Gastrointestinal organs and organoids-on-a-chip: advances and translation into the clinics.

Microfluidic organs and organoids-on-a-chip models of human gastrointestinal systems have been established to recreate adequate microenvironments to study physiology and pathophysiology. In the effort to find more emulating systems and less costly models for drugs screening or fundamental studies, gastrointestinal system organoids-on-a-chip have arisen as promising pre-clinicalin vitromodel. This progress has been built on the latest developments of several technologies such as bioprinting, microfluidics, and organoid research. In this review, we will focus on healthy and disease models of: human microbiome-on-a-chip and its rising correlation with gastro pathophysiology; stomach-on-a-chip; liver-on-a-chip; pancreas-on-a-chip; inflammation models, small intestine, colon and colorectal cancer organoids-on-a-chip and multi-organoids-on-a-chip. The current developments related to the design, ability to hold one or more 'organs' and its challenges, microfluidic features, cell sources and whether they are used to test drugs are overviewed herein. Importantly, their contribution in terms of drug development and eminent clinical translation in precision medicine field, Food and Drug Administration approved models, and the impact of organoid-on-chip technology in terms of pharmaceutical research and development costs are also discussed by the authors.

Microphysiological systems to study colorectal cancer: state-of-the-art.

Basic pre-clinical research based on 2D cultures have been very valuable in colorectal cancer (CRC) research but still have failed to improve patient prognostic outcomes. This is because they simply do not replicate what happensin vivo, i.e.2D cultured cells system cannot replicate the diffusion constraints usually found in the body. Importantly, they also do not mimic the dimensionality of the human body and of a CRC tumour (3D). Moreover, 2D cultures lack the cellular heterogeneity and the tumour microenvironment (TME) such as stromal components, blood vessels, fibroblasts, and cells of the immune system. Cells behave differently whether in 2D and 3D, in particular their different genetic and protein expression panels are very different and therefore we cannot fully rely on drug tests done in 2D. A growing field of research based on microphysiological systems involving organoids/spheroids or patient-derived tumour cells has become a solid base for a better understanding of the TME and as a result is a step towards personalized medicine. Furthermore, microfluidic approaches have also started to open possibilities of research, with tumour-on-chips and body-on-chips being used in order to decipher complex inter-organ signalling and the prevalence of metastasis, as well as CRC early-diagnosis through liquid biopsies. Herein, we focus on the state-of-the-art of CRC research with emphasis on 3D microfluidicin vitrocultures-organoids, spheroids-drug resistance, circulating tumour cells and microbiome-on-a-chip technology.

Elastin-Derived VGVAPG Fragment Decorated Cell-Penetrating Peptide with Improved Gene Delivery Efficacy.

Cell-penetrating peptides (CPPs) are attractive non-viral gene delivery vectors due to their high transfection capacity and safety. Previously, we have shown that cell-penetrating peptide RALA can be a promising gene delivery vector for chronic wound regeneration application. In this study, we engineered a novel peptide called RALA-E by introducing elastin-derived VGVAPG fragment into RALA, in order to target the elastin-binding protein on the cell surface and thus improve delivery efficacy of RALA. The transfection efficiency of RALA-E was evaluated by transfecting the HEK-293T and HeLa cell lines cells with RALA-E/pDNA complexes and the flow-cytometry results showed that RALA-E significantly increased the transfection efficiency by nearly 20% in both cell lines compared to RALA. Inhibition of pDNA transfection on HEK-293T cells via chlorpromazine, genistein and mßCD showed that the inhibition extent in transfection efficiency was much less for RALA-E group compared to RALA group. In addition, RALA-E/miR-146a complexes showed up to 90% uptake efficiency in macrophages, and can escape from the endosome and enter the nucleus to inhibit the expression of inflammation genes. Therefore, the developed RALA-E peptide has high potential as a safe and efficient vector for gene therapy application.

Complex in vitro 3D models of digestive system tumors to advance precision medicine and drug testing: Progress, challenges, and trends.

