A review on injectable chitosan/beta glycerophosphate hydrogels for bone tissue regeneration.

Tissue engineering (TE) is a promising approach for repairing diseased and damaged bone tissue. Injectable hydrogel based strategies offer a wide range of applications in rapid recovery of bone defects by acting as filler materials and depots for delivering various bioactive molecules and averting the need for surgical intervention. Chitosan (CS), a natural polysaccharide, forms a thermosensitive injectable hydrogel through the addition of beta-glycerophosphate (ß-GP). This hybrid hydrogel possesses numerous advantages namely mimicking native extracellular matrix (ECM) and providing an amenable microenvironment for cell growth. In this review, a brief insight into the gelation mechanism of CS/GP hydrogels, modifications, bioactive additives and their applications in treating bone defects are presented.

Three-Dimensional Porous Sponges from Collagen Biowastes.

Three-dimensional, functional, and porous scaffolds can find applications in a variety of fields. Here we report the synthesis of hierarchical and interconnected porous sponges using a simple freeze-drying technique, employing collagen extracted from animal skin wastes and superparamagnetic iron oxide nanoparticles. The ultralightweight, high-surface-area sponges exhibit excellent mechanical stability and enhanced absorption of organic contaminants such as oils and dye molecules. Additionally, these biocomposite sponges display significant cellular biocompatibility, which opens new prospects in biomedical uses. The approach highlights innovative ways of transforming biowastes into advanced hybrid materials using simple and scalable synthesis techniques.

Highly biocompatible collagen-Delonix regia seed polysaccharide hybrid scaffolds for antimicrobial wound dressing.

Biomaterials based entirely on biological resources are ideal for tissue engineering applications. Here we report the preparation of hybrid collagen scaffolds comprising gulmohar seed polysaccharide (GSP) and cinnamon bark extract as cross-linking agent. (1)H NMR spectrum of GSP confirms the presence of galactose and mannose in the ratio of 1:1.54, which was further corroborated using FT-IR. The hybrid scaffolds show better enzyme and thermal stability in contrast to pure collagen scaffold probably due to weak interactions from GSP and covalent interaction through cinnamaldehyde. Gas permeability and scanning electron microscopic analysis show that the porosity of the hybrid scaffolds is slightly reduced with the increase in the concentration of GSP. The infrared and circular dichroic spectral studies show that the secondary structure of the collagen did not change after the interaction with GSP and cinnamaldehyde. The hybrid scaffolds stabilized with cinnamaldehyde show good antimicrobial activity against the common multi-drug resistant wound pathogens. These results suggest that the prepared hybrid scaffolds have great potential for antimicrobial wound dressing applications.

Melatonin in functionalized biomimetic constructs promotes rapid tissue regeneration in Wistar albino rats.

The development of hybrid scaffolds mimicking the extracellular matrix with bioactive factors has great potential to regenerate tissues in tissue engineering and wound-healing applications. Herein, poly(dialdehyde) gum acacia was synthesized by the selective oxidation of gum acacia and was blended with collagen and melatonin to fabricate biomimetic hybrid scaffolds. The inclusion of poly(dialdehyde) gum acacia improved the stability of collagen and immobilized the melatonin in the hybrid scaffolds. The prepared hybrid scaffolds showed significant biocompatibility when cultured with the Swiss 3T6 mouse fibroblast cell lines in vitro. When subjected to open excisional skin wounds in Wistar albino rats in vivo, the collagen-poly(dialdehyde) gum acacia-melatonin hybrid scaffolds accelerated re-epithelialization and collagen deposition. The results indicate that the melatonin-immobilized hybrid scaffold promotes rapid tissue regeneration and wound repair owing to its antioxidant and anti-inflammatory properties, thereby demonstrating its potential for application in burns and chronic wounds.

Biomimetic hybrid porous scaffolds immobilized with platelet derived growth factor-BB promote cellularization and vascularization in tissue engineering.

