Carriers, concepts

Liposomes represent highly versatile drag carriers, offering almost infinite possibilities to alter structural and physicochemical characteristics. This feature of versatility enables the formulation scientist to modify liposomal behaviour in vivo and to tailor liposomal formulations to specific therapeutic needs. It has taken two decades to develop the liposome carrier concept to a pharmaceutical product level, but commercial preparations are now available in important disease areas and many more formulations are currently undergoing clinical trials. Examples of the different applications and commercial products of various types of liposomal systems are given below. 

Gregoriadis, G. (1978), Liposomes in therapeutic and preventive medicine The development of the drug-carrier concept, Ann. N.Y. Acad. Sci., 308, 343-370. 

Hudecz, F. and Szekerke, M. (1980) Investigation of drug-protein interactions and the drug-carrier concept by the use of branched polypeptides as model systems. Synthesis and characterization of the model peptides. Coll. Czech. Chem. Commun. 45, 933—940. 

The mould carrier concept for fixing and centring is designed for quick mould carrier removal or exchange. 

G. Gregoriadis, Liposomes in Therapeutic and Preventive Medicine The Development of Drug-Carrier Concept, Ann. N. Y. Acad. Sci. 308 343 (1978). 

Most nonexempt nonacute hazardous waste generated on location is considered a small quantity. In this case, the waste may remain on location for 90 days. At that time, a Department of Transportation licensed motor carrier must transfer the waste to a EPA certified TSDF for disposal. Appropriate documentation and packaging must be conformed to. The operator continues to be liable for the waste as denoted by the cradle to grave concept [233],... 

The percolation theory [5, 20-23] is the most adequate for the description of an abstract model of the CPCM. As the majority of polymers are typical insulators, the probability of transfer of current carriers between two conductive points isolated from each other by an interlayer of the polymer decreases exponentially with the growth of gap lg (the tunnel effect) and is other than zero only for lg < 100 A. For this reason, the transfer of current through macroscopic (compared to the sample size) distances can be effected via the contacting-particles chains. Calculation of the probability of the formation of such chains is the subject of the percolation theory. It should be noted that the concept of contact is not just for the particles in direct contact with each other but, apparently, implies convergence of the particles to distances at which the probability of transfer of current carriers between them becomes other than zero. 

Its main features are given by the use of a stream of inert carrier gas which percolates through a bed of an adsorbent covered with adsorbate and heated in a defined way. The desorbed gas is carried off to a detector under conditions of no appreciable back-diffusion. This means that the actual concentration of the desorbed species in the bed is reproduced in the detector after a time lag which depends on the flow velocity and the distance. The theory of this method has been developed for a linear heating schedule, first-order desorption kinetics, no adsorbable component in the entering carrier gas (Pa = 0), and the Langmuir concept, and has already been reviewed (48, 49) so that it will not be dealt with here. An analysis of how closely the actual experimental conditions meet the idealized model is not available. 

A variety of other clinically important infections, such as brucellosis, listeriosis, salmonellosis, and various Mycobacterium infections, are of interest as these are often localized in organs rich in MPS cells. Liposome encapsulation has been demonstrated to improve therapeutic indices of several drugs in a number of infectious models. The natural avidity of macrophages for liposomes can also be exploited in the application of the vesicles as carriers of immunomodulators to activate these cells to an microbicidal, antiviral, or tumoricidal state. These studies were recently reviewed by Emmen and Storm (1987), Popescu et al. (1987), and Alving (1988). In addition to the treatment of "old" infectious diseases, the concept of MPS-directed drug delivery is of considerable interest for the therapy AIDS, possibly enabling control of human immunodeficiency virus replication in human macrophages. 

Eor galvanic circuits (cells) the OCV generally is not zero. In contrast to metal circuits, where electrons are the sole carriers, in galvanic circuits the current is transported by different carriers in the different circuit parts (i.e., by electrons and by ions). Hence when substituted into Eq. (2.9), the chemical potentials of the carriers in the intermediate circuit parts will not cancel. The concept of OCV in the case of... 

Among these one of the most promising concepts is the development of single electron (SE) devices, which retain their scalability down to the molecular level. At present, due to exploitation of charging (Coulomb) effects in metallic SE devices comprising tunnel junctions with submicrometer size, individual charge carriers can be handled... 

In the sixties of past century, a few patents issued to Bergbau Chemie [5,48,49] and to Mobil Oil [50-52], respectively described the use of CFPs as supports for catalytically active metal nanoclusters and as carriers for heterogenized metal complexes of catalytic relevance. For the latter catalysts the term hybrid phase catalysts later came into use [53,54], At that time coordination chemistry and organo-transition metal chemistry were in full development. Homogeneous transition metal catalysis was expected to grow in industrial relevance [54], but catalyst separation was generally a major problem for continuous processing. That is why the concept of hybrid catalysis became very popular in a short time [55]. 

The concept of immunoassay was first described in 1945 when Landsteiner suggested that antibodies could bind selectively to small molecules (haptens) when they were conjugated to a larger carrier molecule. This hapten-specific concept was explored by Yalow and Berson in the late 1950s, and resulted in an immunoassay that was applied to insulin monitoring in humans. This pioneering work set the stage for the rapid advancement of immunochemical methods for clinical use. 

---