Digestive system cancers account for nearly half of all cancers around the world and have a high mortality rate. Cell culture and animal models represent cornerstones of digestive cancer research. However, their ability to enable cancer precision medicine is limited. Cell culture models cannot retain the genetic and phenotypic heterogeneity of tumors and lack tumor microenvironment (TME). Patient-derived xenograft mouse models are not suitable for immune-oncology research. While humanized mouse models are time- and cost-consuming. Suitable preclinical models, which can facilitate the understanding of mechanisms of tumor progression and develop new therapeutic strategies, are in high demand. This review article summarizes the recent progress on the establishment of TME by using tumor organoid models and microfluidic systems. The main challenges regarding the translation of organoid models from bench to bedside are discussed. The integration of organoids and a microfluidic platform is the emerging trend in drug screening and precision medicine. A future prospective on this field is also provided.

In-situ formed elastin-based hydrogels enhance wound healing via promoting innate immune cells recruitment and angiogenesis.

Harnessing the inflammation and angiogenesis is extremely important in wound healing. In this study, we developed bioactive elastin-based hydrogels which can recruit and modulate the innate immune cells and accelerate angiogenesis in the wound site and subsequently improve wound regeneration. These hydrogels were formed by visible-light cross-linking of acryloyl-(polyethylene glycol)-N-hydroxysuccinimide ester modified elastin with methacrylated gelatin, in order to mimic dermal microenvironment. These hydrogels showed highly tunable mechanical properties, swelling ratios and enzymatic degradation profiles, with moduli within the range of human skin. To mimic the in vivo degradation of the elastin by elastase from neutrophils, in vitro co-culture of the hydrogels and neutrophils was conducted. The derived conditioned medium containing elastin derived peptides (EDP-conditioned medium) promoted the expression of both M1 and M2 markers in M1 macrophages in vitro. Additionally, the EDP-conditioned medium induced superior tube formation of endothelia cells in Matrigel. In mice wound model, these elastin-based hydrogels attracted abundant neutrophils and predominant M2 macrophages to the wound and supported their infiltration into the hydrogels. The outstanding immunomodulatory effect of the elastin-based hydrogels resulted in superior angiogenesis, collagen deposition and dermal regeneration. Hence, these elastin-based hydrogels can be a promising regenerative platform to accelerate wound repair.

UNC13B Promote Arsenic Trioxide Resistance in Chronic Lymphoid Leukemia Through Mitochondria Quality Control.

In clinical practice, arsenic trioxide can be used to treat a subset of R/R CML patients, but resistance tends to reappear quickly. We designed an experiment to study arsenic trioxide resistance in K-562 cells. Previously, we identified the UNC13B gene as potentially responsible for arsenic trioxide resistance in K-562 cells via gene chip screening followed by high-content screening. We aimed to investigate the role and mechanism of the UNC13B gene in K-562 cells, an arsenic trioxide-resistant chronic myeloid leukemia cell line. In vitro lentiviral vector-mediated UNC13B siRNA transfection was performed on K-562 cells. The roles of UNC13B in cell proliferation, apoptosis and cell cycle pathways, and colony formation were analyzed by CCK-8 assay, fluorescence-activated cell sorting, and soft agar culture, respectively. Gene chip screening was used to define the possible downstream pathways of UNC13B. Western blot was performed to further validate the possible genes mediated by UNC13B for arsenic trioxide resistance in patients with chronic myeloid leukemia. UNC13B downregulation significantly inhibited growth, promoted apoptosis, decreased colony formation, reduced the duration of the G1 phase, and increased the duration of the S phase of K-562 cells. Western blot results confirmed that UNC13B may modulate the apoptosis and proliferation of arsenic trioxide-resistant chronic myeloid leukemia cells through the mediation of MAP3K7, CDK4, and PINK1. UNC13B is a potential therapeutic target for patients with arsenic trioxide-resistant chronic myeloid leukemia.

Prevention of acute graft-vs.-host disease by targeting glycolysis and mTOR pathways in activated T cells.

