Effect of an immobilization matrix and capsule membrane permeability on the viability of encapsulated HEK cells

All-aqueous synthesis of alginate complexed with fibrillated protein microcapsules for membrane-bounded culture of tumor spheroids

Water-in-water (W/W) emulsions provide bio-compatible all-aqueous compartments for artificial patterning and assembly of living cells. Successful entrapment of cells within a W/W emulsion via the formation of semipermeable capsules is a prerequisite for regulating on the size, shape, and architecture of cell aggregates. However, the high permeability and instability of the W/W interface, restricting the assembly of stable capsules, pose a fundamental challenge for cell entrapment. The current study addresses this problem by synthesizing multi-armed protein fibrils and controlling their assembly at the W/W interface. The multi-armed protein fibrils, also known as 'fibril clusters', were prepared by cross-linking lysozyme fibrils with multi-arm polyethylene glycol (PEG) via click chemistry. Compared to linear-structured fibrils, fibril clusters are strongly adsorbed at the W/W interface, forming an interconnected meshwork that better stabilizes the W/W emulsion. Moreover, when fibril clusters are complexed with alginate, the hybrid microcapsules demonstrate excellent mechanical robustness, semi-permeability, cytocompatibility and biodegradability. These advantages enable the encapsulation, entrapment and long-term culture of tumor spheroids, with great promise for applications for anti-cancer drug screening, tumor disease modeling, and tissue repair engineering.

Fabrication and Performance Evaluation of Gelatin/Sodium Alginate Hydrogel-Based Macrophage and MSC Cell-Encapsulated Paracrine System with Potential Application in Wound Healing

A gelatin/sodium alginate-based hydrogel microsphere has been fabricated after reaction condition optimization. Macrophages (RAW246.7) and adipose mesenchymal stem cells (ADSC) have been subsequently encapsulated in the microsphere in order to construct a 3D paracrine system for wound healing treatment. The synthesized microsphere displayed neglectable cytotoxicity toward both encapsulated cells until 10 days of incubation, indicating promising biocompatibility of the microsphere. A qRT-PCR and ELISA experiment revealed positive regulation of cytokines (Arg-1, IL-6, IL-8, IL-10, bFGF, HGF, VEGF, TLR-1, and CXCL13) expression regarding macrophage phenotype transformation and anti-inflammatory performance both inside the microsphere and in the microenvironment of established in vitro inflammatory model. Additionally, positive tendency of cytokine expression benefit wound healing was more pronounced in a fabricated 3D paracrine system than that of a 2D paracrine system. Furthermore, the 3D paracrine system exhibited more efficiently in the wound healing rate compared to the 2D paracrine system in an in vitro model. These results suggested the current paracrine system could be potentially used as a robust wound healing dressing.

Polymeric Approaches to Reduce Tissue Responses Against Devices Applied for Islet-Cell Encapsulation

Immunoisolation of pancreatic islets is a technology in which islets are encapsulated in semipermeable but immunoprotective polymeric membranes. The technology allows for successful transplantation of insulin-producing cells in the absence of immunosuppression. Different approaches of immunoisolation are currently under development. These approaches involve intravascular devices that are connected to the bloodstream and extravascular devices that can be distinguished in micro- and macrocapsules and are usually implanted in the peritoneal cavity or under the skin. The technology has been subject of intense fundamental research in the past decade. It has co-evolved with novel replenishable cell sources for cure of diseases such as Type 1 Diabetes Mellitus that need to be protected for the host immune system. Although the devices have shown significant success in animal models and even in human safety studies most technologies still suffer from undesired tissue responses in the host. Here we review the past and current approaches to modulate and reduce tissue responses against extravascular cell-containing micro- and macrocapsules with a focus on rational choices for polymer (combinations). Choices for polymers but also choices for crosslinking agents that induce more stable and biocompatible capsules are discussed. Combining beneficial properties of molecules in diblock polymers or application of these molecules or other anti-biofouling molecules have been reviewed. Emerging are also the principles of polymer brushes that prevent protein and cell-adhesion. Recently also immunomodulating biomaterials that bind to specific immune receptors have entered the field. Several natural and synthetic polymers and even combinations of these polymers have demonstrated significant improvement in outcomes of encapsulated grafts. Adequate polymeric surface properties have been shown to be essential but how the surface should be composed to avoid host responses remains to be identified. Current insight is that optimal biocompatible devices can be created which raises optimism that immunoisolating devices can be created that allows for long term survival of encapsulated replenishable insulin-producing cell sources for treatment of Type 1 Diabetes Mellitus.

