5.1.1. Material

Membranes comprise of inorganic, organic, polymeric, and composite materials. Mostly, the organic/polymeric membranes are made of materials such as polycarbonate (PCL), polyethylene terephthalate (PET), and polysulfones, etc. (Table 2). These composite materials contain two different materials and combine apolymer and an inorganic material (e.g., a polymer with a ceramic). They are developed in particular to improve the stability, permeability, and selectivity [110].

### 5.1.2. Size, Shape, and Order of Pores

Membranes are classified according to their size, distribution of size, order, and shape. Hence, membranes pores<2 nm are called microporous, those with pores 2–50 nm mesoporous, and those with pores>50 nm macroporous. The shape of the pores can be cylindrical, slit-like, conical, or irregular in shape. The pores should be well arranged in a vertical order instead of in a tortuous network [111]. The porous network for drug delivery depends upon the following properties:

