By using chicken bones to simulate human bones (which are many times stronger) students see the amazing strength of bones. In the class demonstration, a point load is applied to a bone with a gradual increase in load (weight) until the bone can no longer support it and fails (fractures). In the hands-on student activity, student teams work as biomedical engineers to create and design casts or splints that immobilize body parts to help the body heal. They also explore the strength of materials as they test the strength of their casts/splints.

Engineers are always experimenting with new materials to make improved splints and casts that immobilize injured body parts to help the body mend. click for copyright

• Gather materials, and make copies of the Bone Breaking Design Worksheet and Bone Breaking Group Testing Table, one each per team.
• Thoroughly clean the chicken bones. Make a small fracture in each bone by taking a flathead screwdriver and carefully tapping it with a hammer until the bone cracks, being careful not to completely break the bone. Set aside one bone for the demonstration.
• Place cast- and splint-making materials on a separate table to serve as the "class store."
• (optional) If making plaster of Paris casts, cut newspaper into 2-inch (4-cm) strips. Make the paper-mâché mix in advance or have another adult make it during class.

Using two classroom tables or desks, follow the next steps to set-up the load testing area for the class demonstration.

1. Move tables or desks to create an open 1.5-inch (~4-cm) span between them (see Figure 1).

Figure 1. (left) Arrange two tables to create a 1.5-inch (3.8-cm) open span between their tops. (right) Connect the S-hooks to the pieces of chain link. click for copyright

2. Using the S-hooks, connect a hook to each end of the link chain (see Figure 1).
3. Hook an end of the chain, using the S-hook to the bucket handle (see Figure 2).

Figure 2. Use an S-hook to attach the chain to the bucket handle. click for copyright

4. Divide the class into teams of two or three students each.
5. While at their desks, give each team a fractured chicken bone to observe. It should be similar to the one you are using for the demonstration, or pass around the bone that you are using for the demonstration to each group. Review pertinent concepts and functions of bones and the skeletal system.
6. Have each group study their bones for characteristics, such as size, color, shape, strength, etc. Encourage students to examine the bone by sight, touch and smell. Tell them not to taste the bone or break it.
7. Using Part 1: Gathering Information on the activity worksheet, have students draw the bone, write down any observations about it (size, color, strength, etc.), as well as a prediction of the total amount of load (weight) that the bone will be able to carry before failure (fracture).
8. Once students have finished Part 1 of their worksheets, have all groups gather around the testing station.

Figure 3. (left) Tape the chicken bone securely to tabletops, across the open span. (right) Using a second S-hook, attach the loose end of the chain to the middle of the bone. click for copyright

9. Using duct tape, take the demonstration bone and tape it across the open span of the tables/desks making sure the bone is fastened tightly to each side (see Figure 3).
10. Use an S-hook to attach the loose end of the chain to the middle of the bone (see Figure 3). The chain and bucket should hang in the middle of the opening (see Figure 4). Make sure the bucket is suspended above the floor.

Figure 4. Adjust the chain link to hang the bucket from the bone so it is above the floor and between the tabletop opening. click for copyright

11. For safety, keep bone pieces, marrow and other fragments from flying, by placing a clear plastic bin or container over the bone while you are adding weight to the bucket.
12. In 5-lb (2.3-kg) increments, carefully add weight into the bucket, pausing for 5-10 seconds to allow the additional weight to settle. Do not drop weights into bucket; place them gently into the bucket. (Note: Most chicken bones are capable of holding 40-50 lbs [18-23 kg].).
13. Continue to add weight until the bone cracks.
14. Have students record on their worksheets the amount of weight that caused the demonstration bone to fail (fracture).

