Biology subjects

Kakar, A.

Publications and source records attributed to Kakar, A..

4 recordsLinked to original sources

bioRxiv2026

Collagen-based bilayered biomimetic tubular materials for vascular and airway applications

Biomimetic tubular scaffolds hold great promise for tackling unmet clinical needs thanks to their biocompatibility and recapitulation of cellular microenvironments, conferring the ability to promote regeneration. Potential applications include small-diameter vascular implants and grafts for airway repair, for which no viable off-the-shelf solutions currently exist. The tubular materials (4 and 8 mm internal and external diameters) presented here consist purely of type I collagen, contain no chemical crosslinkers, and reproduce the multi-scale architecture of the native tissue including the presence of collagen fibrils. A novel two-step protocol provides materials with distinct concentric layers. A porous external structure, obtained by means of ice templating combined with collagen topotactic fibrillogenesis, favours oriented cell colonization. A smooth and much less porous internal layer provides mechanical and water-tightness properties relevant for in vivo implantation and promotes the formation of an endothelial monolayer under both static and flow conditions. The compliance of the double-layered materials under physiological pressure is close to that of piglet carotid arteries. The materials are also determined to be sufficiently flexible to provide the ability to perform ex vivo anastomosis with bronchi, although the relatively low value of suture retention strength remains a limitation for in vivo suturing.

bioengineering↗

bioRxiv2023

Tunable biomimetic materials elaborated by ice templating and self-assembly of collagen for tubular tissue engineering

Synthetic tubular grafts currently used in clinical context fail frequently, and the expectations that biomimetic materials could tackle these limitations are high. However, developing tubular materials presenting structural, compositional and functional properties close to those of native tissues remains an unmet challenge. Here we describe a combination of ice templating and topotactic fibrillogenesis of type I collagen, the main component of tissues extracellular matrix, yielding highly concentrated yet porous tubular collagen materials with controlled hierarchical architecture at multiple length scales, the hallmark of native tissues organization. By modulating the thermal conductivity of the cylindrical molds, we tune the macroscopic porosity defined by ice. Coupling the aforementioned porosity patterns with two different fibrillogenesis routes results in a new family of materials whose textural features and the supramolecular arrangement of type I collagen are achieved. The resulting materials present hierarchical elastic properties and are successfully colonized by human endothelial cells and alveolar epithelial cells on the luminal side, and by human mesenchymal stem cells on the external side. The results reported here demonstrate the relevance of the proposed straightforward protocol, likely to be adapted for larger graft sizes, to address ever-growing clinical needs such as peripheral arterial disease or tracheal and bronchial reconstructions.

bioengineering↗

bioRxiv2022

The membrane activity of the amphibian Temporin B peptide analog TB_KKG6K sheds light on the mechanism that kills Candida albicans

Temporin B (TB) is a 13 amino acid long, cationic peptide secreted by the granular glands of the European frog Rana temporaria. We could recently show that the modified TB peptide analog TB_KKG6K rapidly killed planktonic and sessile Candida albicans at low {micro}M concentrations and was neither hemolytic nor cytotoxic to mammalian cells in vitro. The present study aimed to shed light into its mechanism of action, with a focus on its fungal cell membrane activity. We utilized different fluorescent dyes to prove that it rapidly induces membrane depolarization and permeabilization. Studies on model membrane systems revealed that the TB analog undergoes hydrophobic and electrostatic membrane interactions showing a preference for anionic lipids and identified phosphatidylinositol and cardiolipin as possible peptide targets. Fluorescence microscopy using FITC-labelled TB_KKG6K in the presence of the lipophilic dye FM4-64 indicated that the peptide compromises membrane integrity and rapidly enters C. albicans cells in an energy independent manner. Peptide treated cells analyzed by cryo-based electron microscopy exhibited no signs of cell lysis; however, subcellular structures were disintegrated, suggesting that intracellular activity may form part of the killing mechanism of the peptide. Taken together, this study proved that the TB_KKG6K compromises C. albicans membrane function, which explains the previously observed rapid, fungicidal mode of action and promises its great potential as a future anti-Candida therapeutic. ImportanceFungal infections with the opportunistic human pathogen C. albicans are associated with high moratility rates in immunocompromised patients. This is partly due to the yeasts ability to rapidly develop resistance towards currently available antifungals. Small, cationic, membrane-active peptides are promising compounds to fight against resistance development as many of them effectuate rapid fungal cell death. This fast killing is believed to hamper the development of resistance, as the fungi do not have sufficient time to adapt to the antifungal compound. We prevously reported that the synthetic variant of the amphibian Temporin B peptide, TB_KKG6K, rapidly kills C. albicans. In the current study, the mechanism of action of the TB analog was investigated. We show that this TB analog is membrane-active and impairs cell membrane function, highlighting its potential to be developed as an attractive alternative anti-C. albicans therapeutic, which may hinder the development of resistance.

microbiology↗

bioRxiv2017

Factor analysis on the Tasmanian topsoil microscopic community

To help with stand restoration, the influence of width size on the Tasmanian topsoil microscopic community was studied in an Athrotaxis cupressoides stand suffering from hail storm damage. The functional diversity of topsoil microbial groups was estimated from degradation of 31 substrates on Bencho EcoPlates. Using Factor Analysis (FA) we found width size had a significant influence on average column colorimetric disseminator analysis (AVGCLR) and on the Rao indices of topsoil microbial diversity. Compared with large widths, small widths had higher AVGCLR. The ten widths were divided into three groups by cluster analysis and FA: group 1 reflected large widths, while groups 2 and 3 reflected small widths. Thirty-one sole carbon sources were divided into three groups by FA. Using an eigenvector greater than 0.5 as a standard for checking carbon (C) sources, nineteen kinds of C sources included in principal components 1 and 2 had a relatively high influence on the topsoil microbial community, including carbohydrates, amino acids and carboxylic acids. This indicates that the use by topsoil microorganisms of carboxylic acids, sugars and amino acids was greater than other C sources. These findings suggest that width size played a key role in the topsoil microbial diversity after a natural disturbance.

ecology↗