Graft-versus-host disease (GvHD) is a common life-threatening complication that can occur following allogeneic hematopoietic stem cell transplantation. This occurs if donor T cells recognize the host as foreign. During acute GvHD (aGVHD), activated T cells utilize glycolysis as the main source of energy generation. Therefore, inhibition of T cell glycolysis is a potential treatment strategy for aGVHD. In the present study, the effects of the combination of the glycolysis inhibitor 3-bromopyruvate (3-BrPA) and the mTOR inhibitor rapamycin (RAPA) on a mode of aGVHD were explored. In vitro mixed lymphocyte culture model was established by using splenocytes from C57BL/6 (H-2b) mice as responder and inactivated splenocytes from BALB/c (H-2d) mice as stimulator. In this model, 3-BrPA treatment (0-100 µmol/l) was found to suppress cell viability, increase cell apoptosis and reduce IFN-γ secretion, in a concentration-dependent manner. 3-BrPA treatment (0-100 µmol/l) was found to suppress cell viability, increase cell apoptosis and reduce IFN-γ secretion, in a concentration-dependent manner. In addition, combined treatment with 3-BrPA (0-100 µmol/l) alongside RAPA (20 µmol/l) exhibited synergistic effects on inhibiting cell viability and IFN-γ production, compared with those following either treatment alone. An aGVHD model was established by injection of bone marrow cells and spleen cells from the donor-C57BL/6(H-2b) mice to the receptor-BALB/c(H-2d) mice which were underwent total body irradiation first. In the aGVHD model, 3-BrPA (10 mg/kg/day), RAPA (2.5 and 5 mg/kg/day) and both in combination (5 and 2.5 mg/kg/day for 3-BrPA and RAPA, respectively) were all found to alleviate the damage caused by aGVHD, in addition to prolonging the survival time of mice with acute GvHD. In particular, the combined 3-BrPA and RAPA treatment resulted in the highest median survival time among all groups tested. In addition, the effects induced by combined 3-BrPA and RAPA treatment were found to be comparable to those in the 5 mg/kg/day RAPA group but superior to the 3-BrPA group with regards to the cumulative survival profile, GvHD score and lung histological score. The 3-BrPA and RAPA combination group also exhibited the lowest IFN-γ levels among all groups. Therefore, the combination of inhibiting both glycolysis and mTOR activity is a promising strategy for acute GvHD prevention.

Development of a cellulose-based prosthetic mesh for pelvic organ prolapse treatment: In vivo long-term evaluation in an ewe vagina model.

The use of vaginal surgical mesh to treat pelvic organ prolapse (POP) has been associated with high rates of mesh-related complications. In the present study, we prepared new kinds of meshes based on bacterial cellulose (BC) and collagen-coated BC (BCCOL) using a laser cutting method and perforation technique. The mechanical properties of pre-implanted BC meshes, including breaking strength, suture strength and rigidity, were equal to or exceeded those of available clinically used polypropylene meshes. An in vitro cellular assay revealed that BCCOL meshes exhibited enhanced biocompatibility by increasing collagen secretion and cell adhesion. Both BC and BCCOL meshes only caused weak inflammation and were surrounded by newly formed connective tissue composed of type I collagen after implantation in a rabbit subcutaneous model for one week, demonstrating that the novel mesh is fully biocompatible and can integrate into surrounding tissues. Furthermore, a long-term (ninety days) ewe vaginal implantation model was used to evaluate foreign body reactions and suitability of BC and BCCOL meshes as vaginal meshes. The results showed that the tissue surrounding the BC meshes returned to its original physiology as muscle tissue, indicating the excellent integration of BC meshes into the surrounding tissues without triggering severe local inflammatory response post-implantation. The collagen coating appeared to induce a chronic inflammatory response due to glutaraldehyde remnants. The present exploratory research demonstrated that the developed BC mesh might be a suitable candidate for treating POP.

An efficient and user-friendly method for cytohistological analysis of organoids.