1. After the class demonstration, discuss with students their observations during the load testing: What did you notice as more weight was added? How strong is a chicken bone? Were you surprised to see the chicken bone carry that much weight? Do you think a human bone could withstand more or less weight?
2. Review the healing process for fractured bones and the various biomedical devices (casts and splints) used to help heal bones, clarifying the differences between each.
3. Have student teams return to their desks and complete worksheet Part 2, Analyzing the Information.
4. Once students have finished Part 2, review the engineering design process with them and explain that they will be acting as biomedical engineers, designing their own type of cast or splint as a team. Explain to students that when engineers design a new or improved product, they work in groups and follow the steps of the engineering design process: 1) understand the problem or need, 2) come up with creative ideas, 3) select the most promising idea, 4) communicate and make a plan to describe the idea, 5) create a prototype or model of the design, and 6) evaluate what you have made, thinking of possible improvements.
5. Introduce the design concepts and constraints for the activity. Either provide students with already-specified constraints that serve to limit and guide the design challenge, or brainstorm with the class to come up with additional constraints/design goals. Consider the following (or some combination) as suggestions for design goals/constraints: strength of the cast or splint, weight of the cast or splint, cost to make the cast or splint, most realistic cast or splint for usability.
6. (optional step; follow if using cost as a design constraint) Reveal to students the types of "store" materials available for the construction of casts and splints, and the "cost" of each material (for purposes of this activity). Explain that one of their design constraints is cost; they may spend up to a certain amount of money (such as $200 in play money), but no more, to make their device. Hand out the play money to each team.
7. Have students pick a specific type of cast (splint or plaster cast) to design. Give them 5-10 minutes to complete their design on their worksheets, including Part 3.
8. Once students have completed their design and obtained teacher approval, direct one team at a time to obtain (or use their play money to buy) from the "store" (teacher) the necessary materials for their medical device.
9. After teams have supplies, have them create their model casts, building around their broken chicken bones.
10. For teams that want to make a plaster cast, follow the paper-mâché-making steps (next section). Note: Making a plaster cast requires an extra 15-20 minutes plus overnight drying time, so allow enough time for this option.
11. Once all groups have completed their splint or cast, have students pick up and clean their work areas.

1. Mix three parts warm water with one part flour and one part white glue. Stir until a smooth, creamy mixture is obtained.
2. Cut newspaper into 2-inch (5-cm) strips.
3. Dip each strip into the mixture and squeegee any excess material with fingers.
4. Wrap the wet paper strips around the bone or bone covered with gauze, to make the cast. Help students, as necessary.
5. Continue to dip and wrap the strips until the cast is finished. Let the groups decide how thick or thin they want their casts.
6. Once all groups have completed their casts, have students pick up and clean their work areas.

1. Recap with students their activity from the previous day(s). Briefly review the strength of bones, the types of bone disorders (such as fractures, osteoporosis, etc.), the methods and types of medical devices used to assist in these conditions, and the activity itself thus far (design goals, materials, etc.)
2. Give teams time to make any final adjustments or alterations to their designs, or finish their casts/splints if they have not already done so.
3. Once all groups have completed their casts/splints, gather around the testing station.
4. Have teams number off to decide the order to test their casts. Or, provide a pre-selected list for the order.
5. Guide each team to test the strength of their casts and how well they protect the fractured bones. For each team's cast/splint, use the testing station with bucket and weights, and repeat steps 9 through 14 from the bone-breaking demonstration.
6. To keep all students engaged during the load testing, have students fill out the testing table to track the weight that each group's design was able to hold.
7. Conclude by engaging students in the post-activity described in the Assessment section. Ask them to think about the materials in the different cast/splints, what worked and what did not, and what they might do to improve their designs.

Exploratory Discussion: As a class, discuss the following topics:

• What is a bone fracture? (Answer: A medical condition in which a bone is cracked or broken.)
• Review the human skeletal system and the importance of bone strength.
• Have you ever had a broken bone? If so, what was done to help heal the bone?

True/False Trivia: As a discussion extension, ask the following true/false questions and have students respond with thumbs up for true or thumbs down for false. Tally the votes on the board. Then, ask the same questions at the end of the activity and compare results.

• True/False: Engineers create devices that help heal broken bones. (Answer: True)
• True/False: Engineers do not need to know about the strength of bones in designing devices to help heal broken bones. (Answer: False. Engineers must study the strength of bones to determine what types of materials might help protect and support the bones.)
• True/False: Engineers improve our lives by inventing things that can help repair our bodies. (Answer: True. Biomedical engineers study the body and are interested in designing devices to help make our lives better.)

Worksheet: Have students record observations, record results, design their casts and answer questions on their worksheets. Review their worksheets to gauge their understanding of the subject matter.

Engineering Design: Before and during the design and construction portion of the activity, remind students of the engineering design process steps: Define the problem (Ask), brainstorm ideas (Imagine), design (Plan), build and test (Create), and re-design (Improve).

Closing Discussion: As a class, review the activity results and use the following questions to lead a concluding discussion:

• What happened to the chicken bone as more weight was added to the bucket?
• Which casts/splints worked best? Why? What were they made of? Which materials worked best? What construction techniques worked best?
• Based on the testing results from your and other groups, what could you do to improve your design?
• Do you think human bones would be able to support more or less weight? Why? Would you make any changes to your cast/splint for a human bone? How?
• What is a bone fracture? What types of medical devices are used to heal or repair a bone fracture? Would you change your design for fractures on an arm compared to a leg?
• What is biomedical engineering? How are biomedical engineers and the human body related?