Dopamine secretion by PC12 cells microencapsulated in a hydroxyethyl methacrylate--methyl methacrylate copolymer

Formulation and Characterization of Microcapsules Encapsulating PC12 Cells as a Prospective Treatment Approach for Parkinson's Disease

Parkinson's disease (PD) is the second most common neurological disorder, associated with decreased dopamine levels in the brain. The goal of this study was to assess the potential of a regenerative medicine-based cell therapy approach to increase dopamine levels. In this study, we used rat adrenal pheochromocytoma (PC12) cells that can produce, store, and secrete dopamine. These cells were microencapsulated in the selectively permeable polymer membrane to protect them from immune responses. For fabrication of the microcapsules, we used a modified Buchi spray dryer B-190 that allows for fast manufacturing of microcapsules and is industrially scalable. Size optimization of the microcapsules was performed by systematically varying key parameters of the spraying device. The short- and long-term stabilities of the microcapsules were assessed. In the in vitro study, the cells were found viable for a period of 30 days. Selective permeability of the microcapsules was confirmed via dopamine release assay and micro BCA protein assay. We found that the microcapsules were permeable to the small molecules including dopamine and were impermeable to the large molecules like BSA. Thus, they can provide the protection to the encapsulated cells from the immune cells. Griess's assay confirmed the non-immunogenicity of the microcapsules. These results demonstrate the effective fabrication of microcapsules encapsulating cells using an industrially scalable device. The microcapsules were stable, and the cells were viable inside the microcapsules and were found to release dopamine. Thus, these microcapsules have the potential to serve as the alternative or complementary treatment approach for PD.

Polymer microcapsules and microbeads as cell carriers for in vivo biomedical applications

Polymer microcarriers are being extensively explored as cell delivery vehicles in cell-based therapies and hybrid tissue and organ engineering. Spherical microcarriers are of particular interest due to easy fabrication and injectability. They include microbeads, composed of a porous matrix, and microcapsules, where matrix core is additionally covered with a semipermeable membrane. Microcarriers provide cell containment at implantation site and protect the cells from host immunoresponse, degradation and shear stress. Immobilized cells may be genetically altered to release a specific therapeutic product directly at the target site, eliminating side effects of systemic therapies. Cell microcarriers need to fulfil a number of extremely high standards regarding their biocompatibility, cytocompatibility, immunoisolating capacity, transport, mechanical and chemical properties. To obtain cell microcarriers of specified parameters, a wide variety of polymers, both natural and synthetic, and immobilization methods can be applied. Yet so far, only a few approaches based on cell-laden microcarriers have reached clinical trials. The main issue that still impedes progress of these systems towards clinical application is limited cell survival in vivo. Herein, we review polymer biomaterials and methods used for fabrication of cell microcarriers for in vivo biomedical applications. We describe their key limitations and modifications aiming at improvement of microcarrier in vivo performance. We also present the main applications of polymer cell microcarriers in regenerative medicine, pancreatic islet and hepatocyte transplantation and in the treatment of cancer. Lastly, we outline the main challenges in cell microimmobilization for biomedical purposes, the strategies to overcome these issues and potential future improvements in this area.

Synthetic ECM: Bioactive Synthetic Hydrogels for 3D Tissue Engineering

The specific microenvironment that cells reside in fundamentally impacts their broader function in tissues and organs. At its core, this microenvironment is composed of precise arrangements of cells that encourage homotypic and heterotypic cell-cell interactions, biochemical signaling through soluble factors like cytokines, hormones, and autocrine, endocrine, or paracrine secretions, and the local extracellular matrix (ECM) that provides physical support and mechanobiological stimuli, and further regulates biochemical signaling through cell-ECM interactions like adhesions and growth factor sequestering. Each cue provided in the microenvironment dictates cellular behavior and, thus, overall potential to perform tissue and organ specific function. It follows that in order to recapitulate physiological cell responses and develop constructs capable of replacing damaged tissue, we must engineer the cellular microenvironment very carefully. Many great strides have been made toward this goal using various three-dimensional (3D) tissue culture scaffolds and specific media conditions. Among the various 3D biomimetic scaffolds, synthetic hydrogels have emerged as a highly tunable and tissue-like biomaterial well-suited for implantable tissue-engineered constructs. Because many synthetic hydrogel materials are inherently bioinert, they minimize unintentional cell responses and thus are good candidates for long-term implantable grafts, patches, and organs. This review will provide an overview of commonly used biomaterials for forming synthetic hydrogels for tissue engineering applications and techniques for modifying them to with bioactive properties to elicit the desired cell responses.

