Microneedles Flashcards
Name 4 advantages of microneedles over hypodermic needles
- Easy to use
- Painless
- Safe needle disposal
- Eliminate pathogens by reuse of needles
How do microneedles achieve painless delivery of drugs?
The microneedles do not penetrate the dermis where the blood vessels and nerve fibres are present which on contact would precipitate ‘pain’
Considering pharmacokinetics, what advantages do microneedles have?
Better bioavailability and faster absorption
How is photolithography undertaken when making solid silicon microneedles?
A silicon wafer is taken
Oxide and nitride deposition
spin photoresist
exposure with photomask
How can polymer microneedles be made from combining photolithography and micro moulding
A silicone mould is first made through lithography followed by filling a mould with polymer melt or liquid monomers that are UV curable
How can hollow microneedles be made using reactive ion etching
A silicone wafer is used to start
Hole etched using reactive etching and material around hole is etched away to form a microneedle out of the plane.
How can hollow microneedles be made using Sacrificial micromolding + selective electrodeposition
(A) Fabrication of the master structure with a laser ablated cavity.
(B) Creation of a micromould based on the master structure featuring a protruding pillar that will become the lumen exit hole in the final device.
(C) Creation of a replica using the micromould.
(D) Sputtering a gold seed layer onto the replica.
(E) Electrodeposition of metal everywhere except the cavity, followed by dissolving of the sacrificial base material to release the metal hollow microneedle.
What are the FOUR ways microneedles can be used?
- Solid microneedles
- Drug coated microneedles
- Drug encapsulated microneedles
- Hollow microneedles for drug delivery through the bore
How do solid microneedles exert their effect?
They interrupt the skin barrier micropores formed and the drug formulation can be applied after to penetrate into the skin more effectively.
What are the 5 considerations when making drug coated microneedles?
For a drug coated microneedle there are 5 considerations:
- Controlled wetting and spreading of drug solution on microneedles
- Drug should be water-soluble for coating dissolution into skin.
- Adhesion between dried drug coating and microneedle should be enough during insertion into skin
- Coating excipients and solvent should be safe.
- Coating process is compatible with the drug
What are drug encapsulated microneedles and what materials are used?
These are microneedles that encapsulate the drug in the microneedles and are left in the skin after insertion.
Materials:
Rapid dissolving - Water-soluble sugars and polymers(dextran, polyvinylpyrrolidone), photopolymerisable liquid monomers (methacrylic acid).
Slow dissolving – biodegradable polymers (PLGA)
What are hollow microneedles and what needs to be considered for them to exert their effect?
hollow microneedles can be used for infusion of liquid formulations into the skin or, alternatively, for diffusion into the skin through the needle bore.
Considerations for making hollow microneedles:
Enough mechanical strength during insertion
Leak-free infusion into skin and coupling to a drug reservoir
What are the advantages and disadvantages of hollow microneedles?
Advantages:
Enable great control over the amount and timing of drug delivery.
Separation of the microneedles from drug during manufacturing
Use already existing drug liquid formulations
Disadvantage:
Requiring drug reservoir, pump, microfluidic networks, making the whole system more complex
