Silk Mesh Research Articles

Fabrication of bioactive silk composite meshes for hernia repair and guided soft tissue remodeling: In silico, in vitro and in vivo models

ObjectivesPost-operative complications stemming from incompatible meshes often lead to delayed wound healing, seroma, infections, inappropriate tissue infiltration and pain. The present study was outlined to develop biocompatible composite hand-knitted silk meshes modified with polymers and natural extracts. Our study introduced hand-knitted B. mori silk fibroin as the primary mesh material, offering superior mechanical strength and biocompatibility. The spin-assisted dip coating achieved desirable morphology, internal structures, thickness, and surface roughness. Moreover, the application of biopolymeric composite coatings containing polymers and natural extracts introduced antimicrobial character, facilitated cell attachment, migration, proliferation, potentiating gene expression and accelerating the process of wound healing. These composite meshes are a viable solution for addressing post-op complications in hernia and soft tissue repair surgeries. MethodIn this study, 9 silk-based composite meshes (modified with polymeric-extract blends through spin-assisted dip coating) were successfully developed. Experimental variants were then subjected to various characterizations including SEM, DMA and chemical analysis (FTIR and GC-MS). Modified meshes were evaluated for their physiological characteristics and biological responses (the basic criterion for the selection of composite silk mesh). The biological testing included (antimicrobial susceptibility testing, in vitro cell viability assay, cell attachment assay (NIH3T3 and hUc-MSCs), in vitro cell migration, in vitro gene expression analysis with NIH3T3, in silico molecular docking with bioactive ligands of HE extract and in vivo analysis with PHBV-HE and PHBV-Control composite meshes in rat models. ResultsResults showed that all variants exhibited a multi-fiber morphology with significant surface coating, allowing for optimal drug release up to 72 h. This release facilitated antibacterial properties and biocompatibility, as evidenced by in vitro cell viability, migration assays and gene expression analysis. Among the variants, the PHBV-HE composite mesh demonstrated superior results. In the case of PHBV-coated polymeric controls, the SEM analysis concluded that the presence of coating reduced the pore size up to 39.62 % whereas, fiber diameter was increased by up to 19.89 % as compared to the control. The presence of a coating on the mesh improved the mechanical strength/modulus by 165.89 %, UTS by 185.38 % and reduced the % strain by 64.67 %. The fast release of HE from PHBV-HE composite mesh was 90.7% up to 72h, confirming that it can induce antibacterial activity against surgical infections. ConclusionPHBV-HE showed the highest cell viability, wound healing and gene expression. Based on appreciable biological evaluation results shown by PHBV-HE, in rat hernia models, only the PHBV-HE variant was tested for in-vivo analysis. Results confirmed its non-toxic nature and wound-healing abilities. Enhanced cell proliferation and wound healing observed both in vitro and in vivo indicated that PHBV-HE holds promise as a biomedical implant suggesting its potential for effective hernia and soft tissue repair and regeneration.

Fabrication of green composite hand knitted silk mesh reinforced with silk hydrogel

Soft tissue defects like hernia and post-surgical fistula formation can be resolved with modern biomaterials in the form of meshes without post-operative complications. In the present study hand knitted silk meshes were surface coated with regenerated silk fibroin hydrogel and pure natural extracts. Two phytochemicals (Licorice extract (LE) and Bearberry extract (BE)) and the two honeybee products (royal jelly (RJ) and honey (HE)) were incorporated separately to induce antibacterial, anti-inflammatory, and wound healing ability to the silk hydrogel coated knitted silk meshes. Meshes were dip coated with a blend of 4 % silk hydrogel (w/v) and 5 % extracts. Dried modified meshes were characterized using SEM, DMA, GC–MS and FTIR. Antimicrobial testing, in-vitro cytotoxicity, in-vitro wound healing and Q-RT-PCR were also performed.SEM analysis concluded that presence of coating reduced the pore size up to 47.7 % whereas, fiber diameter was increased up to 17.9 % as compared to the control. The presence of coating on the mesh improved the mechanical strength/Young's modulus by 1602.8 %, UTS by 451.7 % and reduced the % strain by 51.12 %. Sustained release of extracts from MHRJ (62.9 % up to 72 h) confirmed that it can induce antibacterial activity against surgical infections. Cytocompatibility testing and gene expression results suggest that out of four variables MHRJ presented best cell viability, % wound closure and expression of wound healing marker genes. In-vivo analyses in rat hernia model were carried out using only MHRJ variant, which also confirmed the non- toxic nature and wound healing characteristics of the modified mesh. The improved cell proliferation and activated wound healing in vitro and in vivo suggested that MHRJ could be a valuable candidate to promote cell infiltration and activate soft tissue and hernia repair as a biomedical implant.

