组织工程的实验方法

My name is Ali Kamasi and I am currently a assistant professor at the Harvard MIT's Division of Health Sciences and Technology. And I have a joint appointment with Harvard Medical School, specifically at Brigham and Women's Hospital, which is a affiliate of Harvard Medical School. And my research areas are in microscale tissue engineering and biomes area.

So my background academically is more to, and initially started in chemical engineering. I did my undergraduate in chemical engineering at University of Toronto, and subsequently I became very interested in more biology oriented engineering. So I did a master's in biomedical engineering continuing in University of Toronto, working specifically in stem cell differentiation.

And then I, I came to MIT and I did my PhD with Professor of Robert Langer in, in, in bioengineering. And afterwards, after a few months of postdoc, I joined my current position. The research areas that we focus on is really at the interface between biology, engineering and material science.

So, and what we are trying to do is to try to address questions that bio biologists have been trying to answer for a long time, but try to do it in a way that previously could not be done by bringing in new technologies and new perspectives in, into understanding these questions. And one of the major medical problems we're trying to address is really this shortage of organs. How do we generate three dimensional organs that could be potentially transplanted so that, you know, for, you know, obviously there's a huge shortage of organ pro like, and many patients require transplantable organs and there's huge waiting lists.

So one of the things that we and other people in the field of tissue engineering and trying to do is try to generate approaches where we can make artificial tissues. And along the same concept, one of the major problems that exists right now, which is, which is also in drug discovery and finding new drugs, is how do we generate better models that represent tissues outside the body so that we can test drugs and chemicals and see what their effects are on these kind of tissues. And then once we can do that properly, then we can have much better predictive behavior of which drugs are actually gonna be effective.

So you don't have the, you know, the recalls on of the drugs after they've been approved and the side effects and you can have a much better drug discovery process. Microfluidic devices are a subsection of what we call microscale technologies. And what on this microscale technologies, I, maybe I'll explain what start with that.

What they're trying to do is try to mimic the complexity of biological tissues or biological systems. So most cells are around tens of micrometers. And to really understand cells at those dimensions, you need to have technologies to be able to engineer what a cell sees and what a cell senses at length scales that are ranges from much smaller than 10 micrometers to larger than 10 micrometers.

So you can have individual cells and be able to, to be able to manipulate their surroundings. So what a system like microfluidics allows us to do is try, allows us to have very tight control over how soluble factors are delivered to cells. So an example of that is being able to have a microfluidic channel and generate a concentration gradient of a, a chemokine or a growth factor or a cytokine in there.

And what it allows us to do now is to try to mimic what happens during normal development or within biological systems where there are concentration gradients throughout an organism that actually tells the cell what they, what it should do. So what with microfluidic systems, we can generate these kinds of biological complexity in a very rapid controlled manner and then analyze cell behavior directly in, in exposure to these kind of concentration gradients or biological biologically and spatially oriented signals. So tissue engineering originated probably now around 20, 30 years ago with the idea of trying to use transplantable cells and merge them with materials so that we can either, you know, generate better three dimensional tissues and really initially started off by people trying to get biodegradable materials, make foams out of them.

And so that, you know, they're very porous structures. And then seeding these foams with cells. So as cells kind of move around inside this foam, they settle in particular places and as time goes on, the cells will start depositing their own biological matrix.

And since these materials are biodegradable, the materials degrade over time and what you're left with is a completely biological tissue. And this approach has been particularly useful for, you know, some simpler organs, such things such as cartilage. And there's actually been things such as our artificial skin that has actually been FDA approved.

So it's been clinically viable. Where this approach potentially could use more help is with respect to more complex structures like, like the heart where, or the liver, where you really have very controlled cell cell interactions and very controlled complexity and architecture at the micro scale. So one of the original ideas with tissue engineering, which was that when you put the cells, the cells kind of rearrange themselves to actually generate some of this complexity that you see in the normal body.

But that, and that does happen to certain extent, but it doesn't happen all the way. So a tissue engineered organ at the microstructure level, it still would be different from a truly native biological tissue. And that's because the cells just don't assemble themselves as they would completely during, during, during development.

So what we try to do is to, with respect to the microscale and moving tissue engineering at the microscale, is to try to recapture this complexity. So how do we do that? So, and what are the complexities that we want to generate?

Well, one of the things is vascularization tissues are very, very vascular and that supply, that supplies the tissue with oxygen and nutrients and other things that it needs. So right now it's very difficult to get to actually engineer large structures of tissues and be able to supply all the cells with the proper amounts of nutrients and oxygen. One thing that microscale technologies allows us to do is actually potentially to engineer the micro vasculature directly in our three dimensional structures.

Another thing that microscale technologies allows us to do is to try to control how different cell types interact within this three dimensional structure. So you may want to have, you know, a cell type in a particular structure and have a secondary cell type next to it just as it would in in in the body. And using microscale technologies, we can try to recapture these kind of geometries and complexities that are present in the body within our three-dimensional structure.

