 We actually have a pretty full schedule. So I'd like to welcome everyone to the College of Engineering, Purdue Engineering Distinguished Lecture Series. We're very pleased to have here today as Distinguished Lecturer, one of our very own Professor Christy Anse, University of Colorado. But before we do that, let me remind you that after the lecture today, there is also a panel. This will be held in the Henson Atrium right after the conclusion of the lecture. So without further ado, let me introduce our Dean of Engineering. Professor Meng Chang is the John A. Edwardson Dean of the College of Engineering. His research received the 2013 Allenty Waterman Award. His online courses and textbooks have reached over 250,000 students and he co-founded several startup companies and a non-profit consortium. So please welcome Dean Chang to do the introduction. Thank you, Sang, and good afternoon, everyone. Such a pleasure to be here at the first of spring semester, Purdue Engineering Distinguished Lecture Series. We launched this about a year ago and bring in some of the very brightest minds in engineering across the country and the world to Purdue Engineering as part of our aspiration to achieve the pinnacle of excellence at scale. In today's Distinguished Lecture, welcoming her back to the watermaker land and also a personification of what pinnacle of excellence means. Professor Kristi Anseph is the Tasong Distinguished Professor of Chemical and Biological Engineering at University of Colorado, Boulder. And she is a graduate from this very school, the Davidson School of Chemical Engineering and her accomplishments will take about two hours to describe at the very least We're here to listen to her, so I will abbreviate that by highlighting that Professor Anseph is one of the very few engineers in the nation who is a member of all three national academies. National Academy of Engineering, National Academy of Medicine, I guess that time is called the Institute of Medicine and the National Academy of Sciences. All three at the same time and actually at a younger age then, I'll say some of the other, a handful of individuals who are engineers elected to all three academies. That perhaps is the shortest description length, the summary that I can find to describe the fantastic achievement by one of our best and brightest alum. And also she works at the interface between engineering and medicine. And as we explore the future for the whole college of engineering, including the great Davidson School of Chemical Engineering, that intersection is immensely interesting. So I'm looking forward, Kristi, to your distinguished lecture talking about the soft material for hard biological problems. Thank you so much and welcome back. Well, thank you for the kind introduction and it's certainly a pleasure to always come back and visit Purdue. I have to confess I first arrived on this campus in 1989, so it's been 30 years. But I've had many occasions to come back and it's always a pleasure to see all of the exciting advancements, all the new things going on in the School of Chemical Engineering and beyond. And what I wanted to tell you a little bit about today is how chemical engineers, bioengineers, material scientists engineers are needed to converge together and come together and be able to solve problems in biology and medicine that can be really impactful to society. And what I hope to convince you today is give you a little bit of a snippet of some of the ways that we've been interested in this area. And so the first is to maybe provide a little bit of context. So we're very interested in how we can design material micro-environments here represented by the yellow strands or scaffolding that can interface with living cells. So cells in our body reside in a tissue micro-environment or a material micro-environment and we're interested in culturing these cells, placing them in these three-dimensional environments and in an application standpoint we're interested in coaxing these tissues to reform tissues that could in this case repair or regenerate tissues in our body and this happens to be articular cartilage that's on all the ends of our bones and it allows us to move our joints without pain. We started working on this problem almost 20 years ago and it took about a decade to get these into human medicine but cartilage is one of the tissues that we can regenerate and repair as an alternative to total joint replacements. But as the field moves forward and as we began to also think about and tackle even more complex problems or questions sometimes we don't know all the information that's necessary. What signals do we need to give to the cells to recreate or reform tissues that might comprise multiple cell types or need a blood supply or a nerve supply or have a particular metabolic function? So in that instances we sometimes look at and think about material micro-environments and designing ways to track cell function in real time so we can understand this outside in-signal and if we can understand that then we can begin to coordinate complex events and begin to tackle even harder problems that exist. And so in this spectrum my own group has worked with many different types of material systems and one that I want to talk to you about today is one that I first learned about as an undergrad at Purdue doing research in a laboratory and that's the picture here of these macroscopic picture of a hydrogel. So a hydrogel if you could see the molecular level features you would see long macromolecular chains that would normally dissolve in water but because of interactions between those chains it renders them insoluble and instead they imbibe large amounts of water and when they do that that makes them very interesting systems for placing living cells in. It recapitulates many of the soft tissue micro-environments in our body. When you put cells in these environments they can secrete and the signals that they secrete to talk to one another can rapidly diffuse