A ferrocene based glucose biosensor with an extended linear measuring range

The work described in this research is centred on the performance of ferrocene as a mediator to replace oxygen in the oxidation of glucose. Three immobilization methods were studied to minimize the leaking of the mediator. Glucose oxidase (GOD) and ferrocene mediator were immobilized in cross-linked poly(vinyl alcohol) (CLPVA), composite sol-gel-silica (SGS)/CLPVA/nafion and layer-by-layer (multilayer) covalent attachment. The biosensor response was evaluated amperometrically at 0.363V (vs. Ag/AgCl). The results showed that SGS/CLPVA/nafion membrane demonstrated the highest ability in retaining the enzyme and mediator whilst CLPVA membranes showed the poorest ability. The low current response with high Michaelis-Menten constant (Km app) and slow response time was observed in CLPVA membrane. Relative to that, SGS/CLPVA/nafion membrane and multilayered membrane were able to achieve larger current responses with lower Km app at faster response time. CLPVA was able to retain only 10% of the initial current whilst SGS/CLPVA/nafion and multilayered membranes were able to retain about 83% and 76% respectively of the initial current after 2 months of storage. All membranes showed good sensitivity with good stability except the CLPVA membranes. The Km app value for multilayered membrane was increased up to 28.68mM after the addition of nafion to the membrane. With such a high Km app, multilayered-nafion membrane can be applied as the enzymatic layer for a glucose biosensor since the value nearly encompasses the relevant concentration of glucose in blood which is from 1mM to 30mM. Subsequently, three types of external membranes were attached to the multilayered-nafion membranes to extend the linearity of sensor response and also to protect the biosensor. The external layers were cross-linked poly(2-hydroxyethyl methacrylate) (pHEMA), cellulose acetate incorporated poly(2-hydroxyethyl methacrylate) (CA-pHEMA) and cellulose acetate incorporated poly(ethylene glycol) (CA-PEG). Among these three types outer membranes, multilayered-nafion membranes with cross-linked pHEMA demonstrated acceptable Km app, which was around 40.58mM with high sensitivity and fast response time towards the glucose. Overall, the ferrocene based glucose biosensor showed very promising performances

Citric acid: a green cross-linker of biomaterials for biomedical application

The application of biomaterials in biomedicine currently suffers some drawbacks, such as inflammation and immunological responses due to mismatching and/or limited compatibility. Biomaterials that are cross-linked with citric acid (CA), also called citrate-based biomaterials (CBBs), have exhibited advanced in-vitro and in-vivo material properties that make them suitable for various biomedical applications. Tunable mechanical properties, biocompatibility, and biofunctionality are among other factors that make CBBs interesting in this field. To emphasize the safety and greenness nature of CA, in this review, we have highlighted the history, potential considerations of exploration, and a summarized stage-wise criterion for developing CBBs. We also discuss several points of view about the application of CA and CBBs in many different aspects of biomedicine, such as in tissue engineering, cancer therapy, and wound dressings

Development of antibacterial, degradable and pH-responsive chitosan/guar gum/polyvinyl alcohol blended hydrogels for wound dressing

The present research is based on the fabrication preparation of CS/PVA/GG blended hydrogel with nontoxic tetra orthosilicate (TEOS) for sustained paracetamol release. Different TEOS percentages were used because of their nontoxic behavior to study newly designed hydrogels’ crosslinking and physicochemical properties. These hydrogels were characterized using Fourier-transform infrared spec-troscopy (FTIR), scanning electron microscopy (SEM), and wetting to determine the functional, surface morphology, hydrophilic, or hydrophobic properties. The swelling analysis in different media, degradation in PBS, and drug release kinetics were conducted to observe their response against corresponding media. The FTIR analysis confirmed the components added and crosslinking between them, and surface morphology confirmed different surface and wetting behavior due to different crosslinking. In various solvents, including water, buffer, and electrolyte solutions, the swelling behaviour of hydrogel was investigated and observed that TEOS amount caused less hydrogel swelling. In acidic pH, hydrogels swell the most, while they swell the least at pH 7 or higher. These hydrogels are pH-sensitive and appropriate for controlled drug release. These hydrogels demonstrated that, as the ionic concentration was increased, swelling decreased due to decreased osmotic pressure in various electrolyte solutions. The antimicrobial analysis revealed that these hydrogels are highly antibacterial against Gram-positive (Staphylococcus aureus and Bacillus cereus) and Gram negative (Pseudomonas aeruginosa and Escherichia coli) bacterial strains. The drug release mechanism was 98% in phosphate buffer saline (PBS) media at pH 7.4 in 140 min. To analyze drug release behaviour, the drug release kinetics was assessed against different mathematical models (such as zero and first order, Higuchi, Baker–Lonsdale, Hixson, and Peppas). It was found that hydrogel (CPG2) follows the Peppas model with the highest value of regression (R2 = 0.98509). Hence, from the results, these hydrogels could be a potential biomaterial for wound dressing in biomedical applications

