Heparin-binding domain of fibrin(ogen) binds growth factors and promotes tissue repair when incorporated within a synthetic matrix

By binding growth factors (GFs), the ECM tightly regulates their activity. We recently reported that the heparin-binding domain II of fibronectin acts as a promiscuous high-affinity GF-binding domain. Here we hypothesized that fibrin, the provisional ECM during tissue repair, also could be highly promiscuous in its GF-binding capacity. Using multiple affinity-based assays, we found that fibrin(ogen) and its heparin-binding domain bind several GFs from the PDGF/VEGF and FGF families and some GFs from the TGF-β and neurotrophin families. Overall, we identified 15 unique binding interactions. The GF binding ability of fibrinogen caused prolonged retention of many of the identified GFs within fibrin. Thus, based on the promiscuous and high-affinity interactions in fibrin, GF binding may be one of fibrin's main physiological functions, and these interactions may potentially play an important and ubiquitous role during tissue repair. To prove this role in a gain-of-function model, we incorporated the heparin-binding domain of fibrin into a synthetic fibrin-mimetic matrix. In vivo, the multifunctional synthetic matrix could fully mimic the effect of fibrin in a diabetic mouse model of impaired wound healing, demonstrating the benefits of generating a hybrid biomaterial consisting of a synthetic polymeric scaffold and recombinant bioactive ECM domains. The reproduction of GF-ECM interactions with a fibrin-mimetic matrix could be clinically useful, and has the significant benefit of a more straightforward regulatory path associated with chemical synthesis rather than human sourcing

Controlled release nanoparticle-embedded coatings reduce the tissue reaction to neuroprostheses

Controlled release coatings were developed for neuroprostheses with the aim of combating the tissue reaction following implantation in the brain. The coatings consist of poly(propylene sulfide) drug-eluting nanoparticles embedded in a poly(ethylene oxide) matrix. The nanoparticles are loaded with dexamethasone, an anti-inflammatory drug known to have an effect on the cells activated during the damage caused by implantation. The nanoparticles are not affected by the coating process and the drug remains bioactive after it is released. The coating was applied to microfabricated cortical neuroprostheses consisting of platinum and polyimide. Coated drug-eluting devices were implanted in the cortex of rats. After implantation the matrix dissolves, exposing the electrode surfaces, while the nanoparticles remain in the vicinity of the tissue–implant interface. Using electrical impedance spectroscopy and comparative histology, a long-term decrease in the tissue response in comparison to control devices was observed. These coatings can therefore be used to increase the reliability and long-term efficacy of neuroprostheses

Superparamagnetic Nanoparticles as a Powerful Systems Biology. Characterization Tool in the Physiological Context

Recently, functionalized superparamagnetic iron oxide nanoparticles (SPIONs) have been utilized for protein separation and therapeutic delivery of DNA and drugs. The development of new methods and tools for the targeting and identification of specific biomolecular interactions within living systems is of great interest in the fields of systems biology, target and drug identification, drug delivery, and diagnostics. Magnetic separation of organelles and proteins from complex whole-cell lysates allows enrichment and elucidation of intracellular interaction partners for a specific immobilized protein or peptide on the surface of SPIONs

Bedform migration in a mixed sand and cohesive clay intertidal environment and implications for bed material transport predictions

Many coastal and estuarine environments are dominated by mixtures of non-cohesive sand and cohesive mud. The migration rate of bedforms, such as ripples and dunes, in these environments is important in determining bed material transport rates to inform and assess numerical models of sediment transport and geomorphology. However, these models tend to ignore parameters describing the physical and biological cohesion (resulting from clay and extracellular polymeric substances, EPS) in natural mixed sediment, largely because of a scarcity of relevant laboratory and field data. To address this gap in knowledge, data were collected on intertidal flats over a spring-neap cycle to determine the bed material transport rates of bedforms in biologically-active mixed sand-mud. Bed cohesive composition changed from below 2 vol% up to 5.4 vol% cohesive clay, as the tide progressed from spring towards neap. The amount of EPS in the bed sediment was found to vary linearly with the clay content. Using multiple linear regression, the transport rate was found to depend on the Shields stress parameter and the bed cohesive clay content. The transport rates decreased with increasing cohesive clay and EPS content, when these contents were below 2.8 vol% and 0.05 wt%, respectively. Above these limits, bedform migration and bed material transport was not detectable by the instruments in the study area. These limits are consistent with recently conducted sand-clay and sand-EPS laboratory experiments on bedform development. This work has important implications for the circumstances under which existing sand-only bedform migration transport formulae may be applied in a mixed sand-clay environment, particularly as 2.8 vol% cohesive clay is well within the commonly adopted definition of “clean sand”

VISUALIZATION AND ANALYSIS OF MURAL THROMBOGENESIS (PLATELET ADHESION, COLLAGEN, POLYURETHANE, DIGITAL IMAGE PROCESSING)

