Page 402 - IJB-9-6

International Journal of Bioprinting Biofabrication for islet transplantation

between islets and ECM using synthetic peptides and of nutrients and oxygen for islet cells located at the center
polymer scaffolds . VEGF within transplants stimulates of the capsules . Encapsulation techniques can be broadly
[25]
[16]
angiogenesis, improves the viability of engrafted islets, classified into two categories based on the size: micro-
and enhances the duration of normalized glycemia in and macroencapsulation. In microencapsulation, a small
diabetic mice after transplantation [17,18] . Therefore, the local number of islets are enclosed in tiny capsules, typically less
delivery of proangiogenic factors may improve the clinical than a millimeter in size. These microcapsules facilitate
outcomes of islet transplantation. the rapid diffusion of nutrients and oxygen, leading to

Co-culture of angiogenesis-supporting cells can high rates of islet survival because the favorable surface
also promote network growth around or within the area-to-volume ratio in the microcapsules is beneficial for
transplanted islets. Among the endothelial cells, human efficient mass transport. Nevertheless, microencapsulation
umbilical vein endothelial cells (HUVECs) are widely has limitations, such as the need for a large transplantation
used for demonstrating this idea because of their ability site to accommodate the necessary number of capsules, a
to spontaneously assemble into tubular structures in an suitable microvascular bed for immediate nutrient access,
ECM . Several studies have examined the transplantation difficulties in capsule removal, and insufficient long-term
[19]
of pancreatic islets embedded in endothelialized survival rates for functional islets to meet daily insulin
[26]
scaffolds [20,21] . A previous study showed that islets demands .
embedded in a HUVECs module returned diabetic In contrast, macroencapsulation entails the entrapment
mice to normal glycemia. HUVECs seeded on modules of a higher quantity of islets inside larger capsules, commonly
maintain the structural integrity of modular implants . several millimeters in magnitude. These enlarged capsules
[22]
Furthermore, facilitating the prompt sprouting of islet allow the assembly of an elevated number of islets, leading
endothelial cells post-transplantation could enhance the to enhanced glycemic management and augmented
engraftment process during the phase when the islets are insulin secretion . Nevertheless, macroencapsulation
[27]
most susceptible. This could serve as an alternative that faces certain obstacles, such as the challenge of ensuring
depends solely on revascularization from the adjacent proficient exchange of nutrients and oxygen, as well
tissue, a process that typically requires several weeks . as the potential degradation of capsules over time .
[26]
[23]
Despite the hurdles faced by both microencapsulation
3. Biomaterial-based islet encapsulation and macroencapsulation, the encapsulation approach
strategies still holds potential for islet transplantation and offers
a possible solution for sustained glycemic regulation in
Several biomaterial-based strategies have highlighted patients with diabetes. Current research efforts are directed
the crucial role of the extracellular environment in toward enhancing the properties of biomaterial in order
governing cellular behavior, emphasizing the need for to overcome the constraints of existing technology and
regenerative materials that provide biological cues to ultimately improve the outcomes of islet transplantation .
[28]
cells . Biomaterials have emerged as promising solutions
[24]
to address medical challenges, and current investigations The integration of islets within the selectively permeable
have emphasized the significance of the extracellular membrane of a macroencapsulation device has been
milieu in modulating cellular behavior. Islet encapsulation recognized as an effective approach for circumventing the
technology is a biomaterial-based approach that involves immune response, thereby enabling the transport of insulin
[28]
enveloping islets within biocompatible materials and from transplanted cellular entities . Macroencapsulation
creating a supportive structure that closely mimics the devices, typically ranging in size from millimeters to
micro- and macroenvironments of native islets. centimeters, offer the advantage of accommodating
multiple islets within a single construct, allowing for
3.1. Islet encapsulation strategies efficient encapsulation. The sizable dimensions of
Recently, islet encapsulation has been widely used to macroencapsulation devices afford remarkable adjustability
provide not only mechanical and biochemical support but because the membrane size, thickness, and pore size can
also an immune barrier for encapsulated islets. During be precisely tailored. Thus, a single microencapsulation
encapsulation, living cells are suspended in a biomaterial device is able to accommodate the substantial number of
designed to act as a transport barrier, allowing nutrients, islets required for diabetes treatment.
oxygen, and waste products to diffuse while providing a
barrier to larger objects such as antibodies and immune Thus, the utilization of macroencapsulation devices,
cells. The three-dimensional (3D) matrix of the capsule which act as physical barriers between transplanted
fosters a supportive growth environment for islets, cells and their recipients, has emerged as a promising
preventing merging and interference with the availability strategy to address specific challenges by eliminating the

Volume 9 Issue 6 (2023) 394 https://doi.org/10.36922/ijb.1024