Congealing

Rapidly cooled materials are often unstable as a result of changes in their physical properties due to imperfect crystallization. In the process of congealing, melted material is atomized into droplets that are very quickly solidified. This increases the possibility of the material crystallizing in different metastable forms. Congealing is applicable to formation of nanostructured materials, like nanoparticles and nano-capsules. Nanostructured materials have a relatively large proportion of their atoms associated with the grain boundary and the method used to develop the nanograins has a strong influence on the resulting grain boundary structure.

Isothermal microcalorimetry was used to observe the change in the thermodynamic state of spray-congealed carnauba wax during storage [549]. In order to accelerate the thermodynamic change in the spray-congealed wax, three annealing procedures were developed using isothermal microcalorimetry. By means of annealing, a spray-congealed product closer to a thermodynamically stable state was achieved.

Hard shell capsules containing four theophylline compounds of different solubilities (theophylline, etofylline, diprophylline, and proxyphylline) were prepared with saturated polyglycolyzed glycerides (Gelucires) [550]. A polyvalent formulation was obtained after granulation by melting and congealing and use of glyceryl behenate (Compritol) as a lubricant of the solidified suspensions.

Pseudoephedrine HCl-carnauba wax microparticles were prepared by a multiple emulsion-melt dispersion technique

[551]. A heated aqueous drug solution was emulsified into the wax melt (w/o emulsion), followed by emulsification of this primary emulsion into a heated external aqueous phase (w/o/w emulsion). The drug-containing microparticles were formed after cooling and congealing of the wax phase. The encapsulation efficiencies were above 80% and actual drug loadings close to 50% were achieved.

An emulsion-congealing technique was used to prepare prolonged release lipid micropellets containing ketoprofen

[552]. The lipid matrix consisted of cottonseed oil/beeswax mixture and was emulsified at 70 °C into 0.1 N HC1 containing Tween 60 and gelatin.

The progress toward the development of a single dose tetanus vaccine is limited by the poor stability of the protein antigen, tetanus toroid, during its encapsulation in, and release from, biodegradable polymer microspheres. To investigate alternative microencapsulation approaches for improving the stability of the tetanus toroid under these conditions, a two-step microencapsulation method was devised to form microcapsules which consisted of forming micro-cores of the tetanus toroid in a hydrophilic support matrix by spray-congealing, followed by coating the microcores with poly(lactide-co-glycolide) by an oil-in-oil solvent extraction method [553]. Several protein stabilizers including gelatin (with or without poloxamer 188), dextran, sodium glutamate, and polyethylene glycol were examined as potential core materials.

The effects of operating conditions in the spray-congealing process on the release and the micromeritic properties of clarithromycin wax matrix were evaluated

[554]. An atomizer that operates with ultrasonic energy was described which obtained microparticulate drug delivery systems through spray-congealing or spray-drying technologies

[555]. The formulations under examination contained theophylline and fenbufen as model drugs and stearic acid, carnauba wax, Cutina HR, and Compritol 888 ATO as low melting excipients. Nonaggregate and spherical-shaped microparticles were obtained with all the materials tested.

The attrition milling iron powders and blends of iron powders produced micrometer-size particles composed of nano-size grains [556]. Mechanical cold-working powder resulted in dislocation generation, multiplication, and congealing that produced grain refinement. Mechanical alloying of substi-tutional aluminium atoms into iron powder resulted in the aluminum atoms substituting for iron atoms in the grain boundary cells. Attrition milling iron powder in nitrogen gas resulted in nitrogen atoms being adsorbed onto the particle surface.

Marking on a silicon wafer with a small dot matrix was performed using a diode-pumped second-harmonic generation laser of yttrium aluminum garnet, liquid-crystal-display mask, and projection optics [557].

As a novel alternative to the incorporation into hard gelatin capsules or tablets, extended-release (Aquacoat- or Eudragit RS-coated) or enteric (Eudragit L-coated) pellets were embedded into congealed tablet-shaped polyethylene glycol (PEG) plugs of different molecular weights, which rapidly released the pellets upon contact with aqueous Ruids [558]. The lower-molecular-weight PEGs (600 and 1000) were not suitable carrier materials, since they dissolved the coatings or significantly increased their permeability. The release characteristics of the original pellets were maintained after embedding the pellets into the higher-molecular-weight PEG 4000 or 10,000.

The degree of bitterness of clarithromycin dry syrup was evaluated using several methods [559]. Using the inversion method, shaking method, and paddle method, a reasonable correlation between the bitter taste and the amount dissolved was not observed. A minicolumn packed with clar-ithromycin dry syrup was used for the release test.

The methods were used in ink application and combining ink-labeled biopsy specimens into fewer containers with the goal of maintaining information regarding location while minimizing expense [560]. The ink adhered well to dry cores, but these cores exhibited dehydration artifacts. Placing the cores on a wet sponge avoided dehydration but caused ink spread. With protocol, all biopsy specimens were placed on separate moistened gauze sponges. Specimens from the right side of the prostate were marked with green ink, and those from the left side were marked with black ink using a cotton swab. After applying 1% acetic acid to each core, the left and right cores from each location were placed in a single container. This method curbed pathology expenses and maintained tumor location information.

The utilization of a spray-congealing technique using an ultrasonic atomizer to prepare enhanced-release, solventfree microspheres of carbamazepine-Gelucire 50/13 in different drug-to-polymer ratios was considered [561]. The spherically shaped and nonaggregated microparticles were obtained and the microspheres had a good encapsulation efficiency (>90% in the prevalent size fraction).

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