Biomaterials for Personalized Cell Therapy

Cell therapy has already had an important impact on healthcare and provided new treatments for previously intractable diseases. Notable examples include mesenchymal stem cells for tissue regeneration, islet transplantation for diabetes treatment, and T cell delivery for cancer immunotherapy. Biomaterials have the potential to extend the therapeutic impact of cell therapies by serving as carriers that provide 3D organization and support cell viability and function. With the growing emphasis on personalized medicine, cell therapies hold great potential for their ability to sense and respond to the biology of an individual patient. These therapies can be further personalized through the use of patient-specific cells or with precision biomaterials to guide cellular activity in response to the needs of each patient. Here, the role of biomaterials for applications in tissue regeneration, therapeutic protein delivery, and cancer immunotherapy is reviewed, with a focus on progress in engineering material properties and functionalities for personalized cell therapies.

Artificial inorganic biohybrids: The functional combination of microorganisms and cells with inorganic materials

Biohybrids can be defined as the functional combination of proteins, viable cells or microorganisms with non-biological materials. This article reviews recent findings on the encapsulation of microorganisms and eukaryotic cells in inorganic matrices such as silica gels or cements. The entrapment of biological entities into a support material is of great benefit for processing since the encapsulation matrix protects sensitive cells from shear forces, unfavourable pH changes, or cytotoxic solvents, avoids culture-washout, and simplifies the separation of formed products. After reflecting general aspects of such an immobilization as well as the chemistry of the inorganic matrices, we focused on manufacturing aspects and the application of such biohybrids in biotechnology, medicine as well as in environmental science and for civil engineering purpose.

STATEMENT OF SIGNIFICANCE

The encapsulation of living cells and microorganisms became an intensively studied and rapidly expanding research field with manifold applications in medicine, bio- and environmental technology, or civil engineering. Here, the use of silica or cements as encapsulation matrices have the advantage of a higher chemical and mechanical resistance towards harsh environmental conditions during processing compared to their polymeric counterparts. In this perspective, the article gives an overview about the inorganic material systems used for cell encapsulation, followed by reviewing the most important applications. The future may lay in a combination of the currently achieved biohybrid systems with additive manufacturing techniques. In a longer perspective, this would enable the direct printing of cell loaded bioreactor components.

Viability and Functionality of Bovine Chromaffin Cells Encapsulated into Alginate-PLL Microcapsules with a Liquefied Inner Core

Implantation of adrenal medullary bovine chromaffin cells (BCC), which synthesize and secrete a combination of pain-reducing neuroactive compounds including catecholamines and opioid peptides, has been proposed for the treatment of intractable cancer pain. Macro- or microencapsulation of such cells within semi-permeable membranes is expected to protect the transplant from the host's immune system. In the present study, we report the viability and functionality of BCC encapsulated into microcapsules of alginate-poly-L-lysine (PLL) with a liquefied inner core. The experiment was carried out during 44 days. Empty microcapsules were characterized in terms of morphology, permeability, and mechanical resistance. At the same time, the viability and functionality of both encapsulated and nonencapsulated BCC were evaluated in vitro. We obtained viable BCC with excellent functionality: immunocytochemical analysis revealed robust survival of chromaffin cells 30 days after isolation and microencapsulation. HPLC assay showed that encapsulated BCC released catecholamines basally during the time course study. Taken together, these results demonstrate that viable BCC can be successfully encapsulated into alginate-PLL microcapsules with a liquefied inner core.

Drug delivery with living cells

The field of drug delivery has grown tremendously in the past few decades by developing a wide range of advanced drug delivery systems. An interesting category is cell-based drug delivery, which includes encapsulation of drugs inside cells or attached to the surface and subsequent transportation through the body. Another approach involves genetic engineering of cells to secrete therapeutic molecules in a controlled way. The next-generation systems integrate expertise from synthetic biology to generate therapeutic gene networks for highly advanced sensory and output devices. These developments are very exciting for the drug delivery field and could radically change the way we administer biological medicines to chronically ill patients. This review is covering the use of living cells, either as transport system or production-unit, to deliver therapeutic molecules and bioactive proteins inside the body. It describes a wide range of approaches in cell-based drug delivery and highlights exceptional examples.

Cell microencapsulation with synthetic polymers

The encapsulation of cells into polymeric microspheres or microcapsules has permitted the transplantation of cells into human and animal subjects without the need for immunosuppressants. Cell-based therapies use donor cells to provide sustained release of a therapeutic product, such as insulin, and have shown promise in treating a variety of diseases. Immunoisolation of these cells via microencapsulation is a hotly investigated field, and the preferred material of choice has been alginate, a natural polymer derived from seaweed due to its gelling conditions. Although many natural polymers tend to gel in conditions favorable to mammalian cell encapsulation, there remain challenges such as batch to batch variability and residual components from the original source that can lead to an immune response when implanted into a recipient. Synthetic materials have the potential to avoid these issues; however, historically they have required harsh polymerization conditions that are not favorable to mammalian cells. As research into microencapsulation grows, more investigators are exploring methods to microencapsulate cells into synthetic polymers. This review describes a variety of synthetic polymers used to microencapsulate cells.