through this environment so we use a lot of mass transfer principles and understand that as well as some of the mechanical cues that cells get and the three-dimensional structure cues they get from this environment are very reminiscent of what biological cues would be like within our tissues. So this is just a picture where we've given the cells a fluorescent label that they uptake and then one can also visualize these and use lots of advanced imaging and quantitative image analysis to understand how cells respond to these micro-environments and so now the engineering comes in because you're trying to coordinate a complex series of events from the seconds after you assemble this to what happens days and weeks and months later as the cells begin to remodel and recreate tissues and also on different size scales from a small receptor on a cell and how it binds and interacts with that material all the way up to a size of a cell that might be microns cell interactions and movement and eventually to a three-dimensional millimeter-centimeter structure that you're trying to recreate or repair. Now, there are lots of different chemistries that one can use to make these types of material and micro-environments and so I'm just going to tell you about one that we've worked with extensively and it's based upon polyethylene glycol or PEG. This is the chemical structure of PEG. I wasn't quite sure of my audience. When I was a young assistant professor, one of the classes that I was assigned to teach was general chemistry for all the engineers and I'm a chemical engineer so I thought this was a great class. It was really foundational to a lot of engineering principles but then I quickly learned that a lot of the double E's and mechanical engineers they chose those pathways because they really didn't like chemistry side of things but you can think of this many different ways but this is a very hydrophilic polymer. It's pretty unique in that these two carbons with this ether linkage makes it a very highly mobile system. It has lots of waters of hydration. This polymer, synthetic polymer is one of the most widely used in medical applications in human medicine. It's used to modify lots of drugs and it influences their bioavility and stability so it's also very useful as a biomaterial and we can modify the ends of these PEGs with lots of different substituents so that when we dissolve this in water and suspend it with our cells we can catalyze different reactions. It'll go a transition from a liquid to a solid phase and embed the cells in this micro environment. So we're interested in using this because of its historical application in humans but also because when we have this PEG molecule when you culture cells you culture them in this complex molue of many different components or if you implant it in the body there are many different proteins that are present and a lot of biomaterials get modified by nonspecific interactions of their proteins and the cells see those nonspecific interactions but when you use PEGs it minimizes that so now intellectually when I want to start modifying my material scaffold I can better understand that how specific interactions or chemistries that I put in influence the cells and it doesn't get masked by those nonspecific interactions so we started and we began a lot of our work with PEG and when you begin to put cells inside of these so while the PEGs are really nice they form these molecularly controlled structures that influence a lot of properties cells do not recognize this chemistry at all so it's not something they inherently interact with so when you put cells in these environments they typically take on a spherical morphology they're not interacting with the material these happen to be the cells found in your cartilage and that is a natural morphology for a cartilage cell so these types of hydrogels can be very useful for the cartilage tissue engineering example it also promotes a lot of cell-cell interactions and so some cells in our body inherently want to interact with one another more so than with the matrix or material environment and so this happens to be islet cluster islets which are cluster of cells found in your pancreas that are responsible for making insulin and they coordinate together to respond to different glucose together in a very elegant feedback control mechanism and the cell-cell interactions and the size of that islet are very important to that but many many cells get important signals from the material environment and here I'm just showing one movie here these happen to be stem cells found in your bone marrow that when your bone breaks they're highly migratory and they go to that environment and help with its healing when you put those types of cells into these hydrogel environments they'd like to attach but they can't they're secreting and making all kinds of proteins trying to modify their environment and it diffuses out of the material matrix they're trying to move towards one another because they think they're in a wounded environment and eventually they undergo a cell death a programmed cell death in biology we call it anoekis it's a cell death because of lack of matrix interactions so if we were to culture these cells in just a peg environment they would die in a course of a day or two so we can begin to now think about depending upon the cells I'm putting in this environment what types of chemistry and signals should I introduce and so one of the ways that we think about this is we think about going from our pegs which are a blank slate that provide a three-dimensional structure to these cells and perhaps some mechanical cues to how do I begin to modify this environment to recapitulate some of the ways that the cells interact in our bodies so they will bind to certain chemistries there'll be certain linkers that they can degrade it'll also store different types of cues that can be released and promote wound healing and one of the ways that we think about this is