Semiautomatic macroencapsulation of large numbers of porcine hepatocytes by coextrusion with a solution of AN69 polymer

Microencapsulation for Pharmaceutical Applications: A Review

In order to improve bioavailability, stability, control release, and target delivery of active pharmaceutical ingredients (APIs), as well as to mask their bitter taste, to increase their efficacy, and to minimize their side effects, a variety of microencapsulation (including nanoencapsulation, particle size <100 nm) technologies have been widely used in the pharmaceutical industry. Commonly used microencapsulation technologies are emulsion, coacervation, extrusion, spray drying, freeze-drying, molecular inclusion, microbubbles and microsponge, fluidized bed coating, supercritical fluid encapsulation, electro spinning/spray, and polymerization. In this review, APIs are categorized by their molecular complexity: small APIs (compounds with low molecular weight, like Aspirin, Ibuprofen, and Cannabidiol), medium APIs (compounds with medium molecular weight like insulin, peptides, and nucleic acids), and living microorganisms (such as probiotics, bacteria, and bacteriophages). This article provides an overview of these microencapsulation technologies including their processes, matrix, and their recent applications in microencapsulation of APIs. Furthermore, the advantages and disadvantages of these common microencapsulation technologies in terms of improving the efficacy of APIs for pharmaceutical treatments are comprehensively analyzed. The objective is to summarize the most recent progresses on microencapsulation of APIs for enhancing their bioavailability, control release, target delivery, masking their bitter taste and stability, and thus increasing their efficacy and minimizing their side effects. At the end, future perspectives on microencapsulation for pharmaceutical applications are highlighted.

Advances in polymer-based cell encapsulation and its applications in tissue repair

Cell microencapsulation is a more widely accepted area of biological encapsulation. In most cases, it involves fixing cells in polymer scaffolds or semi-permeable hydrogel capsules, providing the environment for protecting cells, allowing the exchange of nutrients and oxygen, and protecting cells against the attack of the host immune system by preventing the entry of antibodies and cytotoxic immune cells. Hydrogel encapsulation provides a three-dimensional (3D) environment similar to that experienced in vivo, so it can maintain normal cellular functions to produce tissues similar to those in vivo. Embedded cells can be genetically modified to release specific therapeutic products directly at the target site, thereby eliminating the side effects of systemic treatments. Cellular microcarriers need to meet many extremely high standards regarding their biocompatibility, cytocompatibility, immunoseparation capacity, transport, mechanical, and chemical properties. In this article, we discuss the biopolymer gels used in tissue engineering applications and the brief introduction of cell encapsulation for therapeutic protein production. Also, we review polymer biomaterials and methods for preparing cell microcarriers for biomedical applications. At the same time, in order to improve the application performance of cell microcarriers in vivo, we also summarize the main limitations and improvement strategies of cell encapsulation. Finally, the main applications of polymer cell microcarriers in regenerative medicine are summarized.

Noninvasive bioluminescent quantification of viable stem cells in engineered constructs

Bioluminescence from murine stem cells tagged with the luciferase gene reporter and distributed within three-dimensional scaffolds of two different materials is quantified in vitro and in vivo. The luminescence emitted from cells adhering to the scaffolds tested is monitored noninvasively using a bioluminescence imaging system. Monitoring the kinetics of luciferase expression via bioluminescence enables real-time assessment of cell survival and proliferation on scaffolds both in vitro and in vivo over prolonged (8 weeks) periods of time.

In vitro and in vivo bioluminescent quantification of viable stem cells in engineered constructs

Bioluminescent quantification of viable cells inside three-dimensional porous scaffolds was performed in vitro and in vivo. The assay quantified the bioluminescence of murine stem (C3H10T1/2) cells tagged with the luciferase gene reporter and distributed inside scaffolds of either soft, translucent, AN69 polymeric hydrogel or hard, opaque, coral ceramic materials. Quantitative evaluation of bioluminescence emitted from tagged cells adhering to these scaffolds was performed in situ using either cell lysates and a luminometer or intact cells and a bioluminescence imaging system. Despite attenuation of the signal when compared to cells alone, the bioluminescence correlated with the number of cells (up to 1.5 x 10(5)) present on each material scaffold tested, both in vitro and noninvasively in vivo (subcutaneous implants in the mouse model). The noninvasive bioluminescence measurement technique proved to be comparable to the cell-destructive bioluminescence measurement technique. Monitoring the kinetics of luciferase expression via bioluminescence enabled real-time assessment of cell survival and proliferation on the scaffolds tested over prolonged (up to 59 days) periods of time. This novel, sensitive, easy, fast-to-implement, quantitative bioluminescence assay has great, though untapped, potential for screening and determining noninvasively the presence of viable cells on biomaterial constructs in the tissue engineering and tissue regeneration fields.

