An important step towards a prevascularized islet microencapsulation device: in vivo prevascularization by combination of mesenchymal stem cells on micropatterned membranes

A hybrid implant combining a macroporous device with immunoprotective microcapsules for cell therapy applications: A conceptual in vitro study

Cell encapsulation strategies including macro- and micro-delivery devices have been widely used in cell therapy due to their ability to provide immunoprotection to the transplanted cells. While both strategies can provide mechanical and physiochemical support for maintaining cell survival and function, they each have their limitations. In this study, we report the design and fabrication of a hybrid implant combining the advantages of both macro- and micro-cell delivery devices. The hybrid implant comprises a microwell-array macroporous device fabricated from non-degradable clinically approved polyvinylidene fluoride (PVDF) combined with immunoprotective alginate microcapsules. The microwell design provides a vessel to retain individual microcapsules, while the pores enable unhindered mass transport of nutrients and oxygen to the encapsulated cells and support vascular ingrowth. We show that both rodent pseudoislets and primary human islets maintain their viability and function inside the hybrid implant in a proof-of-concept study. Mechanically, it is strong and flexible suitable for surgical handling and for eventual retrieval for replacement. The hybrid implant also supports the growth of human umbilical vein endothelial cells (HUVEC) across its surface allowing in vitro "prevascularization", which can potentially accelerate blood vessel formation in poorly vascularized transplantation sites such as the subcutaneous space. In conclusion, the hybrid cell delivery device, which confers immunoprotection and allows prevascularization, can act as a protective container during surgical handling and retrieval of microencapsulated cells opening a wide range of cell therapy applications including stem cells.

Supporting islet function in a PVDF membrane based macroencapsulation delivery device by solvent non-solvent casting using PVP

Type 1 diabetic (T1D) patients are life-long dependent on insulin therapy to keep their blood glucose levels under control. An alternative cell-based therapy for exogenous insulin injections is clinical islet transplantation (CIT). Currently the widespread application of CIT is limited, due to risks associated with the life-long use of immunosuppressive drugs to prevent rejection of donor cells. An immunoprotective macroencapsulation device can protect allogeneic islet cells against the host immune system and allow exploring extrahepatic transplantation sites. We report on the characterization and creation of porous polyvinylidene fluoride (PVDF) membrane-based devices intended for islet and beta-cell transplantation. We hypothesize that by incorporating polyvinyl-pyrrolidone (PVP) into a PVDF solution the permeability of PVDF membranes for insulin and glucose can be improved by solvent-non solvent casting to create submicrometer porous films. We show that the use of water-soluble PVP, can significantly increase glucose diffusion through these membranes while still having the ability to block immune cells from migrating through these membranes. Human donor islets loaded into devices made from these thin PVDF/PVP membranes showed a 92 ±  4% viability after 8 days similar to their free-floating counterparts. The glucose responsiveness of human donor islets encapsulated inside PVDF/PVP membrane-based devices was significantly improved compared to islets seeded in devices made from PVDF membranes without PVP, with a stimulation index of 3.2 for PVDF/PVP devices and 1.3 for PVDF-alone devices at day 8. Our data show that by addition of PVP as pore forming agent during membrane fabrication at a specific ratio the diffusion characteristics can be tuned such that human islet function in these closed macrodevices, can be kept at the same level as non-encapsulated islets, while the membrane can still serve as a protective barrier preventing the entry of primary human macrophages and damaging beta cells.

A xenogenic-free culture medium for cell micro-patterning systems as cell-instructive biomaterials for potential clinical applications

Cell micro-patterning controls cell fate and function and has potential for generating therapeutically usable mesenchymal stromal cell (MSC) populations with precise functions. However, to date, the micro-patterning of human cells in a translational context has been impossible because only ruminant media supplements, e.g. fetal bovine serum (FBS), are established for use with micro-patterns (MPs). Thus, there are currently no good manufacturing practice (GMP)-compliant media available for MPs. This study tested a xenogenic-free human plasma and platelet lysate (hP + PL) medium supplement to determine its compatibility with MPs. Unfiltered hP + PL medium resulted in significant protein deposition, creating a 'carpet-like' layer that rendered MPs ineffective. Filtration (3×/5×) eliminated this effect. Importantly, quantitative comparison using droplet digital PCR revealed that human MSCs in all media types exhibited similar profiles with strong myogenic Calponin 1/Transgelin 2 (TAGLN2) and weaker osteogenic alkaline phosphatase/Runt-related transcription factor 2 marker expression, and much weaker adipogenic (lipoprotein lipase/peroxisome proliferator-activated receptor gamma) and chondrogenic (collagen type II/aggrecan) expression, with profiles being dominated by myogenic markers. Within these similar profiles, an even stronger induction of the myogenic marker TAGLN2 by all hP + PL- compared to FBS-containing media. Overall, this suggested that FBS can be replaced with hP + PL without altering differentiation profiles. However, assessing individual MSC responses to various MP types with defined categories revealed that unfiltered hP + PL medium was unusable. Importantly, FBS- and 3× filtered hP + PL media were comparable in each differentiation category. Summarized, this study recommends 3× filtered hP + PL as a xenogenic-free and potentially GMP-compliant alternative to FBS as a culture medium supplement for micro-patterning cell populations in both basic and translational research that will ensure consistent and reliable MSC micro-patterning for therapeutic use.

