L3 Liposomes, Calcium Phosphate & Silica NP

Question 1

1. Which of the following molecules is NOT present in a typical glycerophospholipid?

(A) Glycerol
(B) Phosphate
(C) Fatty acid
(D) Ethylene glycol

Answer 1

(D) Ethylene glycol

A glycero phospho lipid is a three-component molecule that forms the bilipid membrane layer that is responsible for ‘membranizing’ the vesicles and the cell.

See image - Hydrophilic stays together, Hydrophobic stays together.

Question 2

Label either “hydrophilic” or “hydrophobic” in the indicated regions of the liposome to describe the hydrophilicity of these regions (see image).

(1 mark)

Answer 2

• Outside the liposome (green) - hydrophilic heads = hydrophilic - interact with the ‘water’ of the extracellular/intracellular environment
• Inside the core of the liposome (green) - hydrophilic heads = hydrophilic - retains the water inside the core that was trapped during the fabrication process
• In between - hydrophobic tails = hydrophobic - basically the ‘border’ of the liposome

Implications = you can load both hydrophilic drugs/molecules inside the core/adsorbed on the external surface of the liposome, and hydrophobic drugs in the ‘yellow region’ (see image again)

Question 3

A liposome with a diameter of 20 nm with one bilipid layer as its vesicular wall would generally be considered as a

(A) Single unilamellar vesicle
(B) Simple unilamellar vesicle
(C) Small unilamellar vesicle
(D) Unilamellar vesicle

Answer 3

(C) Small unilamellar vesicle

Others: LUV (large), GUV (giant), MLV (multilamellar), MVV (multivesicular)
You can control what you get during the fabrication process - if you don’t employ additional processes like sonication (ultrasonic vibration to physically breakdown or separate particle) or filtration, then you’re more likely to get MLV, MVV, GUV, etc.

Question 4

Which of the following statements about liposomes is FALSE?

(A) Diameters of liposomes are roughly between 20nm to 10um.
(B) Liposomes consist of a bilipid layer
(C) Liposomes consist of a monolipid layer.
(D) Liposomes are generally larger than micelles (monolipid vesicles) and
dendrimers (branched polymers).

Answer 4

(C) Liposomes consist of a monolipid layer.

Regarding (B), Liposomes consist of a bilipid layer –> mainly a structural characteristic

Question 5

The main advantage of liposomes over many other nanoparticle systems is that…

(A) Liposomes can be made into diameters of less than 50nm.
(B) The half-life of liposomes in the blood can be controlled.
(C) Liposomes can be injected into the body intravenously. (good, but also other NPs can be injected through the blood as well)
(D) Liposomes are generally non-toxic and biodegradable.

Answer 5

(D) Liposomes are generally non-toxic and biodegradable.

The other three options are also ‘good’ properties/characteristics of liposomes, but of course, the main advantage is the cytocompatibility/biocompatibility

Regarding:

• (A) Liposomes can be made into diameters of less than 50nm. –
• good, but other NP can also achieve this*
• (B) The half-life of liposomes in the blood can be controlled – good, but also other NPs can achieve this, size or otherwise
• (C) Liposomes can be injected into the body intravenously – good, but also other NPs can be injected through the blood as well

Question 6

6. Which of the following liposomes of given diameters would have the shortest half-life in the bloodstream?

(A) 20 nm
(B) 50 nm
(C) 100 nm
(D) 250 nm

Answer 6

(D) 250 nm

Size is inversely proportional to halflife in the blood
= small size, longer halflife
= larger size, shorter halflife
→ MPS: bigger particles, easier protein corona formation, detection and MPS clearance

Question 7

Which of the following statements regarding liposomal drug
delivery is TRUE?

(A) Liposomes can only carry hydrophilic drugs
(B) Liposomes can only carry very small biomolecules, such as nucleic acids
(C) Liposomes can only carry hydrophobic drugs
(D) Liposomes can carry both, or either, hydrophilic and/or hydrophobic drugs

Answer 7

(D) Liposomes can carry both, or either, hydrophilic and/or hydrophobic drugs

Think about the physical structure of liposomes: three compartments - outside (hydrophilic) layers (hydrophobic) core (hydrophilic) - and drugs can be incorporated in any of these three parts

Question 8

TRUE or FALSE?

Liposomes can be loaded with only drugs in its core.

Answer 8

FALSE

Liposomes can be loaded inside the core or on the outside of the liposome or in between.

Not only drugs, but other molecules like DNA, RNA, other proteins, fluorescent molecules.

In image: blue = hydrophilic molecules, red = hydrophobic molecules.

Question 9

Name ONE other organic nanoparticle aside from ‘liposomes’.

Answer 9

• Micelles (single lipid layer vesicles)
• Dendrimers (branched polymers starting from a core - the more ‘generations’ or ‘layers’ the bigger the dendrimer is)
• Polymersomes (‘synthetic liposomes’ whose ‘glycerophospholipid’ is made of a synthetic polymer chain with hydrophilic ends and hydrophobic body）

Question 10

10. The most common mechanism by which liposomes are able to deliver drugs to cells is via

(A) Endocytosis and subsequent endosomal escape of cargo
(B) Adsorption and subsequent drug release on the surface of target cell
(C) Direct membrane fusion
(D) Lipid exchange

Answer 10

(A) Endocytosis and subsequent endosomal escape of cargo

(C) and (D) rarely occurs, primarily due to the presence of proteins in the cell membrane that hinder these processes.

