Radial matrix constraint influences tissue contraction and promotes maturation of bi-layered skin equivalents

Human skin equivalents (HSEs) serve as important tools for mechanistic studies with human skin cells, drug discovery, pre-clinical applications in the field of tissue engineering and for skin transplantation on skin defects. Besides the cellular and extracellular matrix (ECM) components used for HSEs, physical constraints applied on the scaffold during HSEs maturation influence tissue organization, functionality, and homogeneity. In this study, we introduce a 3D-printed culture insert that exposes bi-layered HSEs to a static radial constraint through matrix adhesion. We examine the effect of various diameters of the ring-shaped culture insert on the HSE's characteristics and compare them to state-of-the-art unconstrained and planar constrained HSEs. We show that radial matrix constraint of HSEs regulates tissue contraction, promotes fibroblast and matrix organization that is similar to human skin in vivo and improves keratinocyte differentiation, epidermal stratification, and basement membrane formation depending on the culture insert diameter. Together, these data demonstrate that the degree of HSE's contraction is an important design consideration in skin tissue engineering. Therefore, this study can help to mimic various in vivo skin conditions and to increase the control of relevant tissue properties.

Injectable collagen hydrogel combines human umbilical cord mesenchymal stem cells to promote endometrial regeneration in rats with thin endometrium

The regeneration of thin endometrium still remains as a great challenge in the field of reproductive medicine. Stem cells-based therapy has been considered as a promising strategy for the restoration of thin endometrium. However, the low transplantation and retention rate of stem cells and loss of stemness due to in vitro expansion limits the therapeutic efficacy. In our study, we combined collagen hydrogel and human umbilical cord mesenchymal stem cells (uMSCs) for improving the regeneration of thin endometrium, by using the potent pluripotency and low immunogenicity of uMSCs and collagen hydrogel that promotes the anchorage and proliferation of stem cells. Results showed that collagen hydrogel has favorable biocompatibility and the capacity to enhance the cell viability and expression of stemness-associated genes (including organic cation/carnitine transporter4 (Oct-4), Nanog homeobox (Nanog) and SRY-box transcription factor 2 (SOX2)) of uMSCs. The combination of collagen hydrogel and uMSCs prolonged the retention time of the constructs in the uterine cavity and improved endometrial thickness compared with uMSCs alone, leading to increase the fertility of the rats with thin endometrium. These highlighted therapeutic prospects of collagen hydrogel combined with uMSCs for the minimally invasive therapy of thin endometrium in the clinic.

Neuro-regenerative behavior of adipose-derived stem cells in aligned collagen I hydrogels

Peripheral nerve injuries persist as a major clinical issue facing the US population and can be caused by stretch, laceration, or crush injuries. Small nerve gaps are simple to treat, and the nerve stumps can be reattached with sutures. In longer nerve gaps, traditional treatment options consist of autografts, hollow nerve guidance conduits, and, more recently, manufactured fibrous scaffolds. These manufactured scaffolds often incorporate stem cells, growth factors, and/or extracellular matrix (ECM) proteins to better mimic the native environment but can have issues with homogenous cell distribution or uniformly oriented neurite outgrowth in scaffolds without fibrous alignment. Here, we utilize a custom device to fabricate collagen I hydrogels with aligned fibers and encapsulated adipose-derived mesenchymal stem cells (ASCs) for potential use as a peripheral nerve repair graft. Initial results of our scaffold system revealed significantly less cell viability in higher collagen gel concentrations; 3 mg/mL gels showed 84.8 ± 7.3% viable cells, compared to 6 mg/mL gels viability of 76.7 ± 9.5%. Mechanical testing of the 3 mg/mL gels showed a Young's modulus of 6.5 ± 0.8 kPa nearly matching 7.45 kPa known to support Schwann cell migration. Further analysis of scaffolds coupled with stretching in vitro revealed heightened angiogenic and factor secretion, ECM deposition, fiber alignment, and dorsal root ganglia (DRG) neurite outgrowth along the axis of fiber alignment. Our platform serves as an in vitro testbed to assess neuro-regenerative potential of ASCs in aligned collagen fiber scaffolds and may provide guidance on next-generation nerve repair scaffold design.

Alginate microspheres-collagen hydrogel, as a novel 3D culture system, enhanced skin wound healing of hUCMSCs in rats model

While stem cell transplantation has emerged as a promising approach to improving wound healing outcomes, the application of stem cells to date has been limited by the poor survival and retention of these cells once transplanted. The survival, development, and migratory activity of transplanted cells can be improved through the use of three-dimensional (3D) culture systems. Here, a novel alginate microsphere-collage hydrogel (AMS-Col gel) 3D culture system was developed and found to improve human umbilical cord mesenchymal stem cell (hUCMSC) survival, permitting their sustained release so as to promote wound healing. Through hematoxylin and eosin staining and Masson's trichrome staining, the prepared hUCMSCs-AMS-Col gel was found to exhibit wound healing activity. On day 7 following the hUCMSCs-AMS-Col gel treatment of model wounds, improved collagen fiber deposition and re-epithelialization were evident, with complete epithelial regeneration as of day 14 and near-total wound healing was evident as of day 21. This hUCMSCs-AMS-Col gel was also associated with increased VEGF and FGF2 expression. Together, these data indicate that AMS-Col gels are a promising and novel form of 3D cell culture system capable of improving hUCMSC-mediated wound healing, highlighting the potential clinical utility of this regenerative strategy.