Agarose-chitosan hydrogel-immobilized horseradish peroxidase with sustainable bio-catalytic and dye degradation properties

Herein, we developed and characterized robust agarose-chitosan hydrogel using N‑hydroxysuccinimide (NHS) as a mild chemical cross-linker. The hydrogel offered a simple, effective and eco-friendlier support material with >90% of immobilization efficiency of horseradish peroxidase. The surface morphology and functional properties of the agarose-chitosan hydrogel with and without immobilized horseradish peroxidase were investigated by scanning electron microscopy and Fourier-transform infrared, respectively. The agarose-chitosan hydrogel-immobilized horseradish peroxidase (ACH-HRP) exhibited wide-working pH and temperature stability, and promising reusability for its substrate oxidation. The ACH-HRP preserved a better activity under acidic environments, pH 4.0 (38 vs. 5.9%), and well stabilized under alkaline conditions, retaining a 3.9-folds greater activity than a free counterpart at pH 10. With reference to a free enzyme, 1.6- and 4-fold greater catalytic activity was achieved at 50 and 70 °C, respectively, by the immobilized HRP. Further, the hydrogel displayed insignificant loss in enzyme functionality sustaining above 90% and 60% of original activity after 5 and 10 continuous cycles of use. HPLC profile corroborated the enzyme-assisted Reactive Blue 19 (RB-19) degradation, whereas UPLC/MS analysis scrutinized the dye degradation intermediates and a tentative mechanistic degradation pathway was proposed. In conclusion, the results demonstrate that ACH-HRP is a promising option for use as industrial biocatalyst in diverse biotechnological applications.

Preparation and Characterization of Chitosan-Agarose Composite Films

Nowadays, there is a growing interest to develop biodegradable functional composite materials for food packaging and biomedicine applications from renewable sources. Some composite films were prepared by the casting method using chitosan (CS) and agarose (AG) in different mass ratios. The composite films were analyzed for physical-chemical-mechanical properties including tensile strength (TS), elongation-at-break (EB), water vapor transmission rate (WVTR), swelling ratio, Fourier-transform infrared spectroscopy, and morphology observations. The antibacterial properties of the composite films were also evaluated. The obtained results reveal that an addition of AG in varied proportions to a CS solution leads to an enhancement of the composite film's tensile strength, elongation-at-break, and water vapor transmission rate. The composite film with an agarose mass concentration of 60% was of the highest water uptake capacity. These improvements can be explained by the chemical structures of the new composite films, which contain hydrogen bonding interactions between the chitosan and agarose as shown by Fourier-transform infrared spectroscopy (FTIR) analysis and the micro-pore structures as observed with optical microscopes and scanning electron microscopy (SEM). The antibacterial results demonstrated that the films with agarose mass concentrations ranging from 0% to 60% possessed antibacterial properties. These results indicate that these composite films, especially the composite film with an agarose mass concentration of 60%, exhibit excellent potential to be used in food packaging and biomedical materials.

