Skin Absorption Strategies Quiz

The outermost layer of skin, a barrier that prevents most molecules from penetrating the body.

A method of delivering actives through the skin using electrical current, increasing permeability.

A method of delivering actives through the skin using ultrasound, causing temporary pores.

The movement of molecules through the spaces between skin cells.

The movement of molecules directly through skin cells.

The movement of molecules through hair follicles, sebaceous glands, and sweat glands.

Substances that increase the permeability of the stratum corneum, allowing more actives to penetrate the skin.

A method of increasing the concentration of an active ingredient in a formulation, enhancing its penetration.

A numerical value that indicates how well a solvent will dissolve a specific solute. It's based on the ability of the solvent to form strong interactions with the solute molecules.

A measure of the strength of the intermolecular forces that hold a substance together in its condensed state (liquid or solid).

The energy required to vaporize a substance at its boiling point, converting it from a liquid to a gas.

A mathematical expression that relates the cohesive energy density to the solubility parameter. It accounts for van der Waals forces.

A more advanced model that expands on the Hildebrand SP by accounting for three types of intermolecular forces: hydrogen bonding, dipole-dipole interactions, and van der Waals forces.

The process where a solute dissolves in a solvent, forming a homogeneous mixture.

The concentration of a substance in a solution that is in equilibrium with a solid phase of the substance.

The process where a solute distributes itself between two immiscible phases, like oil and water.

A measure of how well a substance dissolves in a solvent. Higher values indicate greater solubility.

A property indicating the tendency of a substance to move from one phase (like a formulation) to another (like the skin).

The process by which a substance moves through the skin, typically from a formulation into the body. This is influenced by factors like solubility, partition coefficient and diffusion.

The rate at which a substance moves through a membrane (like skin) based on the concentration difference across the membrane. It's related to both the permeability and the concentration gradient.

The thermodynamic activity of a substance in a formulation. It represents the tendency of the substance to move from the formulation into the skin.

The thermodynamic activity of a substance in the skin. Represents the tendency of the substance to remain in the skin.

The maximum thermodynamic activity of a substance, often assigned a value of 1. It's associated with the saturated solubility of the substance in a solvent.

The Hansen Solubility Parameters (HSP) model is a 3D representation of solubility, where a molecule's solubility is determined by its position relative to a sphere representing the solvent. If the molecule falls within the sphere, it's considered soluble.

The Hansen Solubility Parameters (HSP) are numerical values that represent the different intermolecular forces (dispersion, polar, and hydrogen bonding) responsible for a substance's solubility. The 3 components of the HSP are: δd (dispersion force), δp (polar force), and δh (hydrogen bonding force).

The distance (Ra) between two molecules in the HSP model is a measure of their solubility difference. It is calculated using the equation: Ra² = 4(δd₁ - δd₂)² + (δp₁ - δp₂)² + (δh₁ - δh₂)² where δd, δp, δh represent the respective HSP components of each molecule.

The radius of interaction in the HSP model represents the range of solubility for a particular solvent. It defines the boundary of the sphere in which molecules are considered soluble in that solvent.

The HSP values for different molecules can be used to predict their solubility in a given solvent. If the HSP values are close, the molecules are more likely to be soluble. If they are far apart, they are less likely to be soluble.

The different models for calculating solubility parameters (SPs) are used to estimate the solubility of a molecule in a given solvent. Hansen, Van Krevelen, and Hoftyzer are some examples of these models.

While there are different models for calculating solubility parameters, it's generally recommended to stick with one model for consistency when comparing different substances.

The tendency of a substance to move between different phases (like from a vehicle to the skin) is influenced by its affinity to those phases. A substance with a high affinity for a vehicle will be less likely to move towards the skin.

A substance's tendency to move from a vehicle to another phase (like the skin) is inversely proportional to its affinity to the vehicle. The higher the affinity, the lower the thermodynamic activity.

Even if a high percentage of an active ingredient partitions from a vehicle, it might not be effective if the vehicle can't hold enough of it in the first place. This relates to both the active's affinity and the vehicle's capacity.

By using a combination of solvents with varying affinities for the active ingredient, it's possible to fine-tune the rate of release and penetration into the skin, maximizing formulation effectiveness.

Propylene glycol (PG), 1–2 pentanediol (1-2P), 1–5 pentanediol (1-5P), 1–2 hexanediol (HEX), isopropyl alcohol (IPA), isopropyl myristate (IPM), glycerol (GLY), Transcutol® (TC), Capryol 90® or propylene glycol monocaprylate (PGMC) Type II, Lauroglycol 90® or propylene glycol monolaurate (PGML) Type II, Labrafac® or medium chain triglycerides of caprylic (C8) and capric (C10) acids, dipropylene glycol (DiPG), tripropylene glycol (TriPG) are common solvents used in skin formulations.

When the solubility parameters of a substance and a solvent are close, it indicates that the substance has a higher likelihood of dissolving well in that solvent. This is because they have similar 'stickiness' or cohesive forces, leading to better compatibility.

Binary solvent systems are mixtures made of two different solvents, while ternary solvent systems involve three different solvents. These mixtures often exhibit different properties compared to the individual solvents, such as altered solubility and permeability.

Permeability refers to the ability of a substance to pass through a barrier, such as the skin. In this context, it indicates how much of a substance can penetrate the skin from a formulation.

In this context, the saturated solubility of a substance in a solvent is the maximum concentration of that substance that can be dissolved in that solvent at a given temperature and pressure. It's like the limit of how much sugar you can dissolve in a cup of coffee.

The experimental data suggests that while using binary or ternary solvent systems might decrease the saturated solubility of the substance, it can actually lead to an increase in the amount that penetrates the skin. This indicates that the solubility and permeability are not always directly related, and other factors like solvent interactions are also important.

The maximum value of the y-axis in the graphs represents the highest concentration of the substance that was achieved in the experiment. This value may vary depending on the solvent system and the substance being tested.