In vivo remodelling of vascularizing engineered tissues

A critical aspect of creating vascularized tissues is the remodelling that occurs in vivo, driven in large part by the host response to the tissue construct. Rather than a simple inflammatory response, a beneficial tissue remodelling response results in the formation of vascularised tissue. The characteristics and dynamics of this response are slowly being elucidated, especially as they are modulated by the complex interaction between the biomaterial and cellular components of the tissue constructs and the host. This process has elements that are similar to both wound healing and tumour development, and its features are illustrated by reference to the bottom-up generation of a tissue using modular constructs. These modular constructs consist of mesenchymal stromal cells (MSC) embedded in endothelial cell (EC)-covered collagen gel rods that are a few hundred microns in size. Particular attention is paid to the role of hypoxia and macrophage recruitment, as well as the paracrine effects of the MSC and EC in this host response.

Intelligent Surfaces for Cell and Tissue Delivery

Cell transplantation remains a powerful approach for promising numerous biomedical applications to promote tissue regeneration. Therefore, smart delivery systems of therapeutic cells, as well as therapeutic oligonucleotides and proteins, are required. Although cells have been conventionally delivered by direct injection to target sites, a number of clinical studies showed a limitation due to poor cell retention and survival at the sites, resulting in insufficient effect on tissue/organ repair. Therefore, at present, numerous delivery strategies have been developed, and a variety of polymeric materials play important roles. For example, encapsulation in semi-permeable membrane made from biocompatible polymers (e.g. alginate-poly(l-lysine)-alginate) allows xenograft islets to be delivered in vivo without immune suppression. With progress in tissue engineering, scaffold-based cell/tissue delivery reached the mainstream for regenerating damaged tissues. Various kinds of scaffolds have been fabricated from natural and synthetic polymers, such as collagen or poly(l-lactic-co-glycolic acid), and allowed to provide appropriate nutritional conditions and spatial organization for cell growth. Whereas these scaffolds produce reliable architectures to design cell/tissue delivery, scaffold-free cell/tissue delivery also has opened up a new class technology in the field of regenerative medicine. Thermo-responsive poly(N-isopropylacrylamide)-grafted surfaces allow one to fabricate tissue-like cell monolayers, “cell sheets”, and deliver the cell-dense tissue with associated extra-cellular matrix (ECM) to damaged sites without scaffold implantation. The chapter focuses on unique cell/tissue delivery techniques using the intelligent surfaces. This technology has already been applied to human clinical studies for tissue regeneration, and microfabricated thermo-responsive surfaces are further developing for delivering more complex tissue.

Fabrication and optimization of alginate hydrogel constructs for use in 3D neural cell culture

Two-dimensional (2D) culture systems provide useful information about many biological processes. However, some applications including tissue engineering, drug transport studies, and analysis of cell growth and dynamics are better studied using three-dimensional (3D) culture systems. 3D culture systems can potentially offer higher degrees of organization and control of cell growth environments, more physiologically relevant diffusion characteristics, and permit the formation of more extensive 3D networks of cell-cell interactions. A 3D culture system has been developed using alginate as a cell scaffold, capable of maintaining the viability and function of a variety of neural cell types. Alginate was functionalized by the covalent attachment of a variety of whole proteins and peptide epitopes selected to provide sites for cell attachment. Alginate constructs were used to entrap a variety of neural cell types including astroglioma cells, astrocytes, microglia and neurons. Neural cells displayed process outgrowth over time in culture. Cell-seeded scaffolds were characterized in terms of their biochemical and biomechanical properties, effects on seeded neural cells, and suitability for use as 3D neural cell culture models.

Inorganic nanoporous membranes for immunoisolated cell-based drug delivery

Materials advances enabled by nanotecbnology have brought about promising approaches to improve the encapsulation mechanism for immunoisolated cell-based drug delivery. Cell-based drug delivery is a promising treatment for many diseases but has thus far achieved only limited clinical success. Treatment of insulin dependent diabetes mellitus (IDDM) by transplantation of pancreatic beta-cells represents the most anticipated application ofcell-based drug delivery technology. This review outlines the challenges involved with maintaining transplanted cell viability and discusses how inorganic nanoporous membranes may be useful in achieving clinical success.

Pheochromocytoma-induced cardiomyopathy is modulated by the synergistic effects of cell-secreted factors

BACKGROUND

Pheochromocytomas are rare tumors derived from the chromaffin cells of the adrenal medulla. Although these tumors have long been postulated to induce hypertension and cardiomyopathy through the hypersecretion of catecholamines, catecholamines alone may not fully explain the profound myocardial remodeling induced by these tumors. We sought to determine whether changes in myocardial function in pheochromocytoma-induced cardiomyopathy result solely from catecholamines secretion or from multiple pheochromocytoma-derived factors.