Novel in situ liquefying antimicrobial wrap for preventing tissue expander infections following breast reconstructive surgeries

Breast reconstruction surgeries using tissue expanders (TEs) have highly reported infection rates. To decrease this, we developed a method for disinfecting TEs and surgical pockets, where an antimicrobial solution was applied as a solid film at implantation that subsequently liquefied in situ to provide extended prophylaxis. Silicone discs cut from TEs were covered with gelatin-based films containing minocycline (M) and rifampin (R). Discs and films soaked in saline were subsequently challenged with pathogen at days 1, 3, 7, and 10 and quantified for potential biofilm formation. Discs that were not harvested at each specific time points were refreshed with sterile saline. The discs were challenged with clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis (MRSE), and multidrug-resistant Pseudomonas aeruginosa (MDR-PA). Recoveries of adherent organisms from uncovered silicone discs and gelatin-wrapped discs without added antimicrobial agents were >5 × 10(4) CFU/disc for each organism at each time point. Experimental 0.1%M/0.05%R gelatin films completely inhibited all challenge organisms from attaching to the silicone (p < 0.05) at each time point through day 10. Cytotoxicity was assessed by incubating films with HEK-293T human fibroblasts. There were no significant differences in HEK-293T cell survival between controls and any of the antimicrobial films. The in situ liquefying, bioabsorable, antimicrobial wrap prevented biofilm formation by microorganisms on silicone surfaces in vitro with minimal cytotoxicity.

Encapsulated cells for long-term secretion of soluble VEGF receptor 1: Material optimization and simulation of ocular drug response

Anti-angiogenic therapies with vascular endothelial growth factor (VEGF) inhibiting factors are effective treatment options for neovascular diseases of the retina, but these proteins can only be delivered as intravitreal (IVT) injections. To sustain a therapeutic drug level in the retina, VEGF inhibitors have to be delivered frequently, every 4-8weeks, causing inconvenience for the patients and expenses for the healthcare system. The aim of this study was to investigate cell encapsulation as a delivery system for prolonged anti-angiogenic treatment of retinal neovascularization. Genetically engineered ARPE-19 cells secreting soluble vascular endothelial growth factor receptor 1 (sVEGFR1) were encapsulated in a hydrogel of cross-linked collagen and interpenetrating hyaluronic acid (HA). The system was optimized in terms of matrix composition and cell density, and long-term cell viability and protein secretion measurements were performed. sVEGFR1 ARPE-19 cells in the optimized hydrogel remained viable and secreted sVEGFR1 at a constant rate for at least 50days. Based on pharmacokinetic/pharmacodynamic (PK/PD) modeling, delivery of sVEGFR1 from this cell encapsulation system is expected to lead only to modest VEGF inhibition, but improvements of the protein structure and/or secretion rate should result in strong and prolonged therapeutic effect. In conclusion, the hydrogel matrix herein supported the survival and protein secretion from the encapsulated cells. The PK/PD simulation is a convenient approach to predict the efficiency of the cell encapsulation system before in vivo experiments.

Polymers in cell encapsulation from an enveloped cell perspective

In the past two decades, many polymers have been proposed for producing immunoprotective capsules. Examples include the natural polymers alginate, agarose, chitosan, cellulose, collagen, and xanthan and synthetic polymers poly(ethylene glycol), polyvinyl alcohol, polyurethane, poly(ether-sulfone), polypropylene, sodium polystyrene sulfate, and polyacrylate poly(acrylonitrile-sodium methallylsulfonate). The biocompatibility of these polymers is discussed in terms of tissue responses in both the host and matrix to accommodate the functional survival of the cells. Cells should grow and function in the polymer network as adequately as in their natural environment. This is critical when therapeutic cells from scarce cadaveric donors are considered, such as pancreatic islets. Additionally, the cell mass in capsules is discussed from the perspective of emerging new insights into the release of so-called danger-associated molecular pattern molecules by clumps of necrotic therapeutic cells. We conclude that despite two decades of intensive research, drawing conclusions about which polymer is most adequate for clinical application is still difficult. This is because of the lack of documentation on critical information, such as the composition of the polymer, the presence or absence of confounding factors that induce immune responses, toxicity to enveloped cells, and the permeability of the polymer network. Only alginate has been studied extensively and currently qualifies for application. This review also discusses critical issues that are not directly related to polymers and are not discussed in the other reviews in this issue, such as the functional performance of encapsulated cells in vivo. Physiological endocrine responses may indeed not be expected because of the many barriers that the metabolites encounter when traveling from the blood stream to the enveloped cells and back to circulation. However, despite these diffusion barriers, many studies have shown optimal regulation, allowing us to conclude that encapsulated grafts do not always follow nature's course but are still a possible solution for many endocrine disorders for which the minute-to-minute regulation of metabolites is mandatory.

