Microstructured silk fiber scaffolds with enhanced stretchability

Despite extensive research, current methods for creating three-dimensional (3D) silk fibroin (SF) scaffolds lack control over molecular rearrangement, particularly in the formation of β-sheet nanocrystals that severely embrittle SF, as well as hierarchical fiber organization at both micro- and macroscale. Here, we introduce a fabrication process based on electrowriting of aqueous SF solutions followed by post-processing using an aqueous solution of sodium dihydrogen phosphate (NaH2PO4). This approach enables gelation of SF chains via controlled β-sheet formation and partial conservation of compliant random coil structures. Moreover, this process allows for precise architecture control in microfiber scaffolds, enabling the creation of 3D flat and tubular macro-geometries with square-based and crosshatch microarchitectures, featuring inter-fiber distances of 400 μm and ∼97% open porosity. Remarkably, the crosslinked printed structures demonstrated a balanced coexistence of β-sheet and random coil conformations, which is uncommon for organic solvent-based crosslinking methods. This synergy of printing and post-processing yielded stable scaffolds with high compliance (modulus = 0.5-15 MPa) and the ability to support elastic cyclic loading up to 20% deformation. Furthermore, the printed constructs supported in vitro adherence and growth of human renal epithelial and endothelial cells with viability above 95%. These cells formed homogeneous monolayers that aligned with the fiber direction and deposited type-IV collagen as a specific marker of healthy extracellular matrix, indicating that both cell types attach, proliferate, and organize their own microenvironment within the SF scaffolds. These findings represent a significant development in fabricating organized stable SF scaffolds with unique microfiber structures and mechanical and biological properties that make them highly promising for tissue engineering applications.</p

Co-axial Printing of Convoluted Proximal Tubule for Kidney Disease Modeling

Despite the increasing incidence of kidney-related diseases, we are still far from understanding the underlying mechanisms of these diseases and their progression. This lack of understanding is partly because of a poor replication of the diseasesin vitro,limited to planar culture. Advancing towards three-dimensional models, hereby we propose coaxial printing to obtain microfibers containing a helical hollow microchannel. These recapitulate the architecture of the proximal tubule (PT), an important nephron segment often affected in kidney disorders. A stable gelatin/alginate-based ink was formulated to allow printability while maintaining structural properties. Fine-tuning of the composition, printing temperature and extrusion rate allowed for optimal ink viscosity that led to coiling of the microfiber's inner channel. The printed microfibers exhibited prolonged structural stability (42 days) and cytocompatibility in culture. Healthy conditionally immortalized PT epithelial cells and a knockout cell model for cystinosis (CTNS-/-) were seeded to mimic two genotypes of PT. Upon culturing for 14 days, engineered PT showed homogenous cytoskeleton organization as indicated by staining for filamentous actin, barrier-formation and polarization with apical markerα-tubulin and basolateral marker Na+/K+-ATPase. Cell viability was slightly decreased upon prolonged culturing for 14 days, which was more pronounced inCTNS-/-microfibers. Finally,CTNS-/-cells showed reduced apical transport activity in the microfibers compared to healthy PT epithelial cells when looking at breast cancer resistance protein and multidrug resistance-associated protein 4. Engineered PT incorporated in a custom-designed microfluidic chip allowed to assess leak-tightness of the epithelium, which appeared less tight inCTNS-/-PT compared to healthy PT, in agreement with itsin vivophenotype. While we are still on the verge of patient-oriented medicine, this system holds great promise for further research in establishing advancedin vitrodisease models

Engineering the (vascularized) Proximal Tubule, a Guide Towards Functionality

This thesis focused on the fabrication of kidney proximal tubule models. A coaxial printing system allowed the robust and straightforward fabrication of coiled perfusable microfibers, replicating the kidney proximal convoluted tubules. The formed alginate-gelatin microfibers offer a complex tubular shape in which the cells exhibit mature markers, such as functional transporters and polarized monolayers. Moreover, this model has proven to support both healthy and cystinotic proximal tubule cell lines and allows for mechanistically studying tubulopathies. Though distinctive 3D-printing strategies offer opportunities to mimic the structure of the convoluted proximal tubule, printing resolution remains restricted for soft hydrogel materials. Therefore, a unique method was studied, whereby post-printing treatment induced resolution enhancement of methacrylated hyaluronic acid / gelatin methacryloyl (HAMA/GelMA) based hydrogels. This shrinking technique opens a wide application to create higher resolutions for 3D printing. However, we also found that the polycationic shrinking reagents used were relatively toxic for our cells of interest. Therefore, more research is needed to prevent the direct exposure of cells to the shrinking reagents. Using melt electrowriting, scaffolds were fabricated that are self-supportive, yet small-sized and highly porous. These scaffolds enable direct access to the basolateral and luminal cell sides to facilitate solute exchange with vasculature in immediate proximity, which is critical for functional proximal tubule constructs. The polymer applied, polycaprolactone, is used to prepare biomaterials that generally show good biocompatibility and is compatible with implantation in the future. Kidney proximal tubule cells and glomerular endothelial cells form polarized monolayers in our tubules, form their own extracellular matrix, and show functionality for important kidney transporters. In our preliminary results we showed initial work with induced pluripotent stem cell-derived kidney organoids, which is very promising for the development of implantable proximal tubule grafts. The aim was to develop vascularized kidney tubules for studying the clearance of protein bound uremic toxins, while gaining knowledge for the development of implantable kidney tubules. The developed models allow for studying transepithelial secretion of uremic toxins, an overarching application for these constructs. This will further advance our understanding of the kidney secretion processes and aid in studying interventions to main proximal tubule function in chronic kidney disease conditions in vitro. Furthermore, while fundamental by nature, our research deliverables enhance mechanistic insight in additive manufacturing and kidney development processes. Altogether, our findings will further advance the field of kidney engineering, while working towards kidney replacement therapies