METHODS AND RESULTS

Isolated cardiomyocytes incubated with pheochromocytoma-conditioned growth media contracted at a higher frequency than cardiomyocytes incubated with norepinephrine (NE) only. Sprague-Dawley rats and black-6 mice were implanted with agarose-encapsulated pheochromocytoma (PC12) cells, dihydroxyphenylalanine decarboxylase knock-out PC12 cells deficient in NE (PC12-KO), or NE-secreting pumps. PC12 cell implantation increased left ventricular dilation by 35+/-6% and 9.6+/-1.4% and reduced left ventricular fractional shortening by 20+/-3% and 28+/-4% in rats and mice compared with animals dosed only with NE, respectively. Elimination of NE secretion in PC12-KO cells induced neither cardiac dilation (3.9%+/-1.8% increase versus control) nor changes in (1.9%+/-0.4% reduction) fractional shortening compared to controls.

CONCLUSIONS

Pheochromocytomas induce a greater degree of cardiomyopathy than equivalent doses of NE, suggesting pheochromocytoma-induced cardiomyopathy is not solely mediated by NE, rather pheochromocytoma secretory factors in combination with catecholamines act synergistically to induce greater cardiac damage than catecholamines alone.

Biomedical Technologies for in vitro Screening and Controlled Delivery of Neuroactive Compounds

Cell culture models can provide information pertaining to the effective dose, toxiciology, and kinetics, for a variety of neuroactive compounds. However, many in vitro models fail to adequately predict how such compounds will perform in a living organism. At the systems level, interactions between organs can dramatically affect the properties of a compound by alteration of its biological activity or by elimination of it from the body. At the tissue level, interaction between cell types can alter the transport properties of a particular compound, or can buffer its effects on target cells by uptake, processing, or changes in chemical signaling between cells. In any given tissue, cells exist in a three-dimensional environment bounded on all sides by other cells and components of the extracellular matrix, providing kinetics that are dramatically different from the kinetics in traditional two-dimensional cell culture systems. Cell culture analogs are currently being developed to better model the complex transport and processing that occur prior to drug uptake in the CNS, and to predict blood-brain barrier permeability. These approaches utilize microfluidics, hydrogel matrices, and a variety of cell types (including lung epithelial cells, hepatocytes, adipocytes, glial cells, and neurons) to more accurately model drug transport and biological activity. Similar strategies are also being used to control both the spatial and temporal release of therapeutic compounds for targeted treatment of CNS disease.

Evaluation of silicon nanoporous membranes and ECM-based microenvironments on neurosecretory cells

Understanding the interactions between microfabricated synthetic interfaces and cultured cells expressing a neuronal phenotype are critical for advancing research in the field of neural engineering such as neural recording and stimulation and neural microdevice interactions with the human brain. Here we explore the integration of these two components for therapeutic applications of neural prostheses. Microfabricated silicon nanoporous membranes were investigated for their effects on survival, proliferation, and differentiation of the well-known PC12 clonal line. Specifically, cell morphology, examined through fluorescence staining, were comparable in many respects on both silicon membrane and widely-used polystyrene culture surfaces. The attachment and differentiation of PC12 cells cultured on collagen and laminin-modified membranes and standard tissue culture surfaces were similar. Lastly, the differentiation response and tyrosine hydroxylase activity of PC12 cells embedded in a type I collagen matrix on experimental membrane substrates while exposed to NGF were significant and indistinguishable from tissue-culture polystyrene (TC-PS) surfaces. Results from this research suggest that microfabricated silicon nanoporous membranes may be useful, biocompatible permselective structures for neuroprosthetic applications and that collagen may be a useful immobilizing matrix for PC12 cells loaded in implantable macroencapsulation devices designed for the treatment of neurodegenerative disorders.

Single-cell-bioreactors as end of miniaturization approaches in biotechnology: progresses with characterised bioreactors and a glance into the future

Incidents with single cells and their genesis have not been the major focus of science up to now. This fact is supported by the difficulties one faces when wanting to monitor and cultivate small populations of cells in a defined compartment under controlled conditions, in vitro. Several approaches of up- and down-scaling have often led to poorly understood results which might be better elucidated by understanding the cellular genesis as a function of its microenvironment. This review of the approaches of scale-up and scale-down processes illustrates technical possibilities and shows up their limitations with regard to obtainable data for the characterisation of cellular genesis and impact of the cellular microenvironment. For example, stem cell research advances underline the lack of information about the impact of the microenvironment on cellular development. Finally, a proposal of future research efforts is given on how to overcome this lack of data via a novel bioreactor setup.