Preparation of cell-encapsulation devices in confined microenvironment

The entrapment of cells into hydrogel microdevice in form of microparticles or microfibers is one of the most appealing and useful tools for cell-based therapy and tissue engineering. Cell encapsulation procedures allow the immunoisolation of cells from the surrounding environment, after their transplantation and the maintenance of the normal cellular physiology. Factors affecting the efficacy of microdevices, which include size, size distribution, morphology, and porosity are all highly dependent on the method of preparation. In this respect, microfluidic based methods offer a promising strategy to fabricate highly uniform and morphologically controlled microdevices with tunable chemical and mechanical properties. In the current review, various cell microencapsulation procedures, based on a microfluidics, are critically analyzed with a special focus on the effect of the procedure on the morphology, viability and functions of the embedded cells. Moreover, a brief introduction about the optimal characteristics of microdevice intended for cell encapsulation, together with the currently used materials for the production is reported. A further challenging application of microfluidics for the development of "living microchip" is also presented. Finally, the limitations, challenging and future work on the microfluidic approach are also discussed.

Facile synthesis of radial-like macroporous superparamagnetic chitosan spheres with in-situ co-precipitation and gelation of ferro-gels

Macroporous chitosan spheres encapsulating superparamagnetic iron oxide nanoparticles were synthesized by a facile and effective one-step fabrication process. Ferro-gels containing ferrous cations, ferric cations and chitosan were dropped into a sodium hydroxide solution through a syringe pump. In addition, a sodium hydroxide solution was employed for both gelation (chitosan) and co-precipitation (ferrous cations and ferric cations) of the ferro-gels. The results showed that the in-situ co-precipitation of ferro-ions gave rise to a radial morphology with non-spheroid macro pores (large cavities) inside the chitosan spheres. The particle size of iron oxide can be adjusted from 2.5 nm to 5.4 nm by tuning the concentration of the sodium hydroxide solution. Using Fourier Transform Infrared Spectroscopy and X-ray diffraction spectra, the synthesized nanoparticles were illustrated as Fe₃O₄ nanoparticles. In addition, the prepared macroporous chitosan spheres presented a super-paramagnetic behaviour at room temperature with a saturation magnetization value as high as ca. 18 emu/g. The cytotoxicity was estimated using cell viability by incubating doses (0∼1000 µg/mL) of the macroporous chitosan spheres. The result showed good viability (above 80%) with alginate chitosan particles below 1000 µg/mL, indicating that macroporous chitosan spheres were potentially useful for biomedical applications in the future.

Microencapsulated mammalian cells for simultaneous production of VEGF165b and IFNα

Targeted and simultaneous delivery VEGF165b and IFN alpha in anti-angiogenic and other applications could offer several advantages. For this a system was design using artificial cell alginate-poly-L-lysine- alginate (APA) microcapsules. Result confirms the ability of this system for simultaneous production of these proteins for 28-days. The IFN alpha on a 3 days period increased from 8 ± 0.36 μg/ml at day 10 to 27 ± 2.4 μg/ml at day 16 and then dropped to 6.5 ± 0.5 μg/ml. The VEGF165b on a 3 days period increased from 2.7 ± 0.7 μg/ml at day 10 to 6.9 ± 1 μg/ml at day 16.

