Microneedle Technology

Microneedle-Mediated Transdermal Delivery of Genetic Materials, Stem Cells, and Secretome: An Update and Progression

“…The skin comprises several layers: the epidermis, dermis, and subcutaneous [ 12 ]. The basal membrane separates the epidermis and dermis layers, while there is no membrane between the dermis and subcutaneous layer [ 11 ].…”

“…The basal membrane separates the epidermis and dermis layers, while there is no membrane between the dermis and subcutaneous layer [ 11 ]. The epidermis, the outermost layer, consists of four stratified layers: the stratum corneum as the outermost layer, followed by the stratum granulosum , stratum spinosum, and the stratum basale as the bottom [ 12 , 13 ]. The dermis layer contains various skin appendages such as hair follicles, sebaceous glands, eccrine and apocrine sweat glands [ 11 ].…”

“…It also houses sensory nerve endings, lymphatic vessels, and blood vessels connected to systemic circulation [ 13 ]. The subcutaneous layer, known as the hypodermis, is the deepest layer and consists of adipose cells or fat [ 11 , 12 ].…”

“…Transdermal drug delivery can occur through two main pathways: diffusion through the epidermis layers (intercellular and transcellular) or via skin appendages, such as hair follicles and sweat glands, which is illustrated in Figure 1 [ 12 ]. In the intercellular pathway, drug molecules move through the gaps between corneocyte cells.…”

“…The transcellular pathway is favorable for lipophilic drugs due to the composition of the stratum corneum membrane, while the intercellular pathway is better suited for hydrophilic drugs [ 14 , 15 ]. Despite the absence of the stratum corneum , the trans-appendageal pathway is not the primary route for drug permeation, as skin appendages only make up around 0.1% of the skin [ 11 , 12 ].…”