Microencapsulation Report

Abstract: The expansion of umbilical cord blood mononuclear cells (UCB MNCs) was investigated in a novel co-culture system by means of encapsulation of rabbit bone marrow (BM) mesenchymal stem cells (MSCs) in alginate beads (Alg beads). Three kinds of media were applied and the experiments lasted for 7 days. The total nucleated cell density was measured every 24 h. Flow cytometric assay for CD34⁺ cells and methylcellulose colony assays were carried out at 0, 72 and 168 h. It was found that the encapsulated MSCs illustrated remarkable effects on UCB MNCs expansion regardless of whether serum is present in culture media or not. At the end of 168 h co-culture, the total nucleated cell number was multiplied by 15 ± 2.9 times, and CD34⁺ cells 5.3 ± 0.3 times and colony-forming units in culture (CFU-Cs) 5.6 ± 1.2 times in the serum-free media supplemented with conventional dose of cytokines, which was very similar to the results in the containing 20% serum media. While in the control, i.e. MNC expansion without encapsulated MSCs, however, total nucleated cells density changed mildly, CD34⁺ cells and CFU-Cs showed little effective expansion. It is demonstrated that the encapsulated stromal cells can support the expansion of UCB MNCs effectively under the experimental condition.

Authors: Yang Liu;  Tianqing Liu;  Xuehu Ma;  Xiubo Fan;  Chunyu Bao; Zhanfeng Cui

Source: Journal of Microencapsulation, Volume 26, Issue 2 March 2009, pages 130 – 142

Abstract: A common method used to prepare polymeric nanoparticles in pharmaceutical technology is emulsion-diffusion. However, this method has several disadvantages due to the long duration of the process. At the diffusion step of conventional emulsion-diffusion, high pressure treatment could replace the addition of great quantities of water resulting in diffusion of the solvents from the internal phase to the external phase. The objective of the present study was to develop a novel method for nanoparticle formulation by combining high pressure treatment with the emulsion-diffusion method to avoid an additional diffusion step in the aqueous phase. After emulsification at 11 000 rpm, the emulsions were pressurized at 100, 200 and 300 Mpa, each for 300, 600, 900 or 1200 s. The mean size and morphology of the nanoparticles were analysed by Mastersizer®, TEM and SEM. The mean size of pressurized emulsion nanoparticles was the same at 100 MPa for holding times up to 600 s. Also, the pressurized emulsion nanoparticle size increased and the peak and width of the size distribution curve was higher and slightly narrower depending on the pressure and the holding time. This study shows that pressure treatment can produce polymer membranes surrounding the oil surface owing to the precipitation of PCL, inducing the diffusion of solvent from the interior to the exterior based on TEM images. From these results, it is believed that high pressure treatment should be considered as a successful alternative for preparing nanoparticles.

Authors: Mi-Yeon Lee;  Sang-Gi Min;  Sandrine Bourgeois; Mi-Jung Choi

Source: Journal of Microencapsulation, Volume 26, Issue 2 March 2009, pages 122 – 129

Abstract: Chitosan microparticles for delivery of proteins were prepared by spray-drying technique. The effects of formulation (molecular weight and concentration of chitosan) and process variables (inlet drying air temperature and spray rate) on size and morphology of microparticles were characterized. Size of microparticles was mainly controlled by formulation variables, while particle morphology was influenced by both formulation and process variables investigated in this study. Bovine serum albumin (BSA), as a model protein, was loaded into microparticles at different levels. BSA-loaded chitosan microparticles were characterized in terms of physicochemical properties and integrity of encapsulated protein, which was studied by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and circular dichroism. Size of microparticles ranged between 3.760-8.681 µm, of which BSA-loaded microparticles were larger in size than their corresponding blank microparticles. All microparticles showed dented or distorted surface, especially when BSA was incorporated, with positive surface charge exposed. Burst release of protein was observed. The effect was more pronounced as BSA loading level was increased. Integrity of entrapped protein could be retained when BSA was incorporated at high loading level. In conclusion, chitosan microparticles for delivery of protein could be efficiently prepared by spray-drying technique. The encapsulated protein was capable of retaining its integrity after the preparation process.

