A tissue engineering team successfully grows a 2cm-thick liver construct in a bioreactor using hepatocytes seeded on a PLGA scaffold. Within 48 hours, cells in the centre of the construct begin to die while peripheral cells survive. What engineering problem is responsible for this failure?

The PLGA scaffold degraded too quickly, releasing cytotoxic monomers Lack of vascularisation — cells deeper than ~200 μm from a blood supply cannot receive sufficient oxygen and nutrients by diffusion alone The bioreactor temperature was 0.5°C above optimal, denaturing enzymes Hepatocytes are naturally programmed to die after 48 hours in culture

A researcher wants to create a scaffold for bone tissue engineering that promotes osteoblast attachment and mineralisation. Which biomaterial combination best matches the mechanical and biological requirements of bone?

Collagen hydrogel alone — because bone is primarily made of collagen PDMS (silicone elastomer) — because it is flexible and biocompatible Hydroxyapatite composite — it mimics the mineral phase of natural bone and provides binding sites for osteoblasts PLGA alone — because it degrades faster than hydroxyapatite

A pharmaceutical company uses a lung-on-a-chip device to test a candidate asthma drug instead of animal models. The device contains human airway epithelial cells and pulmonary endothelial cells in adjacent microchannels with rhythmic mechanical stretch simulating breathing. Why might this device predict human drug response more accurately than a mouse model?

Mouse models are unethical, so any alternative is automatically more valid It uses human cells in a biomechanical environment that mimics human lung physiology, whereas mouse lungs differ in anatomy, cell biology, and immune response The microfluidic chip tests 1,000 compounds simultaneously, increasing statistical power Chips use artificial intelligence to predict outcomes without biological cells

A person with Type 1 diabetes wears a continuous glucose monitor (CGM) that reads interstitial glucose every 5 minutes and transmits the value to a smartphone app. The data is integrated with an insulin pump that automatically adjusts insulin delivery. What does this closed-loop system represent in engineering control terms?

An open-loop system — the pump delivers insulin at fixed intervals without sensing glucose A feedforward system — insulin is delivered based on predicted meal carbohydrate content alone A feedback control system — the sensor measures the controlled variable (glucose) and the controller (algorithm) adjusts the actuator (pump) to maintain it within a target range A proportional control system only — it adjusts insulin proportionally to current glucose with no integral or derivative term

A nanoparticle drug delivery system is designed to treat pancreatic cancer. The nanoparticles are coated with antibodies targeting a receptor overexpressed on pancreatic cancer cells. The drug is encapsulated inside and released when the nanoparticle encounters the low pH of the tumour microenvironment. What problem with conventional chemotherapy does this system aim to solve?

Conventional chemotherapy cannot enter cancer cells; nanoparticles penetrate cell membranes Conventional chemotherapy is too expensive; nanoparticles reduce manufacturing cost Conventional chemotherapy distributes systemically and damages healthy dividing cells (causing hair loss, nausea, immune suppression); targeted nanoparticles aim to concentrate drug at the tumour and reduce systemic toxicity Conventional drugs degrade too quickly in the blood; nanoparticles prevent any degradation

A patient with ALS (amyotrophic lateral sclerosis) has completely lost the ability to speak and move but retains intact cognition. A BCI research team implants a 96-electrode array into the patient's motor cortex. The patient imagines moving their hand, and the BCI decodes intended letters to produce speech output. What is the most significant long-term engineering challenge limiting this system?

The patient's motor cortex stops generating signals once paralysis is complete Current computers are not fast enough to decode neural signals in real time Long-term biocompatibility and signal stability — the brain's immune response gradually encapsulates electrodes in scar tissue, degrading signal quality over months to years The implant cannot be approved by regulators because all brain surgery is prohibited

A start-up proposes implanting a BCI that gives healthy individuals the ability to control a drone with their thoughts and receive sensor data from the drone as a new perceptual stream. An ethicist argues this crosses an important line from therapy into enhancement. What is the core distinction the ethicist is drawing?

Therapy requires a prescription; enhancement requires only a consumer purchase Therapy restores or replaces a lost or absent function; enhancement adds capabilities that exceed the normal human baseline in a healthy person Therapy uses approved devices; enhancement uses unapproved devices The distinction is not real — all medical interventions are enhancements of some kind

A clinical-grade 3D bioprinter deposits alternating layers of human chondrocytes embedded in alginate hydrogel to create a cartilage patch for a knee repair procedure. The printed construct is then cultured for three weeks before implantation. Why is the post-printing culture period necessary?

The culture period allows the alginate to fully polymerise using UV light The printer ink contains antibiotics that must degrade before implantation Cells need time to proliferate, deposit extracellular matrix, and develop mechanical properties approaching native cartilage before the construct can withstand joint loading The culture period is required by FDA regulations regardless of the construct's state

A low-income country wants to use lab-on-a-chip technology to diagnose sepsis in rural clinics without laboratory infrastructure. The device must identify bacteria and measure inflammatory markers from a finger-prick blood sample in under 30 minutes and cost less than $2 per test. Which microfluidic design principle makes this cost target achievable?

Microfluidic channels are cheap because they only require silicon wafers Integrating sample preparation, reaction, and detection on a single disposable chip eliminates the need for expensive benchtop instruments and trained laboratory staff The low cost comes from replacing antibodies with cheaper dye molecules Government subsidies in low-income countries cover the remaining cost difference

A biomedical start-up develops a novel implantable biosensor for real-time intracranial pressure monitoring. There is no predicate device on the market, and the condition it targets (refractory intracranial hypertension) is life-threatening. Which FDA pathway is most appropriate, and why?

510(k) — because all implantable sensors have predicate devices PMA only — because any implanted device automatically requires PMA regardless of risk Breakthrough Device Designation followed by De Novo request — Breakthrough accelerates review for life-threatening conditions; De Novo establishes a new device type when no predicate exists No FDA review is needed for diagnostic devices that do not deliver therapy

A state-of-the-art myoelectric prosthetic hand with individual finger control costs $90,000. A 3D-printed body-powered hand costs $50. For a child amputee in a low-income country, the expensive device would provide dramatically superior function. An engineer argues the field must prioritise designing the $90,000 hand's capabilities into a $500 device. What ethical principle is driving this argument?

Beneficence — the engineer wants to benefit the maximum number of patients Non-maleficence — the expensive device could harm the child if it fails Equity — the obligation to design technologies that are accessible to patients across the full global economic spectrum, not only those who can afford premium devices Autonomy — the child's right to choose any prosthetic regardless of cost

A university research team wants to conduct a first-in-human trial of a novel biodegradable neural electrode in patients with treatment-resistant epilepsy. Before any participant can be enrolled, the team must obtain approval from an Institutional Review Board (IRB). What is the IRB's primary function in this context?

To review the patent application for the neural electrode before publication To independently review the protocol and ensure that risks to participants are minimised, proportionate to potential benefits, and that informed consent is adequate To approve the device for commercial sale once the trial is complete To fund the research in exchange for a share of future commercial revenues