (heck even my advisor’s thesis was on this topic, along with past lab members Leo, Quinn, Talar, Anandika, Cynthia, and Norman). These approaches have led to high levels of protein expression in vitro, but not in test animals. Also, previous approaches did not load genetic material into injectable gels…and just like a vaccine, if our gene therapy isn’t injectable, it limits applicability. My thesis work is focused on improving our delivery strategies to achieve effective genetic material delivery from injectable hydrogels into the brain. Once this is achieved, my goal is to express proteins that can regulate endogenous protein expression of pro-repair factors to promote recovery after stroke.

If you’re a student who recognizes that non-viral gene delivery is trending, contact us and add in the message that you’re interested in my project! #evan #genedelivery

Since MAP scaffolds are a highly versatile biomaterial that have been shown to support cell growth, we are hoping they can be used to combat cancer as well. So far, we have experimented with different polymer types, as well as varying material stiffness, and our custom MAP scaffolds are already showing promising results – with more functionality on the way.

Our focus is on glioblastoma multiform, an aggressive brain cancer with particularly low survival rates. If you’re a student with a passion to fight cancer using pro-repair matrices, contact us and add in the message that you are interested in my project! #alex #healingcancer

At the risk of sounding nerdy…I have a favorite immune cell: the macrophage. Macrophage cells are such an important mediator in our immune system, and I’ve always been fascinated by their many roles in healing wounds. I want to understand how MAP can modulate macrophage phenotype toward different behaviors – like promoting wound closure vs. causing implant rejection. In particular, my thesis is following up on leads that suggest that the degree of confinement dictates the phenotype of macrophages. My work revolves around using the unique microstructure of MAP to answer questions related to immune activation and regenerative wound healing. I am also changing the biochemical properties of MAP to study its range from immune-stealthy to immune-reactive.

If you’re a student who is equally as intrigued by the role of microstructure on macrophage phenotype and wound healing, contact us and add in the message that you’re interested in my project! #yining #macrophages

Since the amniotic membrane is used to promote healing of non-healing wounds, I will incorporate components of the amniotic membrane – which I will produce recombinantly – into HA hydrogels.

If you’re a student who’s excited about scarless healing and synthetic placenta biomaterials, contact us and add in the message that you’re interested in my project! #drew #syntheticplacenta

Modified building blocks

Our starting materials are hydrogel polymers, such as

• hyaluronic acid
• polyethylene glycol
• poly(propylene sulfide)
• heparin
• poly(allyl mercaptan)

We chemically engineer these polymers to precisely fit our needs, like adding handles that allow the strands to link to one another and form a gel. Our polymer modifications include end-group modifications, side-chain modifications, and even attachment of biologically relevant ligands that make our materials more biocompatible and useful for therapeutic applications. We also use these polymers to create higher-level building blocks called hydrogel microparticles, which you can read more about on our MAP Scaffolds page.

In vivo work

In vivo studies are performed in a living organism and are an essential and exciting part of the research we do. These types of experiments are invaluable because they not only teach us about biocompatibility, but we also get the full effect of a living tissue. This means we gain access to the complicated signaling pathways that would be impossible to recreate in a test tube, and therefore, we get a complete picture of the healing process. Understanding our in vivo results bring us one step closer to developing a product that can help real patients.

My project is to leverage this plasticity window with a ‘repair soup’ to promote healing after stroke. In particular, I am working on strategies that would trap locally-secreted plasticity-proteins into our biomaterial in an effort to extend the window of cellular change. The end goal of course is to reduce physical impartment caused by stroke.

If you’re a student who wants to work on promoting recovery after stroke – particularly using biomaterial approaches that sequester plasticity-proteins – contact us and add in the message that you are interested in my project! #shangjing #repairsoup

After talking with Prof. Segura, I also learned that the brain is 50% lipids by weight. Lipids do much more than make us fat – they’re active players in signaling and normal tissue function. I’ll be reading and learning about lipid biology, especially in the context of stroke, so that I can guide my synthesis to include brain-active materials. By using self-assembling lipids, I aim to make nanoparticles that are entirely bioactive.

If you’re a student who has an inkling for chemistry and who wants to work on drug delivery to the brain after stroke, contact us and add in the message that you’re interested in my project! #briana #fatbiomaterials

Although their name would imply that NPCs become neural cells (e.g., nerves), I am interested in how these cells also play a role in blood vessel formation. There is a synergistic relationship between growing blood vessels in the brain and NPCs. Low blood vessel growth results in low NPC migration, but also NPCs secrete factors that are essential for blood vessel sprouting and maturation. My studies revolve around the use of MAP scaffolds as well as our VEGF delivery technology CLUVENA to promote NPC migration and vascularization. In addition, I am changing the physical and biochemical cues of the scaffold to modulate NPC phenotype and mature vessel formation.

If you’re a student interested in working on strategies to promote recovery after stroke focusing on NPCs and vascularization, contact us and add in the message that you’re interested in my project! #kat #brainheroes

In vitro work

In vitro studies are performed in the lab outside of a living organism – think test tubes and petri dishes. These types of experiments allow us to characterize important properties of our scaffolds, like how much they deform or how well the molecules we’ve attached get released. It also offers us the luxury of studying the effects of our material on specific phenomenon, like cell behavior and vessel growth, in a controlled environment. It’s basically Step 1 in understanding what we’ve created.

Although their name would imply that NPCs become neural cells (e.g., nerves), I am interested in how these cells also play a role in blood vessel formation. There is a synergistic relationship between growing blood vessels in the brain and NPCs. Low blood vessel growth results in low NPC migration, but also NPCs secrete factors that are essential for blood vessel sprouting and maturation. My studies revolve around the use of MAP scaffolds as well as our VEGF delivery technology CLUVENA to promote NPC migration and vascularization. In addition, I am changing the physical and biochemical cues of the scaffold to modulate NPC phenotype and mature vessel formation.

If you’re interested in working on strategies to promote recovery after stroke focusing on NPCs and vascularization, contact us and add in the message that you’re interested in my project! #kat #brainheroes

Stem cell delivery

Tbd

Wound healing

Tbd

Bells and whistles

We hate to be boring, so we’re always exploring new features to incorporate into our materials. Most of our scaffolds include additional bioactive signals that help make our material more effective at promoting healing, like:

• peptides / proteins
• nucleic acids
• small molecules
• cells

These additions can be used to attract and influence cells that make their way into the scaffold, or the material can be designed as a drug depot that releases factors at desired time points.