Pupal warning color development in above‐ground pupating species but cryptic color in ground‐surface pupating species of the nine‐spotted diurnal moths (Erebidae: Arctiinae: Syntomini)

AbstractInsects usually have cryptic colors to avoid detection by visually hunting predators. However, if the insects acquire toxic or repellent substances against predators, some of them develop conspicuous coloration to exhibit their unpalatability. Such warning colors allow insects to survive. In the nine‐spotted diurnal moths (Erebidae: Arctiinae: Syntomini), we found the above‐ground pupating species to have conspicuous colored pupae, but the ground‐surface pupating species to have cryptic colored pupae. In this study, the relationships between unpalatability and coloration of these pupae are examined among three species of Amata and one species of Syntomoides. Pupae of the two species (A. germana and A. flava) are conspicuous in their color pattern with seven black dotted lines longitudinally on their pale‐yellow bodies. These pupae are exposed to the aerial predators in a coarse silk mesh hanging from leaves and/or branches. The other two species (A. fortunei and S. imaon) pupate in spaces under stones, fallen twigs and leaves on the ground surface, and the pupae in a coarse silk cocoon is cryptic dark brown. Their pupation site selections are reproduced in the rearing glass vessels. Palatability assessment using lizards as a potential predator suggests that pupae of A. germana, A. flava and A. fortunei are unpalatable and the lizard's feeding response decreases with experience. However, pupae of S. imaon are all eaten (palatable). Finally, the possible evolutionary scenario of pupal colors of these four species is discussed in relation to pupation site selection and palatability.

Sustainable Approach toward the Development of Next-Generation Gas Sensors

The increase in the usage of non-biodegradable substrates and the generation of toxic wastes from laboratories has led to a sharp increase in the pollution caused by the electronics industry. In this study, we report on a novel approach to tackle this by successfully fabricating a completely biodegradable and eco-friendly chemiresistive gas sensor. The substrate was made of bioplastic and was coated with a silk mesh. This substrate was thoroughly studied for its flexibility, tensile strength, biodegradability, and thermal stability. It was found that the bioplastic/silk substrate exhibited superior results as compared to the bioplastic substrate without silk. Further, a green synthesized CuO/ZnO heterostructure from clove extract was utilized as a receptor layer. It was observed that the device fabricated on a bioplastic/silk substrate outperforms the device with bioplastic substrates at room temperature, as well as at elevated temperature (i.e., 50 °C). The device exhibited an ideal piezotronics behavior demonstrating that the chemiresistive gas sensor with green synthesized CuO/ZnO heterostructures on a bioplastic/silk substrate can be very well used over curvilinear surfaces. Therefore, the sustainable approach toward the development of biodegradable and eco-friendly toxic gas sensors taken in this study can be an alternative to the current high-temperature sensors.

Reconstruction of Rabbit Anterior Cruciate Ligament by Bone Marrow-Derived Mesenchymal Stem Cell Implantation Through a Weft-Knitted Silk Mesh Scaffold Covering a Whip-Shaped Core

To investigate the feasibility of using whip core wrapped by silk weft knitted mesh sheath as a scaffold and bone marrow-derived mesenchymal stem cells (BMSCs) to reconstruct the rabbit anterior cruciate ligament (ACL), BMSC implantation using the mesh-whip scaffold was performed to construct a BMSC-scaffold complex. Then, the BMSC-scaffold complex was implanted into an animal model of an ACL deficient rabbit. Regenerated ACLs were then taken from the animal model three and six months after implantation, followed by hematoxylin-eosin and Masson staining, quantitative RT-PCR detection, as well as mechanical performance evaluation. The results showed that many Sharpey’s fibers had arranged regularly between the neo-ACL and the bone three months after surgery, and an interface structure formed six months after surgery. Regenerated ligaments contained silk fibers and suficient collagen. Type I collagen, type III collagen, and tenascin-C were all highly expressed in the experimental group compared to the control group (no BMSC implantation) in the regenerated ligaments. In addition, the maximum pullout force values of neo-ACL in the three- and six-month experimental groups were 70.6±17.8 N and 122.8±25.7 N, respectively. The findings suggest that BMSC implantation using the mesh-whip scaffold is a promising method to reconstruct rabbit ACL.