Present and Future Developments in Hepatic Tissue Engineering for Liver Support Systems : State of the art and future developments of hepatic cell culture techniques for the use in liver support systems

The liver is the most important organ for the biotransformation of xenobiotics, and the failure to treat acute or acute-on-chronic liver failure causes high mortality rates in affected patients. Due to the lack of donor livers and the limited possibility of the clinical management there has been growing interest in the development of extracorporeal liver support systems as a bridge to liver transplantation or to support recovery during hepatic failure. Earlier attempts to provide liver support comprised non-biological therapies based on the use of conventional detoxification procedures, such as filtration and dialysis. These techniques, however, failed to meet the expected efficacy in terms of the overall survival rate due to the inadequate support of several essential liver-specific functions. For this reason, several bioartificial liver support systems using isolated viable hepatocytes have been constructed to improve the outcome of treatment for patients with fulminant liver failure by delivering essential hepatic functions. However, controlled trials (phase I/II) with these systems have shown no significant survival benefits despite the systems' contribution to improvements in clinical and biochemical parameters. For the development of improved liver support systems, critical issues, such as the cell source and culture conditions for the long-term maintenance of liver-specific functions in vitro, are reviewed in this article. We also discuss aspects concerning the performance, biotolerance and logistics of the selected bioartificial liver support systems that have been or are currently being preclinically and clinically evaluated.

The viability and function of primary rat hepatocytes cultured on polymeric membranes developed for hybrid artificial liver devices

Bioartificial liver devices require membranes to support the function and viability of hepatocytes because they are anchorage-dependent cells. This study investigated the ability of several polymeric membranes to support the functions of primary hepatocyte cultures. Tailor-made membranes were sought by synthesizing acrylonitrile copolymers with different comonomers resulting in ionic, hydrophilic, or reactive functional groups on the polymer surface. Hepatocyte morphology and viability were assessed by confocal microscopy, and function by the content and activities of cytochrome P450, and the expression of glutathione S-transferases. Hydrophilic membranes (polyacrylonitrile and acrylonitrile copolymerized with 2-acrylamino-2-methyl-propane sulfonic acid) were more biocompatible than hydrophobic membranes such as polysulfone. The chemistry of the hydrophilic group was important; amine groups had a deleterious effect on maintenance of the primary hepatocytes. The biocompatibility of hydrophobic membranes was improved by collagen coating. Improving the chemistry of membranes for artificial liver devices will enhance the phenotypic stability of the cells, enabling us to prolong treatment times for patients.

Morphology and metabolism of Ba-alginate-encapsulated hepatocytes with galactosylated chitosan and poly(vinyl alcohol) as extracellular matrices

Lactobionic acid, bearing a beta-galactose group, was coupled with chitosan to provide synthetic extracellular matrices together with poly(vinyl alcohol) (PVA). The hepatocytes encapsulated in Ba-alginate capsules with galactosylated chitosan (GC) and PVA as extracellular matrices showed aggregation morphologies as the incubation time increased. Ba-alginate-encapsulated hepatocytes with GC exhibited a higher metabolic function in albumin secretion compared to those entrapped in Ba-alginate beads and monolayer-cultured on a collagen-immobilized polystyrene dish. The ammonia removal ability of monolayer-cultured hepatocytes decreased with increasing culture time and disappeared completely after three days. In contrast, the ammonia removal ability of encapsulated and entrapped hepatocytes increased with increasing incubation time in the first seven and five days, respectively. Thereafter, the entrapped hepatocytes lost ammonia removal ability quickly while the encapsulated hepatocytes kept a relatively high ammonia removal ability up to 13 days. The trace amount of GC in the core matrices enabled encapsulated cells to enhance their ammonia removal and albumin secretion ability. The results obtained with 3-(3,4-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) also showed that the capsules incorporated with GC can provide a better microenvironment for cell aggregation along with nutrition and metabolite transfer. Due to the nature of the liquid core, the encapsulated hepatocytes showed very good mobility. This facilitated cell-cell interaction and cell-matrix interaction.

Survival and differentiation of porcine hepatocytes encapsulated by semiautomatic device and allotransplanted in large number without immunosuppression

BACKGROUND/AIMS

The aim of this study was to evaluate the survival and functions of porcine hepatocytes transplanted in large quantities in the peritoneal cavity of allogeneic animals following semiautomatic encapsulation.

METHODS

Isolated porcine hepatocytes and a polymer solution composed of AN69 were coextruded through a double lumen spinneret. Minitubes containing hepatocytes were transplanted in the peritoneal cavity of 12 pigs (4 x 10(9) cells/animal) in the absence of immunosuppressive therapy. Seven, 15, and 21 days after transplantation, minitubes was collected and processed for analyses. The morphology was examined under light and electron microscopy. Albumin synthesis was assessed by semi-quantitative reverse transcription-polymerase chain reaction. Cytochrome P450 3A (CYP3A) gene expression was analyzed by Western blot and by testosterone 6-beta-hydroxylation assay.

RESULTS

The device allowed to encapsulate 55 x 10(6) hepatocytes/min. Hepatocytes exhibited normal structural and ultrastructural features up to day 21. Albumin gene expression decreased progressively between days 0 and 21. The amount of CYP3A protein and 6-beta-hydroxylase activity were approximately 2-fold lower at days 7 and 15 than in freshly encapsulated hepatocytes, and further decreased thereafter.

CONCLUSIONS

The preservation of hepatocyte functions during 1-2 weeks is encouraging for potential short-term use of such bioartificial liver in future clinical application.