Temporary Matrix Research Articles

Effect of the Addition of Inorganic Fillers on the Properties of Degradable Polymeric Blends for Bone Tissue Engineering.

Bone tissue exhibits self-healing properties; however, not all defects can be repaired without surgical intervention. Bone tissue engineering offers artificial scaffolds, which can act as a temporary matrix for bone regeneration. The aim of this study was to manufacture scaffolds made of poly(lactic acid), poly(ε-caprolactone), poly(propylene fumarate), and poly(ethylene glycol) modified with bioglass, beta tricalcium phosphate (TCP), and/or wollastonite (W) particles. The scaffolds were fabricated using a gel-casting method and observed with optical and scanning electron microscopes. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR), differential scanning calorimetry (DSC), thermogravimetry (TG), wettability, and degradation tests were conducted. The highest content of TCP without W in the composition caused the highest hydrophilicity (water contact angle of 61.9 ± 6.3°), the fastest degradation rate (7% mass loss within 28 days), moderate ability to precipitate CaP after incubation in PBS, and no cytotoxicity for L929 cells. The highest content of W without TCP caused the highest hydrophobicity (water contact angle of 83.4 ± 1.7°), the lowest thermal stability, slower degradation (3% mass loss within 28 days), and did not evoke CaP precipitation. Moreover, some signs of cytotoxicity on day 1 were observed. The samples with both TCP and W showed moderate properties and the best cytocompatibility on day 4. Interestingly, they were covered with typical cauliflower-like hydroxyapatite deposits after incubation in phosphate-buffered saline (PBS), which might be a sign of their excellent bioactivity.

Characterization and In Vitro Evaluation of Porous Polymer-Blended Scaffolds Functionalized with Tricalcium Phosphate.

Bone tissue is one of the most transplanted tissues. The ageing population and bone diseases are the main causes of the growing need for novel treatments offered by bone tissue engineering. Three-dimensional (3D) scaffolds, as artificial structures that fulfil certain characteristics, can be used as a temporary matrix for bone regeneration. In this study, we aimed to fabricate 3D porous polymer scaffolds functionalized with tricalcium phosphate (TCP) particles for applications in bone tissue regeneration. Different combinations of poly(lactic acid) (PLA), poly(ethylene glycol) (PEG with molecular weight of 600 or 2000 Da) and poly(ε-caprolactone) (PCL) with TCP were blended by a gel-casting method combined with rapid heating. Porous composite scaffolds with pore sizes from 100 to 1500 µm were obtained. ATR-FTIR, DSC, and wettability tests were performed to study scaffold composition, thermal properties, and hydrophilicity, respectively. The samples were observed with the use of optical and scanning electron microscopes. The addition of PCL to PLA increased the hydrophobicity of the composite scaffolds and reduced their susceptibility to degradation, whereas the addition of PEG increased the hydrophilicity and degradation rates but concomitantly resulted in enhanced creation of rounded mineral deposits. The scaffolds were not cytotoxic according to an indirect test in L929 fibroblasts, and they supported adhesion and growth of MG-63 cells when cultured in direct contact.

ИСПОЛЬЗОВАНИЕ ПРЕПАРАТОВ ГИАЛУРОНОВОЙ КИСЛОТЫ ДЛЯ СТИМУЛЯЦИИ РЕГЕНЕРАЦИИ ПРИ РАЗВИТИИ ТРОФИЧЕСКИХ НАРУШЕНИЙ У ПАЦИЕНТОВ С ХРОНИЧЕСКИМИ ОБЛИТЕРИРУЮЩИМИ ЗАБОЛЕВАНИЯМИ АРТЕРИЙ НИЖНИХ КОНЕЧНОСТЕЙ

Trophic ulcers as a result of chronic vascular diseases of the lower extremities are an urgent and complex task of surgical treatment. Local treatment of the ulcer is an important role after revascularization. Hyaluronic acid (HA) preparations are among the most promising in this regard. HA provides increased tissue resistance to ischemia, suppression of the inflammatory response, stimulation and acceleration of tissue regeneration. HA ensures the formation of a temporary matrix in a fresh wound, facilitates the diffusion of nutrients and cleans the wound from products of cellular metabolism. Secondly, it takes an active part in the proliferation and migration of keratinocytes, which make up the bulk of the epidermis. Due to the insignificant use of HA in local therapy of trophic disorders of chronic vascular diseases of the lower extremities, it is interesting to further study the effect as part of complex and pathogenetically oriented treatment in patients of this group.

