Dr. Ritu Raman: A Biological Architect

How a new professor is reimagining the building blocks of engineering.

Dr. Ritu Raman, Assistant Professor at MIT. Photo courtesy of IF/THEN.


Dr. Raman grew up shuffling between India, Kenya and the US in a family of engineers. She fondly remembers her parents building communication towers in rural villages in Kenya, and was inspired to pursue engineering because she saw that innovation could help solve the problems that plagued the world. She also credits her family for teaching her to be observant of her surroundings; this allowed her to challenge traditional engineering and pursue a relatively new, but hugely impactful area of research. She earned her B.S. in Mechanical Engineering from Cornell University in 2012, and her M.S. (2013) and Ph.D. (2016) in Mechanical Engineering at the University of Illinois at Urbana-Champaign. She started work as a postdoctoral fellow at the Langer Lab at MIT, where she opened her own lab in 2021. Her lab is currently focused on engineering biological actuators.


Table of Contents:

Engineering with a twist

What are biological actuators?

How are biological actuators built?

3D Printing

A future with biological actuators

 

Engineering with a twist


What do engineers build with? When we ponder this question, you might think of synthetic (human-made) materials.

On the left individual pieces of wood are stacked to become a log cabin. On the right individual cells make up living tissue which in turn makes up a liver.
Materials like wood can be used to engineer houses. What kinds of structures could be engineered using biological materials, like cells?

For example, we imagine electrical engineers that use different conductive components and wires to build electronic devices– such as phones, televisions, and computers– or civil engineers that use cement and wood to build roads and houses. However, what doesn't always come to mind are engineers that build with natural, living materials like DNA or living tissues. Through her research, Dr. Ritu Raman is trying to bridge this gap and incorporate biology into her engineering.




An Assistant Professor of Mechanical Engineering at MIT, Dr. Raman is pushing the boundaries of engineering. She believes that the future of environmentally friendly and adaptive engineering lies in the glorious potential of building with biological materials or biofabrication.


What is the motivation for choosing biological materials over synthetic ones? To illustrate what makes biological materials unique, let’s consider an example. Imagine that you’re walking on the street and suddenly your phone falls to the ground and the screen cracks. That’s it, it’s doomed, you’ll have to get the screen replaced. Now put yourself in place of the phone. If you fell, you’d get a scratch or a cut that would heal within days, no problem at all. The cells in your body would sense the injury and coordinate an appropriate response.

On the left a phone screen cracks and remains damaged. On the right a knee is skinned, but a bandaid is applied and the skin will heal.
Biological systems are special because of their ability to heal themselves!

It is this ability to sense, process, and adapt to the environment that makes living materials (such as the cells that make up our bodies) a unique and irreplaceable building material. This is what intrigues Raman; she insists that “No synthetic material or machine we have built to date can match the level of immense complexity and innate responsiveness observed in biological systems.”

 

What are biological actuators?

On top an arm flexes to demonstrate how the muscles within contract and extend to produce motion. On the bottom a machine has actuators that contract and expand to produce motion similar to the arm's.

An actuator is a device that takes in some form of energy (electricity, hydraulic pressure, or air pressure) to produce controlled motion.


Complex machines, such as robots, are built of multiple actuators that work together with electrical signals to produce movement. In the human body, muscles and tendons are actuators that work together with our brain and our nervous system (made up of our spinal cord and nerves) to help us sense and adapt to our surroundings.



To illustrate the difference between abiotic and biotic (man-made and natural) actuators, let us consider a robot’s machinery compared to your body. A robot arm will only move as much as it is programmed to. Similarly, the robot will not get stronger or gain a larger range of motion if we repeatedly instruct it to perform the same motion.

Diagram of an arm flexing

Now imagine if this is you. Suppose you start lifting weights every day. As time goes on, you will notice that you get stronger and are able to lift heavier and heavier weights. This is because your muscles adapt to the signals they receive from your brain. As you change your habits, your muscles change too! This is what makes biological actuators so impressive.


 

How are biological actuators built?


There have been recent advances in technology that allow bioengineers, such as Raman, to build with biological materials. She is interested in engineering living muscle tissues. To understand how to engineer this tissue, we must first understand how this biological system sends and receives signals to coordinate muscular movement.



Skeletal muscle is composed of long fibers, called myofibrils, that are made up of two proteins: myosin and actin. When the muscles receive signals in the form of electric impulses from the central nervous system (CNS), the myofibrils slide past each other allowing the muscle to contract and expand. This produces movement.