'Multiple and short-range' cross-linking of dialdehyde carboxymethyl cellulose contributes to regulating the physicochemical property of collagen fibril

Collagen fibril hydrogel (CH), with controllable micro-structure, sufficient modifying sites and excellent biocompatibility, has received widely attention in the regulation of biomacromolecules. Herein, dialdehyde carboxymethyl cellulose (DCMC) in different -CHO contents and molecular weights demonstrated two types of cross-linking behaviors to CH, 'limited and long-range' or 'multiple and short range' cross-linking, corresponding to -CHO content ranged from 0 to  53 % and 53- 90 %, respectively. In regard of structure, non-destroying effect of DCMC on collagen was supported by FT-IR and XRD analysis. CH cross-linked by DCMC (CH-DC) showed declining porosity and aggregating fibrils as -CHO content of DCMC rising. In regard of physicochemical properties, DCMC with >53 % -CHO strengthened the hydrophilicity, thermal stability and degradation resistance of CH-DC. Also, there was 110 % growth on gel strength, 86 Pa enhancements on storage modulus, and 4.6 times decrease on the swelling ratio of CH-DC. Results indicated that DCMC with 79 % -CHO remarkably improved the physicochemical properties of CH via developing sufficient Schiff-base bonds with collagen fibril in a short distance. This study distinguished two patterns of DCMC cross-linking from physicochemical view. In other words, DCMC is potential to meet the requirement of protein-based materials with different expectations by adjusting its -CHO content and molecular weight.

Implantation of a nerve protector embedded with human GMSC-derived Schwann-like cells accelerates regeneration of crush-injured rat sciatic nerves

BACKGROUND

Peripheral nerve injuries (PNIs) remain one of the great clinical challenges because of their considerable long-term disability potential. Postnatal neural crest-derived multipotent stem cells, including gingiva-derived mesenchymal stem cells (GMSCs), represent a promising source of seed cells for tissue engineering and regenerative therapy of various disorders, including PNIs. Here, we generated GMSC-repopulated nerve protectors and evaluated their therapeutic effects in a crush injury model of rat sciatic nerves.

METHODS

GMSCs were mixed in methacrylated collagen and cultured for 48 h, allowing the conversion of GMSCs into Schwann-like cells (GiSCs). The phenotype of GiSCs was verified by fluorescence studies on the expression of Schwann cell markers. GMSCs encapsulated in the methacrylated 3D-collagen hydrogel were co-cultured with THP-1-derived macrophages, and the secretion of anti-inflammatory cytokine IL-10 or inflammatory cytokines TNF-α and IL-1β in the supernatant was determined by ELISA. In addition, GMSCs mixed in the methacrylated collagen were filled into a nerve protector made from the decellularized small intestine submucosal extracellular matrix (SIS-ECM) and cultured for 24 h, allowing the generation of functionalized nerve protectors repopulated with GiSCs. We implanted the nerve protector to wrap the injury site of rat sciatic nerves and performed functional and histological assessments 4 weeks post-surgery.

RESULTS

GMSCs encapsulated in the methacrylated 3D-collagen hydrogel were directly converted into Schwann-like cells (GiSCs) characterized by the expression of S-100β, p75NTR, BDNF, and GDNF. In vitro, co-culture of GMSCs encapsulated in the 3D-collagen hydrogel with macrophages remarkably increased the secretion of IL-10, an anti-inflammatory cytokine characteristic of pro-regenerative (M2) macrophages, but robustly reduced LPS-stimulated secretion of TNF-1α and IL-1β, two cytokines characteristic of pro-inflammatory (M1) macrophages. In addition, our results indicate that implantation of functionalized nerve protectors repopulated with GiSCs significantly accelerated functional recovery and axonal regeneration of crush-injured rat sciatic nerves accompanied by increased infiltration of pro-regenerative (M2) macrophages while a decreased infiltration of pro-inflammatory (M1) macrophages.

CONCLUSIONS

Collectively, these findings suggest that Schwann-like cells converted from GMSCs represent a promising source of supportive cells for regenerative therapy of PNI through their dual functions, neurotrophic effects, and immunomodulation of pro-inflammatory (M1)/pro-regenerative (M2) macrophages.

Construction of in vitro 3-D model for lung cancer-cell metastasis study

Background

Cancer metastasis is the main cause of mortality in cancer patients. However, the drugs targeting metastasis processes are still lacking, which is partially due to the short of effective in vitro model for cell invasion studies. The traditional 2-D culture method cannot reveal the interaction between cells and the surrounding extracellular matrix during invasion process, while the animal models usually are too complex to explain mechanisms in detail. Therefore, a precise and efficient 3-D in vitro model is highly desirable for cell invasion studies and drug screening tests.

