BME 161: Introduction to User-Centered Biomedical Design
Estimated study time: 8 minutes
Table of contents
Sources and References
Primary texts — Ulrich, Eppinger, and Yang, Product Design and Development, 7th ed. (McGraw-Hill). Dieter and Schmidt, Engineering Design, 5th ed. (McGraw-Hill).
Supplementary texts — Norman, The Design of Everyday Things, revised ed. (Basic Books). Wickens, Hollands, Banbury, and Parasuraman, Engineering Psychology and Human Performance, 4th ed. (Routledge). Yock et al., Biodesign: The Process of Innovating Medical Technologies, 2nd ed. (Cambridge).
Online resources — Stanford d.school Design Thinking Bootleg. NASA Human Integration Design Handbook (NASA/SP-2010-3407). FDA Applying Human Factors and Usability Engineering to Medical Devices (guidance). IEC 62366-1 Medical devices — application of usability engineering. MIT OCW 2.744 Product Design.
Chapter 1: The Engineering Design Process
1.1 What Design Is
Engineering design is the systematic, intelligent generation and evaluation of specifications for artifacts whose form and function achieve stated objectives while satisfying constraints. In biomedical contexts the objectives are framed around the user — patient, clinician, caregiver — and the constraints include safety, regulation, and the physical limits of the human body. The process iterates among understanding, ideating, prototyping, and testing, with the problem itself reframed as understanding deepens.
1.2 A Canonical Process Model
A useful five-phase breakdown: (1) needs identification and problem definition, (2) concept generation, (3) concept selection and specification, (4) embodiment and detailed design, (5) verification, validation, and transfer. Milestones punctuate phase transitions with design reviews that examine completeness, feasibility, and risk.
Chapter 2: Needs Assessment and Problem Framing
2.1 Stakeholders and Context
A medical device does not exist in isolation: it is deployed into a workflow involving clinicians, patients, technicians, procurement, IT, and reimbursement. Stakeholder mapping — primary, secondary, tertiary users and the institutions that surround them — exposes conflicting needs that the design must reconcile.
2.2 Observation, Interview, Ethnography
Needs are rarely what users first articulate. Contextual inquiry combines observation in the real environment with brief clarifying interviews, producing rich, grounded data. Ethnographic techniques attend to artifacts (what is scribbled on tape over buttons), workarounds (how people defeat safety interlocks), and emotional cues. Structured methods include the “5 whys”, laddering, and critical-incident interviews.
2.3 From Need Statements to Specifications
Well-formed needs statements are neutral about solution — “the device must support continuous monitoring during transport” rather than “add wireless Bluetooth”. Quality Function Deployment (QFD) translates weighted needs into engineering specifications via the House of Quality, revealing conflicts and correlations. Each specification should be testable, with a metric, units, and an acceptance value.
Chapter 3: Concept Generation and Selection
3.1 Structured Ideation
Function decomposition maps overall function (e.g., “deliver insulin”) into subfunctions (store, meter, infuse, sense, alarm). Morphological charts list candidate means for each subfunction; combinations yield concept variants. Divergent techniques — brainstorming, SCAMPER, TRIZ principles — expand the search; convergent techniques narrow it.
3.2 Decision Matrices
Pugh concept selection scores alternatives relative to a datum on weighted criteria, \( +1/0/-1 \). Weighted decision matrices provide quantitative ranking:
\[ S_k = \sum_i w_i s_{ik} , \]with weights \( w_i \) from the stakeholder-driven criteria hierarchy. Sensitivity to weight uncertainty should be tested before selection is locked.
3.3 Function Analysis
Value engineering asks, for each function, what it costs and what it contributes. The ratio value = function/cost guides design to eliminate superfluous features and reinforce essential ones. In biomedical devices, regulatory cost is often dominated by function-related risk, making deliberate function pruning a cost-control strategy.
Chapter 4: Human Factors and Ergonomics
4.1 Physical Ergonomics
Anthropometric design uses percentile-based body dimensions (e.g., 5th female to 95th male) to size handles, reaches, clearances, and display heights. Static strength, grip, pinch, and range of motion constrain actuator forces and control layouts. Fitts’ law quantifies pointing time as
\[ T = a + b \log_2\!\left(\frac{D}{W} + 1\right) , \]with distance \( D \) and target width \( W \), guiding button size and spacing.
4.2 Cognitive Ergonomics
Working memory, attention, and decision-making under time pressure shape display design. Gestalt grouping, preattentive features (colour, size, orientation), and information hierarchy drive visual attention. Alarm philosophy (IEC 60601-1-8) requires distinguishable priority, minimized false positives, and clear recovery paths — alarm fatigue is a leading source of clinical harm.
4.3 User Capabilities and Accessibility
Designs must accommodate users with impaired vision, hearing, dexterity, or cognition. Inclusive design principles (CEN/CENELEC Guide 6) turn these constraints into features that benefit all users. Pediatric and geriatric populations require particular anthropometric and cognitive attention.
Chapter 5: Prototyping, Testing, and Documentation
5.1 Prototype Fidelity
Prototypes answer specific questions. Low-fidelity sketches and foam-core models explore form and reach; mid-fidelity 3D prints and breadboards explore fit and function; high-fidelity engineering prototypes approach the final design and support formative usability testing. Fidelity should match the question asked.
5.2 Usability Testing
IEC 62366-1 separates formative evaluation (iterative, shapes the design) from summative validation (proves residual risk is acceptable). Representative users perform representative tasks in representative use environments. Data include time on task, error rates, observed use errors, near-misses, and verbal protocols. Use errors are not user errors: the design owns them.
5.3 Design Documentation
The Design History File (DHF) records inputs, outputs, reviews, verification, validation, and changes. The Device Master Record (DMR) specifies how the device is built; the Device History Record (DHR) records how each unit was built. Configuration control and traceability are not bureaucratic — they are the auditable evidence that the device you shipped is the device you designed.
Chapter 6: Professionalism, Ethics, and Project Management
6.1 Professional Engineering Practice
In Canada, engineering practice is regulated provincially; the iron ring, the Code of Ethics of PEO, and the duty to hold paramount the safety, health, and welfare of the public define the practitioner’s obligations. Biomedical devices add Health Canada and FDA oversight and an obligation to consider vulnerable patient populations.
6.2 Research and Testing Ethics
Human-subject testing requires Research Ethics Board approval under TCPS 2 (Canada) or IRB approval under the Common Rule (U.S.). Informed consent, privacy, and data protection are baseline; proportionality of risk to benefit and fair subject selection are essential. Animal testing follows the Canadian Council on Animal Care principles of Replacement, Reduction, and Refinement.
6.3 Project Management
Work-breakdown structures decompose deliverables; Gantt charts sequence them; critical-path analysis identifies activities that determine project duration. Earned value metrics — CPI and SPI — flag schedule and cost drift. Risk registers tracked through the project tie probability and severity to mitigations, echoing the medical-device risk file required by ISO 14971.
