Students reflect on their experiences making silly putty (the previous hands-on activity in the unit), especially why changing the borax concentration alters the mechanical properties of silly putty and how this pertains to tissue mechanics. Students learn why engineers must understand tissue mechanics in order to design devices that will be implanted or used inside bodies, to study pathologies of tissues and how this alters tissue function, and to design prosthetics. Finally, students learn about collagen, elastin and proteoglycans and their roles in giving body tissues their unique functions. This prepares them for the culminating design-build-test activity of the unit.

Students learn about homeostasis and create models by constructing simple feedback systems using Arduino boards, temperature sensors, LEDs and Arduino code. Starting with pre-written code, students instruct LEDs to activate in response to the sensor detecting a certain temperature range. They determine appropriate temperature ranges and alter the code accordingly. When the temperature range is exceeded, a fan is engaged in order to achieve a cooling effect. In this way, the principle of homeostasis is demonstrated. To conclude, students write summary paragraphs relating their models to biological homeostasis.

Students learn how viruses invade host cells and hijack the hosts' cell-reproduction mechanisms in order to make new viruses, which can in turn attack additional host cells. Students also learn how the immune system responds to a viral invasion, eventually defeating the viruses -- if all goes well. Finally, they consider the special case of HIV, in which the virus' host cell is a key component of the immune system itself, severely crippling it and ultimately leading to AIDS. The associated activity, Tracking a Virus, sets the stage for this lesson with a dramatic simulation that allows students to see for themselves how quickly a virus can spread through a population, and then challenges students to determine who the initial bearers of the virus were.

After students have complete the associated activity to collect and graph acceleration data from walking human subjects, they learn more about gait analysis---the study of human motion, which is used as biometric data for human medical diagnostics and (non-human) comparative biomechanics. They learn about the steps that comprise the universal process of engineering analysis—data collection, data analysis, mathematical modeling and reporting—and consider how these steps could be applied to analyze a person's gait, which prepares them to conduct the second associated activity.

Students discuss several human reproductive technologies available today pregnancy ultrasound, amniocentesis, in-vitro fertilization and labor anesthetics. They learn how each technology works, and that these are ways engineers have worked to improve the health of expecting mothers and babies.

Students are presented with the unit's grand challenge problem: You are the lead engineer for a biomaterials company that has a cardiovascular systems client who wants you to develop a model that can be used to test the properties of heart valves without using real specimens. How might you go about accomplishing this task? What information do you need to create an accurate model? How could your materials be tested? Students brainstorm as a class, then learn some basic information relevant to the problem (by reading the transcript of an interview with a biomedical engineer), and then learn more specific information on how heart tissues work their structure and composition (lecture information presented by the teacher). This prepares them for the associated activity, during which students cement their understanding of the heart and its function by dissecting sheep hearts to explore heart anatomy.

Students learn about electric motors and rotational sensors. They learn that motors convert electrical energy to mechanical energy and typically include rotational sensors to enable distance measuring. They also learn the basics about gear trains and gear ratios. Students create a basic program using the LEGO MINDSTORMS(TM) NXT interface to control a motor to move a small robot. Then, through a 10-minute mini-activity, they make measurements and observations to test a LEGO rotation sensor's ability to measure distance in rotations. This prepares them for the associated activity during which they calculate how many wheel rotations are needed to travel a distance. A PowerPoint® presentation, worksheet and pre/post quizzes are provided.

Students gain a rigorous background in the primary human "sensors," as preparation for comparing them to some electronic equivalents in the associated activity. A review of human vision, hearing, smell, taste and touch, including the anatomies and operational principles, is delivered through a PowerPoint® presentation. Students learn the concept of "stimulus-sensor-coordinator-effector-response" to describe the human and electronic sensory processes. Student pairs use blindfolds, paper towels and small candies in a taste/smell sensory exercise. They take pre/post quizzes and watch two short online videos. Concepts are further strengthened by conducting the associated activity the following day, during which they learn about electronic touch, light, sound and ultrasonic sensors and then "see" sound waves while using microphones connected to computers running (free) Audacity® software.

Students use DNA profiling to determine who robbed a bank. After they learn how the FBI's Combined DNA Index System (CODIS) is used to match crime scene DNA with tissue sample DNA, students use CODIS principles and sample DNA fragments to determine which of three suspects matches evidence obtain at a crime location. They communicate their results as if they were biomedical engineers reporting to a police crime scene investigation.

Student teams learn about and devise technical presentations on four reproductive technology topics pregnancy ultrasound, amniocentesis, in-vitro fertilization or labor anesthetics. Each team acts as a panel of engineers asked to make a presentation to a group of students unfamiliar with the reproductive technology. Each group incorporates non-lecture elements into its presentation for greater effectiveness. As students learn about the technologies, by creating a presentation and listening to other groups' presentations, they also learn more about the valuable skill of technical communications.

Students experience the engineering design process as they design and construct lower-leg prostheses in response to a hypothetical zombie apocalypse scenario. Like the well-known Apollo 13 story during which engineers were challenged to fix the crippled spacecraft with limited supplies in order to save astronauts' lives, in this activity, students act as engineers during an imaginary disaster in which a group member's leg was amputated in order to survive a zombie attack. Building on what they learned and researched in the associated lesson, they design and fabricate a replacement prosthetic limb using given specific starting material and limited additional supplies, similar to how engineers design for individuals while working within constraints. A more-advanced scenario challenges students to design a prosthesis that is able to provide a more-specific movement function.