Cell encapsulation utilizing PEG-fibrinogen hydrogel supports viability and enhances productivity under stress conditions

Microfluidic Generation of Thin-Shelled Polyethylene Glycol-Tyramine Microgels for Non-Invasive Delivery of Immunoprotected β-Cells

Transplantation of microencapsulated pancreatic cells is emerging as a promising therapy to replenish β-cell mass lost from auto-immune nature of type I diabetes mellitus (T1DM). This strategy intends to use micrometer-sized microgels to provide immunoprotection to transplanted cells to avoid chronic application of immunosuppression. Clinical application of encapsulation has remained elusive due to often limited production throughputs and body's immunological reactions to implanted materials. This article presents a high-throughput fabrication of monodisperse, non-immunogenic, non-degradable, immunoprotective, semi-permeable, enzymatically-crosslinkable polyethylene glycol-tyramine (PEG-TA) microgels for β-cell microencapsulation. Monodisperse β-cell laden microgels of ≈120 µm, with a shell thickness of 20 µm are produced using an outside-in crosslinking strategy. Microencapsulated β-cells rapidly self-assemble into islet-sized spheroids. Immunoprotection of the microencapsulated is demonstrated by inability of FITC-IgG antibodies to diffuse into cell-laden microgels and NK-cell inability to kill microencapsulated β-cells. Multiplexed ELISA analysis on live blood immune reactivity confirms limited immunogenicity. Microencapsulated MIN6β1 spheroids remain glucose responsive for 28 days in vitro, and able to restore normoglycemia 5 days post-implantation in diabetic mice without notable amounts of cell death. In short, PEG-TA microgels effectively protect implanted cells from the host's immune system while being viable and functional, validating this strategy for the treatment of T1DM.

Development of a local controlled release system for therapeutic proteins in the treatment of skeletal muscle injuries and diseases

The present study aims to develop and characterize a controlled-release delivery system for protein therapeutics in skeletal muscle regeneration following an acute injury. The therapeutic protein, a membrane-GPI anchored protein called Cripto, was immobilized in an injectable hydrogel delivery vehicle for local administration and sustained release. The hydrogel was made of poly(ethylene glycol)-fibrinogen (PEG-Fibrinogen, PF), in the form of injectable microspheres. The PF microspheres exhibited a spherical morphology with an average diameter of approximately 100 micrometers, and the Cripto protein was uniformly entrapped within them. The release rate of Cripto from the PF microspheres was controlled by tuning the crosslinking density of the hydrogel, which was varied by changing the concentration of poly(ethylene glycol) diacrylate (PEG-DA) crosslinker. In vitro experiments confirmed a sustained-release profile of Cripto from the PF microspheres for up to 27 days. The released Cripto was biologically active and promoted the in vitro proliferation of mouse myoblasts. The therapeutic effect of PF-mediated delivery of Cripto in vivo was tested in a cardiotoxin (CTX)-induced muscle injury model in mice. The Cripto caused an increase in the in vivo expression of the myogenic markers Pax7, the differentiation makers eMHC and Desmin, higher numbers of centro-nucleated myofibers and greater areas of regenerated muscle tissue. Collectively, these results establish the PF microspheres as a potential delivery system for the localized, sustained release of therapeutic proteins toward the accelerated repair of damaged muscle tissue following acute injuries.

Cocktail-like gradient gelatin/hyaluronic acid bioimplant for enhancing tendon-bone healing in fatty-infiltrated rotator cuff injury models