when we design materials we think well how do we make them dynamic and one of the ways that we do this is on one hand we think about trying to make our materials recapitulate the materials in our body cells naturally remodel and interact with this material and we design different types of cell dictated dynamic matrices that the cell decides the changes that are all occurring and then on the other hand sometimes we want to be active experimenters and we want to be able to trigger changes around the cell and watch how the cells respond to that and that's something that allows us to gain some particular information about how a particular cell can coax a cell to move in a certain direction or to divide so a lot of the work in my group half of it is designing and interfacing new types of polymer chemistries and engineering them to promote these times of interactions so some of this is a way that I can tell you about some of the chemistry that we're interested in so we're going to start over here and look at how we design materials that mimic the tissues in our body and one of the ways that we begin to do that is we take advantage of an emerging paradigm that's evolved in the chemistry field where they talk about different types of click reactions so these are reactions between two species that occur with high specificity even in a complex milieu these two reaction partners will find one another the reactions will proceed with high efficiency and quantitation without usually need for purification and the bio click reactions are ones that can occur in living systems in the presence of cells and tissues and there's a whole milieu of different types of click reactions and reaction partners that I can begin to think about using to modify my pegs and so the idea is I can take different reaction partners and modify these end groups and mix and match different chemistries to introduce functionality and make hydrogels out of this now my own group has focused a lot on the development of this last one here it's called a thiolene coupling reaction so we use thiol groups and we react them with unsaturatedene now the reason we're interested in this is because it's one of the few reactions that you can use light to catalyze and I'll show you some examples about how light can be particularly beneficial when making biomaterials because you have spatial control of the reaction as well as temporal control of the reaction and so we take advantage of this thiolene reaction so now we have to think about which thiols should I use and which inns should I use and so we spent some time thinking about this and in the biomaterials community one of the thiols that has been of large interest is an amino acid called cysteine and so I'll show you that in just a minute but when we began to think about modifying our peg gels and making them more like our tissues the biomaterials and bioengineering community has been very interested in incorporating short peptide sequences that are found in full length proteins so these are peptides that can be synthesized automatically on solid phase peptide synthesizers we know a lot about certain peptide sequences that cells will bind to so if we think about a tissue, a soft tissue it's water swollen, has certain mechanical properties our hydrogel captures that but when we began to think about other functions we need to incorporate we need to put in functionality cells combine to well we know exactly certain sequences that will bind to those cell receptors we know we want to put in sequences that a cell can degrade we know cells make different enzymes and we know which sequences are found in proteins that they degrade here's one that's found in collagen that will be cleaved we can also screen through and sort of phase display our high throughput screen different peptide sequences that will bind some of the growth factors that are stored in the extracellular matrix with high affinity this one happens to bind one called TGF beta so we can begin to think about putting peptides into our peg gels to recapitulate the tissue environment and this is the way that we think about it and the reactions that we use so we make peptides of interest and we just include cysteine as one of the amino acids so that's our style now the tricky part about this style is that it's not as reactive as some other styles so we had to screen through and find different ways that we could modify our pegs and it turns out that this ring-strained ene is one that is highly reactive with this style so when I mix them together they're stable over long time scales but when I expose it to light I can create a radical on this thiol that will propagate through this ene and this forms a carbon-based radical that just chain transfers back to the thiol and that this goes around so one photon I can get hundreds of different reaction events so it's a very efficient reaction but the important part about this is that I can make lots of different sequences here and control lots of different peg structures and chemistries so the idea is that I can use my peg synthetic component with different multi-arms different molecular weights to control the physical properties of my gel and then I can make amino acid peptide-based sequences that include cysteine and I can mix in different amounts or stoichiometries of those components and if I use robotic liquid handling systems I can make arrays of biomaterials load this up on a microscope that real-time tracks cell behavior and then I can screen through different formulations that lead to the output that I would like to have for cells interacting with that biomaterial and so let me just show you one simple example here I take my forearm peg I modify it with my nor-bornine I make peptide sequences that contain cysteines one on each end so it'll link up into the network and form a cross-link and now I put in those same bone marrow-derived mesenchymal stem cells and now this is low magnification so the cells are the small black dots