Air Temperature and Humidity at the Bottom of Desert Wolf Spider Burrows Are Not Affected by Surface Conditions.

Simple SummaryWe investigated whether trapdoors, which small Negev Desert wolf spiders (Lycosa sp.) use to close their burrows, serve to maintain favorable conditions of temperature and humidity within them. We removed trapdoors from burrow entrances and monitored changes in temperature and relative humidity in their bottoms, where the spiders reside during the day. We also followed the behavioral responses of these spiders to trapdoor removal at different times of the day and in different seasons and monitored temperature and relative humidity in artificial burrows during summer mornings and at midday. At noon, air temperature at the bottom of open artificial burrows increased by less than 1 °C more than in covered ones, and total humidity remained constant, even though air temperature at the soil surface reached 55 °C when the burrow temperature was 35 °C. The relatively small increase in air temperature in uncovered burrows at midday was probably due to the penetration of direct solar radiation. Thus, it is evident that the presence of a trapdoor has a negligible effect on the microclimate at the bottom of these spiders’ burrows and its roles are more likely predator avoidance and prevention of flooding and stones and sand from falling in.Burrows are animal-built structures that can buffer their occupants against the vagaries of the weather and provide protection from predators. We investigated whether the trapdoors of wolf spider (Lycosa sp.; temporary working name "L. hyraculus") burrows in the Negev Desert serve to maintain favorable environmental conditions within the burrow by removing trapdoors and monitoring the ensuing temperature and relative humidity regime within them. We also monitored the behavioral responses of “L. hyraculus” to trapdoor removal at different times of the day and in different seasons. “L. hyraculus” often spun silk mesh in their burrow entrances in response to trapdoor removal during the day, possibly to deter diurnal predators. The frequency of web-spinning peaked on summer mornings, but spiders began spinning webs sooner after trapdoor removal later in the day. In addition, we monitored temperature and relative humidity in artificial burrows in the summer during the morning and at midday. At noon, air temperature (Ta) at the bottom of open burrows increased by <1 °C more than in covered burrows, but water vapor pressure in burrows did not change. The relatively small increase in Ta in uncovered burrows at midday can probably be ascribed to the penetration of direct solar radiation. Thus, air temperature and humidity at the bottom of the burrow are apparently decoupled from airflow at the surface.

Histologic evaluation of therapeutic responses in ischemic myocardium elicited by dual growth factor delivery from composite glycosaminoglycan hydrogels

In this project, the ability of dual growth factor-preloaded, silk-reinforced, composite hyaluronic acid-based hydrogels to elicit advantageous histologic responses when secured to ischemic myocardium was evaluated in vivo. Reinforced hydrogels containing both Vascular Endothelial Growth Factor (VEGF) and Platelet-derived Growth Factor (PDGF) were prepared by crosslinking chemically modified hyaluronic acid and heparin with poly(ethylene glycol)-diacrylate around a reinforcing silk mesh. Composite patches were sutured to the ventricular surface of ischemic myocardium in Sprague-Dawley rats, and the resulting angiogenic response was followed for 28 days. The gross appearance of treated hearts showed significantly reduced ischemic area and fibrous deposition compared to untreated control hearts. Histologic evaluation showed growth factor delivery to restore myofiber orientation to pre-surgical levels and to significantly increase elicited microvessel density and maturity by day 28 in infarcted myocardial tissue (p < 0.05). In addition, growth factor delivery reduced cell apoptosis and decreased the density of elicited mast cells and both CD68+ and anti-inflammatory CD163+ macrophages. These findings suggest that HA-based, dual growth factor-loaded hydrogels can successfully induce a series of beneficial responses in ischemic myocardium, and offer the potential for therapeutic improvement of ischemic myocardial remodeling.