Immobilization of glucose oxidase/ferrocene carboxylic acid in composite silica sol-gel/cross-linked poly (vinyl alcohol)/nafion membrane

A method of tethering a mediator to an enzymatic membrane was studied to construct a non-leaking mediated glucose biosensor. Ferrocene carboxylic acid and glucose oxidase were immobilized in a sol gel derived silica (SGS) matrix containing cross-linked poly (vinyl alcohol) (CLPVA) and Nafion. CLPVA was applied as a solid support due to the ability to form very homogenous films with high quality. SGS was used to increase the encapsulation capacity for the enzyme and mediator. The presence of Nafion, a negatively charged polymer, not only prevented the cracking of pure sol-gel derived silica film but also improved the sensitivity and stability of the enzyme/mediator membrane by minimizing the leaching of the mediator. The biosensor response to glucose was evaluated amperometrically at 0.363V. The immobilization technique resulted in an enzyme/mediator membrane that was simple to cast, had minimal mediator and enzyme losses, worked under lower operating potentials and provided good responses over a wide range of concentrations

Immobilization of glucose oxidase And ferrocene redox polymer in cross-linked poly (vinyl alcohol) with bovine serum albumin as protein stabilizer

A method of tethering a mediator to an enzymatic membrane was studied. Glucose oxidase (GOD) and ferrocene redox polymer were immobilized in cross-linked poly (vinyl alcohol) (CLPVA) with bovine serum albumin (BSA) added as a protein stabilizer. Redox hydrogel polyallylamine ferrocene was prepared by cross-linking polyallylamine hydrochloride with glutaraldehyde and attaching the ferrocene covalently. The biosensor response to glucose was evaluated amperometrically at 0.363V. High BSA concentration resulted in improved current response but lower Kmapp. CLPVA, which had been proven to be an excellent retainer of GOD could not retain both GOD and ferrocene redox polymer effectively, thus affecting the stability of the enzymatic membrane

Angiogenic and osteogenic properties of fibrin in bone tissue engineering

The bone scaffold has become a promising alternative in bone tissue engineering due to the limitation associated with current bone treatments. However, the selection of scaffold material that could accurately mimic the extracellular matrix of native tissue remains challenging. Owing to its biological origin properties, natural materials including fibrin are widely used as scaffold materials as compared to synthetic materials. Fibrin has been recognized as one of the appealing natural biopolymers, which possesses unique characteristic due to its natural formed nano-scaffold, which provide a temporary matrix that facilitates cellular activities of cells. Fibrin has shown remarkable effects over other biomaterials in inducing angiogenesis and osteogenesis in bone regeneration owing to its mechanical and biological properties. In this article, we highlight the significance of fibrin materials in facilitating bone regeneration. We focus on the manipulation of fibrin composition and on the recent developments of fibrin composites in enhancing osteogenesis and angiogenesis for bone healing

Immobilization of glucose oxidase in freeze - thawed PVa and PVa/TMOS membranes

In this work, two methods of glucose oxidase (GOD) immobilization for peroxide based glucose biosensor had been investigated. For the first immobilization method, GOD was immobilized in freeze–thawed poly (vinyl alcohol) (PVA) at three different PVA concentrations (5%, 10% and 15% PVA). The higher the PVA concentration used for immobilization, the better the retention of the enzyme in the membrane. Nevertheless, higher PVA concentration did not necessarily correlate well with enzyme activity. Freeze–thawed PVA–GOD membranes with 10% PVA showed the highest sensitivity to glucose. The performances of freeze–thawed PVA–GOD membranes with 15% and 5% PVA was comparable. For the second immobilization method, GOD was immobilized within PVA/tetramethoxysilane (TMOS) matrix with different (3–glycidoxypropyldimenthylethoxy) silane (3GPDES) concentrations. For the membranes prepared with 1:1 (TMOS: 3GPDES) volumetric ratio, the percentage of enzyme activity remaining at day 40 was about 51%. Meanwhile, membrane prepared with 1:2 (TMOS: 3GPDES) and 1:3 (TMOS: 3GPDES) were quite stable with 69% and 58% of enzyme activity remaining at day 40, respectively. Overall, the glucose biosensor showed very promising performances