here and then in a degradable sequence and a binder watch what happens so as opposed to the cells being bound in the matrix and immobile I can design systems that the cells are attaching and locally degrading through this gel and moving and migrating and if I misspell my amino acid sequence and I change this W tryptophan for an alanine the cells can attach and bind and not move and migrate through this matrix so now you can begin to think about designing hydrogel material microenvironments that can be placed in injuries or in wounded environments where certain cells can infiltrate and move through your matrix environments and others can't I won't go into a lot of detail here but this particular chemistry and its photochemical activation allows spatial control of the chemistry as well as on-demand gelation and so one of my early PhD students working on this, Ben Fairbanks famously printed his image took a photo projected it through a microscope and here's a picture of Ben written with fluorescent chemistry inside of the hydrogel so it gives you an idea of the resolution that one can achieve one can also encapsulate cells within this environment and then use lasers or two photon confocal microscopy to introduce different types of biological signals and different environments and then study cellular responses to those so this can be important if I want to use these for different types of wound healing environments I might like to deliver different molecules and so I'll give you just one example of that where we're going to compare this material system where cells highly migrate through compared to this one which the bone marrow cells can't infiltrate and we're collaborating with an auto laryngology department at the time took me a while to be able to pronounce that but auto laryngology sort of studies your head and neck and injuries to that and so we had a medical clinician who was interested in trying to get bone to regenerate after major fractures to the skull so it's kind of limited the materials that they have to induce regeneration but yet it's very important to be able to have regeneration occur quickly because the bone in your skull protects your brain so he had a model where he was creating a critical size defect in the skull of a rat you can probably see this easier here it's about eight to nine millimeters in diameter and then he put in he called it non-degradable but that was that alanine variant but the cells cannot migrate through very well and you'll see you'll get some after nine weeks peripheral bone regeneration around the edges of the hydrogel it's implanted but here if we put in the degradable material that the bone marrow cells can infiltrate and have this three-dimensional structure of the hydrogel we get a tremendous amount of healing that occurs after just nine weeks so that's kind of interesting because we're just designing a material niche to mimic aspects of the extracellular matrix there's no drug here there are no cells being delivered and it itself can induce healing so the questions and some of the directions that this is going so this technology and these materials have been translated to a start-up mosaic biosciences whose partnering to deliver different types of biologics that can be useful for accelerating wound healing and bone healing and so some of the challenges are that this isn't perfectly healed it takes nine weeks so you can begin to think about what types of signals could I embed inside of these hydrogels that could cause faster bone regeneration and osteogenesis so that's one part of the story about how you can design materials that allow certain types of cells to interact and remodel and I can engineer these with high specificity for particular cells of interest the next part I want to tell you a little bit about are how it can also be useful not just to mimic biology and watch and be a passive observer of how tissues and wound healing and cells interact but how can I actively intervene and use this and modify materials to better understand biological questions that will be important and direct cell function and fate and so this is another type of chemistry that I want to tell you about but I want to put it in the context of an area that's really growing in the biology field right now and this is some of our work that we haven't published yet so I hope you'll find interesting so in biology and medicine there's a high level of interest in identifying and finding different types of stem cells that reside within niches of your body and if I can isolate those cells can I grow them in a dish in a way that they'll reform all the different cell types that are found in the parent tissue so they're called organized and here's just a little picture here where there's a stem cell that's taken from your intestines and it's what I'll tell you a little bit about it grows up into a colony and then it begins to differentiate and form all the different cell types that are found in your intestines with time so it's really interesting and it spontaneously happens when you culture them in hydrogels in a dish now the value of these organoids are that they're defined to recapitulate much of the structure and function of the original tissue or organ that they came from so people are really interested in growing these because now I can begin to think about patient specific cells culturing them in a dish and there's lots of promise for this in trying to understand the nature of different diseases from person to person if it's the intestine or are there organs that can be really useful for drug screening so our intestines absorb many of the drugs that we ingest and so they can be a model for drug discovery and in other cases they can also be a source for transplantable tissue if you have cancer or if you had a large volume of tissue that's injured or has to be removed so we're really interested in using our hydrogel niches to grow organoids and I'll tell you a little bit about the intestinal organoid