Information about the muscle is also sent back to the CNS. This neuromuscular network (muscles + the nervous system) allows communication back and forth between the muscle and the brain. For example, if you decide to run a marathon, first your brain will send a signal to your leg muscles, allowing you to run and gain momentum. After you’ve reached the limit of your stamina, your legs will begin to ache and your brain will receive signals that your muscles are getting tired and might need to rest. Thus, your CNS and muscle fibers coordinate to produce and maintain movement.

This system sounds quite complex, so how do we make it in a lab? Scientists, including Dr. Raman, are still working on developing reliable ways to make these living tissues. But there is promising progress in skeletal muscle tissue engineering that provides a first step in constructing a neuromuscular network from scratch.

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To begin making the skeletal muscle tissue in a lab, we first need cells, which are the building blocks of tissues. In the case of muscle fibers, these cells are called myoblasts. They divide and differentiate (acquire unique functions) to form myofibrils.


Once we have myoblasts, we need to provide them with the nutrients they need to grow and divide to become the actual tissue. For the muscles in our bodies, our bones provide a scaffold that allows the muscle to grow around it. For tissue engineered in a lab, these scaffolds are usually 3D printed. The cool thing about building with live materials is that they can self-assemble. When provided the right growth conditions and a proper scaffold, they grow (just like cells are supposed to), and self-assemble into three-dimensional tissues.


 

3D Printing

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3D printing is the process of building three-dimensional objects using 2D layers stacked on top of each other. Any object (as long as their geometry does not defy physics) can be printed using this technique. Normal 2D printers use ink as their medium to produce images on paper. 3D printers, on the other hand, can print using various media such as plastics, metals, and ceramics, depending on what you, the user, need. So, if I want to print a plastic cube, the 3D printer will take in the plastic I want to print with, melt it at a high temperature, around 200ºC (so it becomes soft enough to flow), and use its nozzle to print specific shapes. As the plastic cools, each layer solidifies, giving rise to a finished 3-dimensional object. For a cube, the 3D printer will print squares, layer by layer (each layer is very thin, typically 1/10th of a millimeter), until a cube is printed.


Using 3D printing technology, we can build scaffolds to allow the skeletal muscle to grow. 3D-printing is now advancing so we can even use cells as input, allowing us to directly print 3D cellular structures!

Cartoon of a 3D printer taking in bone cells as "ink" and printing a bone.
3D printers can be used to create a scaffold for living cells. Some 3D printers can now print biological materials using living cells as "ink"!

 

A future with biological actuators


Now that we have built skeletal muscle in the lab, what do we do with it? Since biological actuators have unique properties that allow them to sense and respond to their environments, one primary application that Dr. Raman is interested in is therapeutics. Many people suffer disease or undergo trauma that restricts their mobility and impacts their quality of life. Some people are born without limbs, and some lose them in devastating accidents. Prosthetic medical technology allows many people to regain mobility, but a prosthetic is static and cannot grow or get stronger over time.


Raman aims to create bio-hybrid implantable devices that can sense and can adapt to the needs of our bodies in real time. So, if the prosthetic implant gets injured, it can heal itself. If the individual regularly exercises, the prosthetic can become stronger. Bio-hybrid implants will revolutionize personalized medicine in a safe and sustainable way by targeting the precise needs of individual patients. Using biological actuators in prosthetics will restore mobility, advance human health, and improve quality of life for many people!


Credits:

Photo courtesy of IF/THEN Collection

Written by Manasvi Verma

Edited by Katie Fraser, Jackie Lodman, Madelyn Leembruggen

Cartoons by Lindsey Oberhelman


Primary sources:

MIT Technology Review 35 Innovators Under 35: Dr. Ritu Raman

Ritu Raman by The Works Museum

Dr Ritu Raman: Skeletal muscle-powered machines (25th June 2020)

Engineered neuromuscular actuators for medicine, meat, and machines by Ritu Raman in RMS Bulletin 2021

Modeling muscle by Ritu Raman in Science 2019

Biofabrication by Ritu Raman


Additional resources:

Learn more about muscles by watching this video

Listen to this podcast to hear Dr. Raman talk about how cool bioengineering can be

Watch this video to learn more about bio-inspired robots

 

Learn more about actuators and muscles!


Build (1.5-2 hours): Engineer a robotic hand from cardboard. What do you use as actuators?


Deepen (10-20 minutes): Watch how muscles contract using molecular mechanisms.


Create (2-3 hours): With an adult's help, use the free software Tinkercad to create a 3D design that could be made with a 3D printer. Optional: Ask your local or school librarian if there is a 3D printer you could learn to use.