Development of hybrid scaffolds with synergistic combination of growth factor is a promising approach to promote early in vivo wound repair and tissue regeneration. Here, we show the rapid wound healing in Wistar albino rats using biomimetic collagen-poly(dialdehyde) guar gum based hybrid porous scaffolds covalently immobilized with platelet derived growth factor-BB. The immobilized platelet derived growth factor in the hybrid scaffolds not only enhance the total protein, collagen, hexosamine, and uronic acid contents in the granulation tissue but also provide stronger tissues. The wound closure analysis reveal that the complete epithelialization period is 15.4 ± 0.9 days for collagen-poly(dialdehyde) guar gum-platelet derived growth factor hybrid scaffolds, whereas it is significantly higher for control, collagen, collagen- poly(dialdehyde) guar gum and povidine-iodine treated groups. Further, the histological evaluation shows that the immobilized platelet derived growth factor in the hybrid scaffolds induced a more robust cellular and vascular response in the implanted site. Hence, we demonstrate that the collagen-poly(dialdehyde) guar gum hybrid scaffolds loaded with platelet derived growth factor stimulates chemotactic effects in the implanted site to promote rapid tissue regeneration and wound repair without the assistance of antibacterial agents.

Thermoresponsive magnetic nanoparticle--aminated guar gum hydrogel system for sustained release of doxorubicin hydrochloride.

Hydrogel based sustained drug delivery system has evolved as an immense treatment method for solid tumors over the past few decades with long term theranostic ability. Here, we synthesized an injectable hydrogel system comprising biocompatible aminated guar gum, Fe3O4-ZnS core-shell nanoparticles and doxorubicin hydrochloride. We show that amination of guar gum resulted in attraction of water molecules thereby forming the hydrogel without using toxic crosslinking agents. Hydrogel formation was observed at 37°C and is stable up to 95°C. The prepared hydrogel is also stable over a wide pH range. The in vitro studies show that the maximum de-gelation and drug release up to 90% can be achieved after 20 days of incubation. Studies reveal that the drug and the core-shell nanoparticles can be released slowly from the hydrogel to provide the healing and diagnosis of the solid tumor thereby avoiding several drug administrations and total excision of organs.

Green synthesis and characterization of hybrid collagen-cellulose-albumin biofibers from skin waste.

Collagen (C) and cellulose are prominent biopolymers from the animal and plant kingdom and widely used in bioengineering. Albumin, on the other hand, is the most abundant plasma protein present in mammalian blood. In this work, collagen extracted from animal skin waste was blended with hydroxyethyl cellulose (HEC) and bovine serum albumin (A) and wet-spun to form hybrid biodegradable C/HEC/A fibers. They were further cross-linked with glutaraldehyde vapors and analyzed. X-ray diffraction and infra-red spectroscopic studies of the hybrid fibers display peaks corresponding to collagen, cellulose, and albumin. Incorporation of cellulose into the biopolymeric matrix leads to a reasonable improvement in mechanical, swelling, and thermal properties of hybrid fibers. Addition of albumin improves the regularity of fiber surface without altering the porosity as observed under a microscope. Hence, the formed hybrid biofibers can be potentially used as a suture material as well as for different biomedical applications due to their improved properties.

Probing horseradish peroxidase catalyzed degradation of azo dye from tannery wastewater.

Biocatalysis based effluent treatment has outclassed the presently favored physico-chemical treatments due to nil sludge production and monetary savings. Azo dyes are commonly employed in the leather industry and pose a great threat to the environment. Here, we show the degradation of C. I. Acid blue 113 using horseradish peroxidase (HRP) assisted with H2O2 as a co-substrate. It was observed that 0.08 U HRP can degrade 3 mL of 30 mg/L dye up to 80% within 45 min with the assistance of 14 µL of H2O2 at pH 6.6 and 30°C. The feasibility of using the immobilized HRP for dye degradation was also examined and the results show up to 76% dye degradation under similar conditions to that of free HRP with the exception of longer contact time of 240 min. Recycling studies reveal that the immobilized HRP can be recycled up to 3 times for dye degradation. Kinetics drawn for the free HRP catalyzed reaction marked a lower K m and higher V max values, which denotes a proper and faster affinity of the enzyme towards the dye, when compared to the immobilized HRP. The applicability of HRP for treating the actual tannery dye-house wastewater was also demonstrated.

