Challenges and Perspectives for Future Considerations in the Bioengineering of a Bioartificial Pancreas.

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.

Perspectives and Challenges on the Potential Use of Exosomes in Bioartificial Pancreas Engineering.

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.

Effect of Alginate Microbead Encapsulation of Placental Mesenchymal Stem Cells on Their Immunomodulatory Function.

In this research we have used different cytokines and progesterone to enhance the immunomodulatory capacity of placental-derived stem cells (PLSCs) prior to their encapsulation. We assessed the effect of microencapsulation of the cells without (control) or after 3-day treatment with interferon gamma (INFγ), interleukin10 (IL-10), or progesterone (P4). Treated PLSCs demonstrated strong immunosuppressive effects on phytohemagglutinin (PHA)-activated peripheral blood mononuclear cells (PBMNCs). INFγ treatment resulted in the strongest immune inhibition among the treated groups. The treatments enhanced soluble human leukocyte antigen (sHLAG) secretion compared to control. The IL-10-treated group showed the highest effect on HLAG secretion compared to other groups. Alginate encapsulation of PLSCs did not affect cell viability, or sHLAG secretion. Also, after treatment the encapsulated PLSCs inhibited PHA-activated PBMNCs in the same manner as unencapsulated cells. We studied two groups of encapsulated PLSCs, one without perm-selective poly-L-ornithine (PLO)-coating and the other with PLO-coating, and measured levels of sHLAG secreted. We found no difference in sHLAG secretion between both groups. In summary, our data show that immunomodulatory function of the PLSC is not affected by encapsulation. These findings provide good promise for potential use of encapsulated PLSCs for immunomodulation treatment of disease by stem cell therapy.

Effect of alginate matrix engineered to mimic the pancreatic microenvironment on encapsulated islet function.

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.

Synergistic effect of CNTF and GDNF on directed neurite growth in chick embryo dorsal root ganglia.

It is often critical to improve the limited regenerative capacity of the peripheral nerves and direct neural growth towards specific targets, such as surgically implanted bioengineered constructs. One approach to accomplish this goal is to use extrinsic neurotrophic factors. The candidate factors first need to be identified and characterized in in vitro tests for their ability to direct the neurite growth. Here, we present a simple guidance assay that allows to assess the chemotactic effect of signaling molecules on the growth of neuronal processes from dorsal root ganglia (DRG) using only standard tissue culture materials. We used this technique to quantitatively determine the combined and individual effects of the ciliary neurotrophic factor (CNTF) and glial cell line-derived neurotrophic factor (GDNF) on neurite outgrowth. We demonstrated that these two neurotrophic factors, when applied in a 1:1 combination, but not individually, induced directed growth of neuronal processes towards the source of the gradient. This chemotactic effect persists without significant changes over a wide (10-fold) concentration range. Moreover, we demonstrated that other, more general growth parameters that do not evaluate growth in a specific direction (such as, neurite length and trajectory) were differentially affected by the concentration of the CNTF/GNDF mixture. Furthermore, GDNF, when applied individually, did not have any chemotactic effect, but caused significant neurite elongation and an increase in the number of neurites per ganglion.