The regeneration of enthesis tissue (native tendon-bone interface) at the post-surgically repaired rotator cuff remains a challenge for clinicians, especially with the emergence of degenerative affection such as fatty infiltration that exacerbate poor tendon-bone healing. In this study, we proposed a cocktail-like hydrogel with a four-layer structure (BMSCs+gNC@GH) for enhancing fatty infiltrated tendon-bone healing. As collagen and hyaluronic acid are the main biomacromolecules that constitute the extracellular matrix of enthesis tissue, this hydrogel was composed of UV-curable gelatin/hyaluronic acid (GelMA/HAMA) dual network gel (GH) with nanoclay (NC) and stem cells loaded. The results showed that NC exhibited a cocktail-like gradient distribution in GH, which effectively mimicked the structure of native enthesis and supported the long-term culture and encapsulation of BMSCs. What's more, the gradient variation of NC provided a biological signal for promoting gradient osteogenic differentiation of cells. Based on the in vivo results, BMSCs+gNC@GH effectively promoted fibrocartilage layer regeneration at the tendon-bone interface and inhibited fatty infiltration. Therefore, BMSCs+gNC@GH group exhibited better biomechanical properties. Thus, this cocktail-like implant may be a promising tissue-engineered scaffold for tendon-bone healing, and it provides a new idea for the development of scaffolds with the function of inhibiting degeneration.

Engineering a material-genetic interface as safety switch for embedded therapeutic cells

Encapsulated cell-based therapies involve the use of genetically-modified cells embedded in a material in order to produce a therapeutic agent in a specific location in the patient's body. This approach has shown great potential in animal model systems for treating diseases such as type I diabetes or cancer, with selected approaches having been tested in clinical trials. Despite the promise shown by encapsulated cell therapy, though, there are safety concerns yet to be addressed, such as the escape of the engineered cells from the encapsulation material and the resulting production of therapeutic agents at uncontrolled sites in the body. For that reason, there is great interest in the implementation of safety switches that protect from those side effects. Here, we develop a material-genetic interface as safety switch for engineered mammalian cells embedded into hydrogels. Our switch allows the therapeutic cells to sense whether they are embedded in the hydrogel by means of a synthetic receptor and signaling cascade that link transgene expression to the presence of an intact embedding material. The system design is highly modular, allowing its flexible adaptation to other cell types and embedding materials. This autonomously acting switch constitutes an advantage over previously described safety switches, which rely on user-triggered signals to modulate activity or survival of the implanted cells. We envision that the concept developed here will advance the safety of cell therapies and facilitate their translation to clinical evaluation.

Biomanufacturing Recombinantly Expressed Cripto-1 Protein in Anchorage-Dependent Mammalian Cells Growing in Suspension Bioreactors within a Three-Dimensional Hydrogel Microcarrier

Biotherapeutic soluble proteins that are recombinantly expressed in mammalian cells can pose a challenge when biomanufacturing in three-dimensional (3D) suspension culture systems. Herein, we tested a 3D hydrogel microcarrier for a suspension culture of HEK293 cells overexpressing recombinant Cripto-1 protein. Cripto-1 is an extracellular protein that is involved in developmental processes and has recently been reported to have therapeutic effects in alleviating muscle injury and diseases by regulating muscle regeneration through satellite cell progression toward the myogenic lineage. Cripto-overexpressing HEK293 cell lines were cultured in microcarriers made from poly (ethylene glycol)-fibrinogen (PF) hydrogels, which provided the 3D substrate for cell growth and protein production in stirred bioreactors. The PF microcarriers were designed with sufficient strength to resist hydrodynamic deterioration and biodegradation associated with suspension culture in stirred bioreactors for up to 21 days. The yield of purified Cripto-1 obtained using the 3D PF microcarriers was significantly higher than that obtained with a two-dimensional (2D) culture system. The bioactivity of the 3D-produced Cripto-1 was equivalent to commercially available Cripto-1 in terms of an ELISA binding assay, a muscle cell proliferation assay, and a myogenic differentiation assay. Taken together, these data indicate that 3D microcarriers made from PF can be combined with mammalian cell expression systems to improve the biomanufacturing of protein-based therapeutics for muscle injuries.