Design considerations and biomaterials selection in embedded extrusion 3D bioprinting.

In embedded extrusion 3D bioprinting, a temporary matrix preserves a paste-like filament ejecting from a narrow nozzle. For granular sacrificial matrices, the methodology is known as the freeform reversible embedding of suspended hydrogels (FRESH). Embedded extrusion 3D bioprinting methods result in more rapid and controlled manufacturing of cell-laden tissue constructs, particularly vascular and multi-component structures. This report focuses on the working principles and bioink design criteria for implementing conventional embedded extrusion and FRESH 3D bioprinting strategies. We also present a set of experimental data as a guideline for selecting the support bath or matrix. We discuss the advantages of embedded extrusion methods over conventional biomanufacturing methods. This work provides a short recipe for selecting inks and printing parameters for desired shapes in embedded extrusion and FRESH 3D bioprinting methods.

Bioactive Lactose-Modified Chitosan Acts as a Temporary Extracellular Matrix for the Formation of Chondro-Aggregates

Spheroids based on chondrocytes are gaining interest in the treatment of injured cartilage tissue due to their regenerative potential. In this study, chondrocyte-based aggregates were formed by culturing cells on a polymeric coating of a lactose-modified chitosan (CTL) and their evolution was followed for 14 days of culture. Morphological analyses through scanning electron microscopy indicated that these cell aggregates formed by a process of cell aggregation rather than proliferation, resulting in structures with an irregular morphology that were up to 1 mm in size. Chondrocytes interact very closely with CTL. In the early days of cellular aggregation, CTL is distributed among the cells, while in later stages, it is localized in the inner part of the aggregates, forming an amorphous matrix. The initial outer position of the polymer is replaced over time by an increased matrix deposition whose main component is type II collagen. Transmission electron microscopy pointed out that the chondrocytes internalized the polymer during the first days of culture. The presence of CTL does not affect the ability of cells to migrate from chondro-aggregates when transferred to uncoated wells, mimicking the ability of cells to colonize a cartilage defect. Overall, these results suggest that CTL plays a role as a temporary matrix for chondrocytes aggregation during chondro-aggregates formation. This opens up innovative therapeutic approaches for cartilage regeneration without the need to use a scaffold to deliver cells to the damaged site.

Thermoresponsive and Injectable Hydrogel for Tissue Agnostic Regeneration.

Injectable hydrogels can support the body's innate healing capability by providing a temporary matrix for host cell ingrowth and neovascularization. The clinical adoption of current injectable systems remains low due to their cumbersome preparation requirements, device malfunction, product dislodgment during administration, and uncontrolled biological responses at the treatment site. To address these challenges, a fully synthetic and ready-to-use injectable biomaterial is engineered that forms an adhesive hydrogel that remains at the administration site regardless of defect anatomy. The product elicits a negligible local inflammatory response and fully resorbs into nontoxic components with minimal impact on internal organs. Preclinical animal studies confirm that the engineered hydrogel upregulates the regeneration of both soft and hard tissues by providing a temporary matrix to support host cell ingrowth and neovascularization. In a pilot clinical trial, the engineered hydrogel is successfully administered to a socket site post tooth extraction and forms adhesive hydrogel that stabilizes blood clot and supports soft and hard tissue regeneration. Accordingly, this injectable hydrogel exhibits high therapeutic potential and can be adopted to address multiple unmet needs in different clinical settings.

