H's Qs

Question 1

Describe three examples of biomimetics to solve engineering problems in the real-world

Answer 1

• Ornilux glass - Derived from looking at spider webs which reflex UV light. Used to stop birds from flying into windows.
• Bullet train - Design inspired by Kingfisher beak which is designed to minimise fluid disturbance on entry to water. Used to stop pressure disturbance for trains in tunnels.
• NASA antenna - Design was calculated using a genetic algorithm.

Question 2

Other examples of biomimetics

Answer 2

Velcro, Spider silk, Dragonfly antibiotic micro-needles, Paris Expo Radiolarians

Question 3

Outline the major constrains of biological evolution.

Answer 3

• Trial and error process (i.e. slow, random mutations)
• No foresight of future changes
• Limited to local resources
• Lock-in to systems with potentially inferior design
• Innovations do not easily transfer across lineages.

Question 4

What are the major limitations and benefits of bio-inspired sensorimotor control design?

Answer 4

Benefits - No limit to energy, optimal design exists as a mathematical function, robust design.

Limitations - Lack of autonomy, adaptive design.

Question 5

Describe the analogy between immunology and computer security frameworks.

Answer 5

• In immunology - antibodies locate and bind to foreign pathogens rendering them inert. In addition to this, there is detection of self, with self-proteins binding to immature T cells in the thymus. If there is a response, these cells are destroyed.
• Computer security frameworks can incorporate aspects of digital ‘self’ detection (though databases of normal patterns of sequences of system calls executed by the operating system) to ensure that user files are not damaged.
• Any new sequences the system calls are scanned for unfamiliar sequences not in the database. A mismatch indicates a possible intrusion by a virus. This enables accurate detection of viruses.

Question 6

Give three examples of implanatable technology for medical devices

Answer 6

• Deep-brain stimulation for Parkinson’s patients, cochlear implants, cardiac pacemaker
• Databases of genetic info used by industrial processes for drug manufacture.
• Messing with AI.

Question 7

Explain the rationale behind the biomimetic use of Horse-Shoe crabs for antibiotics.

Answer 7

• Blood of horse-shoe crabs i) clots when bacteria is detected and ii) is high in AMPs (anti-microbial peptides).
• These AMPs are highly amphipathic (i.e. have positive and negatively charged residues) and have an affinity for strong negative charges.
• Bacterial cytoplasmic membranes’ phospholipids (acidic) are highly negatively charged, thus attract AMPs.
• Once bound, they self-assemble and form pores in the membrane leading to cell death.
• It is hard for bacteria to develop resistance due to lock-in.
• Eukaryotic cells are not affected due to being weakly charged (neutral/zwitterionic), ergo AMPs do not bind.

Question 8

What are the 3 pillars of molecular biomimetics?

Answer 8

• Molecular recognition - allows sensitivity, essential for functionality.
• Self-Assembly - cannot build molecules bit by bit so have to self-assemble
• Genetic manipulation - allows to manipulate the other two pillars.

Question 9

Outline the functions of ion pores in nature, and applications of ion pores in biotechnology

Answer 9

• In nature - Signalling, Complement system, Bacteria use it for competing with other pathogens
• In biotechnology - Lipid-coated nanowire transistors, Characterisation of DNA, Targeted cell death, light activatable neurons.

Question 10

Various biomimetic approaches are being used to develop new wet/dry bio-adhesives. Explain one in detail

Answer 10

• Mussels - Produce a wet adhesive which is charged. Main component of the adhesive is polymers containing DOPA residues with lots of OH groups. DOPA is bio-compatible, which enables use as a biological glue for surgery, as it also promotes wound healing. The mussel-inspired adhesive can also be structured into chains to resist penetration for use in knee cartilage.
• Geckos have strong binding to surfaces but only under dry conditions
• Combine: gecko-mimetic pillar arrays coated with mussel-mimetic polymer film can have good wet/dry reversible adhesives. Useful to glue wounds and amniotic sac repair.

Question 11

Describe how Stomatopods dactyl are able to withstand high levels of damage

Answer 11

• The mantis shrimp uses its dactyl (club) to stun its prey by hitting it very hard.
• Dactyl undergo high levels of acceleration (10,000g) thus need to be strong.
• This is achieved through high levels of crystallisation, and orientation of crystals.
• The helical pattern dissipates the energy efficiently to other directions, withstanding deformation and preventing crack propagation.
• Useful for floor of military vehicles to protect soldiers from explosions underneath. Or applications with intense repetitive loading.

Question 12

1. Outline the organisation of the auditory system in the ear, and central auditory system

Answer 12

• Outer ear - Ear structure designed to focus sounds down the ear canal and into the middle ear
• Middle ear - Amplification of sounds by ossicles (malleus, incus, stapes) and transmits sounds from ear drum to oval window (large to smaller area).
• Inner ear - Converting sounds to neuronal signals.
• Central auditory system - Cochlea-vestibular nerve takes signals to sup. olivary complex, then up to inferior colliculus and medial geniculate body.