PEG-fibrinogen hydrogel microspheres as a scaffold for therapeutic delivery of immune cells

Recent advances in the field of cell therapy have proposed new solutions for tissue repair and regeneration using various cell delivery approaches. Here we studied ex vivo a novel topical delivery system of encapsulated cells in hybrid polyethylene glycol-fibrinogen (PEG-Fb) hydrogel microspheres to respiratory tract models. We investigated basic parameters of cell encapsulation, delivery and release in conditions of inflamed and damaged lungs of bacterial-infected mice. The establishment of each step in the study was essential for the proof of concept. We demonstrated co-encapsulation of alveolar macrophages and epithelial cells that were highly viable and equally distributed inside the microspheres. We found that encapsulated macrophages exposed to bacterial endotoxin lipopolysaccharide preserved high viability and secreted moderate levels of TNFα, whereas non-encapsulated cells exhibited a burst TNFα secretion and reduced viability. LPS-exposed encapsulated macrophages exhibited elongated morphology and out-migration capability from microspheres. Microsphere degradation and cell release in inflamed lung environment was studied ex vivo by the incubation of encapsulated macrophages with lung extracts derived from intranasally infected mice with Yersinia pestis, demonstrating the potential in cell targeting and release in inflamed lungs. Finally, we demonstrated microsphere delivery to a multi-component airways-on-chip platform that mimic human nasal, bronchial and alveolar airways in serially connected compartments. This study demonstrates the feasibility in using hydrogel microspheres as an effective method for topical cell delivery to the lungs in the context of pulmonary damage and the need for tissue repair.

Novel method for quantifying cells on carriers and its demonstration during SARS-2 vaccine development

The most effective way to prevent and control infectious disease outbreak is through vaccines. The increasing use of vaccines has elevated the need to establish new manufacturing strategies. One of the major approaches is cell-based production, which creates a need for high cell density to enable higher cell production levels. This has led to development of the technology of cell carriers, including micro and macro cell carriers. To follow the production process, quantifying the number of cells on these carriers is required, as well as the tracking of their viability and proliferation. However, owing to various carriers' unique structures, tracking the cell's is challenging using current traditional assays that were originally developed for monolayers of adherent cells. The current "gold standard" method is counting cell nuclei, separating cells from the carrier, staining with crystal violet, and visually counting under a microscope. This method is tedious and counts both live and dead cells. A few other techniques were developed but were specific to the carrier type and involved specialized equipment. In this study, we describe a broadly ranging method for counting cells on carriers that was developed and employed as part of the development of severe acute respiratory syndrome coronavirus 2 vaccine. The method is based on the Alamar blue dye, a well-known, common marker for cell activity, and was found to be successful in tracking cell adsorption, cell growth, and viability on carriers. No separation of the cells from the carriers is needed, nor is any specialized equipment; the method is simple and rapid and provides comprehensive details necessary for process control of viral vaccine production in cells. This method can be easily implemented in any of a number of cell-based processes and other unique platforms for measuring the growth of encapsulated cells.

Live reporting for hypoxia: Hypoxia sensor-modified mesenchymal stem cells as in vitro reporters

Natural oxygen gradients occur in tissues of biological organisms and also in the context of three-dimensional (3D) in vitro cultivation. Oxygen diffusion limitation and metabolic oxygen consumption by embedded cells produce areas of hypoxia in the tissue/matrix. However, reliable systems to detect oxygen gradients and cellular response to hypoxia in 3D cell culture systems are still missing. In this study, we developed a system for visualization of oxygen gradients in 3D using human adipose tissue-derived mesenchymal stem cells (hAD-MSCs) modified to stably express a fluorescent genetically engineered hypoxia sensor HRE-dUnaG. Modified cells retained their stem cell characteristics in terms of proliferation and differentiation capacity. The hypoxia-reporter cells were evaluated by fluorescence microscopy and flow cytometry under variable oxygen levels (2.5%, 5%, and 7.5% O₂ ). We demonstrated that reporter hAD-MSCs output is sensitive to different oxygen levels and displays fast decay kinetics after reoxygenation. Additionally, the reporter cells were encapsulated in bulk hydrogels with a variable cell number, to investigate the sensor response in model 3D cell culture applications. The use of hypoxia-reporting cells based on MSCs represents a valuable tool for approaching the genuine in vivo cellular microenvironment and will allow a better understanding of the regenerative potential of AD-MSCs.