so just a tiny bit more background in the biology of our intestines so our intestines we think of them as a tubular structure but if you were to see the more microscopic details the surface of our intestines have these ridges that are called a villus and that's where a lot of the nutrients and drugs are absorbed but where a lot of the action is is right down here in what's called the crypt and in the crypt this is where your intestinal stem cells reside these yellow cells here they're also called LGR5 positive cells and that's just a marker on the cells so you can separate them and they have these supporting cells beside them but the main thing about this is that these stem cells in this tiny crypt grow up the crypt and they regrow all the cells the epithelial cells on your intestines and they do this about every four days or so it's a really dynamic tissue it's pretty amazing the turnover of the cells within our intestines and so it becomes this really interesting model to try to understand and develop and I'm going to tell you a little bit so the one thing you'll see are these intestinal stem cells and you might hear me talk about these LGR5 cells and the way this was discovered it was discovered just a few years ago is people took these LGR5 positive cells they grew them into a spherical colony and what makes the organoid so it grows into this spherical colony and then they have these little buds here and these buds are what are called the crypts so it's a little different it's not a tube but these organoids are spheres and these are the little crypts and then you'll see different types of images these you can't see so well but you'll see that the stem cells go to the crypts and they proliferate those are the ones that regenerate and make the whole organoid so that's just a little bit of background so the reason we got interested in this and why we think it's an interesting engineering problem is there's great interest in using these types of organoids for looking at and screening for how our bodies respond to different drugs but to do this and to grow all these organoids right now all the biologists grow this in a material that calls matrigel it's secreted and it's found in... it's secreted by tumor cells it's found in this basement membrane surrounding these cells and it has a highly variable composition it's harder to scale it up if I need to make hundreds and thousands of organoids for drug companies to screen through and the material itself isn't approved for clinical use so we were really interested in designing material microenvironments that could be very useful that I could make organoids reproducibly and uniformly and use a material system that would be systematically reproduced and useful for these types of assays alright so paper from a bioengineering group that we were collaborating on came out in 2016 so this was the only thing that was known about growing these cells and something other than matrigel where they took these single cells and they're trying to grow them into colonies and one of the first things was they found kind of this Goldilocks syndrome was that if the material is too soft the cells wouldn't grow very well if it was too stiff it would hinder their ability to grow into these larger spherical organoids and in the middle it was kind of just right so they could grow these cells and they could tune the mechanics of their hydrogel environment for this but then when they tried to differentiate them and form the intestinal crypts what happened was in matrigel if you differentiate them and give them the right cues they form these crypt buds but in these synthetic gels even in the ones that were just right all the crypts would be inverted and they grow into the middle and then the colonies would just die so what happened was through lots and lots and lots of screening the Lutelf group found out that I needed to start here but then dynamically I needed the material to just soften and degrade with time right when I was differentiating it and it took about three days for that to happen so if they had designed a material that started here and then they differentiate it and they let the material soften they could form these crypt cells and these are just examples and it shows all the different cell types that are found in your intestines so they were able to recapitulate an organoid from the intestines in a synthetic material but the thing about it was that if you look at these and those of you in the front if you can see it very well is that they all have different shapes the crypts have different sizes and it's a fundamental question is does form follow function or does function follow form and if we wanted to have and make these intestines we didn't want some that had 20 crypts and some that had two crypts and some that had big crypts and some that had small crypts so we got very interested in this could we design our hydrogel matrices we'd already done some work and we'd use some of our modeling from chemical engineering about kinetics and statistics where we could make materials that would just break down with time at a pre-engineered rate they'd hydrolyze and that's what the Lutoff group did and this kind of led to random type of organoids I just showed you some of the ways that we could let the organoids decide themselves if we knew what enzymes they were secreting and remodeling so we could make materials like that but also in our group at the time we were designing materials that we could use light to also degrade the material and to change material properties and remove signals not just add them in like we had done with the thylene chemistry so we had designed some linkers that could be cleaved with light and different wavelengths of light so here's the pitch of the story this is the bottom line up front is that when you use these pre-engineered matrices and you tune it just right you can get crypts to form but they're very irregular if you use the cell directed systems you can also get