Adhesive properties: a critical issue in transdermal patch development

Figures & data

Figure 1. Patch modes of failure. When a patch is peeled away from an adherend, four types of failure can occur. Case I (adhesive failure) is the only acceptable form of patches. When the pressure-sensitive adhesive does not strictly adhere to the backing layer, it may transfer to the adherend, leaving no matrix on the backing layer (case II). Case III refers to what happens when the matrix has good adhesive strength but poor cohesive strength. Case IV is a combination of adhesive and cohesive failure at the same time. The shift from one to another type of failure is affected not only by additives but also by peel rate [20].

Table 1. Monomers in common use for the preparation of acrylic pressure-sensitive adhesive copolymers and their glass transition (T_g) values.

Soft monomers	Tg (°C)	Hard monomers	Tg (°C)
Butyl acrylate	−54	Methyl methacrylate	105
Isobutyl acrylate	−40	Vinyl acetate	29
2-Ethyl hexyl acrylate	−85	Styrene	100
Ethyl acrylate	−22	Acrylonitrile	100

Table 2. Effect of pressure-sensitive adhesive (PSA) additives on adhesive properties of patches.

Type of additive	Additive name	PSA type	Investigated adhesive property	Effect on the adhesive properties	Ref.
Active ingredient	Piroxicam	Acrylates	Peel adhesion	Reduction	[44]
	Coumarin	Acrylates	Peel adhesion	none	[20]
	Captopril ethyl esters	Acrylates	Tack	Increase up 13.3%, then decrease	[79]
	Miconazole	Acrylates	Peel adhesion	Reduction	[80]
	Miconazole	Acrylates	Shear adhesion	Reduction	[17]
	Benztropine	Acrylates	Peel adhesion	Increase	[81]
		Acrylates	Tack	Reduction
		Acrylates	Shear adhesion	Reduction
	Nicotine	Acrylates	Peel adhesion	Increase	[48]
			Shear adhesion	Reduction
	Diclofenac	Acrylates	Peel adhesion	Reduction	[48]
			Shear adhesion	Reduction
Plasticizer	PEG 200	Acrylates	Peel adhesion	Increase	[82]
	Propylene glycol	Acrylates	Peel adhesion	Increase	[82]
	Diethyl phthalate	Acrylates	Peel adhesion	Increase	[82]
	Triacetin	Acrylates	Peel adhesion	Increase	[84]
	Triacetin	Acrylates	Tack	Increase	[48]
			Shear adhesion	Increase
	Tributhylcitrate	Acrylates	Tack	Increase	[48]
			Shear adhesion	Increase
	Propylene glycol	Acrylates	Peel adhesion	None	[87]
	Glycerin and/or PEG	Acrylate/water	Tack	Increase	[29]
	Sorbitol	Acrylate/water	Tack	None	[29]
		Acrylate/water	Shear adhesion	Increase	[29]
	PEG	Acrylate/water	Shear adhesion	Decrease	[29]
	Glycerin	Acrylate/water	Shear adhesion	None	[29]
	Glycerin	Gelatine/acrylate	Peel adhesion	None	[83]
	Propylene glycol	Gelatine/acrylate	Peel adhesion	Increase	[83]
Skin penetration	Isopropyl myristate	Silicon	Peel adhesion	Increase	[85]
Enhancer			Shear adhesion	Decrease
	Isopropyl myristate	Acrylate	Shear adhesion	Decrease	[82]
	Isopropyl myristate	Acrylate	Peel adhesion	Decrease	[85]
	Oleic acid	Acrylate	Peel adhesion	Increase	[44]
	Oleic acid	Acrylate	Peel adhesion	Decrease	[86,87]
	Azone®	acrylate/PVA	Peel adhesion	Decrease	[57]
	Sodium lauryl sulfate	Polyisobutylenes	Peel adhesion	Decrease	[88]
	DMSO	Polyisobutylenes	Peel adhesion	Decrease	[88]
	Methyl laurate	Acrylate	Peel adhesion	Decrease	[23]
	Arlacel 80®	Acrylate	Peel adhesion	Decrease	[24]
	Transcutol®	Acrylate	Peel adhesion	Increase	[24]
	Lauric acid	Acrylate	Tack	Increase up 6% then decrease	[94]
Crystallization inhibitors	PAMA	Silicon	Peel adhesion	Decrease	[41,89]
	PAMA	Acrylate	Peel adhesion	None	[55]
	PVP	Acrylate	In vivo	Decrease	[93]
	PVP	Acrylate	Peel adhesion	Increase	[94]
	PVP	Acrylate	Tack	Increase up 15% then decrease	[94]
	PVP	Polyisobutylenes	In vivo	None	[93]

DMSO: Dimethylsulfoxide; PAMA: Poly(amino methylmethacrylate); PVP: Polyvinylpyrrolidone.

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