So we don't have to necessarily hope that they would self assemble directly by in inside the scaffolds. There are a number of challenges. One of the main challenges with respect to how we can engineer tissues is really, even if we make a tissue that is three-dimensional, we we still want it to be functional and there's a variety of mechanical and biochemical metabolic functions that normal tissues do, which these tissue engineered organs need to, you know, to, to basically recapture and mimic.

So what what has been a problem right now is that many tissue engineered organs fall short of their native, you know, biological performance. And part of the problem is with respect to the types of materials that we use right now, they're not necessarily optimized for variety of different applications. And you know, we, we currently, we currently still need to understand the biology of development and the biology of wound healing better to be able to recreate conditions that allows the cells within these three-dimensional scaffolds to really go all the way to what you know, they would in the body during normal development or nor normal wound healing so that we can get final structures that actually mimics a truly regenerated or, you know, developed tissues.

And the biology still is still being explored and developed. So, you know, that's one thing is biology, the other one is better materials. And finally the, I think a big problem is still cell source.

You know, that's why it's really important to try to explore alternative cell sources because our body cells, you know, they're, you know, the adult stem cells are very, you know, potential potentially viable source of cells. Also things like embryonic and also new approaches people are finding using, you know, using skin cells or other cells to actually get very primitive cells where you can try to direct their differentiation and get a viable source of cells. So I would say those are three major problems, you know, better materials, understanding the biology better and getting a better cell source within the next five years.

There there will be a lot of changes with respect to making these microscale technologies more widely applicable to both biologists and tissue engineers. I think a lot of people are now realizing how important it is to really study both biology and generate tissues with microscale resolution. And I I believe that it's gonna be a very, you know, continued trend for the next few years.

And I think another aspect is that there's gonna be a lot more interaction between the people on the, the final end product, whether it's the clinical doctors and, you know, FDA or and other regulatory agents and you know, the basically and the business people. So there's there, there there's gonna be more and more interaction with these entities, with the basic researchers to try to actually go back and try to see what are the major problems in commercializing some of the, the science that has been developed. And I think, and how do we do it in a way that's safe and ethically responsible.

So I think there both scientifically there is, there's still major strides to be made, but also with respect to other things, there's still gonna be, a lot of stuff would be made and I think five years at least will be the, the first few steps and in the next 10, 15 years is, is when really the things are gonna get interesting with respect to how some of these technologies, specifically with respect to both tissue engineering and it's, it's the application of these technologies to drug discovery assays and things, how it's gonna be used in real, real world applications really depends on which organ we're talking about and which kind of application we're talking about. Clearly the first and the most obvious application for, you know, artificial tissues is in the drug discovery area or diagnostics area where you're trying to understand better get better physiological models of that you can have in a tissue culture outside the body and be able to analyze them with, probe them to understand the biology better or probe them to understand, you know, the effective chemicals or drugs. And I think that that in, in that area, the major challenge is to really get something that mimics the native tissue as, as completely as possible so that if your, if your tissue construct says something is toxic, you can be very confident that if you put it in an animal, then it will be it, it will be toxic and it will be very predictive of what response you would get in the animal.

So, and, and I think with respect to the actual therapeutic applications, there are still a lot more hurdles to overcome. And I think the major, the major ones are how do these therapeutic agents going to behave, you know, short term and long term because no one has really, really understands how, you know, foreign cells, let's say, you know, tissue engineered or stem cell drive cells from embryonic stem cells or you know, from other people is gonna behave in, in my body or someone else's body in the long term. And then the other, I think there's also other ethical questions like, you know, how do we actually, you know, is it, what is the best cell source that is, you know, both ethically challenged challenge ethically responsible, but also scientifically and clinically feasible and with respect to actually engineering organs, I think there, the major question is can you have something that both is safe and also it's gonna perform properly And you know, there's a lot of regulatory mechanisms that, you know, any kind of tissue engineered organ has to overcome.

And I think FDA at this point is, is starting to explore how to actually regulate biological tissues that people engineer for therapeutic applications. And I think there's one or two precedences for these kind of products going to on commercialization, but there's not a still very standardized route that you know exactly what's gonna happen to get something from a lab to a final product With respect to some of these artificial biological tissues, it really depends on the organ. So for some of, you know, something like skin, you know, you know, we already have it.

For something like a heart, complete heart, I would say we're very far away. You know, I would say maybe, you know, well probably 50, you know, I want to be very conservative. It may happen sooner, but there are a lot of challenges to get something that properly and has the right complexity and properly functions as a normal biological tissue would.

But I think with respect to a, a smaller things like a heart tissue, you know, and not a complete heart, we're much closer. And I would say, you know, with respect to a clinical application and something that has actually gone through the regulatory process, you know, it's possible to something within, you know, 15 years, you know, to actually have transplantable pieces of heart tissue that you can, you can do. And I think most of this will be in the regulatory stage because right now to approve a drug it takes 12 years.

So even if we have something right now, which we think is perfect, you know, it's gonna take at least a decade to, you know, make sure that it's safe and it also does the proper function so that we can, you know, wide in a widespread manner, use it in patients.