Drugs, delivery

EVA copolymer are used in drug delivery systems (30). Drug delivery systems based on matrices of EVA can be manufactured with extrusion technology. Based on this technology, commercially used systems have been developed. 

The concept of these systems comprises a coaxial fiber. In this fiber, a drug is dispersed or dissolved in a core polymer. The release of the drug from these coaxial fibers is proportional to the concentration gradient in the fiber. If the drug is present in a concentration that exceeds solubility in the membrane, on the adjacent surface the saturated concentration is established. This stationary concentration is responsible for the gradient. 

It has been found that the solubility of drug in the polymer is influenced by the temperature of the extrusion process (30). 

The extrusion temperatures of the polymer far below the melting point of the drug. Upon cooling of the extruded fibers, dissolved drugs may either recrystallize or remain soluble, which results in a supersaturated state. The amount of the dissolved drug can be correlated to the release properties. The state in which the drugs are left after extrusion determine their properties of permeation. 

The intramuscular delivery of nanospheres could be used to provide sustained localized drug delivery or for sustained systemic drug effects. The nanospheres could form a depot at the site of injection from which the drug could be released slowly in the local tissue and then absorbed for the systemic effect. This strategy is useful for drugs which require repeated administration such as growth factors or hormones  

Nanospheres could be used as a colloidal injectable suspension for infusion into a certain diseased body compartment using a catheter. The infused nanospheres could provide a localised sustained drug effect with minimal toxicity. In our studies, we have successfully used nanospheres to localise therapeutic agents (e.g. dexamethasone, U-86983, a 2-aminochromone) into the arterial wall to inhibit restenosis in animal model studies  

Restenosis is the reobstruction of the artery following angioplasty procedure. Proliferation of the smooth muscle cells of the arterial wall in response to the injury due to balloon angioplasty is considered as the main reason for the pathophysiology of restenosis .  

The work from our laboratory was supported by grants from the National Institutes of Health (HL 57234) and the Nebraska Research Initiative-Gene Therapy Program. 

Biomedical applications of nanotechnology—implications for drug targeting and gene therapy. TrendsBiotechnol. 15 217-224. 

A key element in the development process is to select and optimise the most appropriate method for the delivery of the drug. Drugs may be administered by  

As reported in other chapters in this volume, PLA is one of the most used materials for biomedical applications due to biocompatibility and biodegradability, but hydrophobic properties require the encapsulation of water-soluble agents to avoid decomposition and failure of the polymer as a drug-carrier substrate. One of the advantages of coaxial electrospinning is that solid or liquid drugs can be incorporated into electrospun nanofibres and it is possible to encapsulate drugs into a structural shell. 

Controlled release via diffusion properties, porosity or biodegradability of the shell can be adjusted by the selection of parameters in the coaxial electrospinning. He et produced drug-loaded fibres of tetracycline 

Finally, the coaxial electrospinning technique is suitable to prepare coreshell fibres with high-molecular-weight molecules, such as proteins, in-eorporated into them. In this case the formation of the high-molecular-weight fibres is aided by the electrospinning of homogenous polymer solutions.  

Emulsion electrospinning can be also used. Maretschek et al. produced protein-loaded nanofibre non-wovens based on PLLA via emulsion electrospinning. As the hydrophobicity of the non-woven nanofibres affects the release of macromolecules, PLLA was blended with hydrophilic polymers such as poly(ethylene imine) and poly(L-lysine) to modify the release profiles, resulting in an increase in fibre diameter and a decrease in the specific surface area and highly hydrophobic surfaces. 

Sonseca, L. Peponi, O. Sahuquillo, J. M. Kenny and E. Gimenez, Polym. Degrad. Stabil, 2012, 97, 2052. 

The objective of all of these devices is to deliver a drug to the body at a rate predetermined by the design of the device and independent of the changing environment of the body. In conventional medications, only the total mass of drug delivered to a patient is controlled. In controlled drug delivery, both the mass and the rate at which the drug is delivered can be controlled, providing three important therapeutic benefits  

The drug is metered to the body slowly over a long period therefore, the problem of overdosing and underdosing associated with conventional periodic medication is avoided. 

The drug is given locally, ideally to the affected organ directly, rather than systemically as an injection or tablet. Localized delivery results in high concentrations of the drug at the site of action, but low concentrations and hence fewer side effects elsewhere. 

As a consequence of metered, localized drug delivery, controlled release devices generally equal or improve the therapeutic effects of conventional medications, while using a fraction of the drug. Thus, the problems of drug-related side effects are correspondingly lower. 

The concept of controlled delivery is not limited to drugs. Similar principles are used to control the delivery of agrochemicals, fertilizers and pesticides, for example, and in many household products. However, most of the technology development in the past 30 years has focused on drug delivery only this aspect of the topic is covered here. 

Weber and coworkers developed a hydrogel for time-scheduled vaccination that consists of biohybrid materials cross-linked via multiple supramolecular interactions [283]. The hydrogel is based on two eight-arm PEG species with end groups that are either functionalized with fluorescein or with a humanized single-chain 

Each of the above-mentioned applications demands materials with tailored properties to provide an efficient therapy. 

The issues of drug delivery with polymeric matrices have been viewed also from the opposite view, i.e., drug delivery with non-polymeric matrices (4). 

The literature on floating drug delivery systems with special focus on the principal mechanism of floatation to achieve gastric retention 

The role of natural polymers for drug delivery has been reviewed (6). Natural polymers that are important in drug delivery are summarized in Table 8.1. 

Alginate Carrageenan Cellulose Chitosan Marine Hydrocolloids 

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While most vesicles are formed from double-tail amphiphiles such as lipids, they can also be made from some single chain fatty acids [73], surfactant-cosurfactant mixtures [71], and bola (two-headed) amphiphiles [74]. In addition to the more common spherical shells, tubular vesicles have been observed in DMPC-alcohol mixtures [70]. Polymerizable lipids allow photo- or chemical polymerization that can sometimes stabilize the vesicle [65] however, the structural change in the bilayer on polymerization can cause giant vesicles to bud into smaller shells [76]. Multivesicular liposomes are collections of hundreds of bilayer enclosed water-filled compartments that are suitable for localized drug delivery [77]. The structures of these water-in-water vesicles resemble those of foams (see Section XIV-7) with the polyhedral structure persisting down to molecular dimensions as shown in Fig. XV-11. 

Raman spectraof [INFRARED TECHNOLOGY AND RAMAN SPECTROSCOPY - RAMAN SPECTROSCOPY] (Voll4) -role in drug delivery pRUG DELIVERY SYSTEMS] (Vol 8)... 

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