Microchannels Drug Delivery

A system for microchannel structures has been described that is particularly useful for the high precision delivery of drugs (52). 

A silicon substrate with a top surface and with a longitudinal channel formed therein is used. A channel seal is arranged to seal the top surface of the silicon substrate, and to overlie the longitudinal channel. Thus, the longitudinal channel is embedded in the silicon substrate. 

A first seal over the longitudinal channel is achieved by oxidizing at least partially the cross structures. Otherwise, a dielectric seal is arranged to overlie the thermally oxidized cross structures, thereby forming a more complete seal and a substantially planar top surface to the silicon substrate. 

Most advantageously, the dielectric seal is formed by the low pressure chemical vapor deposition of a dielectric layer. The silicon is boron-doped silicon layer that is formed by boron diffusion (52). 

The microchannel formation requires only one mask in addition to those normally used for probe fabrication, and is compatible with on-chip signal-processing circuitry. The flow in these microchannels has been studied theoretically and experimentally (53). 

---

Given the limitations imposed on transdermal systemic drug delivery by the barrier properties of the stratum corneum, new technologies have attempted to completely bypass this obstacle by either the creation of a physical conduit (microneedles) or direct powder delivery via compressed gas. The Alza Corporation technology (Macroflux ) comprises a patch system that contains a microprojection array designed to create superficial microchannels across the stratum corneum.When used in conjunction with their electrotransport system, the Macroflux system provides controlled in vivo delivery of therapeutic doses of... 

N ew opportunities and future directions in the area of microchannel emulsification are most likely in the areas of scale-up [140,141], encapsulation/polymeriza-tion [123, 125, 158, 164—169], rapid quenching of droplets [135], and the use of emulsions as templates for uniform macroporous particle structure formation [172]. MicroChannel emulsification is also likely to open up new opportunities with systems that are highly shear-sensitive [120, 135, 173]. The ability to scale up the process will spur new markets that require high production rates and the production of monodisperse capsules and polymer particles. Such developments will be useful in drug delivery applications and will contribute to the further quantification of micro-particle properties. Additionally, the use of monodisperse emulsions as particle templates is likely to enhance the utility of highly functional nanoparticles in need of a deployment mechanism [172]. 

DRIE is essential in fabrication of small features. DRIE is capable of reproducing accurately practically any features that have been defined by lithography. Fluid dynamics studies of microflows utilize DRIE for making accurately dimensioned microchannels and orifices. Membrane stmctures with small holes are useful in many drug delivery, fuel ceU, and cell probing applications. In a patch clamp application, submicrometer apertures have been etched in 20 pm thick silicon membrane. In catalysis studies a small DRIE fabricated capillary leak into a mass spectrometer enabled increased sensitivity and fast respmise times. Integration of... 

Sintov, A.C., et al. 2003. Radiofrequency-driven skin microchanneling as a new way for electrically assisted transdermal delivery of hydrophilic drugs. J Control Release 89 311. 

Microneedles are a type of micromachined structure that promotes the transport of substance through an interface or media, via enhanced permeability or microchannels. In most cases, microneedles are similar in shape to hypodermic needle but are much smaller in size, enabling localized and painless delivery of drugs into cells or tissues. Microneedles, which can be either singular or grouped in arrays, are prepared using microelectromechanical systems (MEMS)... 

---