Table 5.

In vitro evaluation techniques typically employed for buccal film.

Technique	Principle	Evaluation Parameters	Ranges Units	References
Tensile test	The resistance of the thin strip of film against a dragging force is determined using a texture analyzer or modified balance method. Young modulus measures the deformation tendency of the film	Tensile strength = breaking force (N)/cross-sectional area (cm2) of the film The slope value from stress strain curve measures the Young modulus Percentage at the break, strain energy, energy to break can be calculated	16.6–24.3 MPa	[169,172]
Puncture test	The resistance of the thin film against the compression force until it breaks, cracks, or a desired loss in the force resisting the probe movement occurs	Toughness	0.2–13 mJ	[173,174]
Indentation test	Measure load as a function of penetration depth	Hardness and elastic modulus	1 mPa and ~100 mPa	[175]
Folding endurance	Repeatedly fold the film at 180° angle of the plane at the same plane until it breaks or folded to 300 times without breaking. The number of times the film is folded without breaking is computed as the folding endurance value	Flexibility	~300 count	[176]
Water absorption capacity	Swelling capacity assess bioadhesion behavior and drug release from the film	Percentage hydration is calculated by the equation [(W2 − W1) × 100/W1], where W1 weight of the film, W2 weight of the film after swelling in simulated saliva after predetermined time	5–25%	[177]
Thickness and weight variation	Thickness is determined using electronic digital micrometer, screw gauge, vernier caliper or by scanning electron microscopy images. Weight variation is calculated by subtracting weight of individual film from average weight and then divided by average weight of the film	Uniformity of the dose in the film	50–1000 μm and <50 mg	[169]
Surface morphology	Fixing the films on stubs, sputter coated with gold in an inert environment and imaged	Surface texture, pores, crystallinity, uniformity of drug distribution, thickness	-	[178]
Surface pH	Allowing it to swell by contact with distilled water for a short time (<2 h) at room temperature (25 °C)	pH at the area of application	6.0–7.5	[179]
Crystallinity	Place the sample in the sample holder of X-ray diffractometer and scan	Presence of crystalline or amorphous form of the sample	%	[180]
Thermal analysis	Heating the sample in aluminum pan at elevated temperature at uniform heating rate	Identify the existence of phase transition, recrystallization or molecular interaction of drug within the film	°C	[181]
Fourier-transform infrared spectroscopy	Specific ratio of drug and potassium bromide compressed at particular pressure and scanned	Drug-polymer interaction	cm−1	[182]
Mucoadhesive strength	Buccal film is attached to the probe of the texture analyzer using cyanoacrylate adhesive. Buccal epithelium of rabbit is fixed on the stationary platform of a texture analyzer. The probe of the texture analyzer was brought down gradually till the probe touch the mucosa	Adhesion strength is evaluated using shear stress, peel strength and tensile strength depending on the direction in which the mucoadhesive material is detached from the biological surface	6–7 N	[183]
In vitro drug release	Paddle over disc method using USPXXIV Type 2 apparatus	Release of drug from the prepared film using simulated saliva (pH 6.2)	%	[184]
Ex vivo permeation	Freshly excised buccal mucosa of rabbit using Franz diffusion cell, continuous flow diffusion cell, Ussing chamber, human buccal cell line (TR146), cell culture model	Establishing the absorption of drug across buccal epithelium by means of flux (J) and permeability coefficient (P)	J = μg/cm2/h P = cm/h	[17,181,185]