The quantitative survey metrics assessed over the course of the class all increased from the mid- to end-course time points, indicating an overall positive trend in the students’ course experience (Fig. 3, Additional file 3: Table S3).

When assessed during the mid-course time point, 100 % of students in the class confirmed that the course was being taught at an appropriate level. Additionally, 100 % of students in the class noted that they did not need the biology explained more explicitly in the context of the material being taught. These percentages did not change when assessed again at the end of the course, indicating they already had a strong grounding in the fundamentals of the biological concepts used in the class, and that the instructors thoroughly explained new terminology. Students stated that “Everything we didn’t know was explained very well” and that, more than learning new terminology, they valued learning “about new applications of the knowledge most of us had already been taught which introduced new viewpoints.” Considering 83 % of student indicated that the final project was the aspect of the course they were most looking forward to, it is not surprising that the metric assessing introduction to new topics and concepts showed a demonstrable increase over the semester between the mid- and end-course surveys. Some students indicated that learning new skills that are not a part of standard bioengineering curriculum, such as CAD design and 3D printing, was an important motivator driving enthusiasm regarding the final project. Students also cited the ability to “use some creativity with our designs” as a source of excitement, indicating that the open-ended and ill-structured nature of the final design problem was a source of motivation for the students.

The metric that showed the most significant increase between the mid- and end-course time points concerned assessing whether the format of the course was appropriately suited to the material being taught. Responses to specific questions regarding the format of the class, listed in Table 4, are presented in Fig. 4 and Additional file 4: Table S4. The results indicate that the students were already quite familiar with the main theoretical concepts underlying the field of tissue engineering. Since tissue engineering is a well-developed sub-field of the broader discipline of biomedical engineering, it is unsurprising that a group of senior undergraduates pursuing bioengineering majors would report familiarity with the field. However, student responses also show that the labs helped strengthen understanding of tissue engineering concepts by teaching practical lab techniques applicable to this field. Students stated that core concepts are “much easier to understand when the class is structure more hands on, where we can discuss the concepts and then actually implement them ourselves.” Furthermore, 100 % of the students indicated that the labs leading up to the final project helped them understand the goals of the capstone and main course objectives better, stating “I’m enjoying how each experiment we do on a weekly basis is building up to ultimately building a bio-bot”. The first four labs thus served as practice in versatile experimental techniques, and the cumulative nature of the final project proved to be a fair assessment of the training they received.

During the mid-course survey, the students reported lowest satisfaction with the process of writing lab reports as a method of developing a deeper understanding of course material. Students expressed specifically that they would “like more help with the data analysis”. An important objective of this class, in addition to teaching the design principles of biofabrication, was to establish a solid foundation in practicing the experimental method, as students specifically expressed a desire to “have a much stronger ability to design experiments for cell-culture applications in the future” and expected to “learn both lab techniques as well as the best way to plan out experiments and all the variables necessary to take into account”. To address these concerns, the course format was altered to include 20 min of lab discussion time the week before the due date for each lab report. Student teams presented their results to all the instructors, as well as the other teams, and were given the opportunity to discuss their results prior to writing the lab report. Portions of the lab sessions were also allotted to instructor-led data analysis on practice data sets, followed by guided team-based analysis of data generated during the labs. This led to an increase in the level of satisfaction students reported with the lab reports by the end of course survey, with students specifically stating that the in-class presentations “helped clear up any misunderstandings and forced me to think about why we were doing what we did in lab” and were valuable because of their “informal, discussion-based format”. By the end of the semester, 50 % of the students indicated that the lab reports and in-class presentations were the most useful aspects of the course (the other 50 % cited lab work), and 40 % of students cited lab reports as the aspect of the course that helped them learn most efficiently (the other 60 % cited lab work).

The capstone project was intentionally designed to be open-ended, requiring that students form a hypothesis and devise a robust experiment to test that hypothesis using the techniques taught in previous labs. Specifically, students were asked to design and build a biological machine to achieve a functional behavior relevant to an application in biomedical engineering. The student teams, which were self-assigned, reported no conflicts over the course of the semester. Indeed, two of the teams coalesced to form a larger team for the capstone project, in order to test more sample sets and generate more data. Some students attempted to make the walking bio-bots developed in Lab 4 walk at greater speeds by incorporating flexible 3D printed hinges into the bio-bot skeletons. Other students designed an entirely new 3D printed skeleton, mimicking the natural architecture of the esophagus in the human body, to create a muscle-powered peristaltic pump that could potentially be used as an implant for applications in regenerative medicine. Another group of students incorporated skills taught in other bioengineering undergraduate classes, such as genetic engineering of cells and bioinstrumentation, to incorporate new functionalities into the biological machines they had learned to fabricate. The student projects thus displayed broad diversity in terms of target application, while still maintaining a core focus in biofabrication. This served as additional validation that the capstone design project provided students with the unique opportunity to freely pursue empirical inquiry in the field of biomedical engineering and understand the underlying design rules and principles of “building with biology”.

Students were actively engaged in the final project throughout the semester, and presented their ideas for the capstone to instructors prior to the scheduled start of the final lab. The layered roles of the primary instructor with expertise in teaching fundamental biological concepts, the guest lecturer specializing in the topic area of biofabrication and biological machines, and the teaching assistant well versed in the experimental techniques, provided students with different types and levels of individual mentorship and attention, which has been shown to generate positive learning outcomes [3].

By the end of the semester, 100 % of the students in the class indicated that the course fulfilled their expectations, that they enjoyed the course experience, and that they would recommend the course to other students. Additionally, all the student presented their capstone design projects to professors and graduate students in the department working in relevant research fields, and 50 % of the students in the class signed up to continue working on their final projects the following semester under the guidance of the guest lecturer and course instructor. As ethics training is an especially important component of biomedical engineering education [19, 20], all students were required to participate in a discussion on the ethics of building with biology during one of the regularly scheduled class lectures. During this discussion, students discussed vignettes of specific scenarios involving novel biofabrication technology with other students and the instructors [21]. In future iterations of this class, we would like to formally assess how student perceptions and understanding of the ethics of building biological machines shift over the course of the class, in order to improve the quality and focus of our undergraduate bioengineering ethics education programming.