No abstract

The strong need for the utilization of industrial by-products and biowaste increases as we transition towards a circular economy. On these grounds, the present research aims to explore the applicability of the Symbiotic Culture of Bacteria and Yeast (SCOBY), a by-product of a functional beverage industry, for applications in biomedicine. Herein, hydroxyapatite (HA)-coated SCOBY nanocellulose (SN) nanocomposite (SNHA) was synthesized via a novel biomimetic approach using Serratia marcescens strain by adopting two different in situ approaches. Characterization studies established the presence of functional groups corresponding to pure nanocellulose and HA. Microscopic analysis revealed SN fibers of the dimensions 30–50 nm surrounded by 10–15 nm rod-shaped HA crystals. The SNHA membranes were carbonated and harbored traces of metal ions. A deposition of nano-HA crystals as high as 30–50% was achieved. Overall, the synthesized SNHA membranes reflected increased stability, low crystalline nature and an ion-substituted structure resembling the natural bone; they are thereby suited for bone tissue engineering.

Biomimicry is becoming deep-rooted as part of bioceramics owing to its numerous functional advantages. Naturally occurring hydroxyapatite (HA) apart from primary nano structures are also characterised by various ionic substitutions. The ease of accommodating such key elements into the HA lattice is known to enhance bone healing properties of bioceramics. In this work, hydroxyapatite synthesized via biomimetic approach was substituted with individual as well as multiple cations for potential applications in bone repair. Ion substitutions of Sr, Mg and Zn was carried out on HA for the first time by using Serratia grown in a defined biomineralization medium. The individual ions of varying concentration substituted in Serratia HA (SHA) (Sr SHA, Mg SHA and Zn SHA) were analysed for crystallinity, functional groups, morphology and crystal size. All three showed decreased crystallinity, phase purity, large agglomerated aggregates and needle-shaped morphologies. Fourier transform infrared spectroscopy (FTIR) spectra indicated increased carbonate content of 5.8% resembling that of natural bone. Additionally, the reduced O–H intensities clearly portrayed disruption of HA lattice and subsequent ion-substitution. The novelty of this study lies primarily in investigating the co-substitution of a combination of 1% Sr, Zn and Mg in SHA and establishing the associated change in bone parameters. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images clearly illustrated uniform nano-sized agglomerates of average dimensions of 20–50 nm length and 8–15 nm width for Sr SHA; 10–40 nm length and 8–10 nm width for both Zn SHA and Mg SHA and 40–70 nm length and 4–10 nm width in the case of 1% Sr, Zn, Mg SHA. In both individual as well as co-substitutions, significant peak shifts were not observed possibly due to the lower concentrations. However, cell volumes increased in both cases due to presence of Sr2+ validating its dominant integration into the SHA lattice. Rich trace ion deposition was presented by energy dispersive X-ray spectroscopy (EDS) and quantified using inductively coupled plasma optical emission spectrometer (ICP-OES). In vitro cytotoxicity studies in three cell lines viz. NIH/3T3 fibroblast cells, MG-63 osteosarcoma cells and RAW 264.7 macrophages showed more than 90% cell viability proving the biocompatible nature of 1% Sr, Zn and Mg in SHA. Microbial biomineralization by Serratia produced nanocrystals of HA that mimicked “bone-like apatite” as evidenced by pure phase, carbonated groups, reduced crystallinity, nano agglomerates, variations in cell parameters, rich ion deposition and non-toxic nature. Therefore ion-substituted and co-substituted biomineralized nano SHA appears to be a suitable candidate for applications in biomedicine addressing bone injuries and aiding regeneration as a result of its characteristics close to that of the human bone.