Make a Biohybrid Robot

Abstract

When you think of robots, you might think of things made out of plastic or metal...but what about living materials? Living materials have one big advantage: they can heal and repair themselves if they get damaged. Since it might not always be easy to repair a damaged robot (for example, a robot on another planet), some scientists want to figure out how to include living, or biological, materials in them to create "biohybrid" robots. In this project, you will create your own simple biohybrid robotic system using a live plant as a capacitive touch sensor. 

Summary

Areas of Science

Robotics
Plant Biology

Difficulty

Method

Engineering Design Process

Time Required

Average (6-10 days)

Prerequisites

Previous Arduino experience is recommended. See our How to Use an Arduino page for tutorials.

Material Availability

A kit is available from our partner Home Science Tools®. Additional items required that are not included in the kit. See the Materials section for details. 

Cost

Average ($50 - $100)

Safety

No issues

Credits

Ben Finio, PhD, Science Buddies

Science Buddies is committed to creating content authored by scientists and educators. Learn more about our process and how we use AI.

https://www.youtube.com/watch?v=y7v1xHn3Vmw

Objective

Design a simple biohybrid robotic system with part of a plant as a touch sensor. 

Introduction

Traditional construction materials like metals and plastics have a lot of advantages. They are strong, durable, and we can mold or machine them into almost any shape we want. However, they have one major disadvantage: if they break, they cannot heal or repair on their own! Even a tiny crack in a piece of plastic or metal will stay there forever unless humans do something to fix it.

Compare that to biological materials, or living tissues, like those in the human body. Small cuts and bruises easily heal on their own. If you get a deeper cut or even break a bone, you might need a supporting bandage or cast, but eventually, your body will heal itself. This ability is very important for the survival of humans (and other organisms) — there are lots of ways to get injured out there! Living tissue can also act as a sensor. Electronic sensors typically measure just one thing at a time, like light or sound. However, some living tissue can react to multiple inputs. For example, your skin is sensitive to both pressure and temperature. 

All of these features of living tissue have made scientists interested in creating biohybrid robots. These robots can incorporate both traditional and biological materials to do different things. For example, a robot could have a rigid metal or plastic body covered in a self-healing biological skin that acts as a touch sensor. This can make the robot more durable since the skin can heal itself if the robot crashes into something.

In this project, you will learn how to build a simple biohybrid robotic system with living tissue, like a plant, that acts as a capacitive touch sensor. Capacitive touch sensing is the same technology that lets you type directly on the screen of a smartphone without using a separate keyboard. When you touch a capacitive touch sensor (or a capacitive screen), its capacitance changes. A computer can measure this change and use it to take an action, like making a character appear on the screen, or, in the case of a robot, moving a motor. Watch this video to learn more about capacitive touch sensing on an Arduino:

https://www.youtube.com/watch?v=sya89Et3Go0

The procedure section of this project will show you how to build a simple biohybrid robotic system with one input (the capacitive touch sensor) and one output (a servo motor). It will be up to you to figure out what exactly your biohybrid robotic system should do and how to incorporate living tissue so it can survive long-term. For example, the procedure will use a flower, but you would need to add water to your system to keep the flower alive. What will your biohybrid robot do?

Terms and Concepts

• Tissue
• Sensor
• Biohybrid
• Capacitive

Questions

• What are some advantages and disadvantages of traditional fabrication materials like metals and plastics?
• What are some advantages and disadvantages of biological materials or living tissues when used in robotics?
• How could you incorporate living tissue into a robotic system?
• What type of living tissue would you use? How would you keep it alive?

Materials and Equipment

Recommended Project Supplies

Get the right supplies — selected and tested to work with this project.

View Kit

These are the parts required to make a single motor react using a plant as a touch sensor. Additional parts are required if you want to integrate the bio-hybrid touch sensor with one of our many other Arduino projects. 

• Electronics Kit for Arduino, available from our partner Home Science Tools®.
  
  • Note: this project uses the built-in capacitive touch sensing ability on the Arduino Uno R4. The example code will not work for the Uno R3 or other models. 
• Positional servo motor
• Alligator clips
• Cardboard
• Wooden craft stick
• Tape
• Small cup or container
• Water
• Small fresh plant part (flower, leaf, blade of grass, etc.)
• Windows or Mac computer. See this page if you have a Chromebook. Your computer will need:
  • Access to the Arduino IDE, either installed local version or web-based editor. Watch this video for a comparison of the two options.
  • USB port. The Science Buddies kit comes with a USB-A to C cable. The "C" end plugs into the Arduino, and the "A" end plugs into your computer. You will need an adapter or different cable if your computer only has USB-C ports. Watch this video to learn about the different types of cables and adapters.