523 Silkworm Silk as an Alternative to Two Common Epidermal Substitutes for the Treatment of Acute Superficial Burns

Abstract Introduction During the treatment of superficial burn injuries patients are often confronted with painful dressing changes. Therefore we usually treat these wounds with materials that can stay on the wound and slowly peel off during re-epithelialization. Since 2013 we started using pure silk as cost efficient alternative for the treatment of these wounds. Therefore we wanted to compare it directly with the other dressings. Methods In a prospective intra-individual design we evaluated the wound healing of 50 patients with superficial burn injuries. Hereof 30 patients received both silk and Nylon mesh with collagen and 20 further patients received silk and a synthetic epidermal substitute for the treatment of their burn injuries. Following a standardized case report form, we monitored pain, active bleeding, exudation, dressing change and inflammation. Furthermore we evaluated scar quality objectively with the Cutometer, Mexameter and Tewameter as well as subjectively with the patient and observer scar scale (POSAS) and the Vancouver scar scale (VSS). Results During wound healing no significant differences could be found regarding wound closure, inflammation and acute bleeding. Pain levels fell fast during after dressing application and during wound healing. Long-term results in functional and aesthetic outcome were similar. High satisfaction rates were reported for all dressings, with different individual preferences. Conclusions All three dressings provided a safe and effective healing environment, with low complication rates in regard to infection and exudation. Additionally, no significant differences regarding scarring could be found with an overall pleasing aesthetic outcome. Applicability of Research to Practice Silkworm silk is now the standard of care in our clinic for superficial burns.

Single-cell mass cytometry reveals in vivo immunological response to surgical biomaterials

Adverse events related to surgical mesh implants such as mesh erosion and adhesion are inflammation-related and frequently reported in clinical use; thus, advanced real-time monitoring methods are required to evaluate the interactions between implants and host immune system in order to prevent any unfavorable events. Here, we performed single cell mass cytometry of the blood, characterizing two biomaterial-induced (silk and polypropylene) immune responses in a rodent ventral hernia model to systematically decipher the interactions between the host and implants. Compared to polypropylene, silk mesh induced less immune cell activation with lower proportions of macrophages, monocytes, and neutrophils in the innate system and lower proportions of CD4+ T cells and CD8+ T cells in the adaptive system at 3-week post-implantation. Functional markers (CD115, CD27, and CD62L) involved in the immune cell activation and migration were also downregulated in the silk group. Histological analysis of tissues confirmed that silk mesh implantation led to decreased neutrophils and macrophages recruitment, less fibrosis formation, and better tissue healing, suggesting silk mesh as a superior implant material. Importantly, in patients with abdominal hernia, the ratio of monocytes in blood in the silk group was also significantly lower when compared to the polypropylene group. Our study provides a systematical profile of the material-based foreign body response at single cell resolution, highlighting the impact of biomaterial implants on whole body immune system and introducing an innovative approach to monitor material-based immune response.

Histologic Evaluation of Therapeutic Responses in Ischemic Myocardium Elicited by Dual Growth Factor Delivery from Composite Glycosaminoglycan Hydrogels

In this project, the ability of dual growth factor-preloaded, silk-reinforced, composite hyaluronic acid-based hydrogels to elicit advantageous therapeutic responses when secured to ischemic myocardium was evaluated in vivo. Reinforced hydrogels containing both Vascular Endothelial Growth Factor (VEGF) and Platelet-derived Growth Factor (PDGF) were prepared by crosslinking chemically modified hyaluronic acid and heparin with poly(ethylene glycol)-diacrylate around a reinforcing silk mesh. Composite patches were sutured to the ventricular surface of ischemic myocardium in Sprague-Dawley rats, and the resulting angiogenic response was followed for 28 days. The gross appearance of treated hearts showed significantly reduced ischemic area and fibrous deposition compared to untreated control hearts. Histologic evaluation showed growth factor delivery to restore myofiber orientation to pre-surgical levels and to significantly increase elicited microvessel density and maturity by day 28 in ischemic myocardial tissue (p < 0.05). In addition, growth factor delivery reduced cell apoptosis, decreased the density of elicited mast cells and pro-inflammatory M1 macrophages and increased the density of elicited anti-inflammatory M2 macrophages. These findings suggest that HA-based, dual growth factor-loaded hydrogels can successfully induce a series of beneficial responses in ischemic myocardium, and offer the potential for therapeutic improvement of ischemic myocardial remodeling.