some crypts but it's more complex and you have to add more different cell types and supporting cells and that was one that was recently published a year after this work so what I'm going to show you is that with our photodegradable materials we can design and grow these intestinal stem cell colonies the materials that are just right and then we can come with lasers and pattern in and directly form the size, the shape, and the direction of the crypts and we're very interested again in using this to make hundreds and thousands of crypts and using these for drug screening applications so that's what I'm going to show you a little bit of the story alright so what we did here was we were already using our favorite peg and we were using some of our different click reactions here's an alkyne that we were using that would react with an azide to click together and form hydrogels but the one thing we were doing a little differently was we were putting in this nitrobenzyl ether group that we can photodegrade alright so we could put in different types of peptides but now rather than cysteine we'd have to put in azide functionalities we could mix all this together we follow the gel forming using a rheometer and we can monitor the stiffness evolution of the gel with time when we mix all these together they react and they form a robust gel in about ten minutes if you follow this with time so we model some of those kinetics and then here's a picture we can follow the intestinal stem cells growing into colonies in real time inside of these gels then we recapitulate and we look at so what happens do we also see this mechanosensitiveness when we grow these stem cells inside of our hydrogels and so we embed them inside of these hydrogel matrices and we can tune and control the stiffness of our gel over a couple of factors we can watch the intestinal cells now this is a low magnification here's all the colonies growing and then we can look at the efficiency of which they grow into formed colonies and indeed we see when we have a certain stiffness gel we can have more efficient colony formation and I'm just going to show you some results here with this formulation so here's the more interesting point so now once we have and grow these colonies inside of these gels I can use different wavelengths of light and cleave that linker so as I learned in my reaction engineering class we could model and understand by how this linker absorbed light how it would cleave and with a laser we can control the scanning speed we can control the power we can monitor the cleavage of this reaction just by following the absorbance of that molecule and whether it's cleaved or not and so we look at that analysis and we can get at the kinetics of the cleavage and what's most important here is it sort of follows a classic photochemical reaction, a first order reaction but the important part is with this kinetics and the connectivity of my network so I had also taken a polymer class here and the number of linkers the statistics to form a gel how many I have to cleave before it becomes a liquid again it's no longer an infinite gel and I need to cleave about 84% of the linkers and so the end result is we can calculate how much of a light dose we have to have 13 to 14 microseconds of a pixel dwell time so that means as I'm watching my cells I can go at basically imaging speed and modify the chemistry of the gel around the cells so here's the image here's the intestinal stem cell colony I come with a 405 nanometer laser and I'm just scanning in these two directions changing the chemistry around and then watch and then the cells begin to go down into these degraded regions after 48 hours they've almost completely filled the region and I can do this to a whole bunch of the organoids because it's microseconds to do this and almost all of them grow into the regions that I've modded so the fraction that form these crypts so it's highly efficient and scalable but I've just shown you that the cells go down here but which cells are they and so this is where we have to do some more of the biology and we have certain reporter cells where we can label the stem cells so that they express a green fluorescent protein so those are the crypt cells when we do this we can show it's the crypt cells that are going down the stem cells are going down into these crypts we can magnify them and it's also interesting one of the things that we recapitulate is we get a crypt cell, a supporting cell and that's exactly what's in the tissue and we can show that they're also proliferating so now I can begin to make hundreds and thousands of these organoids we can visualize them in three dimensions you can see this elegant repeating architecture of the crypts we don't pattern them we don't change the gel we don't see the crypts forming when we start to differentiate them and we can show also this isn't as important but we can show that we get all the different cell types that are found in the crypt-villus architecture of your intestinal gut alright so the next part of this is we can also begin to ask why and how does this form so we collaborate a lot with biologists who are very interested in this and now let me blow this up so what's happening is you make an intestinal organoid it goes from a single cell to an organoid that's pushing away the hydrogel and the hydrogel is pushing back in it so think about a balloon that's growing that's being blown up and there's a force acting normal to it and then I relieve it so then what happens is the inside of the balloon we can see by this protein called f-actin and when I relieve that stress it causes the cells to stretch and hopefully you can see some of this stretching and that stretching leads to a mechanical signal in the cells and that mechanical signal causes those cells to differentiate and form the crypt cells and so we're doing a lot of analysis of this and quantitation I'll show you a little movie here it's quite dramatic that you see these shape