Biomedical Engineering: Technology Meets Medicine

Medical Imaging

X-ray: differential absorption by tissues (bone high, soft tissue low), computed tomography (CT) — 3D reconstruction from multiple projections (Hounsfield, Nobel 1979). MRI (Magnetic Resonance Imaging): nuclear magnetic resonance of hydrogen protons in 1.5-7T magnetic field. T1-weighted (anatomy), T2-weighted (pathology), fMRI (BOLD signal for brain activation). Ultrasound: piezoelectric transducers, 2-18 MHz, real-time imaging, Doppler for blood flow. PET (Positron Emission Tomography): ¹⁸F-FDG traces metabolic activity — cancer staging, neurology. SPECT: gamma-emitting radiotracers, myocardial perfusion. Optical imaging: fluorescence (GFP), bioluminescence, photoacoustic imaging. AI in imaging: deep learning for automated diagnosis (>radiologist-level for some conditions).

Prosthetics and Orthotics

Passive prosthetics: body-powered (cable-driven), cosmetic. Myoelectric prosthetics: EMG signals from residual muscles control motors (Ottobock, Össur). Pattern recognition: machine learning classifies muscle signals for intuitive multi-DOF control. Osseointegration: titanium implant directly into bone — eliminates socket, improves control (e-OPRA system). Targeted muscle reinnervation (TMR): redirecting severed nerves to remaining muscles for enhanced control. Sensory feedback: vibrotactile, electrotactile feedback — closing the sensory loop. Bionic legs: powered knee/ankle joints with microprocessor control (C-Leg, Genium). 3D printing: affordable custom prosthetics ($50-500 vs. $5000-50000 traditional). Exoskeletons: ReWalk, Ekso — powered mobility for spinal cord injury patients.

Biomaterials

Biomaterials: materials engineered to interact with biological systems. Classes: metals (Ti, CoCr, stainless steel — orthopedic implants), ceramics (hydroxyapatite, alumina — bone replacement, dental), polymers (UHMWPE, PMMA, silicone), composites. Biocompatibility: material does not elicit adverse immune response, corrosion/wear products are tolerable. Bioactive materials: bond directly to tissue (bioglass, HA). Biodegradable: PLA, PGA, PCL — dissolve over time (sutures, drug delivery, temporary scaffolds). Surface modification: coatings (TiO₂, HA, drug-eluting), nanotopography — control cell adhesion and differentiation. Smart biomaterials: shape-memory alloys (NiTi), pH-responsive hydrogels, self-healing polymers. Drug-eluting stents: sirolimus/paclitaxel coatings prevent restenosis.

Tissue Engineering

Tissue engineering triad: cells + scaffold + signals (growth factors). Scaffold materials: natural (collagen, fibrin, decellularized ECM) and synthetic (PCL, PLA, PEG hydrogels). Fabrication: electrospinning (nanofibers), 3D printing (extrusion, SLA), self-assembling peptides. Bioreactors: provide mechanical stimulation, perfusion, and physiological conditions for tissue maturation. Successes: skin equivalents (Integra, Apligraf — FDA-approved), cartilage (MACI — autologous chondrocytes on collagen membrane). Vascularization: greatest challenge — tissues >200 μm thick need blood supply. Strategies: angiogenic growth factors (VEGF), pre-vascularized scaffolds, 3D-printed vasculature. Organoids: self-organizing 3D structures from stem cells — brain, kidney, intestinal, liver mini-organs for disease modeling and drug testing.

Neural Interfaces

Brain-Computer Interfaces (BCI): decode neural signals for communication and control. Non-invasive: EEG (low spatial resolution, 64-256 electrodes, P300 speller). Invasive: Utah array (microelectrodes in motor cortex, BrainGate — tetraplegic patients type 90 characters/min). Neuralink: 1024-electrode threads, robotic insertion, wireless transmission. Applications: communication for locked-in patients, cursor control, robotic arm control. Cochlear implants: 1M+ users, direct stimulation of auditory nerve — most successful neural prosthetic. Retinal implants: Argus II (60 electrodes), Pixium Prima (378 electrodes). Deep Brain Stimulation (DBS): electrodes in subthalamic nucleus/GPi for Parkinson's, essential tremor, OCD. Closed-loop DBS: responsive neurostimulation (RNS) for epilepsy — detects seizures and stimulates in real-time.

Frequently Asked Questions

What is biomedical engineering?

Biomedical engineering applies engineering principles and design concepts to medicine and biology to develop technologies that improve healthcare, from medical devices to artificial organs.

How does MRI work?

MRI uses strong magnetic fields to align hydrogen protons in the body, then radiofrequency pulses tip them, and the signals emitted during relaxation create detailed images of soft tissues.

What are biomaterials?

Biomaterials are materials engineered to interact with biological systems, including metals for joint replacements, ceramics for dental implants, and biodegradable polymers for temporary scaffolds.

What is a brain-computer interface?

A brain-computer interface decodes neural signals from the brain and translates them into commands for external devices, enabling paralyzed patients to control computers and robotic limbs.

What is tissue engineering?

Tissue engineering combines cells, scaffolds, and biochemical signals to create functional biological substitutes for damaged or diseased tissues and organs.

Try it live

Everything above runs in your browser — open CT Scanner: Filtered Back-Projection Simulator and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.