Photoluminescent properties of spider silk coated with Eu-doped nanoceria

Spider dragline silk was coated with pure as well as Eu-doped ceria nanopowders at the room temperature. The treatment was done by immersion of the spider silk mesh into aqueous solutions of cerium nitrate (Ce(NO3)3) and ammonium hydroxide (NH4OH). Depending on the relationship between Ce3+ ion and ammonium hydroxide concentration, coated fibers exhibited a different thickness. Obtained materials were studied by means of FESEM. It was found that ceria nanoparticles of average size of 3 nm were coated along spider thread. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) confirmed crystal nature of nanoparticle coating of spider silk. By using Williamson-Hall plots, crystallite size and strain were estimated. EDS measurement confirmed the presence of Eu in spider-Eu-doped ceria composite, and according to FTIR analysis, the interaction between CeO2 and spider silk was proposed. The morphology of obtained composite was observed by TEM. The photoluminescence emission spectra of spider silk coated with Eu-doped ceria were measured with two different excitations of 385 and 466 nm. The two-photon excited auto-fluorescence of spider silk coated with Eu-doped ceria was detected using a nonlinear laser scanning microscope. Obtained composite has a potential as a fluorescent labeling material in diverse applications.

Resilience of aquatic net‐spinning caddisfly silk structures to common global stressors

SummaryTwo of the most common consequences resulting from land use and climate change are increased fine sediment loads and shifts in hydrological regimes in freshwater ecosystems.Although a growing number of studies indicate that these stressors are likely to directly affect community composition and organism physiology, little is known about how biological structures produced by aquatic organisms might respond. For example, hydropsychid caddisflies (Trichoptera) are a group of globally distributed aquatic insects that spin silk mesh nets that they use to filter feed. These silk mesh nets are important ecosystem engineering structures in flowing waters that can regulate sediment erosion, food particle delivery by altering near‐bed current velocities, and enhance habitat availability for other macroinvertebrates.We conducted two experiments in laboratory mesocosms to assess the effects of increased fine sediment and drought on hydropsychid caddisfly silk. We compared silk thread diameter, thread count, mesh pore area, and thread tensile strength across treatments in which the silk nets were exposed to high levels of total suspended solids or to stream drying over 2 weeks.We found that caddisfly silk was resilient to both forms of stress and maintained its overall structure and tensile strength.Our findings indicate that biological silk structures may be viable ecosystem engineering tools following short‐lived disturbances associated with increased sediment loads and drying events. Caddisfly silk may be resilient to various forms of environmental change, with important consequences for recovery of aquatic communities.

Fabrication of silk mesh with enhanced cytocompatibility: preliminary in vitro investigation toward cell-based therapy for hernia repair.

Recent studies have demonstrated that combining cells with meshes prior to implantation successfully enhanced hernia repair. The idea is to create a biologic coating surrounding the mesh with autologous cells, before transplantation into the patient. However, due to the lack of a prompt and robust cell adhesion to the meshes, extensive in vitro cultivation is required to obtain a homogenous cell layer covering the mesh. In this context, the objective of this publication is to manufacture meshes made of silk fibres and to enhance the cytoadhesion and cytocompatibility of the biomaterial by surface immobilization of a pro-adhesive wheat germ agglutinin (lectin WGA). We first investigated the affinity between the glycoprotein WGA and cells, in solution and then after covalent immobilization of WGA on silk films. Then, we manufactured meshes made of silk fibres, tailored them with WGA grafting and finally evaluated the cytocompatibility and the inflammatory response of silk and silk-lectin meshes compared to common polypropylene mesh, using fibroblasts and peripheral blood mononuclear cells, respectively. The in vitro experiments revealed that the cytocompatibility of silk can be enhanced by surface immobilization with lectin WGA without exhibiting negative response in terms of pro-inflammatory reaction. Grafting lectin to silk meshes could bring advantages to facilitate cell-coating of meshes prior to implantation, which is an imperative prerequisite for abdominal wall tissue regeneration using cell-based therapy.