changes so we had a spherical forage and then just immediately after doing it it quickly changes its shapes it elongates the cells that are found in the crypt so the distance between them get pushed closer together between the nucleus and the length from the base to the apical side gets stretched out so we can learn a lot about mechanisms as well alright so this is some emerging work and very important work in the field of organoid biology how can you make systems at high scale and reproducibly and making them in defined shape and functions so I think I'll maybe just quickly give you a little bit of a snippet of one last class of materials that we're interested in I told you some about pre-engineered materials I designed materials that they degrade or change at a pre-engineered rate I can design systems that are cell directed and cells remodel and decide or I can design systems that are user directed like the photodegradable systems but an emerging class of materials in science is materials that become adaptable and they have dynamic links between them and they respond so I'll tell you a little bit about adaptable systems these are materials that you have links between the material but the links go on and off it's a reversibility in covalent bonds and so when you have that you can pre-engineer the reversibility there are reverses at a certain rate at a certain temperature or pH cells when they push against it it causes a force against the material and it adapts and remodels and they can also respond to changes in external loads of mechanics or light and heat so let me just tell you a little bit we're interested in putting our organoids in these types of adaptable materials I won't tell you all that story but I'll just tell you a little bit about the chemistry so adaptable materials are really interesting because people are also interested in using them as bioinks so they can be adaptable they can be ejected and when they're ejected they can reform shapes and become solid again so going from flowing to solid they can be responsive so they can print with cells as well and so they're useful for all types of applications combining living systems with material systems to generate complex three-dimensional structures so some of the chemistries that we're interested in let's just focus on this one here where we use our favorite thiolene reaction but we're going to design systems where the thiol reacts with the ene and it creates a symmetric intermediate that will rearrange and regenerate the ene and the thiol will be removed or kicked off so in this way you create a system that's very dynamic rather than a permanent link I have links that can be rearranged in my system and so we make gels with these types of materials using our same azide cyclo octane material and I can react and form gels and they form in a few minutes so a very fast reaction and now I put this allosulfide linker in there and when we do that this is the reaction that I told you about we can exchange in thiols into this ene form an intermediate that I can swap out linkers in my material so this is quite interesting because I can swap out single thiols and break crosslinks in my material I can add in more thiols and cause stiffening in my material and let me just show you one example of why this is really useful I told you about this nitrobenzyl ether group it absorbs light and one photon leads to one cleavage event here in this reaction I can have a stable gel and when I expose it to light it can relax and remodel and one photon leads to hundreds of events so here I'm following the modulus of my material as a function of a radiation time and when I have no thiol exchanging in and out I get a small amount of modification but as I add in more thiol I can adapt and rearrange my molecule to change the modulus and when I add in more and more I can go beyond the critical point that a gel is formed and it'll go from a solid that's softening to a liquid so let me maybe just show I know I'm going a little fast here but we analyzed all the kinetics we're looking at light intensity effects, initiator effects but the whole story here is we can coordinate and look at the kinetics of the cleavage and remodeling with light intensity and we can compare that with what happens with our nitrobenzyl ether group and our allosulfide functionality group so this is a very slow remodeling and this takes fractions of seconds to happen so we can begin to think about making organoids so this is a centimeter thick gel normally light wouldn't even penetrate all the way through this gel and when I expose it to light with my remodeled adaptable group it completely erodes and light can penetrate all the way down to the bottom in less than a minute so I go from a gel, I expose it and within a minute I've gone completely to a liquid system so we're interested in using these types of systems to culture our organoids in forming their shapes and crypts and structures and then we can recover by just exposing and capturing those organoids and using them or transplanting them alright, I think maybe what I'll do is I'll skip through this last example and leave some time for questions apologize for my time management there and I guess what I wanted to tell you with and demonstrate with this talk was there's this great interface of chemistry, material design that can be useful to create new types of systems that can interface with tissues in our bodies with cells in a dish and really be helpful to design systems that can able injuries to heal in our body so the hard biological problem in the first example was generating bone the second hard example that I gave you was one trying to understand a stem cell and how it recapitulates and forms multiple cell types and spatial control of the information that's given that's important for directing all of these features I think there's a lot of advantages in using quantitative analysis to control and modify these environments they can be designed in many different