This project follows the Engineering Design Process. Confirm with your teacher if this is acceptable for your project, and review the steps before you begin.

Before you begin: Review How to Use an Arduino Tutorials 1-3.

1. Decide what plant tissue you will use for your touch sensor. The simplest approach is to pick something that is already growing, like a leaf, flower, or blade of grass. See the Variations section for other ideas. 
2. Put your plant in a small container of water to keep it fresh while you work on your robot.
3. Assemble your circuit, as shown in Figure 1. You can also access a Tinkercad Circuits version of the circuit, where you can zoom. 
   1. Note: the breadboard in Figure 1 has the power (+) buses on the left and the ground (-) buses on the right. The buses on your breadboard may be reversed.   
   2. User jumper wires to connect the servo motor's cable to the breadboard.
      1. Connect the brown wire (ground) to a breadboard ground (-) bus.
      2. Connect the red wire (power) to a breadboard power (+) bus.
      3. Connect the orange wire (signal) to Arduino pin 11. 
   3. Place an LED in the breadboard. Make sure each leg is in a different row.
      1. Connect the long (positive) leg to Arduino pin 8.
      2. Connect the short (negative) leg to a ground bus using a 470 Ω resistor.
   4. Connect your plant to the Arduino.
      1. Put a jumper wire in Arduino pin 0.
      2. Use an alligator clip cable to connect the jumper wire to your plant.
   5. Connect power to your breadboard.
      1. Connect the Arduino 5V pin to the breadboard power (+) bus.
      2. Connect an Arduino GND pin to the breadboard ground (-) bus. 

Image Credit: Ben Finio / Science Buddies

Figure 1. Breadboard diagram for controlling a single servo motor and LED with a capacitive touch sensor.

4. Download the capacitive_touch_servo_LED.ino example code. Open the file and read through the commented code so you understand how it works.
   1. The code uses two different thresholds. One, the threshold variable, is intended to detect when your finger approaches (but does not touch) your plant. This will cause the servo to move the plant away.
   2. The second threshold, set with the setThreshold command, detects when your plant is actually touched. This will make the Arduino light up the LED.
5. For now, unplug the 5V jumper wire so the servo does not have power. This will make it easier to calibrate your code without the servo moving.
6. Upload the program to your Arduino and open the serial monitor. 
7. Watch the output of the serial monitor as you gradually move your finger closer to your plant.
   1. What is the baseline value when your hand is far away?
   2. What is the value when your finger is almost touching the plant?
   3. What is the value when you touch the plant? Does it change depending on where you touch the plant?
8. Adjust the two different threshold values in your code based on the results of your testing. 
9. Reconnect power to your servo and reupload the code.
10. Slowly bring your finger closer to the plant again. Does the servo rotate when you get close to the plant? Does the LED turn on when you touch the plant?
11. Now, to make a reactive robotic system that moves the plant away when you try to touch it, mount the plant to the servo using tape and a wooden craft stick, as shown in Figure 2. Tape the servo to a piece of cardboard or cardstock base so it stands upright. 

Image Credit: Ben Finio. / Science Buddies

Figure 2. Experimental setup with plant mounted to servo arm and connected with an alligator clip.

12. Unplug the 5V power cable to remove power from the servo again.
13. Open the serial monitor and recalibrate your thresholds if necessary (step 7). The capacitive touch feature measures the capacitance between everything connected to the Arduino pin and the environment, so the baseline capacitance can change if you move the wire, alligator clip, or plant. Remember to reupload the code if you change the thresholds. 
14. Slowly move your finger toward the plant from the right.
    1. If your code is calibrated properly, the servo should rotate and move the plant away before you touch it.
    2. If you move your finger away, the servo should rotate back.
    3. Note that the capacitive touch sensing feature cannot sense direction, just an overall change in capacitance on the Arduino pin. The example program is designed so that the servo will rotate away when your hand approaches the plant from the right. If you try approaching from the left, the plant will rotate into your hand.
15. If the servo moves too fast, too slow, or its motion is jerky, try changing the increments to the angle variable in the code, and/or change the length of the delay at the end of the loop() function. Remember to re-upload your code each time you make a change. 
16. So far, this procedure has shown you how to create a simple demonstration of a biohybrid robotic system. You can now incorporate this principle into your own robot design using the engineering design process. Science Buddies has many other Arduino projects you can choose from. Can you use a biohybrid sensor in any of those projects? See the Variations section for more ideas. 

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Global Goals

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.

This project explores topics key to Industry, Innovation and Infrastructure: Build resilient infrastructure, promote sustainable industrialization and foster innovation.

Variations

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