A novel method for the production and evaluation of hernia repair mesh in an in vitro environment

While most hernia mesh researchers use animal models or patient studies to evaluate prostheses, we have developed an in vitro-centric mesh production and examination system to characterize mesh properties that affect the cellular affinity and treatment potential of repair mesh. A loom was designed and constructed, and a feasibility study was conducted on auto-loom woven, degummed silk mesh seeded with murine-derived D1 multipotent mesenchymal stromal cells (MSCs). Meshes of two different pore sizes, 1 mm and 2 mm, were investigated. The seeded meshes were evaluated using a variety of assays to determine cellular metabolic activity, viability, and conformation at time points of 7, 14, and 21 days. The assays showed substantial cell attachment to the mesh at all time points, including penetration of cells into the interior of silk threads. Metabolic activity peaked at Day 14 for both mesh sizes, with a sharp rise in protein production from Day 7 to 14. Based upon the successful production of mesh and acquisition of results from the assays performed, it can be concluded that an in vitro evaluation system for hernia mesh is both possible and likely to produce scientifically relevant results.

Silk–hyaluronan-based composite hydrogels: A novel, securable vehicle for drug delivery

A new, biocompatible hyaluronic acid (HA)-silk hydrogel composite was fabricated and tested for use as a securable drug delivery vehicle. The composite consisted of a hydrogel formed by cross-linking thiol-modified HA with poly(ethylene glycol)-diacrylate, within which was embedded a reinforcing mat composed of electrospun silk fibroin protein. Both HA and silk are biocompatible, selectively degradable biomaterials with independently controllable material properties. Mechanical characterization showed the composite tensile strength as fabricated to be 4.43 ± 2.87 kPa, two orders of magnitude above estimated tensions found around potential target organs. In the presence of hyaluronidase (HAse) in vitro, the rate of gel degradation increased with enzyme concentration although the reinforcing silk mesh was not digested. Composite gels demonstrated the ability to store and sustainably deliver therapeutic agents. Time constants for in vitro release of selected representative antibacterial and anti-inflammatory drugs varied from 46.7 min for cortisone to 418 min for hydrocortisone. This biocomposite showed promising mechanical characteristics for direct fastening to tissue and organs, as well as controllable degradation properties suitable for storage and release of therapeutically relevant drugs.

Anterior cruciate ligament regeneration using mesenchymal stem cells and silk scaffold in large animal model

Although in vivo studies in small animal model show the ligament regeneration by implanting mesenchymal stem cells (MSCs) and silk scaffold, large animal studies are still needed to evaluate the silk scaffold before starting a clinical trial. The aim of this study is to regenerate anterior cruciate ligament (ACL) in pig model. The micro-porous silk mesh was fabricated by incorporating silk sponges into knitted silk mesh with lyophilization. Then the scaffold was prepared by rolling the micro-porous silk mesh around a braided silk cord to produce a tightly wound shaft. In vitro study indicated that MSCs proliferated profusely on scaffold and differentiated into fibroblast-like cells by expressing collagen I, collagen III and tenascin-C genes in mRNA level. Then the MSCs-seeded scaffold was implanted in pig model to regenerate ACL. At 24 weeks postoperatively, the MSCs in regenerated ligament exhibited fibroblast morphology. The key ligament-specific extracellular matrix components were produced prominently and indirect ligament–bone insertion with three zones (bone, Sharpey's fibers and ligament) was observed. Although there was remarkable scaffold degradation, the maximum tensile load of regenerated ligament could be maintained after 24 weeks of implantation. In conclusion, the results imply that silk-based material has great potentials for clinical applications.