Recent Advances in Tissue Engineering Scaffolds and Commercial Applications

Scaffolds for tissue engineering are support structures that help cells grow and multiply after being implanted into a patient. To allow cellular adhesion, proliferation, and differentiation, the optimal scaffolds should have the right surface chemistry and microstructures. Furthermore, the scaffolds must have sufficient mechanical strength and a low rate of biodegradation with no unwanted by-products. Regenerative medicine efforts currently rely on the transplantation of cells in combination with supporting scaffolds and macromolecules to restore pathologically damaged tissue architectures. Biologically active scaffolds, which are based on analogues of the extracellular matrix that have spurred tissue and organ creation, have attracted a lot of attention in recent years. A scaffold is required to restore function or regenerate tissue, as it will serve as a temporary matrix for cell proliferation and extracellular matrix deposition, with further ingrowth until the tissues are completely restored or regenerated. Different technologies have been employed for fabrication of scaffolds for regeneration of different organs and tissues like skin, cartilage, bone, heart, lungs, liver and kidney. This review focuses on the different strategies used to construct the scaffold for the above-mentioned tissues and organs along with their commercial applications. Keywords: Tissue Engineering, Scaffold, Electrospinning, Nanofiber, Heart valve, Kidney Decellularization

Angiogenic and Osteogenic Properties of Fibrin in Bone Tissue Engineering

The bone scaffold has become a promising alternative in bone tissue engineering due to the limitation associated with current bone treatments. However, the selection of scaffold material that could accurately mimic the extracellular matrix of native tissue remains challenging. Owing to its biological origin properties, natural materials including fibrin are widely used as scaffold materials as compared to synthetic materials. Fibrin has been recognized as one of the appealing natural biopolymers, which possesses unique characteristic due to its natural formed nano-scaffold, which provide a temporary matrix that facilitates cellular activities of cells. Fibrin has shown remarkable effects over other biomaterials in inducing angiogenesis and osteogenesis in bone regeneration owing to its mechanical and biological properties. In this article, we highlight the significance of fibrin materials in facilitating bone regeneration. We focus on the manipulation of fibrin composition and on the recent developments of fibrin composites in enhancing osteogenesis and angiogenesis for bone healing.

An XML Privacy-Preserving Data Disclosure Decision Scheme

In order to protect the sensitive data represented as XML documents in a trusted collaborative system where sensitive data are not shared, an XML privacy-preserving data disclosure decision scheme was proposed under the assumption of a trusted server. This scheme is inspired by the idea of separating storage structure and content. Temporary access matrix is used to represent structure authorization and the vector represents the content authorization of leaf node. According to the conversion rules, access matrix not only represents access authorization of all nodes but also keeps the main structure of the XML document. With the combination of the vector and matrix, it can provide different access views for different group users with different purposes. In addition, start-end encoding is used to encode all the nodes for locating nodes and the content; privilege matrix solves the problem of privacy synchronization change for all users. At the same time, authentication polynomials are used to verify different users and improve the security level. The experimental results show that the scheme not only effectively protects XML sensitive data but also reduces the storage pressure on the server side; at the same time, from the response time, we know that it is beneficial for the rapid search and information positioning.

Potential of Fibrin Glue and Mesenchymal Stem Cells (MSCs) to Regenerate Nerve Injuries: A Systematic Review.

Cell-based therapy is a promising treatment to favor tissue healing through less invasive strategies. Mesenchymal stem cells (MSCs) highlighted as potential candidates due to their angiogenic, anti-apoptotic and immunomodulatory properties, in addition to their ability to differentiate into several specialized cell lines. Cells can be carried through a biological delivery system, such as fibrin glue, which acts as a temporary matrix that favors cell-matrix interactions and allows local and paracrine functions of MSCs. Thus, the aim of this systematic review was to evaluate the potential of fibrin glue combined with MSCs in nerve regeneration. The bibliographic search was performed in the PubMed/MEDLINE, Web of Science and Embase databases, using the descriptors (“fibrin sealant” OR “fibrin glue”) AND “stem cells” AND “nerve regeneration”, considering articles published until 2021. To compose this review, 13 in vivo studies were selected, according to the eligibility criteria. MSCs favored axonal regeneration, remyelination of nerve fibers, as well as promoted an increase in the number of myelinated fibers, myelin sheath thickness, number of axons and expression of growth factors, with significant improvement in motor function recovery. This systematic review showed clear evidence that fibrin glue combined with MSCs has the potential to regenerate nervous system lesions.