Encapsulating live cells with water-soluble chitosan in physiological conditions

A new class of microcapsules was prepared under physiological conditions by polyelectrolyte complexation between two oppositely-charged, water-soluble polymers. The microcapsules consisted of an inner core of half N-acetylated chitosan and an outer shell of methacrylic acid (MAA) (20.4%)-hydroxyethyl methacrylate (HEMA) (27.4%)-methyl methacrylate (MMA) (52.2%) (MAA-HEMA-MMA) terpolymer. Both 400 and 150 kDa half N-acetylated chitosans maintained good water solubility and supplied enough protonated amino groups to coacervate with terpolymer at pH 7.0-7.4, in contrast to other chitosan-based microcapsules which must be prepared at pH <6.5. The viscosity of half N-acetylated chitosan solutions between 80 and 3000 cPas allowed the formation of microcapsules with spherical shape. Molar mass, pH and concentration of half N-acetylated chitosan, and reaction time, influenced the morphology, thickness and porosity of the microcapsules. Microcapsules formed with high concentration of half N-acetylated chitosan exhibited improved mechanical stability, whereas microcapsules formed with low concentration of half N-acetylated chitosan exhibited good permeability. This 3D microenvironment has been configured to cultivate sensitive anchorage-dependent cells such as hepatocytes to maintain high level of functions.

Viability of Hydroxyethyl Methacrylate–Methyl Methacrylate-Microencapsulated PC12 Cells after Omental Pouch Implantation within Agarose Gels

Hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA, 75 mol% HEMA). Microcapsules containing viable PC12 cells (as an allogeneic transplant model) were implanted into omental pouches in Wistar rats. Two different capsule preparations were tested, based on differences in polymer solutions during extrusion: 10% HEMA-MMA in TEG, and 9% HEMA-MMA in TEG with 30% poly(vinyl pyrrolidone) (PVP). The omental pouch proved to be an ideal transplant site in terms of implantation, recovery, and blood vessel proximity (nutrient supply). To minimize the fibrous overgrowth and damaged capsules previously seen on implantation of individual capsules, agarose gels were used to embed the capsules before implantation. Cells proliferated within the microcapsule-agarose device during the first 7 days of implantation, but overall cell viability declined over the 3-week period, when compared with similar capsules maintained in vitro. Nonetheless, approximately 50% of the initial encapsulated cells were still viable after 3 weeks in vivo. This approach to HEMA-MMA microcapsule implantation improved cell viability and capsule integrity after 3 weeks in vivo, compared with capsules implanted without agarose.

Functional and Morphological Characteristics of Bovine Adrenal Chromaffin Cells on Macroporous Poly(D,L-lactide-co-glycolide) Scaffolds

Adrenal chromaffin cells (ACCs) secrete several neuroactive substances that are effective in influencing pain sensitivity in the central nervous system as well as enhancing the recovery of the intrinsic nigrostriatal dopaminergic system in patients with Parkinson's disease. ACC transplantation may be upregulated by the use of three-dimensional (3-D) scaffolds. In this study, we determined whether biodegradable poly(D,L-lactic-coglycolic acid) (PLGA) (85:15) sponges could be used as support for chromaffin cells. ACCs were isolated from bovine adrenal glands by standard perfusion (95% purity) followed by additional purification (>99.5% purity). ACC (approximately 5 x 10(5) cells) suspension in collagen (type I) was seeded on prewetted sponges and cultured in DMEM-F12 (1:1) medium (5% fetal bovine serum). The catecholamine and enkephalin levels of the samples were measured by high-performance liquid chromatography and radioimmunoassay. Cell morphology was examined by transmission electron microscopy. Morphological evidence showed prolonged viability of chromaffin cells on scaffolds having pores of 250-400 microm. Cell counts and scanning electron microscopy demonstrated that the majority of seeded cells were located within the scaffold. Chromaffin cells exhibited higher levels of enkephalins and catecholamines on PLGA scaffold compared with their monolayer cultures. By the use of 3-D PLGA as support for ACCs, it is possible to upregulate metabolic function and localize a high number of morphologically healthy-looking cells. Highly purified ACCs cultured on PLGA scaffold may have promise in transplantation studies, because these cells are less immunogenic and may be applied to in vivo settings by using short-term immunosuppression.

Novel hydrogels as supports for in vitro cell growth: poly(ethylene glycol)- and gelatine-based (meth)acrylamidopeptide macromonomers

Conversion of amine groups with vinyl-functional azlactones occurs at room temperature under physiological conditions to afford (meth)acrylamidopeptide-functional macromonomers. Such macromonomers based upon alpha,omega-bisaminopropyl-terminated poly(ethylene glycol) and gelatine were prepared and copolymerized to produce novel hydrogel networks. Compression modulus was inversely proportional to the water content (EWC), which was controlled primarily by the PEG macromonomers with non-modified gelatine, the covalent attachment of gelatine to the hydrogel network gave substantially improved performance with respect to both, adhesion and growth of human fibroplasts.

