Drug delivery systems elements

TOF-SIMS has important potentials in many areas of life science, in fundamental and applied research as well as in product development and control. This holds for the characterization of biological cells and tissues, of sensor and microplate arrays, of drug delivery systems, of implants, etc. In all these areas, relevant surfaces feature a very complex composition and structure, requiring the parallel detect ion of many different molecular species as well as metal and other elements, with high sensitivity and spatial resolution requirements, which are exactly met by TOF-SIMS. 

The nanostructured molecular arrangements from DNA developed by Seeman may find applications as biological encapsulation and drug-delivery systems, as artificial multienzymes, or as scaffolds for the self-assembling nanoscale fabrication of technical elements. Moreover, DNA-protein conjugates may be anticipated as versatile building blocks in the fabrication of multifunctional supramolecular devices and also as highly functional-... 

There is some confusion concerning terminology used for drug delivery when control of drug release is discussed. Within this chapter we will use an empirical approach. When a drug-delivery system does not contain any design element (formulation or process attribute) that is included to modify either spatial or... 

Figure 4.5 Transdermal diffusion-controlled drug delivery systems four design configurations and their basic elements.

Figure 3. Microfluidic Device. (A) Time lapse illustrating repulsion the ejection of 1.9 pm fluorescent polystyrene microsphere particles from an electroactive microwell. After dissolution of the membrane, the fluorescent particles can be seen in the well. White hnes outline the gold electrodes features. Images are taken every 2 s (total of 10 s). (B) Schematic of the electroactive microwell drug delivery system developed here. Scale bar represents 2 mm. (C) Micro fluidic device with electrical leads connected to thin copper wires. Inset Magnified view of microchip from above looking at the region near the membrane. (D) To illustrate the electrokinetic transport processes involved in the ejection stage, a finite element analysis of time-dependent species transport of the system is shown. Images show cut view of species concentration every 60 s up to 300 s after the ejection process.

Polyphenylene sulfide (PPS) is known for its dimensional stability, toughness and rigidity. PPS can be sterilised repeatedly and can be exposed to strong disinfectants without damage. PPS has been used to replace metal in the precision mechanical elements of drug delivery systems. 

Various characterization methods both in vitro and in vivo can provide information to understand, predict, and improve the performance of drug delivery systems. Selection of methods depends on the material properties and their applications. Viscoelastic properties can be measured using both DMA and oscillatory shear rheometry. DSC is a most useful method of measuring thermal transitions. Various microscopic methods are available to obtain the microstrac-ture and shape of the materials. Amorphous and crystaUine materials have different packing patterns of molecules, and these properties can be determined from XRD or density measurements. Surface properties such as surface elemental composition and material porosity can be obtained from various spectroscopic methods as well as from BET measurements. The biocompatibility of the material can be determined from both in vitro and in vivo assays. In vitro dissolution testing can be utilized to correlate with the in vivo performance of polymeric drug delivery systems. All these characterization methods can provide valuable information... 

Polyurethanes have been widely used in drug delivery systems. Kim et al. investigated the feasibility of developing a temperature-responsive braided stent using shape memory polyurethane (SMPU) through finite element analysis.The deployment process of the braided stents inside narrowed... 

Dehvering pharmaceutical agents to specific cells in the body is a difficult task involving complex interactions between many elements. Delivery systems have several fundamental requirements to achieve this task. The delivery vehicle must be ingesti-ble, implantable, or injectable to introduce the dmg into the body. The system must then protect the drug from the body s defense mechanisms in order to accumulate in selected cells. Once at the target, the delivery system should release the enclosed pharmaceutical agent with a controllable and predictable profile. Finally, the delivery vehicle should be biocompatible, nontoxic, and easily eliminated from the body. 

Polyelectrolytes have been widely investigated as components of biocompatible materials. Biomaterials come into contact with blood when used as components in invasive instruments, implant devices, extracorporeal devices in contact with blood flow, implanted parts of hard structural elements, implanted parts of organs, implanted soft tissue substitutes and drug delivery devices. Approaches to the development of blood compatible materials include surface modification to give blood compatibility, polyelectrolyte-based systems which adsorb and/or release heparin as well as polyelectrolytes which mimic the biological activity of heparin. 

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