High-Throughput Digitisation of Natural History Specimens

The Natural History Museum, London (NHM) has embarked on an ambitious Digital Collections Programme to digitise its collections. One aim of the programme has been to improve the workflows and infrastructure needed to support high-throughput digitisation and create comprehensive digital inventories of large scientific collections. Pilot projects have been carried out for a variety of collection types, from which high-throughput imaging workflows have been developed and refined. These workflows have focused on pinned insect specimens (Blagoderov et al. 2012, Paterson et al. 2016, Blagoderov et al. 2017, Price et al. 2018), microscope slides (whole slide and specimen imaging; Allan et al. 2018, Allan et al. 2019) and herbarium sheets. The rate and time taken to digitise specimens is influenced by a number of factors that include, among others, the level of preparation and post-processing required, imaging approach, the type of specimens as well as the complexity and condition of the collection. As part of this presentation we will include information on the rate, cost and time to digitise various NHM collections, illustrating how our processes have improved digitisation efficiency and allowed us to maintain quality. The programme has run a variety of digitisation projects, gathering data about rates of digitisation (preparation, imaging, transcription etc.) and developing improvements. Collection types such as microscope slides and herbarium sheets lend themselves to higher imaging rates, while other collections such as pinned insects, which require greater amounts of specimen handling to remove labels, tend to have lower imaging rates (Fig. 1). In order to increase efficiency, we have developed approaches that minimise specimen handling. For example, workflows for pinned insects such as the Angled Label Image Capture and Extraction (ALICE) do not require the removal of specimen labels from the pin as the system can capture angled images of the labels, thus increasing the imaging rate three-fold (Fig. 1). Another approach taken is to semi-automate mass digitisation using a combination of temporary and permanent Data Matrix barcode labels (Allan et al. 2019). By using multiple barcodes at the imaging stage to encode information associated with each specimen (i.e. unique identifier, location in the collection, taxonomic name, type status etc.; Fig. 2), we can run a series of automated processes, including file renaming, image processing and bulk import into the Museum’s collection management system. Through adaptation of our workflows with this new approach we have increased the efficiency of digitisation processes, illustrating how simple activities, like automated file renaming, reduces image post-processing time, minimises human error and can be applied across multiple collection types.

Stabilisation of amorphous calcium phosphate in polyethylene glycol hydrogels

Acellular polymer-calcium phosphate composites are promising bone graft materials. Hydrogels are suitable for providing a temporary matrix, while calcium phosphate minerals serve as ion depots for calcium and phosphate required for de novo bone formation. Crystalline calcium phosphates are stable under biological conditions and are commonly used in such scaffolds. However, the low solubility of these phases reduces the availability of free ions and potentially obstructs the remodelling necessary for the formation of mineralised tissue. Here, we investigate two different strategies to stabilise amorphous calcium phosphates in a synthetic polyethylene glycol-based hydrogel matrix.In vitro experiments mimicking an injectable application showed that amorphous calcium phosphate (ACP) of variable stability was formed in the hydrogel matrices. In additive-free composites, ACP transformed into brushite within minutes. Citrate or zinc additives were found to stabilise the formed ACP phase to different degrees. In the presence of citrate, ACP was stable for at least 2 h before it transformed into hydroxyapatite within 3–20 days. Partial calcium substitution with zinc (Zn/Ca = 10%) produced zinc-doped ACP of high stability that did not show signs of crystallisation for at least 20 days.The presented methods and findings open new possibilities for the design of novel injectable synthetic bone graft materials. The possibility to produce ACP with tailorable stability promises great potential for creating temporary scaffolds with good osteogenic properties. Statement of significanceSynthetic hydrogel-calcium phosphate (CaP) composites are promising biomaterials to replace human- and animal-derived bone scaffolds. Most reported hydrogel-CaP composite materials employ crystalline CaP phases that lack the osteoinductive properties of autograft. Stabilising amorphous calcium phosphates (ACP) could overcome this limitation, readily delivering calcium and phosphate ions and facilitating remodelling into new bone tissue. The design of synthetic hydrogel-ACP scaffolds, however, requires more understanding of the mineralisation processes in such matrices. This study presents a model system to characterise the complex mineral formation and transformation processes within a hydrogel matrix. We demonstrate a facile route to produce self-mineralising injectable synthetic hydrogels and prove two different strategies to stabilise ACP for different periods within the formed composites.