Creation of designed shape cell sheets that are noninvasively harvested and moved onto another surface

We developed a novel method to obtain designed shape cell sheets for tissue engineering. Shaping of cell sheets were achieved by the use of poly(N-isopropylacrylamide) (PIPAAm) and poly(N,N'-dimethylacrylamide) (PDMAAm) for temperature-responsive cell adhesive and cell nonadhesive domains, respectively. These polymers were covalently grafted onto tissue culture polystyrene (TCPS) dish surfaces by electron beam irradiation with mask patterns. At 37 degrees C, human aortic endothelial cells (HAECs) attached, spread, and proliferated to make a monolayer only on PIPAAm-grafted domains. HAECs did not adhere on PDMAAm-grafted domains for more than 1 month even under the serum-supplemented condition. By reducing the culture temperature below 32 degrees C, PIPAAm changed to hydrophilic and HAEC sheets were detached from PIPAAm-grafted surfaces without any need of an enzyme such as trypsin. Cell-cell junctions were retained in the recovered cell sheets and easily moved to virgin TCPS dishes with the aid of hydrophilically modified polyvinylidenefluoride membranes as a supporter during the transfer. Moved cell sheets rapidly adhered onto the dish surfaces, and the supporter was easily peeled off from the cell layers. HAEC sheets transferred to new dishes revealed the identical shape and size to those before transfer. This novel technique is the only way to create, harvest, and transfer designed shape cell sheets and would have promising applications in tissue engineering.

Objectively assessing bioartificial organs

The metrics used, thus far, to assess bioartificial organ function are shown to be subjective and requiring validation. Therefore, four categories of correlations are proposed based on, respectively, device, in vitro and in vivo evaluations, and clinical function. Examples are presented whereby the correlations among individual indicators are used as a means to expedite the development of immunoisolated cells. Specifically, a case study illustrating the validation of in vitro indicators of in vivo graft function for the bioartificial pancreas (microencapsulated islets) is summarized. This has revealed thresholds with respect to given metrics relating to in vivo device function, the necessity to couple bioartificial organ design with transplant site selection, as well as the lack of objectivity involved in the evaluation and establishment of hypotheses. Specific quantitative indicators illustrate the need for quality-controlled measures, for example, relating to the tolerance of microcapsule diameter and membrane thickness distributions. Qualitative indices representing fibrosis and device properties (e.g., sphericity) are also used to describe the need for in vitro experiments in the development of bioartificial organs.

Intact microglia are cultured and non-invasively harvested without pathological activation using a novel cultured cell recovery method

Because spontaneous host regeneration of damaged tissues is limited, novel therapeutics utilizing cultured cells with the aid of tissue engineering methods are promising alternatives for tissue replacement. One critical shortcoming is current requirement for invasive cell harvest from culture to fabricate cell-based devices. Although microglia that secrete neurotrophic factors are attractive candidates for novel cell transplantation therapy for damaged central nervous system tissue, the intact harvest of cultured microglia is presently not achievable. Therefore, primary microglia were plated onto culture surfaces grafted with the temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPAAm). This surface undergoes rapid, reversible temperature-dependent changes in its hydration state and surface hydrophilicity. Microglia attached and proliferated on PIPAAm-grafted dishes at 37 degrees C. By reducing culture temperature, more than 90% of the cells spontaneously detached from the dishes within several minutes without trypsin or EDTA treatment. Recovered and replated microglia exhibited phenotypic properties comparable to those of primary microglia freshly isolated from brain. By contrast, less than 60% of the cells were harvested by trypsin digestion, and exhibited significant alteration of characteristic cellular properties as monitored by pathological states in vivo. This new technology exhibits utility for the preparation of cell sources required for cell transplantation as well as microglial function analysis.

Tissue engineering as a platform for controlled release of therapeutic agents: implantation of microencapsulated dopamine producing cells in the brains of rats

Tissue engineering can lead to novel controlled release devices and controlled release strategies (e.g., of growth factors) can enhance the performance of tissue engineered constructs. There are however a number of technical challenges that must be overcome before these goals can be realized. The apparently 'simple' challenge of implanting the device (e.g., capsules) in the optimal site must be met. In addition, adequate nutrient supply to the capsules is required to maintain cell viability. To illustrate this problem we describe a guide and delivery cannula technique to provide reliable and reproducible delivery of up to 120 PC12 cell containing capsules into the caudate putamen (CPu). Microencapsulation of mammalian cells is potentially a powerful means of delivering therapeutically important molecules such as insulin. It can also have numerous applications as a platform for gene therapy. However, realizing this potential has been more difficult than first anticipated.

