There is an unrelenting interest in the development of a reliable bioartificial pancreas construct since the first description of this technology of encapsulated islets by Lim and Sun in 1980 because ...it promised to be a curative treatment for Type 1 Diabetes Mellitus (T1DM). Despite the promise of the concept of encapsulated islets, there are still some challenges that impede the full realization of the clinical potential of the technology. In this review, we will first present the justification for continued research and development of this technology. Next, we will review key barriers that impede progress in this field and discuss strategies that can be used to design a reliable construct capable of effective long-term performance after transplantation in diabetic patients. Finally, we will share our perspectives on areas of additional work for future research and development of the technology.
In this minireview, we briefly outline the hallmarks of diabetes, the distinction between type 1 and type 2 diabetes, the global incidence of diabetes, and its associated comorbidities. The main goal ...of the review is to highlight the great potential of encapsulated pancreatic islet transplantation to provide a cure for type 1 diabetes. Following a short overview of the different approaches to islet encapsulation, we provide a summary of the merits and demerits of each approach of the encapsulation technology. We then discuss various attempts to clinical translation with each model of encapsulation as well as the factors that have mitigated the full clinical realization of the promise of the encapsulation technology, the progress that has been made and the challenges that remain to be overcome. In particular, we pay significant attention to the emerging strategies to overcome these challenges. We believe that these strategies to enhance the performance of the encapsulated islet constructs discussed herein provide good platforms for additional work to achieve successful clinical translation of the encapsulated islet technology.
Here, we report two methods that chemically modify alginate to achieve neutral–basic pH sensitivity of the resultant hydrogel. The first method involves direct amide bond formation between alginate ...and 4-(2-aminoethyl)benzoic acid. The second method that arose out of the desire to achieve better control of the degradation rate of the alginate hydrogel involves reductive amination of oxidized alginate. The products of both methods result in a hydrogel vehicle for targeted delivery of encapsulated payload under physiological conditions in the gastrointestinal tract. Two-dimensional diffusion-ordered spectroscopy and internal and coaxial external nuclear magnetic resonance standards were used to establish chemical bonding and percent incorporation of the modifying groups into the alginate polymer. The hydrogel made with alginate modified by each method was found to be completely stable under acidic pH conditions while disintegrating within minutes to hours in neutral–basic pH conditions. We found that, while alginate oxidation did not affect the β-d-mannuronate/α-l-guluronate ratio of alginate, the rate of disintegration of the hydrogel made with oxidized alginate was dependent upon the degree of oxidation.
Paracrine function is a major mechanism of cell-cell communication within tissue microenvironment in normal development and disease. In vitro cell culture models simulating tissue or tumor ...microenvironment are necessary tools to delineate epithelial-stromal interactions including paracrine function, yet an ideal three-dimensional (3D) tumor model specifically studying paracrine function is currently lacking. In order to fill this void we developed a novel 3D co-culture model in double-layered alginate hydrogel microspheres, incorporating prostate cancer epithelial and stromal cells in separate compartments of the microspheres. The cells remained confined and viable within their respective spheres for over 30 days. As a proof of principle regarding paracrine function of the model, we measured shedded component of E-cadherin (sE-cad) in the conditioned media, a major membrane bound cell adhesive molecule that is highly dysregulated in cancers including prostate cancer. In addition to demonstrating that sE-cad can be reliably quantified in the conditioned media, the time course experiments also demonstrated that the amount of sE-cad is influenced by epithelial-stromal interaction. In conclusion, the study establishes a novel 3D in vitro co-culture model that can be used to study cell-cell paracrine interaction.
Exosomes are enclosed within a single outer membrane and exemplify a specific subtype of secreted vesicles. Exosomes transfer signalling molecules, including microRNAs (miRNAs), messenger RNA (mRNA), ...fatty acids, proteins, and growth factors, making them a promising therapeutic tool. In routine bioartificial pancreas fabrication, cells are immobilized in polymeric hydrogels lacking attachment capability for cells and other biological cues. In this opinion article, we will discuss the potential role that exosomes and their specific biofactors may play to improve and sustain the function of this bioartificial construct. We will particularly discuss the challenges associated with their isolation and characterization. Since stem cells are an attractive source of exosomes, we will present the advantages of using exosomes in place of stem cells in medical devices including the bioartificial pancreas. We will provide literature evidence of active biofactors in exosomes to support their incorporation in the matrix of encapsulated islets. This will include their potential beneficial effect on hypoxic injury to encapsulated islets. In summary, we propose that the biofactors contained in secreted exosomes have significant potential to enhance the performance of islets encapsulated in polymeric material hydrogels with perm-selective properties to provide immunoisolation for islet transplants as an insulin delivery platform in diabetes.