ways but there's lots of opportunities and there's a really big need in the field so there are many advances in what we can do with cells and monitoring and tracking them in real time there's lots of advantages in chemistry and new design of materials and characterization of those materials but there's a big gap at the interface we really need a lot of people that bridge those two technologies and engineers play a critical role if we want to understand at the system level and how we can translate this to useful technology for both medicine and pharmaceutics and for the basic biology community so with that I'd like to acknowledge that all of the organoid work was done by Tobin Brown and Ian Morozes two recent Ph.D. graduates and we collaborated with Matias Lutow and one of his post-docs, Nikolce Jerovsky the earlier work on bone was and the Phylene reaction was a collaboration with Chris Bowman, Ben Fairbanks I showed you his picture and Mark Tibbet and April Clarkson did a lot of the work on developing the photodegradable chemistry and Varsharao and Alex Caldwell are doing the work on translating that to some of the bone regeneration and with that I'd just like to really thank you for your attention I hope some of you found different aspects interesting about what I had to say today but everything that I told you about was there was work of these individuals here they do all the hard work in the lab I get to hear about all their exciting results and discoveries and I think most everyone's smiling they're a pretty great group to advise I feel very fortunate to be a faculty member and also a special thanks Purdue was a great place for me to kick off and tell a potential about what chemical engineering can do and it really encouraged me to take a path less taken and it made all the difference so thank you all and I'd be happy to answer questions as is customary we encourage our students to ask the first set of questions first of all thanks for coming to give a okay thanks for coming to give an exciting engaging talk and starting this discussion so obviously you worked a lot with developing user directed materials I was wondering how you started to go through that process of designing these materials how do you delve through all the different types of chemistries and know how to combine them is there a trick to it or do you just have to sift through the literature yeah that's a good question so some of what we do is we think about what has some historical use in a living system so the photo degradable group that we use happened to be one that we were looking at a lot of the photo caging work that had been done molecules that were internalized by cells and then released by photo caging but to be honest I think it's a little bit of a mix of rational design with perhaps some luck in reading the literature and then I think there's also value in combinatorial screening in some cases as well yeah thank you so much for giving this talk awesome I was wondering if you could speak about how your work could be used for the purposes of biological computing and biological storage so the question is how could our materials be used for biological computing and biological storage yeah that's something I haven't thought about specifically but you could imagine trying to design material systems where you'd have changes in readouts or refractive index perhaps high information density that could be stored in a third dimension as well or layered so I think I would probably start by talking about a lot of people that are working on developing those types of systems but good point I have two questions the first one is related to you mentioned that this gel has to be worked or tested to can help with tissue regeneration for the injury treatments so I was thinking about is this gel capable to mimic any tissue injury such like spinal cord injuries and brain injuries since you said the stiffness of the gel could be tunable the second question is the two types of cells you use in this in the work you presented were the bone marrow and intestinal stem cells so I don't quite sure about how those cells they interact with the gel but do you think some other type of cells such as neurons can be applied or culture in this kind of gel because when the neurons are in their embryonic states of development it requires some tracks or glial tracks to migrate do you think this type of gel can like reach that kind of purpose right so the first question was do our hydrogels mimic some aspect of a tissue maybe some of the changes that happen with disease or injury and I didn't talk about some of that work today but that is one of the things that we've done quite a bit of work on is culturing cells and making tissues in these environments where you can dynamically stiffen or soften or injure the material and then watch the injury wound healing response and some of those studies are really nice models I will say for things like disease so in cancer tissues get stiffer and that's why you feel cancer tumors are fibrosis you have heart fibrosis liver fibrosis the tissues get stiffer and we can stiffen on our systems and watch cellular responses but the time course of many of those diseases or neurological diseases is years right or decades and sometimes it's harder to scale or figure out what's the time scale in our in vitro experiments that would mimic a really long time scale of a process that occurs over decades can we accelerate and mimic that in two weeks in a dish or not and then the other question is yes many of these materials can be tailored for other types of cell types so we have worked with neurons you can change chemistry and develop tracks for axonal extension we've worked with heart cells so some of it is just kind of what's the biological question to tailor the materials to well we do have another panel event so I would encourage everyone to attend the panel and of course there will be more opportunities for Q&A at the panel so let's thank Christiana