Methods

Precise micro-fabrication techniques are developed and integrated with soft hydrogels for constructing of 3-D lung-cancer micro-environment, mimicking the pulmonary gland or alveoli as in vivo.

Results

A 3-D in vitro model for cancer cell culture and metastasis studies is developed with advanced micro-fabrication technique, combining microfluidic system with soft hydrogel. The constructed microfluidic platform can provide nutrition and bio-chemical factors in a continuous transportation mode and has the potential to form stable chemical gradient for cancer invasion research. Hundreds of micro-chamber arrays are constructed within the collagen gel, ensuring that all surrounding substrates for tumor cells are composed of natural collagen hydrogel, like the in vivo micro-environment. The 3-D in vitro model can also provide a fully transparent platform for the visual observation of the cell morphology, proliferation, invasion, cell-assembly, and even the protein expression by immune-fluorescent tests if needed.

The lung-cancer cells A549 and normal lung epithelial cells (HPAEpiCs) have been seeded into the 3-D system. It is found out that cells can normally proliferate in the microwells for a long period. Moreover, although the cancer cells A549 and alveolar epithelial cells HPAEpiCs have the similar morphology on 2-D solid substrate, in the 3-D system the cancer cells A549 distributed sparsely as single round cells on the extracellular matrix (ECM) when they attached to the substrate, while the normal lung epithelial cells can form cell aggregates, like the structure of normal tissue. Importantly, cancer cells cultured in the 3-D in vitro model can exhibit the interaction between cells and extracellular matrix. As shown in the confocal microscope images, the A549 cells present round and isolated morphology without much invasion into ECM, while starting from around Day 5, cells changed their shape to be spindle-like, as in mesenchymal morphology, and then started to destroy the surrounding ECM and invade out of the micro-chambers.

Conclusions

A 3-D in vitro model is constructed for cancer cell invasion studies, combining the microfluidic system and micro-chamber structures within hydrogel. To show the invasion process of lung cancer cells, the cell morphology, proliferation, and invasion process are all analyzed. The results confirmed that the micro-environment in the 3-D model is vital for revealing the lung cancer cell invasion as in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09546-9.

Electrical and Immunohistochemical Properties of Cochlear Fibrocytes in 3D Cell Culture and in the Excised Spiral Ligament of Mice

Fibrocyte degeneration in the cochlear lateral wall is one possible pathology of age-related metabolic hearing loss (presbycusis). Within the lateral wall fibrocytes play a role in potassium recycling and maintenance of the endocochlear potential. It has been proposed that cell replacement therapy could prevent fibrocyte degeneration in the CD/1 mouse model of hearing loss. For this to work, the replacement fibrocytes would need to take over the structural and physiological role of those lost. We have grown lateral wall fibrocytes from neonatal CD/1 mice in a 3D-collagen gel culture with the aim of assessing their functional similarity to native lateral wall fibrocytes, the latter in a slice preparation and in excised spiral ligament pieces. We have compared cultured and native fibrocytes using both immuno-labelling of characteristic proteins and single cell electrophysiology. Cultured fibrocytes exhibited rounded cell bodies with extending processes. They labelled with marker antibodies targeting aquaporin 1 and calcium-binding protein S-100, precluding an unambiguous identification of fibrocyte type. In whole-cell voltage clamp, both native and cultured fibrocytes exhibited non-specific currents and voltage-dependent K⁺ currents. The non-specific currents from gel-cultured and excised spiral ligament fibrocytes were partially and reversibly blocked by external TEA (10 mM). The TEA-sensitive current had a mean reversal potential of + 26 mV, suggesting a permeability sequence of Na⁺  > K⁺. These findings indicate that 3D-cultured fibrocytes share a number of characteristics with native spiral ligament fibrocytes and thus might represent a suitable population for transplantation therapy aimed at treating age-related hearing loss.

Ageing modulates human dermal fibroblast contractility: Quantification using nano-biomechanical testing

Dermal fibroblasts play a key role in maintaining homoeostasis and functionality of the skin. Their contractility plays a role in changes observed during ageing, especially in processes such as wound healing, inflammation, wrinkling and scar tissue formation as well as structural changes on extracellular matrix. Although alternations in skin physiology and morphology have been previously described, there remains a paucity of information about the influence of chronological ageing on dermal fibroblast contractility. In this study, we applied a novel nano-biomechanical technique on cell-embedded collagen hydrogels in combination with mathematical modelling and numerical simulation to measure contraction forces of normal human dermal fibroblasts (NHDF). We achieved quantitative differentiation of the contractility of cells derived from 'young' (< 30 years old) and 'aged' (> 60 years old) donors. Transforming growth factor β1 (TGF-β1) was used to stimulate the fibroblasts to assess their contractile potential. NHDF from aged donors exhibited a greater basal contractile force, while in contrast, NHDF from young donors have shown a significantly larger contractile force in response to TGF-β1 treatment. These findings validate our nano-biomechanical measurement technique and provide new insights for considering NHDF contractility in regenerative medicine and as a biomarker of dermal ageing processes.