Organoid culture is a recently developed in vitro three-dimensional (3D) cell culture technology. It has wide applications in tissue engineering studies. However, histological analysis of organoid is quite complex and tedious for researchers. This study proposes a user-friendly, affordable and efficient method for making formalin-fixed paraffin embedded (FFPE) organoid blocks and Optimal Cutting Temperature compound (OCT) embedded frozen organoid blocks. This method implements a key pre-embedding step for preparing paraffin embedded organoid blocks, which could concentrate organoid together without damaging or loss of samples. This method could be used to process even a small number of organoids with high efficiency. In addition, with minor modifications, the method is readily applied for OCT embedded organoid blocks. The slides generated were ready for H&E staining, immunohistochemistry staining and immunofluorescent staining. The method described in this study can be easily used for routine histological analysis of organoid, and could be performed in general pathology labs and requires no dedicated equipment and reagent.

Development and Characterization of High Efficacy Cell-Penetrating Peptide via Modulation of the Histidine and Arginine Ratio for Gene Therapy.

Cell-penetrating peptides (CPPs), as non-viral gene delivery vectors, are considered with lower immunogenic response, and safer and higher gene capacity than viral systems. In our previous study, a CPP peptide called RALA (arginine rich) presented desirable transfection efficacy and owns a potential clinic use. It is believed that histidine could enhance the endosome escaping ability of CPPs, yet RALA peptide contains only one histidine in each chain. In order to develop novel superior CPPs, by using RALA as a model, we designed a series of peptides named HALA (increased histidine ratio). Both plasmid DNA (pDNA) and siRNA transfection results on three cell lines revealed that the transfection efficacy is better when histidine replacements were on the C-terminal instead of on the N-terminal, and two histidine replacements are superior to three. By investigating the mechanism of endocytosis of the pDNA nanocomplexes, we discovered that there were multiple pathways that led to the process and caveolae played the main role. During the screening, we discovered a novel peptide-HALA2 of high cellular transfection efficacy, which may act as an exciting gene delivery vector for gene therapy. Our findings also bring new insights on the development of novel robust CPPs.

Collagen/GAG scaffolds activated by RALA-siMMP-9 complexes with potential for improved diabetic foot ulcer healing.

Impaired wound healing of diabetic foot ulcers has been linked to high MMP-9 levels at the wound site. Strategies aimed at the simultaneous downregulation of the MMP-9 level in situ and the regeneration of impaired tissue are critical for improved diabetic foot ulcer (DFU) healing. To fulfil this aim, collagen/GAG (Col/GAG) scaffolds activated by MMP-9-targeting siRNA (siMMP-9) were developed in this study. The siMMP-9 complexes were successfully formed by mixing the RALA cell penetrating peptide with siMMP-9. The complexes formulated at N:P ratios of 6 to 15 had a diameter around 100 nm and a positive zeta potential about 40 mV, making them ideal for cellular uptake. In 2 dimensional (2D) culture of human fibroblasts, the cellular uptake of the complexes surpassed 60% and corresponded to a 60% reduction in MMP-9 gene expression in low glucose culture. In high glucose culture, which induces over-expression of MMP-9 and therefore serves as an in vitro model mimicking conditions in DFU, the MMP-9 gene could be downregulated by around 90%. In the 3D culture of fibroblasts, the siMMP-9 activated Col/GAG scaffolds displayed excellent cytocompatibility and ~60% and 40% MMP-9 gene downregulation in low and high glucose culture, respectively. When the siMMP-9 complexes were applied to THP-1 macrophages, the primary cell type producing MMP-9 in DFU, MMP-9 gene expression was significantly reduced by 70% and 50% for M0 and M1 subsets, in 2D culture. In the scaffolds, the MMP-9 gene and protein level of M1 macrophages decreased by around 50% and 30% respectively. Taken together, this study demonstrates that the RALA-siMMP-9 activated Col/GAG scaffolds possess high potential as a promising regenerative platform for improved DFU healing.

Robust and nanostructured chitosan-silica hybrids for bone repair application.