In this article, we will review the changes that have occurred in islet transplantation at the birth of Pancreas 30 years ago. The first attempts at β-cell replacement in humans, pancreas and islet ...transplantation, were performed in the 1960s and 1970s. Although pancreas transplantation has been an accepted treatment for severe labile diabetes predating the emergence of the journal, allogeneic islet transplantation remains experimental. Current investigations within islet transplantation focus to improve islet function after transplantation. Improving islet viability during isolation, exploring ways to increase engraftment, and protection from the host immune system are some of the goals of these investigative efforts. The major barriers to clinical islet transplantation are shortage of human pancreas, the need for immunosuppression, and the inadequacy of the islet isolation process. It is generally accepted that islet encapsulation is an immunoisolation tool with good potential to address the first 2 of those barriers. We have therefore devoted a major part of this review to the critical factors needed to make it a clinical reality. With improved islet isolation techniques and determination of the best site of engraftment as well as improved encapsulation techniques, we hope that islet transplantation could someday achieve routine clinical use.
The goal of this chapter is to provide an overview of the different purposes for which the cell microencapsulation technology can be used. These include immunoisolation of non-autologous cells used ...for cell therapy; immobilization of cells for localized (targeted) delivery of therapeutic products to ablate, repair, or regenerate tissue; simultaneous delivery of multiple therapeutic agents in cell therapy; spatial compartmentalization of cells in complex tissue engineering; expansion of cells in culture; and production of different probiotics and metabolites for industrial applications. For each of these applications, specific examples are provided to illustrate how the microencapsulation technology can be utilized to achieve the purpose. However, successful use of the cell microencapsulation technology for whatever purpose will ultimately depend upon careful consideration for the choice of the encapsulating polymers, the method of fabrication (cross-linking) of the microbeads, which affects the permselectivity, the biocompatibility and the mechanical strength of the microbeads as well as environmental parameters such as temperature, humidity, osmotic pressure, and storage solutions.The various applications discussed in this chapter are illustrated in the different chapters of this book and where appropriate relevant images of the microencapsulation products are provided. It is hoped that this outline of the different applications of cell microencapsulation would provide a good platform for tissue engineers, scientists, and clinicians to design novel tissue constructs and products for therapeutic and industrial applications.
Interactions between the pancreatic extracellular matrix (ECM) and islet cells are known to regulate multiple aspects of islet physiology, including survival, proliferation, and glucose-stimulated ...insulin secretion. Recognizing the essential role of ECM in islet survival and function, various engineering approaches have been developed that aim to utilize ECM-based materials to recreate a native-like microenvironment. However, a major impediment to the success of these approaches has been the lack of a robust and comprehensive characterization of the human pancreatic proteome. Herein, by combining mass spectrometry (MS) and multiplex ELISA, we have provided an improved workflow for the in-depth profiling of the proteome, including minor constituents that are generally underrepresented. Moreover, we have further validated the effectiveness of our detergent-free decellularization protocol in the removal of cellular proteins and retention of the matrisome. It has also been established that the decellularized ECM and its derivatives can provide more tissue-specific cues than traditionally used biological scaffolds and are therefore more physiologically relevant for the development of hydrogels, bioinks and medium additives, in order to create a pancreatic niche. The data generated in this study would contribute significantly to the efforts of comprehensively defining the ECM atlas and also serve as a standard for the human pancreatic proteome to provide further guidance for design and engineering strategies for improved tissue engineering scaffolds.
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Islet transplantation is emerging as a therapeutic option for type 1 diabetes, albeit, only a small number of patients meeting very stringent criteria are eligible for the treatment because of the ...side effects of the necessary immunosuppressive therapy and the relatively short time frame of normoglycemia that most patients achieve. The challenge of the immune‐suppressive regimen can be overcome through microencapsulation of the islets in a perm‐selective coating of alginate microbeads with poly‐l‐lysine or poly‐
l‐ornithine. In addition to other issues including the nutrient supply challenge of encapsulated islets a critical requirement for these cells has emerged as the need to engineer the microenvironment of the encapsulation matrix to mimic that of the native pancreatic scaffold that houses islet cells. That microenvironment includes biological and mechanical cues that support the viability and function of the cells. In this study, the alginate hydrogel was modified to mimic the pancreatic microenvironment by incorporation of extracellular matrix (ECM). Mechanical and biological changes in the encapsulating alginate matrix were made through stiffness modulation and incorporation of decellularized ECM, respectively. Islets were then encapsulated in this new biomimetic hydrogel and their insulin production was measured after 7 days in vitro. We found that manipulation of the alginate hydrogel matrix to simulate both physical and biological cues for the encapsulated islets enhances the mechanical strength of the encapsulated islet constructs as well as their function. Our data suggest that these modifications have the potential to improve the success rate of encapsulated islet transplantation.
Inverted microscopy images of alginate beads following 36 h of mechanical agitation. The top row and bottom row are ×2 and ×10 magnification, respectively. From left to right rows, the beads are crosslinked in 25 mM SrCl2, 25 mM SrCl2 with ECM‐alginate, 50 mM SrCl2, and 50 mM SrCl2 with extracellular matrix (ECM)‐alginate. Scale bar: 500 μm for ×2 and 100 μm for ×10.
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