Porous tissue strands: avascular building blocks for scalable tissue fabrication

Abstract

The scalability of cell aggregates such as spheroids, strands, and rings has been restricted by diffusion of nutrient and oxygen into their core. In this study, we introduce a novel concept in generating tissue building blocks with micropores, which represents an alternative solution for vascularization. Sodium alginate porogens were mixed with human adipose-derived stem cells, and loaded into tubular alginate capsules, followed by de-crosslinking of the capsules. The resultant cellular structure exhibited a porous morphology and formed cell aggregates in the form of strands, called 'porous tissue strands (pTSs).' Three-dimensional reconstructions show that pTSs were able to maintain ∼25% porosity with a high pore interconnectivity (∼85%) for 3 weeks. Owing to the porous structure, pTSs showed up-regulated cell viability and proliferation rate as compared to solid counterparts throughout the culture period. pTSs also demonstrated self-assembly capability through tissue fusion yielding larger-scale patches. In this paper, chondrogenesis and osteogenesis of pTSs were also demonstrated, where the porous microstructure up-regulated both chondrogenic and osteogenic functionalities indicated by cartilage-and bone-specific immunostaining, quantitative biochemical assessment and gene expression. These findings indicated the functionality of pTSs, which possessed controllable porosity and self-assembly capability, and had great potential to be utilized as tissue building blocks in distinct applications such as cartilage and bone regeneration.

Hybrid Bioprinting of Zonally Stratified Human Articular Cartilage Using Scaffold‐Free Tissue Strands as Building Blocks

“…It should be noted the used diameter of TSs is satisfactory to maintain the viability of chondrocytes because of their anaerobic nature. [22] Cellular alignment at different depth of TSs demonstrated that cells within ≈50 µm distance from edges were highly oriented along the longitudinal direction of TSs (Figure 4e). At the boundaries of TSs, cell movement subjected to the wall of alginate capsules.…”

“…Although it has been reported that 3D culture (e.g., hydrogel encapsulation and tissue spheroid) induced more reliable chondrogenic differentiation of stem cells than conventional monolayer culture, [32][33][34] TSs in Group 2 exhibited lower chondrogenic functionality, which might be due to their thick nature, limiting the diffusion of chondrogenic differentiation media into the depth of TSs, and hence slowed down the chondrogenesis of ADSCs. [22] In addition, since the differentiated chondrocytes in Group 1 aggregated in the form of TSs, it could be assumed that the 3D environment prevented the chondrocytes from dedifferentiation and preserved their chondrogenic phenotype. [35] Due to these appealing properties of TSs made of predifferentiated chondrocytes, Group 1 was preferred for bioprinting experiments.…”

“…Fabrication of TSs: To obtain human ADSCs, surgically discarded adipose tissues were obtained from patients, who underwent an elective adipose tissue removal process (e.g., panniculectomy) at the Pennsylvania State University (Hershey, PA) with patients' consent and approved by the Institutional Review Board (IRB protocol #4972). Isolation of ADSCs was performed according to the previously published work [22] with verification of flow cytometry against CD73 and CD90. The sorted ADSCs were cultured in DMEM/F12 supplement with 20% FBS, 100 U mL −1 penicillin and 100 µg mL −1 streptomycin at 37°C with 5% CO 2 .…”

Aspiration-assisted bioprinting for precise positioning of biologics

“…In case 2, cell viability was measured to be ~82%. The decrease in cell viability could be due to the aspiration force or dehydration during the rapid transfer or cell damage when spheroids were submerged into the hydrogel substrate; however, viability levels over 80% for bioprinting of spheroids could still be considered moderate, as viability of fabricated cells aggregates even without bioprinting could be in that range (36). In addition to bioprinting of spheroids, the AAB system also enabled the bioprinting of other biologics.…”

Advanced Bottom‐Up Engineering of Living Architectures

“…A high degree of cellular compaction, however, may lead to poor oxygen and nutrients diffusion during maturation periods, culminating in loss of cellular viability and function in fibers' core regions. To tackle this challenge, microporous tissue strands were prepared by adding a porogen agent—alginate microbeads—to cellular suspensions before extrusion inside a hollow alginate tube (Figure D) . Fibers comprising adipose‐derived MSCs (ASCs) generated by this methodology showcased approximately 25% porosity and high pore interconnectivity.…”