Injectable osteogenic and angiogenic nanocomposite hydrogels for irregular bone defects.

Injectable hydrogels with their 3D structure and good moldability serve as excellent scaffolding material for regenerating irregular non load-bearing bone defects. Most of the bone defects do not heal completely due to the lack of vasculature required for the transport of nutrients and oxygen to the regenerating tissues. To enhance vasculature, we developed an injectable hydrogel system made of chitin and poly (butylene succinate) (PBSu) loaded with 250 ± 20 nm sized fibrin nanoparticles (FNPs) and magnesium-doped bioglass (MBG). FNPs were expected to enhance vascularisation and MBG was expected to help induce early osteogenesis. Composite hydrogels were analysed using Fourier transform infra-red spectroscopy, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy, and rheology. Hydrogels with MBG showed a slightly rougher morphology upon SEM analysis. Composites containing 5% MBG and 2% FNPs showed good rheological properties, injectability, temperature stability, biomineralization and protein adsorption. Human umbilical vein endothelial cells (HUVECs) and rabbit-adipose derived mesenchymal stem cells (rASCs) were used for cyto-compatibility studies. Composite gels with 2% FNPs and 2% MBG (composite 1) were considered to be non-toxic to both the cells and were taken for further in vitro studies. Aortic ring assay was carried out to study the angiogenic potential of the hydrogels. The aorta placed with composite hydrogels showed enhanced sprouting of blood vessels. rASCs too showed good spreading on the composite hydrogels. Hydrogels containing MBG showed early initiation of differentiation and higher expression of alkaline phosphatase and osteocalcin confirming the osteoinductive property of MBG. These studies indicate that this composite hydrogel can be used for regenerating irregular bone defects.

Colloidal chitin nanogels: A plethora of applications under one shell.

Chitin nanogels (CNGs) are a relatively new class of natural polymeric nanomaterials which have a large potential in the field of drug delivery and nanotherapeutics. These nanogels being very biocompatible are non-toxic when internalized by cells. In this review various properties, preparation techniques and applications of CNGs have been described. CNGs because of their nano-size possess certain unique properties which enable them to be used in a number of biomedical applications. CNGs are prepared by simple regeneration technique without using any cross-linkers. Various polymers, drugs and fluorescent dyes can be blended or incorporated or labelled with the chitin hydrogel network. Drugs and molecules encapsulated within CNGs can be used for targeted delivery, in vivo monitoring or even for therapeutic purposes. Here various applications of CNGs in the field of drug delivery, imaging, sensing and therapeutics have been discussed.

The ColRS system of Xanthomonas oryzae pv. oryzae is required for virulence and growth in iron-limiting conditions.

Xanthomonas oryzae pv. oryzae, the causal agent of bacterial blight of rice, produces siderophores only under iron-limiting conditions. We screened 15 400 mTn5-induced mutants of X. oryzae pv. oryzae and isolated 27 mutants that produced siderophores even under iron-replete conditions. We found that the mTn5 insertions in 25 of these mutants were in or close to six genes. Mutants with insertions in five of these genes [colS, XOO1806 (a conserved hypothetical protein), acnB, prpR and prpB] exhibited a deficiency for growth on iron-limiting medium and a decrease in virulence. Insertions in a sixth gene, XOO0007 (a conserved hypothetical protein), were found to affect the ability to grow on iron-limiting medium, but did not affect the virulence. Targeted gene disruptants for colR (encoding the predicted cognate regulatory protein for ColS) also exhibited a deficiency for growth on iron-limiting medium and a decrease in virulence. colR and colS mutants were defective in the elicitation of hypersensitive response symptoms on the nonhost tomato. In addition, colR and colS mutants induced a rice basal defence response, suggesting that they are compromised in the suppression of host innate immunity. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that a functional ColRS system is required for the optimal expression of several genes encoding components of the type 3 secretion system (T3SS) of X. oryzae pv. oryzae. Our results demonstrate the role of several novel genes, including colR/colS, in the promotion of growth on iron-limiting medium and the virulence of X. oryzae pv. oryzae.