Engineering the (vascularized) Proximal Tubule, a Guide Towards Functionality

This thesis focused on the fabrication of kidney proximal tubule models. A coaxial printing system allowed the robust and straightforward fabrication of coiled perfusable microfibers, replicating the kidney proximal convoluted tubules. The formed alginate-gelatin microfibers offer a complex tubular shape in which the cells exhibit mature markers, such as functional transporters and polarized monolayers. Moreover, this model has proven to support both healthy and cystinotic proximal tubule cell lines and allows for mechanistically studying tubulopathies. Though distinctive 3D-printing strategies offer opportunities to mimic the structure of the convoluted proximal tubule, printing resolution remains restricted for soft hydrogel materials. Therefore, a unique method was studied, whereby post-printing treatment induced resolution enhancement of methacrylated hyaluronic acid / gelatin methacryloyl (HAMA/GelMA) based hydrogels. This shrinking technique opens a wide application to create higher resolutions for 3D printing. However, we also found that the polycationic shrinking reagents used were relatively toxic for our cells of interest. Therefore, more research is needed to prevent the direct exposure of cells to the shrinking reagents. Using melt electrowriting, scaffolds were fabricated that are self-supportive, yet small-sized and highly porous. These scaffolds enable direct access to the basolateral and luminal cell sides to facilitate solute exchange with vasculature in immediate proximity, which is critical for functional proximal tubule constructs. The polymer applied, polycaprolactone, is used to prepare biomaterials that generally show good biocompatibility and is compatible with implantation in the future. Kidney proximal tubule cells and glomerular endothelial cells form polarized monolayers in our tubules, form their own extracellular matrix, and show functionality for important kidney transporters. In our preliminary results we showed initial work with induced pluripotent stem cell-derived kidney organoids, which is very promising for the development of implantable proximal tubule grafts. The aim was to develop vascularized kidney tubules for studying the clearance of protein bound uremic toxins, while gaining knowledge for the development of implantable kidney tubules. The developed models allow for studying transepithelial secretion of uremic toxins, an overarching application for these constructs. This will further advance our understanding of the kidney secretion processes and aid in studying interventions to main proximal tubule function in chronic kidney disease conditions in vitro. Furthermore, while fundamental by nature, our research deliverables enhance mechanistic insight in additive manufacturing and kidney development processes. Altogether, our findings will further advance the field of kidney engineering, while working towards kidney replacement therapies

Renal Tubular- and Vascular Basement Membranes and their Mimicry in Engineering Vascularized Kidney Tubules

The high prevalence of chronic kidney disease leads to an increased need for renal replacement therapies. While there are simply not enough donor organs available for transplantation, there is a need to seek other therapeutic avenues as current dialysis modalities are insufficient. The field of regenerative medicine and whole organ engineering is emerging, and researchers are looking for innovative ways to create (part of) a functional new organ. To biofabricate a kidney or its functional units, it is necessary to understand and learn from physiology to be able to mimic the specific tissue properties. Herein is provided an overview of the knowledge on tubular and vascular basement membranes' biochemical components and biophysical properties, and the major differences between the two basement membranes are highlighted. Furthermore, an overview of current trends in membrane technology for developing renal replacement therapies and to stimulate kidney regeneration is provided

Renal Tubular- and Vascular Basement Membranes and their Mimicry in Engineering Vascularized Kidney Tubules

The high prevalence of chronic kidney disease leads to an increased need for renal replacement therapies. While there are simply not enough donor organs available for transplantation, there is a need to seek other therapeutic avenues as current dialysis modalities are insufficient. The field of regenerative medicine and whole organ engineering is emerging, and researchers are looking for innovative ways to create (part of) a functional new organ. To biofabricate a kidney or its functional units, it is necessary to understand and learn from physiology to be able to mimic the specific tissue properties. Herein is provided an overview of the knowledge on tubular and vascular basement membranes' biochemical components and biophysical properties, and the major differences between the two basement membranes are highlighted. Furthermore, an overview of current trends in membrane technology for developing renal replacement therapies and to stimulate kidney regeneration is provided

