Entrapment efficiency

A review of chitosan microspheres as carrier for drugs pubUshed recently by Sinha et al. provides insight into the exploitation of the various properties of chitosan to microencapsulate drugs. Various techniques used for preparing chitosan microspheres and evaluation protocols have also been reviewed, together with the factors that affect the entrapment efficiency and release ki-nefics of drugs [194]. 

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],... 

Song, X., Zhao, Y., Hou, S., Xu, F., Zhao, R., He, J., Cai, Z., Li, Y. and Chen, Q. (2008) Dual agents loaded PLGA nanopartides systematic study of particle size and drug entrapment efficiency. European Journal of Pharmaceutics and Biopharmaceutics, 69, 445-453. 

CaC03 precipitation is clearly visible in Figure 14.14, which is a TEM image of halloysite cross-sections. Halloysite has >90% of the tubular form with outer diameter 50 5nm and inner diameter of the lumen 15 nm. The length of the initial halloysite is less than 1 micron, which results in a substantially short diffusion path length. The calculated value of the free inner space indicates the ability to load a maximum 14 3 % of the total volume ofthe halloysite. The entrapment efficiency of 5 % by volume was estimated. 

Figure 3 Plot of the entrapment efficiency expressed as the entrapped oligonucleotide-to-lipid ratio (full circles) and percent entrapment (open circles) as a function of the initial oligonucleotide-to-lipid ratio. The ratios are given in w/w. Abbreviation AS, antisense oligonucleotide.

There are several other ways to entrap solutes inside the liposomes, and the entrapping efficiency depends on the structure of liposomes (small unilamellar, large unilamellar, multilamellar, vesicles, etc.) and from the technique for liposome preparation (Roseman etal., 1978 Cullis etal., 1987 Walde and Ishikawa, 2001). 

The enzyme-containing nanosize silica particles prepared by Jain et al. (33) were characterized for their particle size (dynamic light scattering and TEM), entrapment efficiency, in vitro leaching capacity, and enzyme activity. For all three biomolecules, the entrapment efficiency was 80-90% and the entrapped molecules were found to be stable towards leaching (up to 45 days). The enzymatic activity of the entrapped molecules was lower than that of the corresponding free molecules, a result that was attributed to diffusional constraints. 

As an example, the liposome-entrapment efficiency of md-LErafAON formulation was found to be greater than 80% in two independent experiments (see Note 7). 

The liposome-entrapped rafAON is stored at 4°C and used within 3days after preparation. Entrapment efficiency is verified using at least three independent preparations, and each preparation tested in triplicate. 

The entrapment efficiency is tested immediately after formulation (0 h postpreparation) and on day 8 post-preparation. The liposome-entrapment efficiency of rafAON is unchanged for up to at least 1 week after formulation. 

One phase contains the polysaccharide chitosan (CS) and a diblock copolymer of ethylene oxide and the polyanion sodium tripolyphosphate (TPP). It was stated that the size (200-1000 nm) and zeta potential (between + 20 mV and + 60 mV) of nanoparticles can be conventionally modulated by varying the ratio of CS/PEO to PPO. Furthermore, using BSA as a model protein, it was shown that these new nanoparticles have a high protein loading capacity (entrapment efficiency up to 80 % of the protein) and provide a continuous release of the entrapped protein for up to 1 week [56]. 

Entrapment efficiency depended on the concentration of the core polymeric solution. No attempts have been made to optimize this parameter. Currently, the entrapment efficiencies for proteins are in the 5-20 % range, and the loading efficiencies are between 10-50 %. Figs. 3 and 4 present batch data for variable amounts of OVA in the reaction mixture (System 2). In either case no saturation was reached. 

For a binary system (one polycation and one polyanion on each interaction side), CT/TPP, Calvo et al. [15] described very high entrapment efficiencies from 20 to 92 %. CT/TPP PEO or PEO/PPO polymers were co-entrapped within the final product. Nanoparticles were formed spontaneously by simple mixture of... 

Fig. 3. Effect of initial ovalbumin concentration on entrapment efficiency in a batch system. Nanoparticulate chemistry (System 2) was as follows Core 0.05% HV,0.05% CS, variable amount of OVA, 1-8% Shell 0.05% SP, 0.075% PMCG, 0.05% CaCl2, 1% F-68. C/S ratio = 2/20 (mL/mL). Data are presented as the mean SD (n = 4)...

Fig. 5. Effect of initial BSA concentration and pH of CT solution on entrapment efficiency (mean SD, n = 3) for CT/TPP nanoparticles (reproduced from Calvo et al. 1997, with permission of Plenum Press [15])...

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