What are the physiological functions of water in the human body?
- Regulates internal body temp through sweating and respiration
- assists in flushing waste through urination
- acts as a shock absorber for the brain, spinal cord, and fetus
- active participant in hydrolysis and degradation
- creates turgor pressure for tissue support and swelling
- forms the initial hydration layer for foreign surfaces
- provides structural lift
- Does not form collagen fibers, only hydrates them
What is the ionic strength of a solution containing 0.2 M NaCl and 0.1 M CaCl2?
0.5M
which of the following organs/tissues has the highest Young’s modulus?
- Heart
- lung
-bone
- knee cartilage
- bone (10-20 GPa)
- knee cartilage 1-1.5 MPa
- heart 10-15 kPa
Young’s modulus is a measure of stiffness
why are non-covalent (secondary) bonds essential in biological systems
because they are weak individually but collectively stabilize dynamic biological structures like DNA and proteins
- because they are individually weak, they can break and reform, allowing for dynamic processes like protein folding and DNA replication
hydrogen bonds behave differentyl in solid (20-40 kJ/mol) vs physiological environment (4-8 kJ/mol). Why
A) Water molecules compete for hydrogen bonding sites, weakening polymer–polymer
interactions
B) The high dielectric constant of water increases bond strength
C) Hydrogen bonds convert into covalent bonds in aqueous environments
D) Physiological ionic strength enhances rather than weakens hydrogen bonds
a) water molecules compete for hydrogen bonding sites, weakening polymer-polymer interactions
- the water in physiological environments forms its own hydrogen bonds and compete STRONGLY for the hydrogen bonding sites on polymer chains
- polymers form less hydrogen bonds with other polymer chains and more with the water
b) a high dielectric constant reduces the strength of electrostatic interactions (like ionic bonds) by screening the charges, rather than increasing them
c)hydrogen bonds are non-covalent bonds. they do not become covalent bonds simply by being in water
d) ionic strength (salt concentration) heavily influences ionic bonds via screening (Debye length), but water is the main factor not salt ions
which solution would have the shortest Debye screening length? why?
A) Pure water
B) 0.15 M NaCl
C) 0.15 M CaCl₂
D) All have the same Debye length
C) CaCl2
- Debye length is inversely proportional to the square root of ionic strength. This means higher ionic strength = shorter screening length
a) water has effectively zero ionic strength = long Debye length
Which statement best distinguishes adsorption from absorption? (Select all that apply)
A) Adsorption involves molecules penetrating into the bulk of a material
B) Adsorption occurs on a surface
C) Absorption involves molecules binding only on the outer surface
D) Absorption involves uptake into the bulk
B) adsorption: accumulation of molecules (like proteins) on the surface of a material
D) absorption: Molecules (like water in a hydrogel) penetration into the bulk volume of the material
General sequence of interactions between biomaterials and biological environment is:
A) Water → Protein → Cell
B) Protein → Water → Cell
C) Cell → Protein → Water
D) Ion → Protein → Cell
A) interactions occur based on diffusion speed and size
- water: smallest and most abundant, reaches teh surface in nanosecs/millisecs to form a hydration layer
- proteins: larger than water, arrive in seconds/min via diffusion/convection and adsorb
- cells: largest entities, arrive much later (hours/days) and interact with the adsorbed protein layer, not the bare material
Protein adsorption is often irreversible because:
A) Once the weak bond between protein and surface is formed, they cannot break
B) Desorption would require simultaneous breaking of all surface–protein contacts
C) Adsorbed proteins can freely diffuse back into solution at any time
D) Protein adsorption is a purely entropic process
B) proteins form many non-covalent bonds (van de Waals, H-bonds, hydrophobic) with the surface. it is statistically highly unlikely that all these bonds will break at the exact same instant to allow the protein to detach
- C) is incorrect because it contradicts the Vroman effect and general adsorption kinetics. they are energetically stuck and do not freely exchange or diffuse back into the bulk solution as easily as they arrived
- D) while entropy (release of ordered water) is a major driver, it is not the only driver. Enthalpy also plays a role (greater than zero due to new bond formation)
Explain the cell fate in the following two scenarios (Figure a and b):
A) a: survival, b: apoptosis
B) a: apoptosis, b: survival
C) a: differentiation, b: proliferation
D) a: proliferation, b: differentiation
B) small adhesive patch vs large adhesive patch
- Anchorage dependence: most cells are anchorage-dependent. If a cell is restricted to a tiny area (a), it cannot form enough focal adhesions or spread. This lack of spreading signals the cell to undergo apoptosis (programmed cell death), not survival or proliferation
- spreading: a large adhesive patch (b) allows spreading, which triggers survival and proliferation signals. Differentiation usually requires specific cues (like stiffness or chemical factors) beyond just spreading area
Proteins are often adsorbed to biomaterial surfaces before cells can adhere. How do
these proteins facilitate cell adhesion?