Liquefied capsules containing nanogrooved microdiscs and umbilical cord-derived cells for bone tissue engineering

Background

Surface topography has been shown to influence cell behavior and direct stromal cell differentiation into distinct lineages. Whereas this phenomenon has been verified in two-dimensional cultures, there is an urgent need for a thorough investigation of topography's role within a three-dimensional (3D) environment, as it better replicates the natural cellular environment.

Methods

A co-culture of Wharton's jelly-derived mesenchymal stem/stromal cells (WJ-MSCs) and human umbilical vein endothelial cells (HUVECs) was encapsulated in a 3D system consisting of a permselective liquefied environment containing freely dispersed spherical microparticles (spheres) or nanogrooved microdiscs (microdiscs). Microdiscs presenting 358 ± 23 nm grooves and 944 ± 49 nm ridges were produced via nanoimprinting of spherical polycaprolactone microparticles between water-soluble polyvinyl alcohol counter molds of nanogrooved templates. Spheres and microdiscs were cultured in vitro with umbilical cord-derived cells in a basal or osteogenic medium within liquefied capsules for 21 days.

Results

WJ-MSCs and HUVECs were successfully encapsulated within liquefied capsules containing spheres and microdiscs, ensuring high cellular viability. Results show an enhanced osteogenic differentiation in microdiscs compared to spheres, even in basal medium, evidenced by alkaline phosphatase activity and osteopontin expression.

Conclusions

This work suggests that the topographical features present in microdiscs induce the osteogenic differentiation of adhered WJ-MSCs along the contact guidance, without additional differentiation factors. The developed 3D bioencapsulation system comprising topographical features might be suitable for bone tissue engineering approaches with minimum in vitro manipulation.

Strategy for Clinical Setting of Co-transplantation of Mesenchymal Stem Cells and Pancreatic Islets

Islet transplantation may be the most efficient therapeutic technique for patients with type 1 diabetes mellitus (T1DM). However, the clinical application of this method is faced with numerous limitations, including isolated islet apoptosis, recipient rejection, and graft vascular reconstruction. Mesenchymal stem cells (MSCs) possess anti-apoptotic, immunomodulatory, and angiogenic properties. Here, we review recent studies on co-culture and co-transplantation of islets with MSCs. We have summarized the methods of preparation of co-transplantation, especially the merits of co-culture, and the effects of co-transplantation. Accumulating experimental evidence shows that co-culture of islets with MSCs promotes islet survival, enhances islet secretory function, and prevascularizes islets through various pretransplant preparations. This review is expected to provide a reference for exploring the use of MSCs for clinical islet co-transplantation.

Skin precursor‐derived Schwann cells accelerate in vivo prevascularization of tissue‐engineered nerves to promote peripheral nerve regeneration

Prevascularization strategies have become a hot spot in tissue engineering. As one of the potential candidates for seed cells, skin precursor-derived Schwann cells (SKP-SCs) were endowed with a new role to more efficiently construct prevascularized tissue-engineered peripheral nerves. The silk fibroin scaffolds seeded with SKP-SCs were prevascularized through subcutaneously implantation, which was further assembled with the SKP-SC-containing chitosan conduit. SKP-SCs expressed pro-angiogenic factors in vitro and in vivo. SKP-SCs significantly accelerated the satisfied prevascularization in vivo of silk fibroin scaffolds compared with VEGF. Moreover, the NGF expression revealed that pregenerated blood vessels adapted to the nerve regeneration microenvironment through reeducation. The short-term nerve regeneration of SKP-SCs-prevascularization was obviously superior to that of non-prevascularization. At 12 weeks postinjury, both SKP-SCs-prevascularization and VEGF-prevascularization significantly improved nerve regeneration with a comparable degree. Our figures provide a new enlightenment for the optimization of prevascularization strategies and how to further utilize tissue engineering for better repair.

Emerging strategies for beta cell transplantation to treat diabetes

Beta cell replacement has emerged as an attractive therapeutic alternative to traditional exogenous insulin administration for management of type 1 diabetes (T1D). Beta cells deliver insulin dynamically based on individual glycometabolic requirements, providing glycemic control while significantly reducing patient burden. Although transplantation into the portal circulation is clinically available, poor engraftment, low cell survival, and immune rejection have sparked investigation of alternative strategies for beta cell transplantation. In this review, we focus on current micro- and macroencapsulation technologies for beta cell transplantation and evaluate their advantages and challenges. Specifically, we comment on recent methods to ameliorate graft hypoxia including enhanced vascularization, reduction of pericapsular fibrotic overgrowth (PFO), and oxygen supplementation. We also discuss emerging beta cell-sourcing strategies to overcome donor shortage and provide insight into potential approaches to address outstanding challenges in the field.