Small molecules combined with collagen hydrogel direct neurogenesis and migration of neural stem cells after spinal cord injury

Complete spinal cord injury (SCI) leads to cell death, interruption of axonal connections and permanent functional impairments. In the development of SCI treatments, cell transplantation combined with biomaterial-growth factor-based therapies have been widely studied. Another avenue worth exploring is the generation of neurons from endogenous neural stem cells (NSCs) or reactive astrocytes activated by SCI. Here, we screened a combination of four small molecules, LDN193189, SB431542, CHIR99021 and P7C3-A20, that can increase neuronal differentiation of mouse and rat spinal cord NSCs. Moreover, the small molecules loaded in an injectable collagen hydrogel induced neurogenesis and inhibited astrogliogenesis of endogenous NSCs in the injury site, which usually differentiate into astrocytes under pathological conditions. Meanwhile, induced neurons migrated into the non-neural lesion core, and genetic fate mapping showed that neurons mainly originated from NSCs in the parenchyma, but not from the central canal of the spinal cord. The neuronal regeneration in the lesion sites resulted in some recovery of locomotion. Our findings indicate that the combined treatment of small molecules and collagen hydrogel is a potential therapeutic strategy for SCI by inducing in situ endogenous NSCs to form neurons and restore damaged functions.

Collagen hydrogels loaded with fibroblast growth factor-2 as a bridge to repair brain vessels in organotypic brain slices

Vessel damage is a general pathological process in many neurodegenerative disorders, as well as spinal cord injury, stroke, or trauma. Biomaterials can present novel tools to repair and regenerate damaged vessels. The aim of the present study is to test collagen hydrogels loaded with different angiogenic factors to study vessel repair in organotypic brain slice cultures. In the experimental set up I, we made a cut on the organotypic brain slice and tested re-growth of laminin + vessels. In the experimental set up II, we cultured two half brain slices with a gap with a collagen hydrogel placed in between to study endothelial cell migration. In the experimental set up I, we showed that the number of vessels crossing the cut was tendencially increased with the addition of fibroblast growth factor-2 (FGF-2), vascular endothelial growth factor, or platelet-derived growth factor-BB compared to the control group. In the experimental set up II, we demonstrated that a collagen hydrogel loaded with FGF-2 resulted in a significantly increased number of migrated laminin + cells in the gap between the slices compared to the control hydrogel. Co-administration of several growth factors did not further potentiate the effects. Taken together, we show that organotypic brain slices are good models to study brain vessels and FGF-2 is a potent angiogenic factor for endothelial cell proliferation and migration. Our results provide evidence that the collagen hydrogels can be used as an extracellular matrix for the vascular endothelial cells.

Hair follicle stem cells differentiation into bone cells on collagen scaffold

The hair follicle is a dynamic structure which contains different niches for stem cells, therefore; it has been considered as valuable and rich sources of stem cells, due to easy access, multipotency and non-oncogenic properties. In the present study, the differentiation capacities of hair follicle stem cells into bone cells on the natural collagen scaffolds were investigated. The stem cells were extracted from the hair follicle bulge area of male Wistar rats' whisker and cultured until 3rd passage, then osteogenic differentiations were induced by culturing the cells in the specific osteogenic medium. After 3 weeks, the differentiation parameters, including morphological changes, levels of calcification and expression of the bone specific genes were detected. The hydrogel preparation and scaffold fabrication was carried out using the extracted collagen and was studied by scanning electron microscope. Comparison of the stem cells' growth and changes on the scaffold and non-scaffold conditions showed that, in the both situation, the cells revealed differentiation signs of osteocytes, including large and cubic morphology with a star-shaped nucleus. Staining by Alizarin-red and Von-Kossa methods showed the presence of red and black calcium mass on the scaffold. Expression of the osteopontin and alkaline phosphatase genes confirmed the differentiation. Considerable porosity in the surface of the scaffold was recorded by scanning electron microscopy, which made it convenient for cells' attachment and growth. The data showed that the bulge stem cells possess significant capacity for osteoblastic differentiation and collagen scaffolds were found to be an appropriate matrix for growth and differentiation of the cell.

Tissue mimetic hyaluronan bioink containing collagen fibers with controlled orientation modulating cell migration and alignment