In this study, chitosan-silica hybrids (CSHs) with superior mechanical strength and homogeneous dispersion of nano-sized silica particles were synthesized via a facile sol-gel method aiming for bone regeneration. The effects of varied acidic conditions of sol-gel reaction and inorganic/organic ratios on the performance of the hybrid were investigated. CSHs synthesized under weak acidic conditions (acetic acid, pH 4.0) showed a homogeneous nanostructure and robust strength (maximum compressive strength: 42.6 ± 3.3 MPa and 271 ± 31 MPa in wet and dry forms, respectively). However, those developed under the strong acidic condition (HCl, pH 4.0) and the strong acid condition plus lower pH (HCl, pH 2.8) tended to aggregate and exhibited inferior mechanical properties (compressive strength: 6.3 ± 0.3 MPa in wet form at pH 2.8). Under the latter conditions, the interactions between silica and chitosan were weak. Moreover, the mechanical properties of the CSHs could be tuned in a wide range by conveniently varying the inorganic/organic composition ratio between 50% and 70%. In vitro cytocompatibility study indicated that CSHs were non-cytotoxic. These results suggested that the weak acidic sol-gel process were essential for fabricating chitosan-silica hybrids with high mechanical strength, which had potential to be applied as a bone substitute.

Core-shell silk hydrogels with spatially tuned conformations as drug-delivery system.

Hydrogels of spatially controlled physicochemical properties are appealing platforms for tissue engineering and drug delivery. In this study, core-shell silk fibroin (SF) hydrogels of spatially controlled conformation were developed. The core-shell structure in the hydrogels was formed by means of soaking the preformed (enzymatically crosslinked) random coil SF hydrogels in methanol. When increasing the methanol treatment time from 1 to 10 min, the thickness of the shell layer can be tuned from about 200 to about 850 µm as measured in wet status. After lyophilization of the rehydrated core-shell hydrogels, the shell layer displayed compact morphology and the core layer presented porous structure, when observed by scanning electron microscopy. The conformation of the hydrogels was evaluated by Fourier transform infrared spectroscopy in wet status. The results revealed that the shell layer possessed dominant ß-sheet conformation and the core layer maintained mainly random coil conformation. Enzymatic degradation data showed that the shell layers presented superior stability to the core layer. The mechanical analysis displayed that the compressive modulus of the core-shell hydrogels ranged from about 25 kPa to about 1.1 MPa by increasing the immersion time in methanol. When incorporated with albumin, the core-shell SF hydrogels demonstrated slower and more controllable release profiles compared with the non-treated hydrogel. These core-shell SF hydrogels of highly tuned properties are useful systems as drug-delivery system and may be applied as cartilage substitute. Copyright © 2016 John Wiley & Sons, Ltd.

Tumor Growth Suppression Induced by Biomimetic Silk Fibroin Hydrogels.

Protein-based hydrogels with distinct conformations which enable encapsulation or differentiation of cells are of great interest in 3D cancer research models. Conformational changes may cause macroscopic shifts in the hydrogels, allowing for its use as biosensors and drug carriers. In depth knowledge on how 3D conformational changes in proteins may affect cell fate and tumor formation is required. Thus, this study reports an enzymatically crosslinked silk fibroin (SF) hydrogel system that can undergo intrinsic conformation changes from random coil to ß-sheet conformation. In random coil status, the SF hydrogels are transparent, elastic, and present ionic strength and pH stimuli-responses. The random coil hydrogels become ß-sheet conformation after 10 days in vitro incubation and 14 days in vivo subcutaneous implantation in rat. When encapsulated with ATDC-5 cells, the random coil SF hydrogel promotes cell survival up to 7 days, whereas the subsequent ß-sheet transition induces cell apoptosis in vitro. HeLa cells are further incorporated in SF hydrogels and the constructs are investigated in vitro and in an in vivo chick chorioallantoic membrane model for tumor formation. In vivo, Angiogenesis and tumor formation are suppressed in SF hydrogels. Therefore, these hydrogels provide new insights for cancer research and uses of biomaterials.

Current Concepts and Challenges in Osteochondral Tissue Engineering and Regenerative Medicine.