NB: More than one mechanism can occur at any one time.

(often receptor-mediated)

Question 11

Name ONE advantage of inorganic nanoparticles in general over organic
nanoparticles.

Answer 11

(most of these should to be do with thermophysical stability)

1. Sterilisation is easier and cheaper
2. Long-term stability → long term storage is possible
3. Easier to modify? If you can’t change the shape of liposome; you can’t change porosity of a liposome (it’s easier to control the physical shape/structure/other parameters with inorganic NP like gold/magnetic NP than liposomes/micelles)
4. Microbial attack (if cells can break down liposomes, bacteria can too)

Question 12

Name ONE disadvantage of inorganic nanoparticles in general over organic nanoparticles.

Answer 12

1. Harder for mass production (main stumbling block for ommercialization - especially keeping consistency)
2. Generally more cytotoxic
3. Less biocompatible
4. Less biodegradable
5. Promote unwanted toxicity - this is related to point 2 - basically same answer

Question 13

Which of the following materials used to make nanoparticles is NOT an inorganic material?

(A) Polyethylene glycol (PEG)
(B) Gold (Au)
(C) Cadmium-based quantum dots
(D) Silica (SiO 2 )

Answer 13

(A) Polyethylene glycol (PEG)

Question 14

Which of the following presents the greatest limitation of calcium phosphate nanoparticles for biomedical engineering?

(A) Aggregation in aqueous environments
(B) Toxicity
(C) Inability to functionalize
(D) Its ability to dissolve in acidic environments

Answer 14

• *(A) Aggregation in aqueous environments** → aggregation impedes succesful use of NP
• Can’t control its final shape and size (changes the parameters that you’ve initially designed for)
• If particle gets bigger, then MPS more likely to clear it

Regarding:

(B) Toxicity ← calcium phosphate NP are the least toxic inorganic NP
(C) Inability to functionalize ← more difficult than others, but still possible and not really a big limitation
(D) Its ability to dissolve in acidic environments ← can be used as a ‘trigger’ for cargo release

Question 15

What is the main advantage of mesoporous silica nanoparticles (MSN) over other inorganic and organic nanoparticles?

Answer 15

Lots of pores → We can employ fabrication methods to increase porosity - more drug to load → increased drug loading efficiency

The design of MSN also allows for controlled drug release with certain ‘gatekeeper molecules’

Question 16

Which of the following pore size ranges is in the meso-pore range, in the context of nanoparticle-based drug delivery?

(A) 0.1 – 1.0 nm
(B) 2 – 50 nm
(C) 100 – 500 nm
(D) > 500 nm

Answer 16

(B) 2 – 50 nm

NB: “meso-pore” term itself is somewhat variable as its exact definition changes with context)

(A mesoporous material is a material containing pores with diameters between 2 and 50 nm, according to IUPAC nomenclature. For comparison, IUPAC defines microporous material as a material having pores smaller than 2 nm in diameter and macroporous material as a material having pores larger than 50 nm in diameter.)

Question 17

Which of the following statement is FALSE about MSN?

A. The pores in the MSN are large enough to allow for drug adsorption.
B. Drugs are often loaded onto MSNs through the process of diffusion.
C. The pore architecture can be controlled by controlling the concentration and temperature of the lyotropic micelle template.
D. It is not possible to functionalize the pore walls because of the mesoporous nature of the pores, which only allows for external surface functionalization of MSNs.

Answer 17

D. It is not possible to functionalize the pore walls because of the mesoporous nature of the pores, which only allows for external surface functionalization of MSNs.

Regarding:

A. The pores in the MSN are large enough to allow for drug adsorption. – True - pores are bigger (2nm-50nm) than drug molecules (~0.5 - 1nm)
B. Drugs are often loaded onto MSNs through the process of diffusion. – True - drugs diffuse into the pores during the fabrication process
(basically, put the NP inside a saturated solution of drugs - drugs seeps in. The solvent used would have to be considered - hydrophobic drugs need nonpolar solvents (chloroform, hexane), hydrophilic drugs need polar solvents (like water). Basically, MSN acts like a sponge
C. The pore architecture can be controlled by controlling the concentration and temperature of the lyotropic micelle template.
True - the micelle architecture depends on conc and temperature

Question 18

Name ONE stimulus (i.e. ‘trigger’) which can be used to open the ‘gates’ of MSN that are incorporated in order to control the release of drugs from the pores.

Answer 18

• Redox* = ‘oxidation/reduction reactions’
• Ionic* = presence of ions (e.g. H⁺ i.e. pH change)
• Photo* (EM waves) = light, near infrared, UV etc.

The above three trigger types can ‘open’ the pores of the MSN using a variety of mechanisms

Question 19

Name ONE mechanism by which the stimulus-controlled ‘gates’ of MSN for drug-release are opened.

Answer 19

Break covalent bonds (a)

Shrinking, swelling or configurational change of polymer chains (b)

Attachment/detachment of bulky groups (c)

“Snap-top” (d), “nanovalve” (e) and propellant-type (f) mechanisms

All aim to open the pores to release inner content

Question 20

Name ONE reported issue with the use of MSN for in vivo drug delivery.

Answer 20

Haemolysis, Melanoma, making large amounts for commercial use.

(NB on haemolysis - not as big of an issue; there are strategies to minimize this effect. The problem is the interaction between blood cells and the surface silanol groups - by having pores, you actually reduce the SiOH-to-blood cell interaction (MSN have less haemolytic activity than
solid silica NP))