Hydrophilic carrier

Hydrophilic nanoparticle carriers have important potential applications for the administration of therapeutic molecules [28,53]. Most of the recently developed hydrophobic-hydrophilic carriers require the use of organic solvents for their preparation and have a limited protein-loading capacity [54,55]. Calvo et al. [56] reported a new approach for the preparation of nanoparticles, made solely of hydrophilic polymer, to address these limitations. The preparation technique, based on an ionic gelation process, is extremely mild and involves the mixing of two aqueous phases at room temperature. 

If it is not possible to improve the bioavailability of a substance as desired by the addition of a solubilizing agent, this is frequently because the surface area of the crystals of active ingredient exposed to the solvent is too small. It is therefore necessary to increase the surface area, to accelerate dissolution. The first solid dispersions with antibiotics in povidone were described in the literature in about i960 [49,60]. In solid solutions and dispersions the active substance is embedded in a hydrophilic carrier to improve its bioavailability. The difference between a solid solution and a solid dispersion can be defined in terms of the state of the active substance. In a solid solution, it is present in an amorphous molecular form, while in a solid dispersion it is in the form of crystals that must be as fine as possible. 

Szczesna-Antczak M, Antczak T, Rzyska M, Bielecki S (2002) Catalytic properties of membrane-bound Mucor lipase immobilized in a hydrophilic carrier. J Mol Catal B-Enzym 19-20 261-268... 

Solid dispersion is defined as one type of method to produce an amorphous compound by incorporating a hydrophobic drug into a hydrophilic carrier (Chiou and Riegelman 1971). It is one of the most studied methods to solubilize and to enhance dissolution rate of biopharmaceutical classification system (BCS) class 2 compounds. For instance, a solid dispersion of ritonavir (Law et al. 2001), ER-3421 (a dual 5-lipoxygenase/cyclooxygenase inhibitor Kushida et al. 2002), was found to have a much higher dissolution rate than the crystalline counterpart and resulted in higher area under curve (AUC) and Cmax in the in vivo study. 

The typical catalyst in fuel cells is platinum (and possibly other platinum group metals). Usually, nanoparticles of these metals are applied on carbon black as a conductive, hydrophilic carrier. In alkaline solution also silver is suitable for ORR. The moderate price of silver permits the application of pure metal as catalyst without a carrier. Additionally, the high conductivity of silver is advantageous. No silver is lost during operation and can be recycled after the ODC service life. However, the high fixed capital may be a problem. 

The conversion of a primary amino group of a PEG derivative into a tertiary alcohol in order to obtain an acid-labile protecting group on this hydrophilic carrier was described by Anzinger and Mutter [76] ... 

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