In the past few years, great progress has been made to validate tissue engineering strategies in preclinical studies and clinical trials on the regeneration of osteochondral defects. In the preclinical studies, one of the dominant strategies comprises the development of biomimetic/bioactive scaffolds, which are used alone or incorporated with growth factors and/or stem cells. Many new trends are emerging for modulation of stem cell fate toward osteogenic and chondrogenic differentiations, but bone/cartilage interface regeneration and physical stimulus have been showing great promise. Besides the matrix-associated autologous chondrocyte implantation (MACI) procedure, the matrix-associated stem cell implantation (MASI) and layered scaffolds in acellular or cellular strategy are also applied in clinic. This review outlines the progresses at preclinical and clinical levels, and identifies the new challenges in osteochondral tissue engineering. Future perspectives are provided, e.g., the applications of extracellular matrix-like biomaterials, computer-aided design/manufacture of osteochondral implant, and reprogrammed cells for osteochondral regeneration.

Bilayered silk/silk-nanoCaP scaffolds for osteochondral tissue engineering: In vitro and in vivo assessment of biological performance.

Novel porous bilayered scaffolds, fully integrating a silk fibroin (SF) layer and a silk-nano calcium phosphate (silk-nanoCaP) layer for osteochondral defect (OCD) regeneration, were developed. Homogeneous porosity distribution was achieved in the scaffolds, with calcium phosphate phase only retained in the silk-nanoCaP layer. The scaffold presented compressive moduli of 0.4MPa in the wet state. Rabbit bone marrow mesenchymal stromal cells (RBMSCs) were cultured on the scaffolds, and good adhesion and proliferation were observed. The silk-nanoCaP layer showed a higher alkaline phosphatase level than the silk layer in osteogenic conditions. Subcutaneous implantation in rabbits demonstrated weak inflammation. In a rabbit knee critical size OCD model, the scaffolds firmly integrated into the host tissue. Histological and immunohistochemical analysis showed that collagen II positive cartilage and glycosaminoglycan regeneration presented in the silk layer, and de novo bone ingrowths and vessel formation were observed in the silk-nanoCaP layer. These bilayered scaffolds can therefore be promising candidates for OCD regeneration.

Bioactive macro/micro porous silk fibroin/nano-sized calcium phosphate scaffolds with potential for bone-tissue-engineering applications.

AIM: The development of novel silk/nano-sized calcium phosphate (silk/nano-CaP) scaffolds with highly dispersed CaP nanoparticles in the silk fibroin (SF) matrix for bone tissue engineering. MATERIALS & METHODS: Nano-CaP was incorporated in a concentrated aqueous SF solution (16 wt.%) by using an in situ synthesis method. The silk/nano-CaP scaffolds were then prepared through a combination of salt-leaching/lyophilization approaches. RESULTS: The CaP particles presented good affinity to SF and their size was inferior to 200 nm when theoretical CaP/silk ratios were between 4 and 16 wt.%, as determined by scanning electron microscopy. The CaP particles displayed a uniform distribution in the scaffolds at both microscopic and macroscopic scales as observed by backscattered scanning electron microscopy and micro-computed tomography, respectively. The prepared scaffolds presented self-mineralization capability and no cytotoxicity confirmed by in vitro bioactivity tests and cell viability assays, respectively. CONCLUSION: These results indicated that the produced silk/nano-CaP scaffolds could be suitable candidates for bone-tissue-engineering applications.

Development of silk-based scaffolds for tissue engineering of bone from human adipose-derived stem cells.