Recapitulating pancreatic cell-cell interactions through bioengineering approaches: the momentous role of non-epithelial cells for diabetes cell therapy

Over the past few years, extensive efforts have been made to generate in-vitro pancreatic micro-tissue, for disease modeling or cell replacement approaches in pancreatic related diseases such as diabetes mellitus. To obtain these goals, a closer look at the diverse cells participating in pancreatic development is necessary. Five major non-epithelial pancreatic (pN-Epi) cell populations namely, pancreatic endothelium, mesothelium, neural crests, pericytes, and stellate cells exist in pancreas throughout its development, and they are hypothesized to be endogenous inducers of the development. In this review, we discuss different pN-Epi cells migrating to and existing within the pancreas and their diverse effects on pancreatic epithelium during organ development mediated via associated signaling pathways, soluble factors or mechanical cell-cell interactions. In-vivo and in-vitro experiments, with a focus on N-Epi cells' impact on pancreas endocrine development, have also been considered. Pluripotent stem cell technology and multicellular three-dimensional organoids as new approaches to generate pancreatic micro-tissues have also been discussed. Main challenges for reaching a detailed understanding of the role of pN-Epi cells in pancreas development in utilizing for in-vitro recapitulation have been summarized. Finally, various novel and innovative large-scale bioengineering approaches which may help to recapitulate cell-cell interactions and are crucial for generation of large-scale in-vitro multicellular pancreatic micro-tissues, are discussed.

In vivovascularization and islet function in a microwell device for pancreatic islet transplantation

Islet encapsulation in membrane-based devices could allow for transplantation of donor islet tissue in the absence of immunosuppression. To achieve long-term survival of islets, the device should allow rapid exchange of essential nutrients and be vascularized to guarantee continued support of islet function. Recently, we have proposed a membrane-based macroencapsulation device consisting of a microwell membrane for islet separation covered by a micropatterned membrane lid. The device can prevent islet aggregation and support functional islet survivalin vitro. Here, based on previous modeling studies, we develop an improved device with smaller microwell dimensions, decreased spacing between the microwells and reduced membrane thickness and investigate its performancein vitroandin vivo. This improved device allows for encapsulating higher islet numbers without islet aggregation and by applying anin vivoimaging system we demonstrate very good perfusion of the device when implanted intraperitoneally in mice. Besides, when it is implanted subcutaneously in mice, islet viability is maintained and a vascular network in close proximity to the device is developed. All these important findings demonstrate the potential of this device for islet transplantation.

Engineering Strategies for Allogeneic Solid Tissue Acceptance

Advances in allogeneic transplantation of solid organs and tissues depend on our understanding of mechanisms that mediate the prevention of graft rejection. For the past decades, clinical practice has established guidelines to prevent allograft rejection, which mostly rely on the intake of nontargeted immunosuppressants as the gold standard. However, such lifelong regimens have been reported to trigger severe morbidities and commonly fail in preventing late allograft loss. In this review, the biology of allogeneic rejection and self-tolerance is analyzed, as well as the mechanisms of cellular-based therapeutics driving suppression and/or tolerance. Bioinspired engineering strategies that take advantage of cells, biomaterials, or combinations thereof to prevent allograft rejection are addressed, as well as biological mechanisms that drive their efficacy.

Generation of Human Stem Cell-Derived Pancreatic Organoids (POs) for Regenerative Medicine

Insulin-dependent diabetes mellitus or type 1 diabetes mellitus (T1DM) is an auto-immune condition characterized by the loss of pancreatic β-cells. The curative approach for highly selected patients is the pancreas or the pancreatic islet transplantation. Nevertheless, these options are limited by a growing shortage of donor organs and by the requirement of immunosuppression.Xenotransplantation of porcine islets has been extensively investigated. Nevertheless, the strong xenoimmunity and the risk of transmission of porcine endogenous retroviruses, have limited their application in clinic. Generation of β-like cells from stem cells is one of the most promising strategies in regenerative medicine. Embryonic, and more recently, adult stem cells are currently the most promising cell sources exploited to generate functional β-cells in vitro. A number of studies demonstrated that stem cells could generate functional pancreatic organoids (POs), able to restore normoglycemia when implanted in different preclinical diabetic models. Nevertheless, a gradual loss of function and cell dead are commonly detected when POs are transplanted in immunocompetent animals. So far, the main issue to be solved is the post-transplanted islet loss, due to the host immune attack. To avoid this hurdle, nanotechnology has provided a number of polymers currently under investigation for islet micro and macro-encapsulation. These new approaches, besides conferring PO immune protection, are able to supply oxygen and nutrients and to preserve PO morphology and long-term viability.Herein, we summarize the current knowledge on bioengineered POs and the stem cell differentiation platforms. We also discuss the in vitro strategies used to generate functional POs, and the protocols currently used to confer immune-protection against the host immune attack (micro- and macro-encapsulation). In addition, the most relevant ongoing clinical trials, and the most relevant hurdles met to move towards clinical application are revised.