Agarose enhances the viability of intraperitoneally implanted microencapsulated L929 fibroblasts

To achieve immunoisolation, mouse L929 fibroblasts were encapsulated in approximately 400 microm poly(hydroxyethyl methacrylate-co-methyl methacrylate) (HEMA-MMA) microcapsules and were subsequently implanted in the peritoneal cavity of syngeneic C3H mice. As a baseline for the use of genetically engineered cells in cell encapsulation therapy, the L929 cells were transfected to express a secreted form of human alkaline phosphatase (SEAP). Implantation of empty microcapsules in a PBS suspension resulted in deformation, aggregation, and poor retrievability of the microcapsules. Incubation of microcapsules with medium containing xenogeneic horse serum prior to implantation increased the thickness of the fibrous tissue surrounding the microcapsules. However, immobilization of the microcapsules in a 4% (w/v) SeaPlaque agarose gel prior to implantation allowed complete recovery of the microcapsules and prevented their aggregation and deformation. As a result, approximately 50% of the encapsulated cells remained viable 21 days postimplantation. Moreover, once the viable cells were released from retrieved microcapsules and regrown as monolayers, they expressed SEAP at a level similar to their encapsulated but nonimplanted counterparts.

Effect of media composition on long-term in vitro stability of barium alginate and polyacrylic acid multilayer microcapsules

For a number of applications stability of microcapsules is a critical factor. Since the maintenance of polyelectrolyte complexes depends considerably on the ion composition we tested the physical properties of barium alginate capsules and searched for conditions to improve stability by a multilayer coating with polyethylenimine (PEI) and polyacrylic acid (PAA). Mechanical stability and diameters were determined in barium alginate capsules and compared with multilayer capsules. Multilayer coating resulted in smaller capsules than barium complexing alone. The difference was more pronounced when CaCl2 was used instead of NaCl during coating. Barium alginate capsules and application of CaCl2 during coating led to continuous pressure profiles, whereas NaCl resulted in bursting at a defined pressure, indicating the additional contribution to mechanical stability by the outer layers. After 7 d culture, mechanical stability of coated capsules decreased in RPMI and NaCl but was most pronounced in sodium citrate. The capsule diameter increased in sodium citrate, less pronounced in NaCl and was significantly different to RPMI and double distilled water. During long-term culture in RPMI, the diameter increased and mechanical stability decreased significantly. Multilayer coating improved mechanical stability which was impeded most in sodium citrate, to a lesser extent by NaCl and RPMI even after long-term exposure.

Cell delivery to the central nervous system

A dysfunctional central nervous system (CNS) resulting from neurological disorders and diseases impacts all of humanity. The outcome presents a staggering health care issue with a tremendous potential for developing interventive therapies. The delivery of therapeutic molecules to the CNS has been hampered by the presence of the blood-brain barrier (BBB). To circumvent this barrier, putative therapeutic molecules have been delivered to the CNS by such methods as pumps/osmotic pumps, osmotic opening of the BBB, sustained polymer release systems and cell delivery via site-specific transplantation of cells. This review presents an overview of some of the CNS delivery technologies with special emphasis on transplantation of cells with and without the use of polymer encapsulation technology.

Microencapsulation of normal and transfected L929 fibroblasts in a HEMA-MMA copolymer

Mouse L929 fibroblasts transfected to express a secreted form of human alkaline phosphatase (SEAP) were encapsulated in approximately 400-microm poly(hydroxyethyl methacrylate-co-methyl methacrylate) (HEMA-MMA) microcapsules as a baseline for the use of genetically engineered cells in encapsulation therapy. Although incubation of microcapsules with serum-containing medium resulted in maintaining the number of live encapsulated cells with the passage of time, incubation in a serum-free medium resulted in a three-fold proliferation of the encapsulated cells within a 3-week observation period. Similar to the results for incubation with serum-containing medium, co-encapsulation with a bovine dermal type I collagen, i.e., the inclusion of a matrix in the core of the capsules, resulted in maintenance of the initial number of live cells with the passage of time. SEAP measurements indicated that the transfected cells not only continued to express the transgene product after encapsulation, but also adapted to the capsule microenvironment to secrete SEAP at progressively larger amounts with the passage of time. However, SEAP expression only occurred when the transfected cells (encapsulated or non-encapsulated) were cultivated in serum-containing medium.

Dose control with cell lines used for encapsulated cell therapy

Cell therapy-use of cells to deliver active factors-is an emerging technique in treatment of neurodegenerative disease. Successful devices maintain cell viability and functionality over extended implant periods. Use of dividing cell lines to deliver therapeutic factors has been studied extensively. One emerging issue is the tendency of cells to continue proliferation within the intracapsular environment-potentially outstripping nutrient supply. This work presents a method of controlling proliferation and delivering therapeutic molecules within a dose range. The method entails encapsulation into a hollow fiber device of discrete numbers of cell-containing microcarriers. Proliferation control is attained by embedding cell-containing microcarriers in nonmitogenic hydrogels. PC-12 cells secreting L-dopa and dopamine was the model cell line tested. Feasibility of the method in controlling growth of normally rapidly dividing cells in the intracapsular environment was demonstrated in vitro and in vivo. Control nonmicrocarrier PC-12 cell devices had approximately fourfold greater expansion in cell number compared to experimental microcarrier-containing devices over 4 weeks in vitro and in vivo after implant into rat striatum. Ability to control dose released over a several-fold range was demonstrated with encapsulated PC-12 cells delivering neurotransmitters and C2C12 mouse myoblast cells delivering neurotrophic factors (CNTF).