Sacrificial Bioprinting of A Mammary Ductal Carcinoma Model

Cancer tissue engineering has remained challenging due to the limitation of the conventional biofabrication techniques to model the complex cancer microenvironment. Here we report the utilization of a sacrificial bioprinting strategy to generate biomimetic mammary duct-like structures within a hydrogel matrix, which was further populated with breast cancer cells, to model the genesis of ductal carcinoma and its subsequent outward invasion. This bioprinted mammary ductal carcinoma model provides a proof-of-concept demonstration of the value of using the sacrificial bioprinting technique for engineering biologically relevant cancer models, which may be possibly extended to other cancer types where duct-like structures are involved. This article is protected by copyright. All rights reserved

Sacrificial Bioprinting of A Mammary Ductal Carcinoma Model

Cancer tissue engineering has remained challenging due to the limitation of the conventional biofabrication techniques to model the complex cancer microenvironment. Here we report the utilization of a sacrificial bioprinting strategy to generate biomimetic mammary duct-like structures within a hydrogel matrix, which was further populated with breast cancer cells, to model the genesis of ductal carcinoma and its subsequent outward invasion. This bioprinted mammary ductal carcinoma model provides a proof-of-concept demonstration of the value of using the sacrificial bioprinting technique for engineering biologically relevant cancer models, which may be possibly extended to other cancer types where duct-like structures are involved. This article is protected by copyright. All rights reserved

A novel KCNJ16 kidney organoid model recapitulates the disease phenotype and shows restoration of lipid accumulation upon treatment with statins

Background: the KCNJ16 gene has been associated with a novel kidney tubulopathy phenotype, viz. disturbed acid-base homeostasis, hypokalemia and altered renal salt transport. KCNJ16 encodes for Kir5.1, which together with Kir4.1 constitutes a potassium channel located at kidney tubular cell basolateral membranes. Preclinical studies provided mechanistical links between Kir5.1 and a disease phenotype, however, the disease pathology remains poorly understood. Here, we aimed at generating and characterizing a novel advanced in vitro human kidney model that recapitulates the disease phenotype to investigate further the pathophysiological mechanisms underlying the disease and potential therapeutic interventions. Methods: we used CRISPR/Cas9 to generate KCNJ16 mutant (KCNJ16+/- and KCNJ16-/-) cell lines from healthy human induced pluripotent stem cells (iPSC) KCNJ16 control (KCNJ16WT). The iPSCs were differentiated following an optimized protocol into kidney organoids in an air-liquid interface. Results: KCNJ16-depleted kidney organoids showed transcriptomic and potential functional impairment of key voltage-dependent electrolyte and water-balance transporters. We observed cysts formation, lipid droplet accumulation and fibrosis upon Kir5.1 function loss. Furthermore, a large scale, glutamine tracer flux metabolomics analysis demonstrated that KCNJ16-/- organoids display TCA cycle and lipid metabolism impairments. Drug screening revealed that treatment with statins, particularly the combination of simvastatin and C75, prevented lipid droplet accumulation and collagen-I deposition in KCNJ16-/- kidney organoids. Conclusions: mature kidney organoids represent a relevant in vitro model for investigating the function of Kir5.1. We discovered novel molecular targets for this genetic tubulopathy and identified statins as a potential therapeutic strategy for KCNJ16 defects in the kidney. Significance Statement: In this study, the use of CRISPR/Cas9 technology resulted in the establishment of a KCNJ16-depleted kidney organoid model, instrumental in elucidating the pathophysiology of the recently reported KCNJ16-associated kidney tubulopathy. Our study substantiates the role of Kir5.1 (KCNJ16) in kidney disease, confirming already described phenotypes, as well as aiding to gain insight in the causal role of Kir5.1 loss in the disease phenotype. Our approach increases the knowledge on KCNJ16-related kidney phenotype, and it states the importance of combining CRISPR/Cas9 technology and advanced in vitro models for complex disease modeling and therapy testing. Furthermore, we encourage the application of our approach to the in vitro modeling of rare and/or underrepresented genetic kidney diseases, for which the availability of patient material is limited

Microstructured silk-fiber scaffolds with enhanced stretchability

Despite extensive research, current methods for creating three-dimensional (3D) silk fibroin (SF) scaffolds lack control over molecular rearrangement, particularly in the formation of β-sheet nanocrystals, as well as hierarchical fiber organization at both micro- and macroscale. In this study, we introduce a fabrication process based on electrowriting of aqueous SF-based solutions followed by post-processing using an aqueous solution of sodium dihydrogen phosphate (NaH2PO4). This approach enables hierarchical assembly of SF chains via β-sheet and α-helix formation. Moreover, this process allows for precise control over micro- and macro-architectures in microfiber scaffolds, enabling the creation of 3D flat and tubular macrogeometries with square-based and crosshatch microarchitectures, featuring inter-fiber distances of 400 µm and approximately 97% open porosity. Remarkably, the printed structures demonstrated restored β-sheet and α-helix structures, which imparted an elastic response of up to 20% deformation and the ability to support cyclic loading without plastic deformation. Furthermore, the printed constructs supported in vitro adherence and growth of human conditionally immortalized proximal tubular epithelial cells and glomerular endothelial cells, with cell viability above 95%. These cells formed uniform, aligned monolayers that deposited their own extracellular matrix. These findings represent a significant development in fabricating organized SF scaffolds with unique fiber structures, mechanical and biological properties, making them highly promising for regenerative medicine applications