Epi-fluorescence video microscopy, digital image processing, and photodiode photometry were used to visualize and analyze mural thrombogenesis on collagen coated glass, polyurethane, and nylon surfaces in contact with flowing whole blood. A parallel plate flow chamber was used as the test system, and wall shear rates of 100, 500, and 1500 sec('-1) were considered. The technique permitted real-time visualization, high resolution, quantitative, off-line measurement of the growth of individual thrombi and high resolution, quantitative, end-point measurement of the accumulation of platelets as a function of position on the surface. Thrombi grew rapidly on the collagen coated surface. These thrombi exhibited little embolization over the two minute exposure times considered. Thrombi rapidly grew and subsequently embolized from the polyurethane surface. These emboli were large for low wall shear rates and very small for high wall shear rates. Small thrombi grew on the nylon coated surface and subsequently embolized. Significant leukocyte adhesion to the nylon surface was seen after a brief stagnation period. Concentration profiles were calculated for adenosine diphosphate, thromboxane A(,2), and thrombin in the neighborhood of a single growing thrombus to evaluate the possible role of the generation and release of these substances in the mechanism of thrombus growth. Thrombin was seen to be of profound importance, even in the presence of heparin and antithrombin III. Thromboxane A(,2) was seen to be of some importance, with a lesser role for adenosine diphosphate. Concentration profiles of these same species were calculated near a large surface in contact with flowing blood. Thrombin was again seen to be of profound importance, even in the presence of heparin and antithrombin III. Thromboxane A(,2) and adenosine diphosphate were also seen to be of importance, albeit not so profound as thrombin

Enhanced proteolytic degradation of molecularly engineered PEG hydrogels in response to MMP-1 and MMP-2

Bioactive hydrogels formed by Michael-type addition reactions of end-functionalized poly(ethylene glycol) macromers with cysteine-containing peptides have been described as extracellular matrix mimetics and tissue engineering scaffolds. Although these materials have shown favorable behavior in vivo in tissue repair, we sought to develop materials formulations that would be more rapidly responsive to cell-induced enzymatic remodeling. In this study, protease-sensitive peptides that have increased k(cat) values were characterized and evaluated for their effects on gel degradability. Biochemical properties for soluble peptides and hydrogels were examined for matrix metalloproteinase (MMP)-1 and MMP-2. The most efficient peptide substrates in some cases overlap and in other cases differ between the two enzymes tested, and a range of k(cat) values was obtained. For each enzyme, hydrogels formed using the peptides with higher k(cat) values degraded faster than a reference with lower k(cat). Fibroblasts showed increased cell spreading and proliferation when cultured in 3D hydrogels with faster degrading peptides, and more cell invasion from aortic ring segments embedded in the hydrogels was observed. These faster degrading gels should provide matrices that are easier for cells to remodel and lead to increased cellular infiltration and potentially more robust healing in vivo

Biomimetic materials in tissue engineering

Biomaterial matrices are being developed that mimic the key characteristics of the extracellular matrix, including presenting adhesion sites and displaying growth factors in the context of a viscoelastic hydrogel. This review focuses on two classes of materials: those that are derived from naturally occurring molecules and those that recapitulate key motifs of biomolecules within biologically active synthetic materials. For biologically derived materials, methods are being sought to gain molecular-level control over biological characteristics and biomechanics. For synthetic, biomimetic materials, chemical schemes are being developed to enable in situ cross-linking and protease-dependent degradation and release of incorporated growth factors. These materials will open new doors to biosurgical therapeutics in tissue engineering and regenerative medicine

Two-dimensional polymeric structures and method for producing thereof

The present invention relates to polymeric structures, in the form of flat membrane-like surfaces or micro- nanostructures such as capsules, characterized in that it comprises a substantially two-dimensional layer of covalently-bonded monomers of R-substituted metal or metalloid oxides. Said polymeric structures in most embodiments have a crystal architecture with a hexagonal lattice, but the nature of the covalent bonds present therein impart a bending flexibility that make the polymeric structures behave as a "soft" crystal. Methods of producing such structures, composition comprising thereof and method of using thereof are also included within the present disclosure

Antigen delivery to dendritic cells by poly(propylene sulfide) nanoparticles with disulfide conjugated peptides: Cross-presentation and T cell activation

Vaccines aiming to activate cytotoxic T cells require cross-presentation of exogenous antigen by antigen-presenting cells (APCs). We recently developed a synthetic nanoparticle vaccine platform that targets lymph node-resident dendritic cells (DCs), capable of mounting an immune response to conjugated antigen. Here, we explore routes of processing and the efficiency of MHC I cross-presentation of OVA peptides conjugated using both reducible and non-reducible linkages, exploring the hypothesis that reduction-sensitive conjugation will lead to better antigen cross-presentation. Both clathrin and macropinocytic pathways were implicated in nanoparticle uptake by colocalization and inhibitor studies. Cross-presentation by DCs was demonstrated by direct antibody staining and in vitro stimulation of CD8(+) T cells from OT-I mice and was indeed most efficient with the reduction-sensitive conjugation. Similarly, we observed IFN-γ production by CD4(+) T cells from OT-II mice. Finally, immunization with the OVA peptide-bearing nanoparticles resulted in in vivo proliferation and IFN-γ production by adoptively transferred CD8(+) OT-I T cells and was also most efficient with reduction-sensitive linking of the peptide antigen. These results demonstrate the relevance of the poly(propylene sulfide) nanoparticle vaccine platform and antigen conjugation scheme for activating both cytotoxic and helper T cell responses