Enhanced Structural Stability and Controlled Drug Release of Hydrophilic Antibiotic-Loaded Alginate/Soy Protein Isolate Core-Sheath Fibers for Tissue Engineering Applications

Tissue engineering involves a multifunctional temporary matrix which regulates tissue regeneration through controlled drug release against infections. A nanofibrous core-sheath structured scaffold comprising a tetracycline-loaded alginate/soy protein isolate (TCH-Alg/SPI) as a core and polycaprolactone (PCL) as a sheath was developed using co-axial electrospinning. Coverage of hydrophobic PCL on TCH-Alg/SPI fibers enhanced their structural stability in aqueous solutions as unsheathed fibers rapidly decomposed and provided fast drug release. Core-sheath fibers exhibited an initial burst release at ~49 % after 6 h of immersion in phosphate-buffered saline (PBS) solution and the sustain release reached ~80 % of total loaded drug on day 14. Release characteristics of TCH-Alg/SPI fibers without PCL covering showed immediate drug release within 48 h. Core-sheath fibers investigated by disk diffusion exhibited antibacterial properties against Staphylococcus aureus and Escherichia coli. The non-toxicity of core-sheath fibers was confirmed by an indirect cytotoxicity test using human dermal fibroblasts which showed compatibility and high cell viability of up to 100 % in treated cells. TCH-Alg/SPI-PCL core-sheath fibers show promise as tissue engineering scaffolds which can act as temporary templates for tissue regeneration and exhibit antibiotic release functions against infections caused by pathogenic microorganisms.

Injectable Macroporous Hydrogel Formed by Enzymatic Cross-Linking of Gelatin Microgels.

Injectable hydrogels can be useful tools for facilitating wound healing since they conform to the irregular shapes of wounds, serving as a temporary matrix during the healing process. However, the lack of inherent pore structures of most injectable hydrogels prohibits desired interactions with the cells of the surrounding tissues limiting their clinical efficacy. Here, we introduce a simple, cost-effective and highly biofunctional injectable macroporous hydrogel made of gelatin microgels crosslinked by microbial transglutaminase (mTG). Pores are created by the interstitial space among the microgels. A water-in-oil emulsion technique was used to create gelatin microgels of an average size of 250μm in diameter. When crosslinked with mTG, the microgels adhered to each other to form a bulk hydrogel with inherent pores large enough for cell migration. The viscoelastic properties of the porous hydrogel were similar to those of nonporous gelatin hydrogel made by adding mTG to a homogeneous gelatin solution. The porous hydrogel supported higher cellular proliferation of human dermal fibroblasts (hDFs) than the nonporous hydrogel over two weeks, and allowed the migration of hDFs into the pores. Conversely, the hDFs were unable to permeate the surface of the nonporous hydrogel. To demonstrate its potential use in wound healing, the gelatin microgels were injected with mTG into a cut out section of an excised porcine cornea. Due to the action of mTG, the porous hydrogel stably adhered to the cornea tissue for two weeks. Confocal images showed that a large number of cells from the cornea tissue migrated into the interstitial space of the porous hydrogel. The porous hydrogel was also used for the controlled release of platelet-derived growth factor (PDGF), increasing the proliferation of hDFs compared to the nonporous hydrogel. This gelatin microgel-based porous hydrogel will be a useful tool for wound healing and tissue engineering.

In vitro characterization of 3D printed scaffolds aimed at bone tissue regeneration.

