**9.5. Determination of entrapment efficiency**

In order to obtain the entrapment efficiency, the concentration of the free drug is to be determined upon preparation of the entrapment, 1 ml of the supernatant is taken and diluted with 3 ml water, and the concentration of the drug is determined by high performance liq‐ uid chromatography (HPLC). Entrapment efficiency is calculated by the following equation: EE(%) <sup>=</sup> total drug <sup>−</sup> free drug \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ total drug <sup>×</sup> <sup>100</sup> (1)

$$\text{EE}(\%) = \frac{\text{total drug} - \text{free drug}}{\text{total drug}} \times 100 \tag{1}$$

#### **9.6. Determination of polydispersity**

The polydispersity index (PDI) is a reflection of the heterogeneity and a measure of the distribution of molecular mass in a given polymer sample. PDI is calculated as the weight average molecular weight, divided by the number of average molecular weight. It indicates the distribution of indi‐ vidual molecular masses in a batch of polymers. PDI value of 1 reflects that the polymer is of the same size and indicates uniformity of the chain length. The following equation denotes the PDI:

$$\text{PDI} = M\_{\text{w}} / M\_{\text{n}} \tag{2}$$

where *M*w is the weight average molecular weight and *M*n is the number average molecular weight.

#### **9.7. Determination of size, size distribution, and zeta potential of nanoparticles**

Scanning electron microscopy (SEM) and dynamic light scattering (DLS) can be used to determine the size of nanoparticle. DLS is used for determining the size distribution and zeta potential of nanoparticles as well. Dynamic light scattering, which is also known as photon correlation spectroscopy, is one of the most widely used methods for the determination of size, size distribution, and zeta potential of nanoparticles. This instrument works through radiation of a light beam into a particulate system with Brownian motion.

#### **9.8. Determination of the thermal characteristic of the delivery system**

Differential scanning calorimetry (DSC) technique is the most common thermal analysis equipment used in the determination of material in the delivery system. This primary technique directly assesses the uptake of heat energy during the fluctuation of temperature in order to specify any connection among temperature and physical properties of samples. Calorimetry is a suitable thermal analysis technique for qualifying the purity, the melting point, and the polymorphic forms of samples [21].

### **9.9.** *In vitro* **drug release study**

polymers, as well as drugs. Cell‐based assays are the most widely used methods for assessing

Thin film hydration method can be one of the methods for the preparation of the drug‐loaded polymeric system. An example is by using a solution of 2 mg/ml of polymer in ethanol (10 ml) and mixed with a solution of 5 mg/ml model drug in ethanol (1 ml). After stirring for 15 minutes at room temperature, the solvent needs to be evaporated by rotary evaporator. The precipitant is then mixed with 20 ml distilled water. The mixture is then centrifuged at 6000 rpm for 10 minutes. The supernatant is then taken for further analysis for entrapment

In order to obtain the entrapment efficiency, the concentration of the free drug is to be determined upon preparation of the entrapment, 1 ml of the supernatant is taken and diluted with 3 ml water, and the concentration of the drug is determined by high performance liq‐ uid chromatography (HPLC). Entrapment efficiency is calculated by the following equation: EE(%) <sup>=</sup> total drug <sup>−</sup> free drug \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ total drug <sup>×</sup> <sup>100</sup> (1)

The polydispersity index (PDI) is a reflection of the heterogeneity and a measure of the distribution of molecular mass in a given polymer sample. PDI is calculated as the weight average molecular weight, divided by the number of average molecular weight. It indicates the distribution of indi‐ vidual molecular masses in a batch of polymers. PDI value of 1 reflects that the polymer is of the same size and indicates uniformity of the chain length. The following equation denotes the PDI:

 PDI = *M*<sup>w</sup> /*M*<sup>n</sup> (2) where *M*w is the weight average molecular weight and *M*n is the number average molecular

Scanning electron microscopy (SEM) and dynamic light scattering (DLS) can be used to determine the size of nanoparticle. DLS is used for determining the size distribution and zeta potential of nanoparticles as well. Dynamic light scattering, which is also known as photon correlation spectroscopy, is one of the most widely used methods for the determination of size, size distribution, and zeta potential of nanoparticles. This instrument works through

Differential scanning calorimetry (DSC) technique is the most common thermal analysis equipment used in the determination of material in the delivery system. This primary

**9.7. Determination of size, size distribution, and zeta potential of nanoparticles**

radiation of a light beam into a particulate system with Brownian motion.

**9.8. Determination of the thermal characteristic of the delivery system**

cell toxicity effects of different polymers or drugs on a particular cell line.

**9.4. Preparation of drug‐loaded polymeric system**

28 Pain Relief - From Analgesics to Alternative Therapies

characteristics of the drug in the polymer.

**9.6. Determination of polydispersity**

weight.

**9.5. Determination of entrapment efficiency**

Drug release from the polymeric system shall be studied to prove good delivery as stipulated. Commonly, the *in vitro* dissolution of the drug from the formulation is done following the available compendium method where standard dissolution apparatus are recommended. Other methods include using dialysis method where the formulation prepared is placed in the dialysis bag. The dialysis bags are then placed in a bath shaker at the temperature of 37°C and rotated at the rate of 100 rpm. Samples were collected at different time intervals and analyzed.