Host response to tissue engineered devices

The two main components of a tissue engineered device are the transplanted cells and the biomaterial, creating a device for the restoration or modification of tissue or organ function. The implantation of polymer/cell constructs combines concepts of biomaterials and cell transplantation. The interconnections between the host responses to the biomaterial and transplanted cells determines the biocompatibility of the device. This review describes the inflammatory response to the biomaterial component and immune response towards transplanted cells. Emphasis is on how the presence of the transplanted cell construct affects the host response. The inflammatory response towards a biomaterial can impact the immune response towards transplanted cells and vice versa. Immune rejection is the most important host response towards the cellular component of tissue engineered devices containing allogeneic, xenogeneic or immunogenic ex vivo manipulated autologous cells. The immune mechanisms towards allografts and xenografts are outlined to provide a basis for the mechanistic hypotheses of the immune response towards encapsulated cells, with antigen shedding and the indirect pathway of antigen presentation predominating. A review of experimental evidence illustrates examples of the inflammatory response towards biodegradable polymer scaffold materials, examples of devices appropriately integrated as assessed morphologically with the host for various applications including bone, nerve, and skin regeneration, and of the immune response towards encapsulated allogeneic and xenogeneic cells.

Materials for immunoisolated cell transplantation

Encapsulated cell therapy provides site-specific continuous delivery of cell-synthesized molecules. Cell encapsulation therapy is based on the concept of immunoisolation. Foreign cells are surrounded with a semi-permeable membrane prior to transplantation to shield them from the host's natural defense system. This membrane is selectively permeable to transport of nutrients and therapeutic agents but relatively impermeable to larger molecules and cells of the hosts' immune system. Most encapsulation devices also utilize an internal matrix to keep cells suspended within the capsule. Proper choice of materials and materials processing techniques to formulate membrane and matrix components is essential to the success of these devices. A successful encapsulation device recreates the natural three-dimensional tissue environment that supports cell function and maintains cell viability. This review summarizes recent developments in materials development for cell encapsulation devices and highlights some ongoing challenges faced by those in the field.

Selected aspects of the microencapsulation of mammalian cells in HEMA-MMA

Microencapsulation of live mammalian cells is one means of creating hybrid artificial organs, like an artificial pancreas or an artificial liver. In addition to creating and developing the methodologies for enclosing cells within the appropriate semipermeable and biocompatible membranes, novel techniques are needed to assess the various features of the resulting capsules. The small size of a capsule or its heterogeneity can lead to additional complexities that go beyond the problem of examining cell behavior in the presence of biomaterials. These problems are illustrated here by comparison of protein release by microencapsulated HepG2 cells within large and small HEMA-MMA (hydroxyethyl methacrylate-methyl methacrylate) capsules, by assessment of the effect of processing conditions on HEMA-MMA microcapsule permeability to horseradish peroxidase at the individual capsule level, and by a confocal microscopy technique for assessing intracapsule cell viability.

Cytomedical therapy for IgG1 plasmacytosis in human interleukin-6 transgenic mice using hybridoma cells microencapsulated in alginate-poly(L)lysine-alginate membrane

Cytomedical therapy for human interleukin-6 transgenic mice (hIL-6 Tgm) was implemented by the intraperitoneal injection of alginate-poly(L)lysine-alginate (APA) membranes microencapsulating SK2 hybridoma cells (APA-SK2 cells) which secrete anti-hIL-6 monoclonal antibodies (SK2 mAb). IgG1 plasmacytosis in the hIL-6 Tgm was suppressed by a single injection of APA-SK2 cells, and the survival time of these mice was remarkably prolonged. The viable cell number and the SK2 mAb-secretion of APA-SK2 cells increased for at least one month both under culture conditions and in allogeneic recipients (in vivo). Moreover, SK2 mAb which were secreted from APA-SK2 cells injected into allogeneic recipients was detected in serum at high concentrations; 3-5 mg/ml from day 14 to day 50 post-injection. In contrast, the injection of free SK2 cells had no therapeutic effect on hIL-6 Tgm. These results strongly suggest that APA membranes microencapsulating cells which were modified to secrete molecules useful for the treatment of a disorder were effective as an in vivo long-term delivery system of bioactive molecules, as 'cytomedicine'.