L8 - Rheology and formulation issues: Topical Products

Question 1

Important PHYSICAL properties of topical products?

i.e How it feels?

Answer 1

Smooth texture, elegant appearance, non greasy and easy to apply

Question 2

Important PHYSIOLOGICAL properties of topical products?

e.g SC main barrrier, make lipid bilayer more leaky/poreus

Answer 2

Non irritating, dont alter membrane perm, low sensitisation effect

Question 3

Flow

Answer 3

Measure of viscosity, the resistance to flow

Question 4

Deformation

Answer 4

Quantifies viscoelasticity - how sample behaves before flow

Question 5

Semi solids are viscoelastic, meaning they?

Answer 5

Have properties of both solid and liquid

elastic = solid
liquid = viscious

Question 6

Rheolgy defines..

Answer 6

1. spread on skin
2. removal from jars/tubes
3. capacity of solids to mix with miscible liquids
4. Release of drug from base
5. Ensure long shelf life/ storage

Question 7

Rheometer is an _____ vicsometer

It has a broarder range of shear rates and also measures ______

Answer 7

Advanced

viscoelasticity

Question 8

Viscometer can measure viscosity = but cant differentiate similar products with similar viscosity = need rheometer.

What is the principle behind rheometer?

Answer 8

Viscosity can be similar but rheological behaviour is different at differnt shear rates

can have more liquid or more solid characteristics

Question 9

Viscometer cannot measure..

Define these 4 things.

Answer 9

Yield stress: stress to elicit flow

High shear viscosity: spreadability and ease of application

Zero shear viscosity: at rest = stable = maintain viscosity/integrity

Thixotropy: regain of internal structure after breakdown

Question 10

Rheometere has ____ shear range, high and low (visco just high)

Products may look simmilar______ at high shear rates

however can___ __ differntly at low shear rates

Answer 10

Rheometer has larger shear range, high and low (visco just high)

Products may look simmilar viscosity at high shear rates

however can behave differntly at low shear rates

Question 11

What are geometrics?

Answer 11

Viscometer attachments to sample different parameters

Question 12

Oscillation testing

_______ applied
_________ measured
____ angle measured

Answer 12

Oscillation testing

Deformation applied
Response measured
Phase angle measured

Question 13

Dynamic Viscoelastic Material Response - determine if material is more elastic or viscous

In phase vs out of phase?

What is inbetween 0-90?

Answer 13

In phase = zero = elastic/solid

Out of phase = 90 = viscoius/liquid

Viscoelastic properties

Question 14

G* = overall ______ to deformation

G’ =

G” =

Answer 14

Resistance

G’ = elasticity

G” = viscosity

Question 15

G’ > G” =

G’ < G” =

Answer 15

G’ > G” = more elastic, less than 45 degrees

G’ < G” = more viscous, more than 45 degrees

Question 16

In phase, angle of ___ more ____ like

Out phase, angle of ___ more ____

Answer 16

In phase, angle of 0 more elastic like

Out phase, angle of 90 more viscous

Question 17

Oscillatoin procedure: Amplitude and frequency.

What does amplitude test determine?

Answer 17

Linear viscoelastic region

LVER

Question 18

Tell me about LVER

Talk about creepflow, internal structure and when a material will flow?

Answer 18

LVER is the region where creep flow happens, very insignifcant as internal structure is maintaned, however once stress surpassed a certain point = internal structure breaks down and material begins to flow

Question 19

True or false

Materials can express differnt viscoelastic properties at differnt shear rates/ frequenceis

Answer 19

True

Question 20

Yield stress

Answer 20

Point right when material begins to flow/slope

Question 21

Mechanical properties of viscoelastic materials: texture anaylzer measures:

Answer 21

Firmness
adhesivness
cohesivness

consistency
spreadalbity
stiffness/elasticity

Question 22

Shear stress vs normal stress

Answer 22

Shear: stress that acts in a dirrection parallel to the material surfaces they deform

Normal: act in directoin perpendicular to surfaces of material they deform

Question 23

Viscoelastic strain?

Answer 23

Measure of realtive displacmentof particles of a material

E = stress/strain

higher VE stress = the more stress you can apply before stretrching actualy occurs

Question 24

Mechanical Properties- Texture Analysis , 4 parameters

F1
A1
A2/A1
A3

Answer 24

F1 - Firmness: max peak

A1 - Consistency: Frimness or thickness

A2/A1 - Cohesivness: rate material disintegrates under mechanical action

A3 - Adhesivness: work to overcome attracrive forces between surface of sample and other materials in contact

Question 25

Consistancy in creams. What two tests are used?

Answer 25

Forward extrusion test: Stimulate force to extrude sample by consumer

Backward extrusion test: indication of product physical failure

Question 26

Cold cream = w/o more sticky, and thick

Warm cream = o/w, less sticky

Princible?

Answer 26

Cold cream, w/o = more resistance to deformatoin

Depends on continous/outside phase = cold cream cold on the outside

Question 27

What is gel strength - measurement

Answer 27

Measure of the ablity of collodial dispersion to retain gel form

Resists flow up to a certain threshold

Question 28

Spreadablity - attacthment probe, measures:

Answer 28

Cone shape, ease of flow, more work = difficult to spread

Question 29

In vitro penetration studies.

What is a diffusion cell, give an example:

Answer 29

Mimic permeation in human skin: FRANZ CELL

Question 30

Diffusion cell properties

Answer 30

1. Inert
2. Allow for membranes of differnt thickness
3. maintainble at a certain temp and be reasonable cost

Question 31

Plot of cummulative amount of chemical permeating in skin during in vitro permeation study:

L = h2 / 6D

what are these

Answer 31

L = Lag time 
H = thickness
D = diffusoin coeffeient