The incidence of fractures and bone-related diseases like osteoporosis has been increasing due to aging of the world's population. Up to now, grafts and titanium implants have been the principal therapeutic approaches used for bone repair/regeneration. However, these types of treatment have several shortcomings, like limited availability, risk of donor-to-recipient infection and tissue morbidity. To overcome these handicaps, new 3D templates, capable of replicating the features of the native tissue, are currently being developed by researchers from the area of tissue engineering. These 3D constructs are able to provide a temporary matrix on which host cells can adhere, proliferate and differentiate. Herein, 3D cylindrical scaffolds were designed to mimic the natural architecture of hollow bones, and to allow nutrient exchange and bone neovascularization. 3D scaffolds were produced with tricalcium phosphate (TCP)/alginic acid (AA) using a Fab@home 3D printer. Furthermore, graphene oxide (GO) was incorporated into the structure of some scaffolds to further enhance their mechanical properties. The results revealed that the scaffolds incorporating GO displayed greater porosity, without impairing their mechanical properties. These scaffolds also presented a controlled swelling profile, enhanced biomineralization capacity and were able to increase the Alkaline Phosphatase (ALP) activity. Such characteristics make TCP/AA scaffolds functionalized with GO promising 3D constructs for bone tissue engineering applications.

In Vitro Effects of Biomaterials on Mesenchymal Stem Cells Viability and Proliferation

Mesenchymal stem cells (MSCs) are increasingly being used in regenerative medicine to repair various tissue types. This study aimed to assess changes in MSCs properties as a result of their interaction with two biomaterials in order to evaluate their in vitro compatibility. We have used two types of biomaterials, as follows: hydroxyapatite anodized titanium (HA-Ti) is used in bone reconstruction; it is hard and remains in the body, while patches of collagen combined with poly-e-caprolactone (C-PCL) are utilized in the reconstruction of soft tissue (particularly the skin); these patches resorb in the body, being only a temporary matrix that fosters and accelerates tissue formation. We have chosen to assess changes in morphology, viability and proliferation of MSCs obtained by lipoaspirate, through direct contact with the biomaterial or in eluate. MSCs properties were assessed by optical microscopy, fluorescence microscopy after acridine orange/ethidium bromide (AO/EB) staining, and the MTT assay. After result interpretation, we gained an image of the cytotoxicity phenomenon seen during the experiment and were able to assess viability of cell in contact with the biomaterials used. HA-Ti shows better interaction with cells, which preserve their viability, and does not influence MSCs growth, proliferation or morphology. In contrast, cells on C-PCL matrix become small, spherical, were detached from the plate and had lower viability percentage.

Extracellular matrix remodeling and matrix metalloproteinases (ajMMP-2 like and ajMMP-16 like) characterization during intestine regeneration of sea cucumber Apostichopus japonicus.

Remodeling of extracellular matrix (ECM) regulated by matrix metalloproteinases (MMPs) is essential for tissue regeneration. In the present study, we used immunohistochemistry (IHC) techniques against ECM components to reveal changes of ECM during intestine regeneration of Apostichopus japonicus. The expression of collagen I and laminin reduced apparently from the eviscerated intestine, while fibronectin exhibited continuous expression in all regeneration stages observed. Meanwhile, we cloned two MMP genes from A. japonicus by RACE PCR. The full-length cDNA of ajMMP-2 like is 2733bp and contains a predicted open reading frame (ORF) of 1716bp encoding 572 amino acids. The full-length cDNA of ajMMP-16 like is 2705bp and contains an ORF of 1452bp encoding 484 amino acids. The predicted protein sequences of each MMP contain two conserved domains, ZnMc_MMP and HX. Homology and phylogenetic analysis revealed that ajMMP-2 like and ajMMP-16 like share high sequence similarity with MMP-2 and MMP-16 from Strongylocentrotus purpuratus, respectively. Then we investigated spatio-temporal expression of ajMMP-2 like and ajMMP-16 like during different regeneration stages by qRT-PCR and IHC. The expression pattern of them showed a roughly opposite trend from that of ECM components. According to our results, a fibronectin-dominate temporary matrix is created in intestine regeneration, and it might provide structural integrity for matrix and promote cell movement. We also hypothesize that ajMMP-2 like and ajMMP-16 like could accelerate cell migration and regulate interaction between ECM components and growth factors. This work provides new evidence of ECM and MMPs involvement in sea cucumber regeneration.