Collagen based magnetic nanocomposites for oil removal applications.

A stable magnetic nanocomposite of collagen and superparamagnetic iron oxide nanoparticles (SPIONs) is prepared by a simple process utilizing protein wastes from leather industry. Molecular interaction between helical collagen fibers and spherical SPIONs is proven through calorimetric, microscopic and spectroscopic techniques. This nanocomposite exhibited selective oil absorption and magnetic tracking ability, allowing it to be used in oil removal applications. The environmental sustainability of the oil adsorbed nanobiocomposite is also demonstrated here through its conversion into a bi-functional graphitic nanocarbon material via heat treatment. The approach highlights new avenues for converting bio-wastes into useful nanomaterials in scalable and inexpensive ways.

Optical bifunctionality of europium-complexed luminescent graphene nanosheets.

Graphene is an intriguing two-dimensional material, which could be modified for achieving tunable properties with many applications. Photoluminescence of graphene due to plasmonic emission is well-known, however, attempts to develop strong luminescent graphene have been difficult. Synthesis of a graphene-based material with a dual optical functionality, namely quenching the fluorescence of organic dyes while maintaining its own self-luminescence, is an interesting and challenging proposition. Here, we demonstrate this optical bifunctionality in a lattice-modified luminescent graphene, where europium(III) cations are complexed with graphene through oxygen functionalities. After excitation at 314 nm, a hypersensitive red emission is observed at 614 and 618 nm showing the complexation of europium(III) with graphene. We demonstrate dual functionality of this graphene by the quenching of luminescence of Rhodamine-B while displaying its own hypersensitive red emission. The decay lifetime observed through the time-resolved spectroscopy confirms its potential for applications in biosensing as well as optoelectronics.

Structural and thermal investigations of biomimetically grown casein-soy hybrid protein fibers.

A hybrid protein fiber from different protein sources such as casein and soybean using wet-spinning technique was prepared. The casein/soybean hybrid fibers were synthesized at different weight ratios such as 100/0 (casein), 75/25, 50/50, 25/75, and 0/100 (soy) and characterized. Electron microscopic analysis confirmed the growth of pure and hybrid fibers and shows an increased surface roughness as the soy concentration increases in the hybrid fibers. Infrared spectra did not exhibit any significant changes in the functional groups between pure and hybrid fibers. X-ray diffraction pattern indicates slight increase in the diffraction peak values of hybrid fibers compared with the neat fibers. Thermal analyses show a moderate increase in the thermal stability of hybrid fibers when compared with the pure fibers. These results implicitly indicate that the casein and soy proteins are homogeneous in the hybrid fiber form. It has been demonstrated that the hybrid fiber with ≥50 wt.% casein content exhibits better morphology and increased thermal stability, which has scope for application in technical and medical industries.

Sodium metasilicate based fiber opening for greener leather processing.

Growing environmental regulations propound the need for a transformation in the current practice of leather making. The conventional dehairing and fiber opening process results in high negative impact on the environment because of its uncleanliness. This process accounts for most of the biochemical oxygen demand and chemical oxygen demand in tannery wastewater and generation of H2S gas. Hence, this study explores the use of a biological material and a nontoxic chemical for performing the above process more cleanly. In this study, the dehairing and fiber opening processes has been designed using enzyme and sodium metasilicate. The amount of sodium metasilicate required for fiber opening is standardized through the removal of proteoglycan, increase in weight, and bulk properties of leathers. It has been found that the extent of opening up of fiber bundles is comparable to that of conventionally processed leathers using a 2% sodium metasilicate solution. This has been substantiated through scanning electron microscopic analysis and softness measurements. The presence of silica in the crust leather enhances the bulk properties of the leather. This has been confirmed from the energy dispersive X-ray analysis. Performance of the leathers is shown to be on par with conventionally processed leathers through physical and hand evaluation. The process also exhibits significant reduction in chemical oxygen demand and total solid loads by 55 and 24%, respectively. Further, this newly developed process seems to be economically beneficial.

