Aims:  The focus of this study was to evaluate the potential use of the predatory bacteria Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus to control the pathogens associated with human infection. Methods and Results:  By coculturing B. bacteriovorus 109J and M. aeruginosavorus ARL‐13 with selected pathogens, we have demonstrated that predatory bacteria are able to attack bacteria from the genus Acinetobacter, Aeromonas, Bordetella, Burkholderia, Citrobacter, Enterobacter, Escherichia, Klebsiella, Listonella, Morganella, Proteus, Pseudomonas, Salmonella, Serratia, Shigella, Vibrio and Yersinia. Predation was measured in single and multispecies microbial cultures as well as on monolayer and multilayer preformed biofilms. Additional experiments aimed at assessing the optimal predation characteristics of M. aeruginosavorus demonstrated that the predator is able to prey at temperatures of 25–37°C but is unable to prey under oxygen‐limiting conditions. In addition, an increase in M. aeruginosavorus ARL‐13 prey range was also observed. Conclusions:  Bdellovibrio bacteriovorus and M. aeruginosavorus have an ability to prey and reduce many of the multidrug‐resistant pathogens associated with human infection. Significance and Impact of the Study:  Infectious complications caused by micro‐organisms that have become resistant to drug therapy are an increasing problem in medicine, with more infections becoming difficult to treat using traditional antimicrobial agents. The work presented here highlights the potential use of predatory bacteria as a biological‐based agent for eradicating multidrug‐resistant bacteria, with the hope of paving the way for future studies in animal models.

Large-gap peripheral nerve injuries present a significant challenge for nerve regeneration due to lack of suitable grafts, insufficient cell penetration, and repair. Biomimetic nanofibrous scaffolds, functionalized on the surface with extracellular matrix proteins, can lead to novel therapies for repair and regeneration of damaged peripheral nerves. Here, nanofibrous scaffolds electrospun from blends of poly(caprolactone) (PCL) and chitosan were fabricated. Taking advantage of the amine groups on the chitosan, the surface of the scaffolds were functionalized with laminin by carbodiimide based crosslinking. Crosslinking allowed laminin to be attached to the surfaces of the PCL-chitosan nanofibers at relatively high concentrations that were not possible using conventional adsorption methods. The nanofibrous meshes were tested for wettability, mechanical properties and cell attachment and proliferation. Blending of chitosan with PCL provided more favorable surfaces for attachment of Schwann cells due to the reduction of the contact angle in comparison to neat PCL. Proliferation rates of Schwann cells grown on PCL-chitosan scaffolds with crosslinked laminin were significantly higher than the rates for PCL-chitosan nanofibrous matrices with adsorbed laminin. PCL-chitosan scaffolds with modified surfaces via crosslinking of laminin could potentially serves as versatile substrates with excellent mechanical and surface properties for in vivo cell delivery for nerve tissue engineering applications.

Receptor protein-tyrosine phosphatase RPTPσ has important functions in modulating neural development and regeneration. Compelling evidence suggests that both heparan sulfate (HS) and chondroitin sulfate (CS) glycosaminoglycans (GAGs) bind to a series of Lys residues located in the first Ig domain of RPTPσ. However, HS promotes and CS inhibits axonal growth. Mutation of these Lys residues abolished binding and signal transduction of RPTPσ to CS, whereas HS binding was reduced, and signaling persisted. This activity was mediated through novel heparin-binding sites identified in the juxtamembrane region. Although different functional outcomes of HS and CS have been previously attributed to the differential oligomeric state of RPTPσ upon GAG binding, we found that RPTPσ was clustered by both heparin and CS GAG rich in 4,6--disulfated disaccharide units. We propose an additional mechanism by which RPTPσ distinguishes between HS and CS through these novel binding sites.