Comparative analysis of poly-glycolic acid-based hybrid polymer starter matrices for in vitro tissue engineering

Biodegradable scaffold matrixes form the basis of any in vitro tissue engineering approach by acting as a temporary matrix for cell proliferation and extracellular matrix deposition until the scaffold is replaced by neo-tissue. In this context several synthetic polymers have been investigated, however a concise systematic comparative analyses is missing. Therefore, the present study systematically compares three frequently used polymers for the in vitro engineering of extracellular matrix based on poly-glycolic acid (PGA) under static as well as dynamic conditions. Ultra-structural analysis was used to examine the polymers structure. For tissue engineering (TE) three human fibroblast cell lines were seeded on either PGA-poly-4-hydroxybutyrate (P4HB), PGA-poly-lactic acid (PLA) or PGA-poly–caprolactone (PCL) patches. These patches were analyzed after 21days of culture qualitative by histology and quantitative by determining the amount of DNA, glycosaminoglycan and hydroxyproline. We found that PGA-P4HB and PGA-PLA scaffolds enhance tissue formation significantly higher than PGA-PCL scaffolds (p<0.05). Polymer remnants were visualized by polarization microscopy. In addition, biomechanical properties of the tissue engineered patches were determined in comparison to native tissue. This study may allow future studies to specifically select certain polymer starter matrices aiming at specific tissue properties of the bioengineered constructs in vitro.

Ventral midline formation in the chick embryo is assisted by a temporary local extracellular matrix structure

Ventral midline formation in the chick embryo is assisted by a temporary local extracellular matrix structure

Endothelial fibrinolytic response onto an evolving matrix of fibrin.

BackgroundFibrin provides a temporary matrix at the site of vascular injury. The aims of the present work were (1) to follow fibrin formation and lysis onto the surface of human dermal microvascular endothelial cells (HMEC-1), and (2) to quantify the secretion of fibrinolytic components in the presence of fibrin.MethodsFibrin clots at different fibrinogen concentrations were formed on top of (model 1) or beneath (model 2) the endothelial cells. Fibrin formation or lysis onto the surface of HMEC-1 cells, was followed by turbidity. Clot structure was visualized by laser scanning confocal microscopy (LSCM). The secretion of uPA and PAI-1 by HMEC-1 cells was quantified by ELISA.ResultsThe rate of fibrin formation increased approximately 1.5-fold at low fibrinogen content (0.5 and 1 mg/mL; p < 0.05) compared to the condition without cells; however, it was decreased at 2 mg/mL fibrinogen (p < 0.05) and no differences were found at higher fibrinogen concentrations (3 and 5 mg/mL). HMEC-1 retarded dissolution of clots formed onto their surface at 0.5 to 3 mg/mL fibrinogen (p < 0.05). Secretion of uPA was 13 × 10−6 ng/mL per cell in the absence of RGD and 8 × 10−6 ng/mL per cell in the presence of RGD, when clots were formed on the top of HMEC-1. However, the opposite was found when cells were grown over fibrin: 6 × 10−6 ng/mL per cell without RGD vs. 17 × 10−6 ng/mL per cell with RGD. The secretion of PAI-1 by HMEC-1 cells was unrelated to the presence of fibrin or RGD, 7 × 10−6 μg/mL per cell and 5 × 10−6 μg/mL per cell, for the apical (model 1) and basal clots (model 2), respectively.ConclusionsHMEC-1 cells influence fibrin formation and dissolution as a function of the fibrin content of clots. Clot degradation was accentuated at high fibrin concentrations. The secretion of fibrinolytic components by HMEC-1 cells seemed to be modulated by integrins that bind RGD ligands.