Question 13

Describe how the middle ear is adapted to amplify sounds.

Answer 13

• Ossicles act as a level to amplify sounds which come in. Large surface area at start, which ends up as a small surface area, thereby concentrating sounds, enabling amplification.

Question 14

Explain how the cochlea functions to convert auditory signals into neuronal activation to detect a broad range of sounds.

Answer 14

• Local resonant frequencies exist in the cochlea: W0(r) = sqrt[K(r)/m(r)]
• Signals will peak here and travel no further due to critical-layer absorption.
• Stiffness changes across the length of the basilar membrane giving a range of detection.
• Auditory nerve fibres are connected along the length of the basilar membrane and each have a specific frequency they are adapted for (have the lowest threshold dB for this frequency).
• Low frequency sounds travel further along the basilar membrane, and require a higher dB to reach the threshold even with their adapted auditory nerves.

Question 15

Describe what is meant by mechano-electrical transduction, and how it is achieved in the inner ear.

Answer 15

• MET is where mechanical sounds are converted to electrical signals.
• Hair cells in the Organ of Corti (sits on basilar membrane) move due to movement of the basilar membrane, leading to influx of sodium ions.
• Calcium ions are released which bind to vesicles, causing neurotransmitter release and action potential propagation.

Question 16

Explain what is meant by the active process in the ear, including uses and consequences.

What signals are amplified the most?

Answer 16

• The active process is where the ear actively uses energy to amplify sounds. The smaller the input intensity the larger the amplification. Lower frequencies also get larger amplification.
• This occurs through 2 mechanisms
  o Spontaneous contractions –> otoacoustic emissions
  o Outer hair cells can change length, shrink and expand in response to membrane potential. (Prestin has different conformations based on membrane potential - Shrinking/expansion). When the outer hair cells change length they can pull the basilar and tectorial membranes closer together. This is mechanical amplification from the active process.
• Non-linear amplification because it only amplifies the propagating wave where the wave peaks.

Question 17

What are the characteristics of the active process?

Answer 17

• Weak signals are amplified more than loud sounds (compressive non-linearity).
• Loss of active process renders a person hard of hearing.
• Otoacoustic emissions are released as a result of the active process.
• The active process is achieved through molecular processes in hair cells.

Question 18

Outline, in brief, what is meant by phase locking and why it is important.

Answer 18

• Phase locking is where action potentials in the auditory nerve are fired in phase with the peaks of a sound signal.
• Different neurons fire at subharmonic frequencies of the sound all in different phases. When combined these give the total sound.
• It important for temporal resolution and therefore pitch perception, frequency discrimination, and differentiating between speakers.

Question 19

Outline the rationale behind cochlear implants, and how they work.

Answer 19

• Cochlear implants are used for patients with sensorineural hearing loss (absence/dysfunction of hair cells), with the implant being used to detect sound and convert to an electrical signal.
• A microphone and signal transmitter is worn on the outside of the head and transmits to a receiver under the skin which has electrodes to stimulate the auditory nerve. They stimulate sections of the cochlear to simulate the natural detection of sounds.
• Different channels are different lengths along the cochlear.
• More channels means a greater sound resolution (quality) allowing for a greater range of sounds
• With only a few channels it is possible to understand human speech but cannot enjoy music.

Question 20

Describe how ears perceive pitch of speech, and why cochlear implants struggle with this process.

Answer 20

• Action potentials in the auditory nerve phase lock to the fundamental frequency and higher harmonics of normal voiced speech. The ability to phase lock allows ears to determine the pitch of speech.
• This is a problem for cochlear implants which cannot accurately phase lock, thereby making it difficult to distinguish speech when more than 1 speaker is present, and making it difficult to perceive music.

Question 21

Detail the three main ways in which sounds can be localised with two ears, giving examples of animals using each one.

Answer 21

• Method 1 - Low frequency sounds can be detected using ITD’s (inter-aural time differences) which measures time difference between ears. This is used to generate a topographical map. . In each half of brainstem there’s an array of coincidence detectors sharply tuned to ITDs. The Jeffress model explains how this works using coincidence detectors in the medial superior olive. This strategy is seen in owls.
• Method 2 - High frequencies can be detected using ILDs (inter-aural level differences), where the amplitude of sounds if measured, and converges on the same detectors as ITDs. This generates a distributed neuronal representation of the sound. Pressure receptors are broadly tuned to ITDs here to allow for better estimation. This strategy is seen in mammals. Large head reduces the intensity of sound in its acoustic shadow.
• Method 3 - Small organisms cannot create a large acoustic shadow (e.g. frogs) have open eustachian tubes which allow for sounds to move across ears internally i.e. ears are coupled through mouth cavity. Therefore, sound coming through each ear stimulates both ears and interacts constructively or destructively in the mouth. This enables IPD (inter-aural pressure detection) at low freqeuncies. This also enhances ITDs and ILDs.