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Inconsistencies in graft osteoconduction and osteoinduction present a clinical challenge in regeneration of large bone defects. Deposition of decellularized extracellular matrix (dECM) on tissue engineered scaffolds offers an alternative approach that can enhance these properties by mimicking bone's molecular complexity and direct infiltrating cells to repair damaged bone. However, dECMs derived from homogenous cell populations do not adequately simulate the heterogeneous and vascularized microenvironment of the bone. In this study, successive culture and decellularization of fibroblasts and endothelial cells (ECs) grown on polycaprolactone microfibers was used to develop a bioactive scaffold with heterogeneous dECM mimicking endothelial basement membrane. These scaffolds had greater amount of protein and minimally increased nucleic acid content than scaffolds with homogenous culture dECM. Coomassie Blue and antibody staining revealed extensive tube formation by ECs on fibroblast dECM. Fibroblast/endothelial dECM significantly enhanced osteoblast attachment, alkaline phosphatase activity, and osteocalcin-and osteopontin-positive extracellular mineral deposits. We demonstrated that the osteoconduction of dECMs can be tailored with the appropriate combination of cells to accelerate osteoblast mineral secretion. The overall concept can be expanded to generate increasingly more complex tissue constructs for regeneration of bone defects and other vascularized tissues. K E Y W O R D S bone tissue engineering, decellularization, extracellular matrix, osteoblasts, vascularization

The goal of this study was to determine the efficacy of the bioactive scaffold system to initiate bone marrow stromal cell (BMSC) differentiation into osteogenic and chondrogenic lineages in various culture media compositions. In the biphasic polymeric scaffolds, the chondrogenic layer contained aligned polycaprolactone nanofibers embedded with chondroitin sulfate and hyaluronic acid, while osteogenic layer carried nano-hydroxyapatite. Many studies for in vitro testing of osteochondral scaffolds incorporate the use of complicated bioreactors or growth factors for the formation of cartilage and bone tissue, thus true efficacy of the scaffold system cannot be determined. The present study compared the effect of several media compositions consisting of osteogenic, chondrogenic components, and control basal media. Scaffolds seeded with BMSCs following 28 days in vitro culture in different induction and basal media were evaluated for osteogenic and chondrogenic markers such as aggrecan, collagen type II, bone sialoprotein, alkaline phosphatase (ALP), and runt-related transcription factor 2 (Runx-2). Cartilage scaffold layer of the biphasic scaffold resulted in the expression of chondrogenic markers such as aggrecan and collagen type II by BMSCs in control and induction media compositions. The bone scaffold layer supported the expression of osteogenic markers such as ALP and Runx-2 by BMSCs in control and induction media compositions. The cartilage scaffold layer under the osteogenic induction media encouraged the growth of hypertrophic cartilage as marked by the positive expression of Runx-2. Expression of collagen type II and aggrecan on the cartilage layer in basal media was confirmed by immunostaining. These studies suggest that the bioactive scaffolds were able to support the osteogenic and chondrogenic phenotype development in the absence of growth factors and induction media.

Extracellular matrix surrounding Schwann cells and neurons provides critical determinants of cellular phenotype during development as well as essential cues in stimulating and guiding regrowth. Using cell sheet technology, we developed a novel scaffold enriched with native extracellular matrix from Schwann cells. Schwann cells were grown into sheets and layered onto polycaprolactone fibers for support. Upon decellularization of these constructs, extracellular matrix remained with few traces of nucleic acids. This method of deposition of extracellular matrix provided more protein than traditional seeding method after decellularization. Additionally, the isolated matrix supported proliferation of Schwann cells better than covalently bound laminin. The proliferation and differentiation of Schwann cells grown on decellularized sheets were complemented by upregulation of Erbb2 and myelin protein zero. Laminin expression of β1 and γ1 chains was also elevated. PC12 cells grown on decellularized sheets produced longer neurite extensions than aligned polycaprolactone fibers alone, proving potential of these scaffolds to be used in future peripheral nerve regenerative studies. Lay Summary Peripheral nerve injuries present a serious clinical need with approximately 50 % of surgical cases achieving only some restoration of function. In order to better guide regenerating nerves, supporting cells of the nerve tissue were grown into sheets and subsequently decellularized, leaving a myriad of surrounding protein as a scaffold. Constructs have been shown to support cell growth and neurite extension in vitro. Future projects will combine various cell types present in the nerve tissue as well as stem cells to fully support and reconstruct architecture of the peripheral nerves.