Silk fibroin is a potent alternative to other biodegradable biopolymers for bone tissue engineering (TE), because of its tunable architecture and mechanical properties, and its demonstrated ability to support bone formation both in vitro and in vivo. In this study, we investigated a range of silk scaffolds for bone TE using human adipose-derived stem cells (hASCs), an attractive cell source for engineering autologous bone grafts. Our goal was to understand the effects of scaffold architecture and biomechanics and use this information to optimize silk scaffolds for bone TE applications. Silk scaffolds were fabricated using different solvents (aqueous vs. hexafluoro-2-propanol (HFIP)), pore sizes (250-500 µm vs. 500-1000 µm) and structures (lamellar vs. spherical pores). Four types of silk scaffolds combining the properties of interest were systematically compared with respect to bone tissue outcomes, with decellularized trabecular bone (DCB) included as a "gold standard". The scaffolds were seeded with hASCs and cultured for 7 weeks in osteogenic medium. Bone formation was evaluated by cell proliferation and differentiation, matrix production, calcification and mechanical properties. We observed that 400-600 µm porous HFIP-derived silk fibroin scaffold demonstrated the best bone tissue formation outcomes, as evidenced by increased bone protein production (osteopontin, collagen type I, bone sialoprotein), enhanced calcium deposition and total bone volume. On a direct comparison basis, alkaline phosphatase activity (AP) at week 2 and new calcium deposition at week 7 were comparable to the cells cultured in DCB. Yet, among the aqueous-based structures, the lamellar architecture induced increased AP activity and demonstrated higher equilibrium modulus than the spherical-pore scaffolds. Based on the collected data, we propose a conceptual model describing the effects of silk scaffold design on bone tissue formation.

Macro/microporous silk fibroin scaffolds with potential for articular cartilage and meniscus tissue engineering applications.

This study describes the developmental physicochemical properties of silk fibroin scaffolds derived from high-concentration aqueous silk fibroin solutions. The silk fibroin scaffolds were prepared with different initial concentrations (8, 10, 12 and 16%, in wt.%) and obtained by combining the salt-leaching and freeze-drying methodologies. The results indicated that the antiparallel ß-pleated sheet (silk-II) conformation was present in the silk fibroin scaffolds. All the scaffolds possessed a macro/microporous structure. Homogeneous porosity distribution was achieved in all the groups of samples. As the silk fibroin concentration increased from 8 to 16%, the mean porosity decreased from 90.8±0.9 to 79.8±0.3% and the mean interconnectivity decreased from 97.4±0.5 to 92.3±1.3%. The mechanical properties of the scaffolds exhibited concentration dependence. The dry state compressive modulus increased from 0.81±0.29 to 15.14±1.70 MPa and the wet state dynamic storage modulus increased by around 20- to 30-fold at each testing frequency when the silk fibroin concentration increased from 8 to 16%. The water uptake ratio decreased with increasing silk fibroin concentration. The scaffolds present favorable stability as their structure integrity, morphology and mechanical properties were maintained after in vitro degradation for 30 days. Based on these results, the scaffolds developed in this study are proposed to be suitable for use in meniscus and cartilage tissue-engineered scaffolding.

Genipin-cross-linked collagen/chitosan biomimetic scaffolds for articular cartilage tissue engineering applications.

In this study, genipin-cross-linked collagen/chitosan biodegradable porous scaffolds were prepared for articular cartilage regeneration. The influence of chitosan amount and genipin concentration on the scaffolds physicochemical properties was evaluated. The morphologies of the scaffolds were characterized by scanning electron microscope (SEM) and cross-linking degree was investigated by ninhydrin assay. Additionally, the mechanical properties of the scaffolds were assessed under dynamic compression. To study the swelling ratio and the biostability of the collagen/chitosan scaffold, in vitro tests were also carried out by immersion of the scaffolds in PBS solution or digestion in collagenase, respectively. The results showed that the morphologies of the scaffolds underwent a fiber-like to a sheet-like structural transition by increasing chitosan amount. Genipin cross-linking remarkably changed the morphologies and pore sizes of the scaffolds when chitosan amount was less than 25%. Either by increasing the chitosan ratio or performing cross-linking treatment, the swelling ratio of the scaffolds can be tailored. The ninhydrin assay demonstrated that the addition of chitosan could obviously increase the cross-linking efficiency. The degradation studies indicated that genipin cross-linking can effectively enhance the biostability of the scaffolds. The biocompatibility of the scaffolds was evaluated by culturing rabbit chondrocytes in vitro. This study demonstrated that a good viability of the chondrocytes seeded on the scaffold was achieved. The SEM analysis has revealed that the chondrocytes adhered well to the surface of the scaffolds and contacted each other. These results suggest that the genipin-cross-linked collagen/chitosan matrix may be a promising formulation for articular cartilage scaffolding.