Authors: Chirasak Kusonwiriyawong;  Wiwat Pichayakorn;  Vimolmas Lipipun; Garnpimol C. Ritthidej

Source: Journal of Microencapsulation, Volume 26, Issue 2 March 2009, pages 111 – 121

Abstract: In 1980, Lim and Sun introduced a microcapsule coated with an alginate/polylysine complex for encapsulation of pancreatic islets. Characteristic to this type of capsule is, that it consists of a plain membrane which is formed during a single procedural step. With such a simple process it is difficult to obtain instantly a membrane optimized with respect to all the properties requested for islet transplantation. To overcome these difficulties, it is recommended to build up the membrane in several consecutive steps, each optimized for a certain property. In this study, we have analysed such a multilayer microcapsule for the encapsulation of pancreatic islets. Therefore, empty and islet containing alginate beads were coated with alternating layers of polyethyleneimine, polyacrylacid or caboxymethylcellulose and alginate. By scanning electron microscopy the thickness of the covering multilayer-membrane was estimated to be less than 800 nm by comparison with an apparatus scale. Ellipsometric measurements showed that the membrane thickness is in the range of 145 nm. Neither the encapsulation procedure, nor the membrane-forming step did impede the stimulatory response of the islets. The encapsulation even lead to a significantly better stimulatory response of the encapsulated islets during week three and five of cell culture. Furthermore, the multilayer-membrane did not deteriorate the biocompatibility of the transplanted microcapsules, allowing an easy tuning of the molecular cut-off and the mechanical stability depending on the polycation–polyanion combination used. The multilayer membrane capsule has obvious advantages compared to a one-step encapsulation procedure. These beads guarantee a high biocompatibility, a precisely adjusted cut-off, an optimal insulin-response and high mechanical stability although the membrane is only 145 nm thick.

Authors: Stephan Schneider, Peter Johannes Feilen, Viola Slotty, Daniel Kampfner, Simon Preuss, Svend Berger, Jürgen Beyer and Rainer Pommersheim

Source: Biomaterials, Volume 22, Issue 14, 2001, Pages 1961-1970

Outline:
1. Introduction
2. Methods and materials
2.1. Islet isolation
2.2. Materials for encapsulation
2.3. Preparation of empty capsules and capsules containing islets (Fig. 1)
2.4. Measurement of the mechanical stability
2.5. Measurement of capsule size and physical integrity
2.6. Permeability measurements
2.7. Preparation of films for ellipsometric measurements
2.8. Culture conditions and insulin secretion
2.9. Transplantation procedure
2.10. Histology
2.11. Quantification of fibrosis as a marker of biocompatibility
2.12. Statistical analysis
3. Results
3.1. Physical integrity of the membrane and in vivo stability assay
4. Discussion
Acknowledgements
References

Abstract: Polysulphone (PSF) microcapsules containing 1-octanol were prepared with solvent extraction method for the recovery of caprolactam. One-step and two-step processes were, respectively, applied to prepare microcapsules. In order to get high extractant loading, a loading method with the assistance of ultrasound has been developed. With the two-step preparation process the extractant loss can be avoided. A very high extractant loading ratio of 5.96 g g-1 and the maximum uptake to caprolactam of 65.6 mg g-1 were achieved. Under the action of ultrasound the extractant loading efficiency is greatly intensified. With the one-step process 1-octanol loading ratio is highly limited. Only 1.74 g g-1 loading ratio and 29.9 mg g-1 uptake to caprolactam were realized. Meanwhile the extractant loss in the one-step process is serious. Considering extraction capacity and extractant loss in the preparation process, it is suggested that PSF microcapsules containing 1-octanol should be prepared with the two-step process. To fasten mass transfer rate, microcapsules with relatively smaller size are desired.

Published in:  Journal of Microencapsulation, Volume 26, Issue 2 March 2009 , pages 104 – 110