Covalent immobilization of DJK-5 peptide on porous titanium for enhanced antibacterial effects and restrained inflammatory osteoclastogenesis

Currently, implant-related bone infection characterized by aggravated infection-induced inflammatory responses and osteolysis, remains a severe challenge in orthopedic surgery, especially in patients with osteoporosis. Attempts to control such responses using biomaterials with combined immunomodulatory and anti-bacterial properties may provide novel strategies. Herein, DJK-5, a class of host defense peptides (HDPs) with established antimicrobial and immunomodulatory functions, was introduced into porous Ti alloy. Our results indicated that the DJK-5 immobilized surfaces showed intrinsically multifunctional properties, including antibacterial ability, anti-inflammation, biocompatibility and osteolysis-inhibiting properties. The results demonstrated that the antibacterial efficiency of DJK-5 functionalized surfaces was over 90 % for both Gram-positive and Gram-negative bacteria. Specifically, DJK-5 functionalized samples also possessed the excellent anti-bacterial activity against a mixture of bacterial strains, including S. aureus, S. epidermidis and P. aeruginosa, with an antibacterial rate against mixed bacteria reaching 91.36 %, as well as reduced biofilm formation. The remarkable anti-bacterial efficacy was likely based on the direct anti-bacterial effect of DJK-5, which destroyed the integrity of bacteria membranes, leading to the leakage of intracellular materials. Additionally, the immobilized DJK-5 surfaces could indirectly kill bacteria through promoted macrophage capacity to bacteria uptake. Furthermore, DJK-5 functionalized surfaces suppressed inflammatory reaction by decreasing the release of pro-inflammatory factors and increasing the secretions of anti-inflammatory factors, and thereby impeded the activation of NF-κB signal pathway, which resulted in the disruption of the actin rings and decreased Tracp5b expressions. Based on these promising findings, the multi-functional DJK-5 immobilized titanium represents an efficient alternative to realize better osseointegration in sever implant-associated bacterial infections.

A crucial role for spatial distribution in bacterial quorum sensing

Quorum sensing (QS) is a process that enables bacteria to communicate using secreted signaling molecules, and then makes a population of bacteria to regulate gene expression collectively and control behavior on a community-wide scale. Theoretical studies of efficiency sensing have suggested that both mass-transfer performance in the local environment and the spatial distribution of cells are key factors affecting QS. Here, an experimental model based on hydrogel microcapsules with a three-dimensional structure was established to investigate the influence of the spatial distribution of cells on bacterial QS. Vibrio harveyi cells formed different spatial distributions in the microcapsules, i.e., they formed cell aggregates with different structures and sizes. The cell aggregates displayed stronger QS than did unaggregated cells even when equal numbers of cells were present. Large aggregates (LA) of cells, with a size of approximately 25 μm, restricted many more autoinducers (AIs) than did small aggregates (SA), with a size of approximately 10 μm, thus demonstrating that aggregate size significantly affects QS. These findings provide a powerful demonstration of the fact that the spatial distribution of cells plays a crucial role in bacterial QS.

Build to understand: synthetic approaches to biology

In this review we discuss how synthetic biology facilitates the task of investigating genetic circuits that are observed in naturally occurring biological systems. Specifically, we give examples where experimentation with synthetic gene circuits has been used to understand four fundamental mechanisms intrinsic to development and disease: multistability, stochastic gene expression, oscillations, and cell-cell communication. Within each area, we also discuss how mathematical modeling has been employed as an essential tool to guide the design of novel gene circuits and as a theoretical basis for exploring circuit topologies exhibiting robust behaviors in the presence of noise.