Hydrophilic polymers drug delivery

Solubilization of vinylpyrrolidone, acrylic acid, and A,A -methylene-bis-acrylamide in AOT-reversed micelles allowed the synthesis in situ of a cross-linked polymer with narrow size distribution confined in the micellar domain. These particles displayed high entrapment efficiency of small hydrophilic drugs and have been considered interesting drug delivery systems [239],... 

New drug delivery systems are of great scientific and commercial interest. Amphiphilic networks composed of about 50/50 hydrophobic PIB and hydrophilic poly(2-(-dimethylamino)ethyl methacrylate) (DMAEMA) polymer segments were found to be biocompatible and to a large extent avascular (7). These PHM-PDMAEMA networks (i, in line with propositions of Weber and Stadler (2), and Sperling (J), denotes PDMAEMA chains linked by PIB chains) gave pH dependent... 

However, the choice of a class of polymer for use in a given drug delivery system is often made for reasons unrelated to its swelling properties the polymer might be chosen on the basis of cost, availability, supplier, biocompatibility, past use history, etc. Thus the hydrophilicity and % will be fixed, and only the crosslink density and the ionic component can be readily adjusted to provide the swell-... 

Polymer micelles are nanometer sized (usually several tens of nanometers) self-assembled particles having a hydrophobic core and hydrophilic outer shell composed of amphiphilic AB- or ABA-type block copolymers, and are utilized as drug delivery vehicles. The first polymer micelle-type drug delivery vehicle was made of PEG-b-poly(aspartic acid) (PEG-b-PAsp), immobilizing the hydro-phobic anticancer drugDXR [188-191]. After this achievement by Kataoka et al., a great amount of research on polymer micelles has been carried out, and there are several reviews available on the subject [192-194]. 

Fig. 30 Types of nanocarriers for drug delivery, (a) Polymeric nanoparticles polymeric nanoparticles in which drugs are conjugated to or encapsulated in polymers, (b) Polymeric micelles amphiphilic block copolymers that form nanosized core-shell structures in aqueous solution. The hydrophobic core region serves as a reservoir for hydrophobic drugs, whereas hydrophilic shell region stabilizes the hydrophobic core and renders the polymer water-soluble.

Poly(2-hydroxyethyl methacrylate) (PHEMA) has been the most widely used polymer in drug delivery applications. It is an extremely hydrophilic... 

Another hydrophilic polymer that has received attention is poly(vinyl alcohol) (PVA). This material holds tremendous promise as a biological drug delivery device because it is nontoxic, hydrophilic and exhibits good mucoadhesive properties (Peppas, 1987). In one of the first applications of this material, Langer and Folkman (1976) investigated the use of copolymers of PHEMA (Hydron ) and PVA as delivery vehicles for polypeptide drugs. 

In the last few years there have been new creative methods of preparation of novel hydrophilic polymers and hydrogels that may represent the future in drug delivery applications. The focus in these studies has been the development of polymeric structures with precise molecular architectures. Stupp et al. (1997) synthesized self-assembled triblock copolymer, nanostructures that may have very promising applications in controlled drug delivery. Novel biodegradable polymers, such as polyrotaxanes, have been developed that have particularly exciting molecular assemblies for drug delivery (Ooya and Yui, 1997). 

The classification of polymers for oral drug delivery can be done by using various means. To make this discipline readily accessible to the novice reader, the hydro-phobic-hydrophilic nature of the polymer was chosen to group polymers since the mechanism of biomacromolecule release from most hydrophobic polymeric devices is similar the mechanism of release from most hydrophilic polymeric devices also have similar mechanisms. Hydrophobic polymers are described first, followed by hydrophilic polymers. 

Diacyllipid-polyethyleneoxide conjugates have been introduced into the controlled drug delivery area as polymeric surface modiLers for liposomes (Klibanov et al., 1990). Being incorporated into the liposome membrane by insertion of their lipidic anchor into the bilayer, such molecules can ster-ically stabilize the liposome against interaction with certain plasma proteins in the blood that results in signiLcant prolongation of the vesicle circulation time. The diacyllipid-PEO molecule itself represents a characteristic amphiphilic polymer with a bulky hydrophilic (PEO) portion and a very short but extremely hydrophobic diacyllipid part. Typically, for other PEO-containing amphiphilic block... 

Delivery systems that use a multicompartment core can theoretically deliver drugs of any solubility [48,49], A basic Push-Pull System consists of two layers the Lrst contains the drug, osmotically active hydrophilic polymer(s), and other pharmaceutical excipients the second layer, often called the push layer, contains a hydrophilic expansion polymer, other osmotically active agents, and the excipients, as shown in Figure 22.6. Poorly water-soluble compounds can be delivered using an ORO Push-Pull tlelivery system by incorporating drug as a micronized form, or as a hot-melt material suspended in a polymer matrix. 

Feldstein, M., Vasiliev, A., and Plate, N. Enhanced drug delivery from transdermal therapeutic systems with hydrophilic polymer matrix. Int. Symp. Contr. Rel. Bioact. Mater. 21 423-424, 1994. 

To restrict water entry into certain parts of the delivery system and to separate the drug layer from the osmotic layer, different materials are used as barrier layers. In a multilayered reservoir, the water-permeable coat consists of hydrophilic polymers. In contrast, water-impermeable layers are formed from latex materials such polymethacrylates (Table 7.1). Further, a barrier layer can be provided between the osmotic composition and the drug layer that consists of substantially fluid-impermeable materials such as high-density polyethylene, a wax, a rubber, and the like.20... 

---