Biofabrication is providing scientists and clinicians the ability to produce engineered tissues with desired shapes and gradients of composition and biological cues. Typical resolutions achieved with extrusion-based bioprinting are at the macroscopic level. However, for capturing the fibrillar nature of the extracellular matrix (ECM), it is necessary to arrange ECM components at smaller scales, down to the micron and the molecular level. Herein, we introduce a bioink containing the tyramine derivative of hyaluronan (HA; henceforth known as THA) and collagen (Col) type 1. In this bioink, similar to connective tissues, Col is present in the fibrillar form, and HA functions as a viscoelastic space filler. THA was enzymatically cross-linked under mild conditions allowing simultaneous Col fibrillogenesis, thus achieving a homogeneous distribution of Col fibrils within the viscoelastic HA-based matrix. The THA-Col composite displayed synergistic properties in terms of storage modulus and shear thinning, translating into good printability. Shear-induced alignment of the Col fibrils along the printing direction was achieved and quantified via immunofluorescence and second-harmonic generation. Cell-free and cell-laden constructs were printed and characterized, analyzing the influence of the controlled microscopic anisotropy on human bone marrow-derived mesenchymal stromal cell (hMSC) migration. Anisotropic HA-Col showed cell-instructive properties modulating hMSC adhesion, morphology, and migration from micropellets stimulated by the presence and the orientation of Col fibers. Actin filament staining showed that hMSCs embedded in aligned constructs displayed increased cytoskeleton alignment along the fibril direction. Based on gene expression of cartilage/bone markers and ECM production, hMSCs embedded in the isotropic bioink displayed chondrogenic differentiation comparable with standard pellet culture by means of proteoglycan production (safranin O staining and proteoglycan quantification). The possibility of printing matrix components with control over microscopic alignment brings biofabrication one step closer to capturing the complexity of native tissues.

Multi-directional cellular alignment in 3D guided by electrohydrodynamically-printed microlattices

Recapitulating aligned cellular architectures of native tissues in vitro is important to engineer artificial tissue analogs with desired biological functions. Here a novel strategy is presented to direct three-dimensional (3D) cellular alignment by embedding cell/collagen hydrogel into the predefined electrohydrodynamically-printed microlattices. The cell/collagen hydrogel, originally filled within the printed microlattices uniformly, was found to gradually develop into densely-populated and highly-aligned bands along the longitudinal direction of the printed microlattices. The cellular alignment was highly dependent on the height, spacing and orientation of the microlattices. The presented method was applicable to multiple cell types including primary cardiomyocytes and the gaps formed between the aligned bands and the lateral walls of the microlattice facilitated the subsequent seeding and rapid alignment of other cell types which enables to engineer anisotropic multicellular tissue constructs. The engineered cardiac patches expressed mature cardiomyocyte-specific phenotypes and exhibited synchronous contractive activities. Multilayer cellular alignment with varied orientation in 3D collagen hydrogel was successfully achieved by using electrohydrodynamically-printed microlattices with layer-specific orientations. This exploration offers a promising way to engineer complex 3D tissue constructs with predefined cellular alignments. STATEMENT OF SIGNIFICANCE: Fabrication of biomimetic highly-aligned complex cellular architectures has a great significance to recapitulate the unique mechanical and physiological functions of the engineered tissues (e.g., heart tissue, neuron, muscle). Here, we introduced a novel strategy to direct 3D cellular alignment by embedding cell/collagen hydrogel into the predefined electrohydrodynamically-printed microlattices without any external stimuli. The microscopical study of the dynamic alignment process of cells and collagen fibers contributed to exploring the mechanism of autonomous formation of highly-aligned cellular bands. Multilayer cellular alignment with varied orientation in 3D collagen hydrogel was successfully achieved by using the microlattices with layer-specific orientations, which showed a promising way to engineer complex 3D tissue constructs with predefined cellular alignments.

Influence of hydrogel network microstructures on mesenchymal stem cell chondrogenesis in vitro and in vivo

Hydrogels, which provide three-dimensional (3D) niches for encapsulating bone marrow mesenchymal stem cells (BMSCs), are becoming a promising tissue engineering solution for chondrogenic differentiation of BMSCs. However, it remains a challenge to design a hydrogel material for effective chondrogenesis of BMSCs because of the complexity of cartilage ECM and cell-matrix interactions. Thus far, various studies have shown the physical-chemical cues of hydrogel materials to impact BMSCs chondrogenesis, but the design of the 3D network microstructure of the hydrogel to induce BMSCs chondrogenesis is still far from optimized. In this study, we successfully prepared two types of collagen hydrogels, namely, the fibrous network and porous network, with the same chemical composition and similar mechanical strength but with two distinct network microstructures. The two different network microstructures significantly influenced mass transfer, protein adsorption, degradability, and contraction of the collagen hydrogels. Moreover, the cells presented distinct proliferation and morphology in the two hydrogels, which consequently modulated chondrogenic differentiation of BMSCs derived from rat. Collagen hydrogels with a fibrous network promoted more chondrogenic differentiation of BMSCs without additional growth factors in vitro and subcutaneous implantation in vivo than those with a porous network. Moreover, fibrous network resulted in less ECM calcification than porous network. However, the fibrous network could not prevent hypertrophy of the chondrogenic cells induced by BMSCs. Overall, these results revealed that the 3D network microstructure of a hydrogel was a key design parameter for the chondrogenic differentiation of BMSCs. STATEMENT OF SIGNIFICANCE: Hydrogels had been used to induce the chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in cartilage tissue engineering, but the key design parameters remain unoptimized. This was mainly due to the different material properties including composition, strength, and microstructure, which would interplay with each other and result in difficulties to investigate the effects for one factor. In this study, we fabricated two collagen hydrogels with the same chemical composition and mechanical strength, but two distinct network microstructures. The effects of the two network microstructures on the chondrogenic differentiation of BMSCs were investigated by in vitro and in vivo assays. The results highlight the effects of network microstructures and provide important information about optimizing the design of future hydrogels in cartilage tissue engineering.