Progress technology in microencapsulation methods for cell therapy

Cell encapsulation in microcapsules allows the in situ delivery of secreted proteins to treat different pathological conditions. Spherical microcapsules offer optimal surface-to-volume ratio for protein and nutrient diffusion, and thus, cell viability. This technology permits cell survival along with protein secretion activity upon appropriate host stimuli without the deleterious effects of immunosuppressant drugs. Microcapsules can be classified in 3 categories: matrix-core/shell microcapsules, liquid-core/shell microcapsules, and cells-core/shell microcapsules (or conformal coating). Many preparation techniques using natural or synthetic polymers as well as inorganic compounds have been reported. Matrix-core/shell microcapsules in which cells are hydrogel-embedded, exemplified by alginates capsule, is by far the most studied method. Numerous refinement of the technique have been proposed over the years such as better material characterization and purification, improvements in microbead generation methods, and new microbeads coating techniques. Other approaches, based on liquid-core capsules showed improved protein production and increased cell survival. But aside those more traditional techniques, new techniques are emerging in response to shortcomings of existing methods. More recently, direct cell aggregate coating have been proposed to minimize membrane thickness and implants size. Microcapsule performances are largely dictated by the physicochemical properties of the materials and the preparation techniques employed. Despite numerous promising pre-clinical results, at the present time each methods proposed need further improvements before reaching the clinical phase.

Effects of PEG hydrogel crosslinking density on protein diffusion and encapsulated islet survival and function

The rational design of immunoprotective hydrogel barriers for transplanting insulin-producing cells requires an understanding of protein diffusion within the hydrogel network and how alterations to the network structure affect protein diffusion. Hydrogels of varying crosslinking density were formed via the chain polymerization of dimethacrylated PEG macromers of varying molecular weight, and the diffusion of six model proteins with molecular weights ranging from 5700 to 67,000 g/mol was observed in these hydrogel networks. Protein release profiles were used to estimate diffusion coefficients for each protein/gel system that exhibited Fickian diffusion. Diffusion coefficients were on the order of 10(-6)-10(-7) cm(2)/s, such that protein diffusion time scales (t(d) = L(2)/D) from 0.5-mm thick gels vary from 5 min to 24 h. Adult murine islets were encapsulated in PEG hydrogels of varying crosslinking density, and islet survival and insulin release was maintained after two weeks of culture in each gel condition. While the total insulin released during a 1 h glucose stimulation period was the same from islets in each sample, increasing hydrogel crosslinking density contributed to delays in insulin release from hydrogel samples within the 1 h stimulation period.

A microfluidic approach to fabricate monodisperse hollow or porous poly(HEMA-MMA) microspheres using single emulsions as templates

We have successfully developed a novel and simple method to controllably prepare monodisperse poly(hydroxyethyl methacrylate-methyl methacrylate) (poly(HEMA-MMA)) microspheres with two distinct structures using single emulsions as templates. By employing a microfluidic emulsification approach to fabricate monomer-contained oil-in-water (O/W) emulsions as templates, and introducing proper initiators and different types of porogens, poly(HEMA-MMA) microspheres with hollow or porous structure are prepared in a controllable way. The shell thickness of hollow microspheres or the porosity of porous microspheres is controllably achieved by simply adjusting the porogen concentration. The prepared poly(HEMA-MMA) microspheres with controllable hollow or porous structures are favored for various potential applications. Furthermore, by using the simple preparation methodology proposed in this study, fabrication of monodisperse porous microspheres or hollow microcapsules with other materials can also be easily achieved.

Preparation of uniform-sized agarose beads by microporous membrane emulsification technique

Uniform-sized agarose beads were prepared by membrane emulsification technique in this study. Agarose was dissolved in boiling water (containing 0.9% sodium chloride) and used as water phase. A mixture of liquid paraffin and petroleum ether containing 4 wt% of hexaglycerin penta ester (PO-500) emulsifier was used as oil phase. At 55 degrees C, the water phase permeated through uniform pores of microporous membrane into the oil phase by a pressure of nitrogen gas to form uniform W/O emulsion. Then the emulsion was cooled down to room temperature under gentle agitation to form gel beads. The effect of oil phase, emulsifier, especially temperature on the uniformity of the beads were investigated and interpreted from interfacial tension between water phase and oil phase. Under optimized condition, the coefficient variation (C.V.) showing the size distribution of the beads was under 15%. This was the first report to prepare uniform agarose beads by membrane emulsification, and to investigate the effect of temperature on the size distribution of the droplets and beads. The beads with different size can be prepared by using membranes with different pore size, and the result showed that there was a linear relationship between the average diameter of beads and pore size of the membranes; beads with diameter from 15 to 60 microm were able to obtain in this study.