Question 22

Explain how the Jeffress model enables sound localisation

Answer 22

• The Coincidence model of detection is where an incoming sound hits once side of the medial superior olive as the sound comes from the other side.
• In each half of brainstem you have an array of coincidence detectors each sharply tuned to a specific ITD. Neurons can work as coincidence detectors as action potentials travel at a certain speed and can therefore introduce delays by making axons longer. Each coincidence detector has a different length delay line from each ear, therefore corresponding to a specific ITD. These detectors all sit in medial superior olive and are good for detecting low frequency sound. This is the system in birds but no evidence of delay lines has been found in mammals.
• Mammals use coincidence detectors in each half of brainstem that are broadly tuned to ITDs. Then compare activity between the two hemispheres. The neurons are broadly tuned to operate at the slope of the tuning curve rather than the peak.

Question 23

Describe the way in which very small organisms such as Ormia ochracea localise sound.

Answer 23

• For very small organisms, the distance between ears is very small (1.5mm in Ormia). To enable localisation, receptors only fire once when sounds are detected, and ITDs are used based on this.
• Differences are in the range of microseconds. In addition to this, the ear has two modes of action -rocking mode, and bending mode. Rocking mode enables sound localisation.

Question 24

Outline the main steps in echolocation.

Answer 24

• Sound is sent out.
• Time delay and the doppler effect indicates distance and relative speed of prey.
• Amplitude of reflection and distance indicates size of prey.
• ILDs and ITDs indicate horizontal direction. Pinna of ear (bats) gives vertical localisation.

Question 25

A shark sees a fish nearby, describe the mechanism by which it localises the fish to an exact position without use of the visual system.

Answer 25

• Sharks have the ability to passively electro-locate (only over short distances).
• Electrical field signals reach the shark and enter the gel chamber which directs signals to the Ampullae of Lorenzini (in their snout), specialised electrical field detectors with a single cell layer of detectors.
• Once here, the signal triggers ion channel opening which causes calcium ion influx, leading to neurotransmitter release.
• A sensing cell reacts when an external electric field produces a small electric potential across its membrane. The firing rate of the nerve indicates the strength and polarity of the external field.
• It is thought that the field’s location relative to the shark is determined by the positions of activated pores on the shark’s body. Metal will enhance the local electric filed whereas plastic will decrease it. Therefore polarity can tell you what the object is made of. This is only a short range sense as electric fields have steep spatial decay.

Question 26

Fish such as Gnathonemus petersii produce electric fields to detect objects. Describe how they are able to localise objects.

Answer 26

• These fish are weakly electric, with their electrical signals decaying significantly over short distances.
• They are able to detect electro-conductive substances which triggers excitation, and non-electroconductive substances which causes inhibition.
• In addition to this, there is modulation of firing rate, and amplitude when attempting to localise a stimulus.

Question 27

Define stochastic resonance, and explain how it assists the Paddlefish to locate prey.

Answer 27

• Stochastic resonance is the phenomenon by which periodic signals that are too weak to be detected normally can be detected through addition of noise to samples i.e. signal + noise reaches threshold.
• The paddlefish’s electroreception was shown to benefit from stochastic resonance when electrical noise was added to its feeding ground, where their prey, Daphnia, emit regular electrical signals from muscle movement.
• Optimal noise levels improved hunting capability significantly (detect weak signals).

Question 28

Explain how butterflies are generate colour without pigmentation.

Answer 28

• In oil films, light can be reflected by the top and bottom surfaces of the film
• Butterflies use structural colour using the chitin in their wings.
• Colour is generated through constructive (reflections in phase)/destructive (not in phase) interference patterns.
• Chitin has different thickness which generates different wavelengths –> different colours. Thicker chitin produces red, whereas thin chitin generates blue.
• The angle of orientation towards a light source also determine which colour is seen.

Question 29

What are the three main mechanisms for structural colour-production in insects

Answer 29

• Layers - Layering of structures generates constructive/destructive interference patterns.
• Gratings - Diffraction can produce more colours as white light comes in, and other colours emerge.
• Photonic crystals - Periodically spaced crystals with a band-gap region (prohibited frequencies) ensures that certain colours propagate through, and others are stopped.

Question 30

A cuttlefish is seen by a predator and engages its’ camouflage system. Describe how a cuttlefish is able to effectively camouflage itself from predators.