Reversing the conventional leather processing sequence for cleaner leather production.

Conventional leather processing generally involves a combination of single and multistep processes that employs as well as expels various biological, inorganic, and organic materials. It involves nearly 14-15 steps and discharges a huge amount of pollutants. This is primarily due to the fact that conventional leather processing employs a "do-undo" process logic. In this study, the conventional leather processing steps have been reversed to overcome the problems associated with the conventional method. The charges of the skin matrix and of the chemicals and pH profiles of the process have been judiciously used for reversing the process steps. This reversed process eventually avoids several acidification and basification/neutralization steps used in conventional leather processing. The developed process has been validated through various analyses such as chromium content, shrinkage temperature, softness measurements, scanning electron microscopy, and physical testing of the leathers. Further, the performance of the leathers is shown to be on par with conventionally processed leathers through bulk property evaluation. The process enjoys a significant reduction in COD and TS by 53 and 79%, respectively. Water consumption and discharge is reduced by 65 and 64%, respectively. Also, the process benefits from significant reduction in chemicals, time, power, and cost compared to the conventional process.

Silicate enhanced enzymatic dehairing: a new lime-sulfide-free process for cowhides.

A conventional dehairing process with sodium sulfide and lime is a major source of the pollution from the tanning industry. In other words, conventional dehairing processes degrade the hair to the extent that it cannot be recovered; thus, these processes become a major contributor to wastewater pollution. In this study, an attempt has been made to develop a lime and sulfide-free dehairing process using a commercial enzyme formulation with the activation of a silicate salt. A dip and pile method of application has been standardized. The amount of enzyme and sodium metasilicate has also been optimized based on complete removal of hair. Enhancement of enzyme activity by the addition of silicate has been demonstrated through activity measurements. Hair removal is found to be complete using scanning electron microscope analysis. Strength and bulk properties of the experimental leathers are comparable to that of control leathers. The process enjoys a significant reduction in chemical oxygen demand (COD) and total solids (TS) by 53 and 26%, respectively. More importantly, the application of enzyme for dehairing results in an 8% area increase in the final leather. Also, the process is proven to be techno-economically feasible.

Progress and recent trends in biotechnological methods for leather processing.

Global environmental regulations are changing the leather-processing industry. Pre-tanning and tanning processes contribute 80-90% of the total pollution in the industry and generate noxious gases, such as hydrogen sulfide, as well as solid wastes, such as lime and chrome sludge. The use of enzyme-based products is currently being explored for many areas of leather making. Furthermore, enzymes are gaining increasing importance in the de-hairing process, eliminating the need for sodium sulfide. This review discusses emerging novel biotechnological methods used in leather processing. One significant achievement is the development of a bioprocess-based de-hairing and fiber-opening methodology to reduce toxic waste.

Natural leathers from natural materials: progressing toward a new arena in leather processing.

Globally, the leather industry is currently undergoing radical transformation due to pollution and discharge legislations. Thus, the leather industry is pressurized to look for cleaner options for processing the raw hides and skins. Conventional methods of pre-tanning, tanning and post-tanning processes are known to contribute more than 98% of the total pollution load from the leather processing. The conventional method of the tanning process involves the "do-undo" principle. Furthermore, the conventional methods employed in leather processing subject the skin/ hide to a wide variation in pH (2.8-13.0). This results in the emission of huge amounts of pollution loads such as BOD, COD, TDS, TS, sulfates, chlorides and chromium. In the approach illustrated here, the hair and flesh removal as well as fiber opening have been achieved using biocatalysts at pH 8.0, pickle-free natural tanning employing vegetable tannins, and post-tanning using environmentally friendly chemicals. Hence, this process involves dehairing, fiber opening, and pickle-free natural tanning followed by ecofriendly post-tanning. It has been found that the extent of hair removal and opening up of fiber bundles is comparable to that of conventionally processed leathers. This has been substantiated through scanning electron microscopic analysis and softness measurements. Performance of the leathers is shown to be on par with conventionally chrome-tanned leathers through physical and hand evaluation. The process also exhibits zero metal (chromium) discharge and significant reduction in BOD, COD, TDS, and TS loads by 83, 69, 96, and 96%, respectively. Furthermore, the developed process seems to be economically viable.