Development of an In Vitro 3D Brain Tissue Model Mimicking In Vivo-Like Pro-inflammatory and Pro-oxidative Responses

To analyze complex inflammatory responses in an in vitro system, we constructed a new 3D in vitro brain tissue model that exhibits in vivo-like tissue responses (e.g. immune cell phenotypes, and molecular response) to inflammatory stimuli. Finite element modeling of oxygen diffusion and cellular oxygen consumption predicted the oxygen profile within 3D structures, consisting of Type I collagen hydrogel embedded with murine microglia. Viability and cytotoxicity analyses supported the mathematical analysis, determining optimal cell growth conditions for 3D construct development. Real-time RT-PCR and ELISA demonstrated significant up-regulation of pro-inflammatory mediators, such as TNF-α, MCP-1, IL-6 and IL-1β, in lipopolysaccharide (LPS)-stimulated in vitro cell culture (2D and 3D) and in vivo mouse model systems. Interestingly, levels of inflammatory responses from the in vitro 3D model system were more similar to in vivo than in vitro 2D. Additionally, in situ dihydroethidium (DHE) assay and immunofluorescence staining revealed that levels of LPS-stimulated reactive oxygen species (ROS) generation and microglial activation from in vitro 3D model system were closer to in vivo than in vitro 2D. These results demonstrated that an in vitro 3D model provides more physiologically relevant pro-oxidative and pro-inflammatory environments in brain than an in vitro 2D model.

Compressed collagen constructs with optimized mechanical properties and cell interactions for tissue engineering applications

In this study, we are introducing a simple, fast and reliable add-in to the technique of plastic compression to obtain collagen sheets with decreased fibrillar densities, representing improved cell-interactions and mechanical properties. Collagen hydrogels with different initial concentrations (1.64mg/mL-0.41mg/mL) were compressed around an electrospun sheet of PLGA. The scaffolds were then studied as non-seeded, or seeded with 3T3 fibroblast cells and cultured for 7days. Confocal microscopy and TEM imaging of non-seeded scaffolds showed that by decreasing the share of collagen in the hydrogel formula, collagen sheets with similar thickness but lower fibrous densities were achieved. Nanomechanical characterization of compressed collagen sheets by AFM showed that Young's modulus was inversely proportional to the final concentration of collagen. Similarly, according to SEM, MTS, and cell nuclei counting, all the scaffolds supported cell adhesion and proliferation, whilst the highest metabolic activities and proliferation were seen in the scaffolds with lowest collagen content in hydrogel formula. We conclude that by decreasing the collagen content in the formula of collagen hydrogel for plastic compression, not only a better cell environment and optimum mechanical properties are achieved, but also the application costs of this biopolymer is reduced.

Human lung fibroblast-derived matrix facilitates vascular morphogenesis in 3D environment and enhances skin wound healing

Extracellular matrix (ECM) is crucial to many aspects of vascular morphogenesis and maintenance of vasculature function. Currently the recapitulation of angiogenic ECM microenvironment is still challenging, due mainly to its diverse components and complex organization. Here we investigate the angiogenic potential of human lung fibroblast-derived matrix (hFDM) in creating a three-dimensional (3D) vascular construct. hFDM was obtained via decellularization of in vitro cultured human lung fibroblasts and analyzed via immunofluorescence staining and ELISA, which detect multiple ECM macromolecules and angiogenic growth factors (GFs). Human umbilical vein endothelial cells (HUVECs) morphology was more elongated and better proliferative on hFDM than on gelatin-coated substrate. To prepare 3D construct, hFDM is collected, quantitatively analyzed, and incorporated in collagen hydrogel (Col) with HUVECs. Capillary-like structure (CLS) formation at 7day was significantly better with the groups containing higher doses of hFDM compared to the Col group (control). Moreover, the group (Col/hFDM/GFs) with both hFDM and angiogenic GFs (VEGF, bFGF, SDF-1) showed the synergistic activity on CLS formation and found much larger capillary lumen diameters with time. Further analysis of hFDM via angiogenesis antibody array kit reveals abundant biochemical cues, such as angiogenesis-related cytokines, GFs, and proteolytic enzymes. Significantly up-regulated expression of VE-cadherin and ECM-specific integrin subunits was also noticed in Col/hFDM/GFs. In addition, transplantation of Col/hFMD/GFs with HUVECs in skin wound model presents more effective re-epithelialization, many regenerated hair follicles, better transplanted cells viability, and advanced neovascularization. We believe that current system is a very promising platform for 3D vasculature construction in vitro and for cell delivery toward therapeutic applications in vivo.

STATEMENT OF SIGNIFICANCE

Functional 3D vasculature construction in vitro is still challenging due to the difficulty of recapitulating the complex angiogenic extracellular matrix (ECM) environment. Herein, we present a simple and practical method to create an angiogenic 3D environment via incorporation of human lung fibroblast-derived matrix (hFDM) into collagen hydrogel. We found that hFDM offers a significantly improved angiogenic microenvironment for HUVECs on 2D substrates and in 3D construct. A synergistic effect of hFDM and angiogenic growth factors has been well confirmed in 3D condition. The prevascularized 3D collagen constructs also facilitate skin wound healing. We believe that current system should be a convenient and powerful platform in engineering 3D vasculature in vitro, and in delivering cells for therapeutic purposes in vivo.