Answer 30

• The cuttlefish has both structural colours and pigmentation to produce camouflage.
• There are 3 distinct structure types - from top to bottom - Chromophores, Iridiophores, Leucophores. Chromophores are balls of coloured pigments which have muscles attached to enable responsive colour (disc). Iridophores change thickness to reflect different colours - enable blue/red shift, and Leucophores provide reflect white light diffusely.

Question 31

Give five examples of biomimetics applications of lessons learnt from cuttlefish.

Answer 31

• Advanced counterfeiting measures
• Efficient solar panel light collection – butterfly wing focuses light onto body
• Adaptive camouflage systems (artificial chromophores)
• Bright energy-efficient displays
• Morphotex dresses

Question 32

Describe the concepts of selectivity and invariance in neurons.

Answer 32

• Selectivity - weak inputs sum together to generate an output (AND function). This occurs in simple cells in the visual cortex.
• Invariance - large single input is enough to trigger a response (OR function). This happens in complex cells in the visual cortex.

Question 33

Outline the similarities between the visual cortex and HMAX model.

Answer 33

• Neurons in V1 have small receptive fields, are sensitive to simple features such as oriented bars, and have limited invariance.
• HMAX implements similar functions to the visual cortex with regards
• to simple/complex cell function to perform tuning.
• Combining this with the hierarchical structure generates a similar system to the visual cortex.
• Performance on rapid object recognition is similar for both HMAX and human visual cortex.

Question 34

Describe the passive dynamic walker model of walking, including a comment on the Specific Cost of Transport

Answer 34

• The passive dynamic walker model is where a system is able to walk using a inverted-pendulum based system which requires no energy. The pivot is at the ground and the pendulum is at the hip.
• The system required being set up to an initial state, which enables movement. The walker is then able to walk downhill. Shows that walking is controlled falling where always have to keep centre of mass over feet and every step is vaulting the centre of mass forwards.
• The specific cost of transport of the passive dynamic walker is comparable to that of a rimless wheel.
• Actuators can be used on such walkers to create finite-state machines which are able to replicate the plantar-flexion response of humans, enabling walking on a flat level.

Question 35

Outline the differences between SLIP models of walking and animal legs

Answer 35

• SLIP systems use springs to enable movement which closely resembles that of human bipedal motion. The system is generic, and able to be applied to systems of four, and six legs.
• SLIP is a basic system of springs whereas animal legs consist of complex anatomy to enable motion.
• SLIP systems can be designed to have more inherent stability than animal legs due to understanding and re-engineering of the system.

Question 36

Cockroaches are able to withstand large levels of lateral impulse perturbation. Describe how this is achieved, commenting on the direction of movement of their legs.

Answer 36

• Cockroaches have 6 legs, and when walking, have 3 legs in contact with the ground in a tripod
• fashion, enabling a strong and stable motion.
• The response is not neuronal, but mechanical, with the legs providing the instantaneous response to lateral translation.
• The front legs contribute to rearward thrust, and the rear legs contribute to forward thrust. The middle legs contribute to both dependent on the motion initiated.

Question 37

Wheel-based motion is often thought of being comparable to leg-based. Give reasons why leg-based motion is better than wheel based.

Answer 37

• Legs are more efficient at clearing obstacles.
• Legs are more compact and lighter than wheels.
• More range of motion than a wheel.
• Can have customised stance.

Question 38

Birds are thought to turn through one of two hypotheses, one hypothesis is force vectoring through body rotations. Describe this hypothesis

Answer 38

• The force vector remains the same, but the bird rotates, hence the motion is now in a different axis, enabling turning.
• (Body independent force redirection or force vectoring through body rotations.)

Question 39

How do flies use passive flapping counter torque to enable rotation?

Answer 39

• Haltiers of flies measure angular yaw rate which is fed back into the wing flapping system to enable rotation. This is followed by active correction to ensure that the desired rotation is stabilised.
• Key factor that makes flies yaw turn: having a wing with high angle of attack on one side and low on the other makes the body turn towards the side with higher angle of attack. There is no need to create torque in the opposite direction to stop turning because the additional drag will stop the turning process.

Question 40

Describe how geckos are able to stick to walls

Answer 40

• Toes are covered in lots of microscopic hairs called setae.
• Van der Waals’ forces enable adhesion (inter-molecular forces due to close proximity). When a gecko puts its’ feet down, it generates attraction forces which sticks it to the wall.
• By loading in one direction the setae stick, in the other direction they peel off and unstick

Question 41

Soft robotics is an emerging field which makes use of soft actuators. Describe two types of soft actuators, and their properties

Answer 41

• Shape memory alloy (metal alloy that has phase transition at low temperatures - by heating it to change phase will cause movement). - Allows for high force and strain but has a low efficiency. Slow relaxation as movement is heat based, high energy required
• McKibben actuator (pneumatic + fibre composite) - High force and medium strain, good precision and efficiency but requires carrying compressed air.