Optimization of the cell seeding density and modeling of cell growth and metabolism using the modified Gompertz model for microencapsulated animal cell culture

Cell microencapsulation is one of the promising strategies for the in vitro production of proteins or in vivo delivery of therapeutic products. In order to design and fabricate the optimized microencapsulated cell system, the Gompertz model was applied and modified to describe the growth and metabolism of microencapsulated cell, including substrate consumption and product formation. The Gompertz model successfully described the cell growth kinetics and the modified Gompertz models fitted the substrate consumption and product formation well. It was demonstrated that the optimal initial cell seeding density was about 4-5 x 10(6) cells/mL of microcapsule, in terms of the maximum specific growth rate, the glucose consumption potential and the product formation potential calculated by the Gompertz and modified Gompertz models. Modeling of cell growth and metabolism in microcapsules provides a guideline for optimizing the culture of microencapsulated cells.

Conformal Coating of Mammalian Cells Immobilized onto Magnetically Driven Beads

A novel cell bead system, comprising a magnetic core, a spherical annulus of agarose-immobilized cells, all conformally coated within a synthetic polymer, is proposed as a means of immunoisolating mammalian cells in a system that provides a balance between low total implant volume, retrievability, and diffusion limitations. A successful immunoisolation system could be used to transplant cells without eliciting an inappropriate host response. Chinese hamster ovary (CHO) cells were immobilized at the periphery of large (approximately 2 mm) agarose beads containing inert magnetic cores (< or = 1 mm) and coated in a hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA) copolymer by interfacial precipitation. The beads were coated in liquid gradients containing polyethylene glycol 200 (PEG) or bromooctane. Although many cells were adversely affected by the coating process, the cells that did survive (30-50% of those loaded into the beads) remained viable for a period of at least 2 weeks. This viability was much higher than achieved previously because of a number of factors, such as the aqueous agarose, the hydrophobic bromooctane intermediate layer, and faster coating times that minimize the exposure of the cells to organic solvents. Also, a mathematical model was used to describe oxygen transport within the annular agarose beads. These results provide evidence that the proposed geometry and the fabrication approach may be useful for a variety of applications that involve cell encapsulation.

In vivo calcium deposition on polyvinyl alcohol matrix used in hollow fiber cell macroencapsulation devices

The encapsulation of genetically modified cells represents a promising approach for the delivery of therapeutic proteins. The functionality of the device is dependent on the characteristics of the biomaterials, the procedures used in its confection and the adaptability of the encapsulated cells in the host. We report conditions leading to the development of calcifications on the polyvinyl alcohol (PVA) matrix introduced in hollow fiber devices for the encapsulation of primary human fibroblasts implanted in mice. The manufacturing procedures, batches of PVA matrix and cell lineages were assessed for their respective role in the development of the phenomenon. The results showed that the calcification is totally prevented by substituting phosphate-buffer saline with ultra-pure sterile water in the rinsing procedure of the matrix. Moreover, a positive correlation was found, when comparing two fibroblast cell lineages, between the level of lactate dehydrogenase (LDH) activity measured in the cells and the degree of calcium deposition. Higher LDH activity may decrease calcium depositions because it generates in the device a more acidic microenvironment inhibiting calcium precipitation. The present study defines optimized conditions for the encapsulation of primary human fibroblasts in order to avoid potentially detrimental calcifications and to allow long-term survival of encapsulated cells.