A scaffold-filter model for studying the chondrogenic differentiation of stem cells in vitro

This study was undertaken to explore the synergistic effect of scaffold materials and a cartilage-like environment on the chondrogenic differentiation of stem cells. Because stem cells encapsulated in a cartilage scaffold will be induced by scaffold molecules as well as permeable molecules from the surroundings, it is impossible to optimize a chondro-inducible scaffold without considering environmental sensitivity. How do we know if a designed scaffold will be sufficient prior to implantation? In this study, bone marrow mesenchymal stem cells (bMSCs) were seeded in various scaffolds, including collagen hydrogel, collage/sodium alginate hydrogel, collagen sponge and silk fibroin sponge. The cell-scaffold complex was encapsulated in a filter pocket to avoid direct contact with co-cultured chondrocytes. Scaffolds differed in the ability to adsorb inducible molecules expressed by chondrocytes, as evidenced by various expressions of cartilage specific proteins and genes. Collagen hydrogel unexpectedly supported chondrogenic differentiation in an environment filled with chondrocytes secretion better than other reinforced scaffolds, which is consistent with the previous experiment in vivo. This result indicated that the environmental sensitivity of a scaffold is important for in vivo chondro-induction. This in vitro scaffold-filter model may be useful as a precursor to investigate the chondro-inducing potential of various scaffolds for cartilage repair.

Sustained delivery of siRNA/PEI complex from in situ forming hydrogels potently inhibits the proliferation of gastric cancer

Background

Gastric cancer remains a major cause of mortality and morbidity worldwide. In recent years, gene-based therapeutic strategies were confirmed promising in cancer inhibition and attracted great attention. RNA interference (RNAi) is a powerful tool for gene therapy and has been widely employed to aid in treatment for various diseases, especially cancers. However, effective delivery of small interfering RNA (siRNA) to target cells in vivo remains a challenge for that it is prone to degradation and only lasts a few days in rapidly dividing cells.

Methods

Due to its biocompatibility and well-established safety profile, collagen represents a favourable matrix for in-site drug delivery. In the study, collagen hydrogel was used as carriers to test the feasibility of localized and sustained delivery of Id1-targeted siRNA for in vivo gastric cancer inhibition. To enhance the siRNA delivery, cationic polyethylenimine (PEI) was further emplored for scallold modification. The efficacy of siRNA delivery and cancer inhibition were evaluated with multimodality of mehods in vitro and in vivo.

Results

Our results showed that addition of polyethylenimine (PEI) to collagen can facilitate entry of Id1-siRNA into target cells, prolong the silencing effect, and further inhibit tumor growth both in vitro and in vivo.

Conclusion

This collagen-based delivery system may facilitate the pathogenesis elucidation and design of effective therapies against gastric cancer.

Characterization of sequential collagen-poly(ethylene glycol) diacrylate interpenetrating networks and initial assessment of their potential for vascular tissue engineering

Collagen hydrogels have been widely investigated as scaffolds for vascular tissue engineering due in part to the capacity of collagen to promote robust cell adhesion and elongation. However, collagen hydrogels display relatively low stiffness and strength, are thrombogenic, and are highly susceptible to cell-mediated contraction. In the current work, we develop and characterize a sequentially-formed interpenetrating network (IPN) that retains the benefits of collagen, but which displays enhanced mechanical stiffness and strength, improved thromboresistance, high physical stability and resistance to contraction. In this strategy, we first form a collagen hydrogel, infuse this hydrogel with poly(ethylene glycol) diacrylate (PEGDA), and subsequently crosslink the PEGDA by exposure to longwave UV light. These collagen-PEGDA IPNs allow for cell encapsulation during the fabrication process with greater than 90% cell viability via inclusion of cells within the collagen hydrogel precursor solution. Furthermore, the degree of cell spreading within the IPNs can be tuned from rounded to fully elongated by varying the time delay between the formation of the cell-laden collagen hydrogel and the formation of the PEGDA network. We also demonstrate that these collagen-PEGDA IPNs are able to support the initial stages of smooth muscle cell lineage progression by elongated human mesenchymal stems cells.