A) Proteins act as a physical cushion, preventing cells from mechanical damage on hard
biomaterials
B) Adsorbed proteins present binding motifs with cells’ integrin receptors for focal adhesion
formation
C) Proteins cover the biomaterial surface, making it rougher and easier for cells to attach
D) Adsorbed proteins increase the local osmotic pressure, forcing cells to spread
B) cells do not bind directly to bare synthetic materials. They use transmembrane receptors called integrins to bind to specific amino acid sequences (like RGD motifs) found on adsorbed proteins (fibronectin, vitronectin)
- a) cells adhere to sense the environment not to be cushioned from damage
- c)roughness affects adhesion but the primary mechanism is biochemical integrin-ligand binding
- d) osmotic pressure drives water movement (swelling in gels) not cell adhesion
Why do even “inert” implants like insulin pumps require replacement over time?
A) They break down chemically and dissolve inside the body.
B) A thick fibrous capsule forms around them, reducing their functionality.
C) Their batteries die and can’t be replaced.
D) Cells grow into them and disable their function.
B) the host response to a non-degradable inert material is fibrous encapsulation. The body walls off the foreign object with collagen. for a sensor or pump, this capsule blocks the diffusion of glucose or insulin, causing the device to fail functionally
- a)an inert material does not chemically break down or dissolve in the body
- c) batteries do die, but this is not the main reason for replacement, since the host response can happen before the batteries die
- d)cells do not grow IN TO them, they are encapsulated by fibrous collagen around the device
Which of the following are main characteristics of metallic bonding?
A) Each metal ion core form metallic bonds with their nearest metal ion cores
B) We can use the “sea of valence electron” to describe the metallic bond.
C) Metallic bond energy can be obtained from the heat required to melt the solid into a liquid.
D) Valence electrons are localized in polar bonds, giving rise to strong elastic modulus.`
B) metallic bonding is defined by positive ion cores surrounded by delocalized valence electrons that are free to move -> high conductivity and ductility
- a) not metallic bonding which are non-directional, but ionic bonding (cation-anion attraction) or covalent bonding (sharing pairs)
- c) bond energy is measured by the enthalpy of vaporization (energy to separate atoms into vapor), not melting
- d) this describes covalent bonding. metals are delocalized
Why does Nitinol exhibit shape memory instead of permanent plastic deformation like
steel?
A) Nitinol slip systems are highly mobile, so dislocations easily revert
B) Martensitic variants reorient under stress but revert to austenite on cooling
C) Nitinol has extremely high stacking fault energy, preventing slip
D) Conventional metals rely on irreversible dislocation slip, but Nitinol relies on reversible phase
transformation
D) Nitinol deforms via a phase transformation (austenite <-> martensite) specifically, it detwins martensite under stress. upon heating the lattice reverts to the austenite phase, restoring the original shape, which is a reversible process
- a) dislocation slip creates permanent plastic deformation.
- b)reverts to austenite upon heating, martensite is low temp
- c) while stacking fault energy affects deformation modes, the fundamental mechanism for shape memory is the diffusionless phase transformation, not stacking fault energy preventing slip
Which of the following correctly describes the structure on
the right?
A) Metallic bond within metals
B) Ionic bond within ceramics
C) Hydrogen bond within polymers
D) Ionic bond within metals
B) Ionic bond within ceramics:: ordered lattice of alternation cations (+) and anions (-), with a strong electrostatic attraction
- hydrogen bond within polymers: while h-bonds exist between polymer chains (secondary), diagrams of crystal lattices like FCC/BCC refer to primary atomic bonding (metallic or ionic), H bonds are too weak to form structural lattices
Which of the following correctly describes the structure on
the right?
A) Metallic bond within metals
B) Ionic bond within ceramics
C) Hydrogen bond within polymers
D) Ionic bond within metals
A) metallic within metals: positive ion cores in a sea of free-floating electrons
Which of the following are INCORRECT about the bonding in bioglass?
A) The backbone of bioglass is made of Si–O covalent bonds forming SiO₄ tetrahedra.
B) Network modifiers like Na⁺, Ca²⁺ are bonded through ionic interactions with non-bridging
oxygens.
C) Combination of covalent Si–O bonds and ionic bonds with modifiers (Na⁺, Ca²⁺)
D) SiO₄ tetrahedra in bioglass also forms repeating unit cells in crystalline structures
D) the definition of a glass (bioglass) is that it is amorphous, meaning it lacks the long-range order (repeating unit cells) found in crystals
- bioglass contains a covalent Si-O backbone modified by ionic interactions with Na/Ca, which disrupt the network to increase reactivity