Biointervention makes leather processing greener: an integrated cleansing and tanning system.

The do-undo methods adopted in conventional leather processing generate huge amounts of pollutants. In other words, conventional methods employed in leather processing subject the skin/hide to wide variations in pH. Pretanning and tanning processes alone contribute more than 90% of the total pollution from leather processing. Included in this is a great deal of solid wastes such as lime and chrome sludge. In the approach described here, the hair and flesh removal as well as fiber opening have been achieved using biocatalysts at pH 8.0 for cow hides. This was followed by a pickle-free chrome tanning, which does not require a basification step. Hence, this tanning technique involves primarily three steps, namely, dehairing, fiber opening, and tanning. It has been found that the extent of hair removal, opening up of fiber bundles, and penetration and distribution of chromium are comparable to that produced by traditional methods. This has been substantiated through scanning electron microscopic, stratigraphic chrome distribution analysis, and softness measurements. Performance of the leathers is shown to be on par with conventionally processed leathers through physical and hand evaluation. Importantly, softness of the leathers is numerically proven to be comparable with that of control. The process also demonstrates reduction in chemical oxygen demand load by 80%, total solids load by 85%, and chromium load by 80% as compared to the conventional process, thereby leading toward zero discharge. The input-output audit shows that the biocatalytic three-step tanning process employs a very low amount of chemicals, thereby reducing the discharge by 90% as compared to the conventional multistep processing. Furthermore, it is also demonstrated that the process is technoeconomically viable.

Zero discharge tanning: a shift from chemical to biocatalytic leather processing.

Beam house processes (Beam house processes generally mean liming-reliming processes, which employ beam.) contribute more than 60% of the total pollution from leather processing. The use of lime and sodium sulfide is of environmental concern (1, 2). Recently, the authors have developed an enzyme-based dehairing assisted with a very low amount of sodium sulfide, which completely avoids the use of lime. However, the dehaired pelt requires opening up of fiber bundles for further processing, where lime is employed to achieve this through osmotic swelling. Huge amounts of lime sludge and total solids are the main drawbacks of lime. An alternative bioprocess, based on alpha-amylase for fiber opening, has been attempted after enzymatic unhairing. This totally eliminates the use of lime in leather processing. This method enables subsequent processes and operations in leather making feasible without a deliming process. A control experiment was run in parallel using conventional liming-reliming processes. It has been found that the extent of opening up of fiber bundles using alpha-amylase is comparable to that of the control. This has been substantiated through scanning electron microscopic, stratigraphic chrome distribution analysis, and softness measurements. Performance of the leathers is shown to be on a par with leathers produced by the conventional process through physical and hand evaluation. Importantly, softness of the leathers is numerically proven to be comparable with that of control. The process also demonstrates reduction in chemical oxygen demand load by 45% and total solids load by 20% compared to the conventional process. The total dry sludge from the beam house processes is brought down from 152 to 8 kg for processing 1 ton of raw hides.

Green route for the utilization of chrome shavings (chromium-containing solid waste) in tanning industry.

Chromium-containing wastes from various industrial sectors are under critical review. Leather processing is one such industrial activity that generates chromium-bearing wastes in different forms. One of them is chrome shavings, and this contributes to an extent of 10% of the quantum of raw skins/hides processed, amounting to 0.8 million ton globally. In this study, the high protein content of chrome shavings has been utilized for reduction of chromium(VI) in the preparation of chrome tanning agent. This approach has been exploited for the development of two products: one with chrome shavings alone as reducing agent and the other with equal proportion of chrome shavings and molasses. The developed products exhibit more masking due to the formation of intermediate organic oligopeptides. This has been corroborated through the spectral, hydrolysis, and species-wise distribution studies. The formation of these organic masking agents helps in chrome tanning by shifting the precipitation point of chromium to relatively higher pH levels. Hence, the developed products find use as chrome tanning agents for leather processing, thus providing a means for better utilization of chrome shaving wastes.