Microfluidics-based skin irritation test using in vitro 3D angiogenesis platform

A global ban on animal experiments has been proposed. Hence, it is imperative to develop alternative models. Artificial skin models should reflect the responses of subcutaneous blood vessels and the immune system to elucidate disease and identify cosmetics' base materials. Notably, in vivo skin-irritation cascades involve disruption of the epidermal barrier and the release of proinflammatory mediators in response to chemical stimuli. Such proinflammatory factors promote angiogenesis and blood vessel permeability, as observed in irritant contact dermatitis. As an alternative to animal models, we propose a novel skin-irritation model based on a three-dimensional in vitro angiogenesis platform, in which irritated keratinocytes biochemically stimulate vascular endothelial growth factors. Our microfluidic platform hosts interactions between keratinocytes and dermal fibroblasts, which promote angiogenic sprouting. We use sodium lauryl sulfate (SLS) and steartrimonium chloride (SC) as chemical irritants. The irritative effects of SLS and SC are of particular interest due to the ubiquity of both SLS and SC in cosmetics. SLS was observed to significantly affect angiogenic performance, with increasing sprout length. Further promotion of vessel sprouting and lumen formation was observed with 10, 20, and 60 μM of SC, despite its classification as nonirritating and use in supposedly safe formulations. This platform provides an alternative to animal testing as a basis for testing cosmetics and pharmaceutical substances, in addition to serving as a disease model for irritant contact dermatitis

CD80 Insights as Therapeutic Target in the Current and Future Treatment Options of Frequent-Relapse Minimal Change Disease

Minimal change disease (MCD) is the most common cause of idiopathic nephrotic syndrome in children, and it is well known for its multifactorial causes which are the manifestation of the disease. Proteinuria is an early consequence of podocyte injury and a typical sign of kidney disease. Steroid-sensitive patients react well with glucocorticoids, but there is a high chance of multiple relapses. CD80, also known as B7-1, is generally expressed on antigen-presenting cells (APCs) in steroid-sensitive MCD patients. Various glomerular disease models associated with proteinuria demonstrated that the detection of CD80 with the increase of urinary CD80 was strongly associated closely with frequent-relapse MCD patients. The role of CD80 in MCD became controversial because one contradicts finding. This review covers the treatment alternatives for MCD with the insight of CD80 as a potential therapeutic target. The promising effectiveness of CD20 (rituximab) antibody and CD80 inhibitor (abatacept) encourages further investigation of CD80 as a therapeutic target in frequent-relapse MCD patients. Therapeutic-based antibody towards CD80 (galiximab) had never been investigated in MCD or any kidney-related disease; hence, the role of CD80 is still undetermined. A new therapeutic approach towards MCD is essential to provide broader effective treatment options besides the general immunosuppressive agents with gruesome adverse effects

Microfluidic vascularized bone tissue model with hydroxyapatite-incorporated extracellular matrix

Current in vitro systems mimicking bone tissues fail to fully integrate the three-dimensional (3D) microvasculature and bone tissue microenvironments, decreasing their similarity to in vivo conditions. Here, we propose 3D microvascular networks in a hydroxyapatite (HA)-incorporated extracellular matrix (ECM) for designing and manipulating a vascularized bone tissue model in a microfluidic device. Incorporation of HA of various concentrations resulted in ECM with varying mechanical properties. Sprouting angiogenesis was affected by mechanically modulated HA-extracellular matrix interactions, generating a model of vascularized bone microenvironment. Using this platform, we observed that hydroxyapatite enhanced angiogenic properties such as sprout length, sprouting speed, sprout number, and lumen diameter. This new platform integrates fibrin ECM with the synthetic bone mineral HA to provide in vivo-like microenvironments for bone vessel sprouting