Pre-crosslinked polymeric collagen in 3-D models of mechanically stiff tissues: blended collagen polymer hydrogels for rapid layer fabrication

Currently one factor hindering the development of collagen hydrogel constructs for tissue engineering is the mismatch between initial cellularity and mechanical strength. The main advantage of collagen hydrogel tissue constructs is their ability to support interstitially seeded cells. However, cells are sensitive to their environment, in particular, substrate stiffness, which cannot easily be replicated within hydrogels without cytotoxic cross-linking treatment. In this study, pre-crosslinked polymeric collagen fibrils are introduced as a starting material, thereby avoiding artificial cross-linking. Shear aggregation of this material in solution results in fibril alignment, but cell addition is only possible when polymeric collagen is blended with its monomeric counterparts to slow the aggregation of collagen fibrils. The hydrogel can then be brought to physiological collagen density by plastic compression. Interstitially seeded fibroblasts were supported for 14days. Although compression of blended gels resulted in some cell death due to increased rate of fluid expulsion, not normally seen in conventional collagen hydrogels, the surviving cell population recovers during subsequent culture. Importantly, the compression process can be controlled and customized to limit cell damage. This is the first report of native polymeric collagen used in a tissue engineering context, for the rapid production of a stiff collagen-cell constructs.

Carbon nanotube-collagen three-dimensional culture of mesenchymal stem cells promotes expression of neural phenotypes and secretion of neurotrophic factors

Microenvironments provided by three-dimensional (3-D) hydrogels mimic native tissue conditions, supplying appropriate physical cues for regulating stem cell behaviors. Here, we focused on carbon nanotubes (CNTs) dispersed within collagen hydrogels to provide 3-D microenvironmental conditions for mesenchymal stem cells (MSCs) in stimulating biological functions for neural regeneration. Small concentrations of CNTs (0.1-1wt.%) did not induce toxicity to MSCs, and even improved the proliferative potential of the cells. MSCs cultured within the CNT-collagen hydrogel expressed considerable levels of neural markers, including GAP43 and βIII tubulin proteins by immunostaining as well as GAP43 and synapse I genes by reverse transcriptase polymerase chain reaction (RT-PCR). Of note was that neurotrophic factors, particularly nerve growth factor and brain derived neurotrophic factor, were significantly promoted by the incorporation of CNTs as confirmed by RT-PCR and Western blot analysis. A model experiment involving neuritogenesis of PC12 cells influenced by those releasing neurotrophic factors from MSCs cultured within the CNT-collagen hydrogel demonstrated the significant enhancement in neurite outgrowth behaviors. Taken together, collagen hydrogel provides excellent 3-D conditions for MSC growth, and a small incorporation of CNTs within the hydrogel significantly stimulates MSC expression of neural markers and secretion of neurotrophic factors.

3D microenvironment of collagen hydrogel enhances the release of neurotrophic factors from human umbilical cord blood cells and stimulates the neurite outgrowth of human neural precursor cells

The umbilical cord blood (UCB) cells have been reported to secrete therapeutic signals, including a series of neurotrophic factors. This suggests the cell source provides suitable therapeutic environments for nerve regeneration that ultimately finds a possible cell therapy for nerve tissue. In this study, we observe a collagen hydrogel provides human UCB cells a proper 3D environment that stimulates the release of various neurotrophic factors. When compared to 2D culture, the 3D hydrogel culture significantly enhanced the expression of a series of neurotrophic factors, including neurotrophins, nerve growth factor, brain-derived neurotrophic factor, and ciliary neurotrophic factor as verified by the gene and protein analysis. To confirm the effects of neurotrophic factors secretion, we allowed an indirect interaction of the UCB-environment with human neural precursor cells (hNPCs). Results showed significantly enhanced neurite outgrowth of hNPCs. Collectively, our findings demonstrate that the collagen-based 3D hydrogel provides excellent environment for UCB-derived cells to release neurotrophic factors that will be ultimately useful for the neural repair and regeneration purposes.

Collagen hydrogels incorporated with surface-aminated mesoporous nanobioactive glass: Improvement of physicochemical stability and mechanical properties is effective for hard tissue engineering

Collagen (Col) hydrogels have poor physicochemical and mechanical properties and are susceptible to substantial shrinkage during cell culture, which limits their potential applications in hard tissue engineering. Here, we developed novel nanocomposite hydrogels made of collagen and mesoporous bioactive glass nanoparticles (mBGns) with surface amination, and addressed the effects of mBGn addition (Col:mBG = 2:1, 1:1 and 1:2) and its surface amination on the physicochemical and mechanical properties of the hydrogels. The amination of mBGn was shown to enable chemical bonding with collagen molecules. As a result, the nanocomposite hydrogels exhibited a significantly improved physicochemical and mechanical stability. The hydrolytic and enzymatic degradation of the Col-mBGn hydrogels were slowed down due to the incorporation of mBGn and its surface amination. The mechanical properties of the hydrogels, specifically the resistance to loading as well as the stiffness, significantly increased with the addition of mBGn and its aminated form, as assessed by a dynamic mechanical analysis. Mesenchymal stem cells cultivated within the Col-mBGn hydrogels were highly viable, with enhanced cytoskeletal extensions, due to the addition of surface aminated mBGn. While the Col hydrogel showed extensive shrinkage (down to ∼20% of initial size) during a few days of culture, the shrinkage of the mBGn-added hydrogel was substantially reduced, and the aminated mBGn-added hydrogel had no observable shrinkage over 21 days. Results demonstrated the effective roles of aminated mBGn in significantly improving the physicochemical and mechanical properties of Col hydrogel, which are ultimately favorable for applications in stem cell culture for bone tissue engineering.