Enzymatic Mechanism Controls Redox-mediated Protein-DNA Interactions at the Replication Origin of Kinetoplast DNA Minicircles

Kinetoplast DNA (kDNA) is the mitochondrial DNA of trypanosomatids. Its major components are several thousand topologically interlocked DNA minicircles. Their replication origins are recognized by universal minicircle sequence-binding protein (UMSBP), a CCHC-type zinc finger protein, which has been implicated with minicircle replication initiation and kDNA segregation. Interactions of UMSBP with origin sequences in vitro have been found to be affected by the protein's redox state. Reduction of UMSBP activates its binding to the origin, whereas UMSBP oxidation impairs this activity. The role of redox in the regulation of UMSBP in vivo was studied here in synchronized cell cultures, monitoring both UMSBP origin binding activity and its redox state, throughout the trypanosomatid cell cycle. These studies indicated that UMSBP activity is regulated in vivo through the cell cycle dependent control of the protein's redox state. The hypothesis that UMSBP's redox state is controlled by an enzymatic mechanism, which mediates its direct reduction and oxidation, was challenged in a multienzyme reaction, reconstituted with pure enzymes of the trypanosomal major redox-regulating pathway. Coupling in vitro of this reaction with a UMSBP origin-binding reaction revealed the regulation of UMSBP activity through the opposing effects of tryparedoxin and tryparedoxin peroxidase. In the course of this reaction, tryparedoxin peroxidase directly oxidizes UMSBP, revealing a novel regulatory mechanism for the activation of an origin-binding protein, based on enzyme-mediated reversible modulation of the protein's redox state. This mode of regulation may represent a regulatory mechanism, functioning as an enzyme-mediated, redox-based biological switch.

In vivo study of anterior cruciate ligament regeneration using mesenchymal stem cells and silk scaffold

Although most in vitro studies indicate that silk is a suitable biomaterial for ligament tissue engineering, in vivo studies of implanted silk scaffolds for ligament reconstruction are still lacking. The objective of this study is to investigate anterior cruciate ligament (ACL) regeneration using mesenchymal stem cells (MSCs) and silk scaffold. The scaffold was fabricated by incorporating microporous silk sponges into knitted silk mesh, which mimicked the structures of ligament extracellular matrix (ECM). In vitro culture demonstrated that MSCs on scaffolds proliferated vigorously and produced abundant collagen. The transcription levels of ligament-specific genes also increased with time. Then MSCs/scaffold was implanted to regenerate ACL in vivo. After 24 weeks, histology observation showed that MSCs were distributed throughout the regenerated ligament and exhibited fibroblast morphology. The key ligament ECM components including collagen I, collagen III, and tenascin-C were produced prominently. Furthermore, direct ligament–bone insertion with typical four zones (bone, mineralized fibrocartilage, fibrocartilage, ligament) was reconstructed, which resembled the native structure of ACL–bone insertion. The tensile strength of regenerated ligament also met the mechanical requirements. Moreover, its histological grading score was significantly higher than that of control. In conclusion, the results imply that silk scaffold has great potentials in future clinical applications.

Decadal basin-scale changes in diatoms, dinoflagellates, and phytoplankton color across the North Atlantic

The Continuous Plankton Recorder (CPR) survey has been used to characterize phytoplankton and zooplankton space-time dynamics in the North Sea since 1931 and in the North Atlantic since 1939. Phytoplankton biomass is assessed from these samples by visual assessment of the green color of the silk mesh, the Phytoplankton Color Index (PCI), and the total count of diatoms and dinoflagellates. Species with a frequency of occurrence greater than 1% in the samples are used as indicator species of the community. We investigated (1) long-term fluctuations of phytoplankton biomass, total diatoms, and total dinoflagellates; (2) geographical variation of patterns; (3) the relationship between phytoplankton and climate forcing in the North Atlantic CPR samples; (4) the relative contribution of diatoms and dinoflagellates to the PCI; and (5) the fluctuations of the dominant species over the period of survey to provide more information on the processes linking climate to changes in the phytoplankton community. As a result of the differences in microscopic analysis methods prior to 1958, our analyses were conducted for the period ranging from 1958 to 2002. The North Atlantic was divided into six regions identified through bathymetric criteria and separated along a North-South axis. Based on 12 monthly time series, we demonstrate increasing trends in PCI and total dinoflagellates and a decrease in total diatoms.

Air Permeability of Silk Mesh as a Function of the Structure and Pressure Difference

A dimensionless parameter characterizing the structure of linen-weave silk mesh was established. An empirical relation was defined for calculating the air permeability of linen-weave silk mesh; the error of the relation does not exceed 7%. The air permeability of the mesh decreases with an increase and increases with a decrease in the dimensionless parameter.