Hydrogel Glucose Sensor with In Vivo Stable Fluorescence Intensity Relying on Antioxidant Enzymes for Continuous Glucose Monitoring

Development and Prospective Applications of 3D Membranes as a Sensor for Monitoring and Inducing Tissue Regeneration

For decades, tissue regeneration has been a challenging issue in scientific modeling and human practices. Although many conventional therapies are already used to treat burns, muscle injuries, bone defects, and hair follicle injuries, there remains an urgent need for better healing effects in skin, bone, and other unique tissues. Recent advances in three-dimensional (3D) printing and real-time monitoring technologies have enabled the creation of tissue-like membranes and the provision of an appropriate microenvironment. Using tissue engineering methods incorporating 3D printing technologies and biomaterials for the extracellular matrix (ECM) containing scaffolds can be used to construct a precisely distributed artificial membrane. Moreover, advances in smart sensors have facilitated the development of tissue regeneration. Various smart sensors may monitor the recovery of the wound process in different aspects, and some may spontaneously give feedback to the wound sites by releasing biological factors. The combination of the detection of smart sensors and individualized membrane design in the healing process shows enormous potential for wound dressings. Here, we provide an overview of the advantages of 3D printing and conventional therapies in tissue engineering. We also shed light on different types of 3D printing technology, biomaterials, and sensors to describe effective methods for use in skin and other tissue regeneration, highlighting their strengths and limitations. Finally, we highlight the value of 3D bioengineered membranes in various fields, including the modeling of disease, organ-on-a-chip, and drug development.

Dipole moment as the underlying mechanism for enhancing the immobilization of glucose oxidase by ferrocene-chitosan for superior specificity non-invasive glucose sensing

Non-invasive methods for sensing glucose levels are highly desirable due to the comfortableness, simplicity, and lack of infection risk. However, the insufficient accuracy and ease of interference limit their practical medical applications. Here, we develop a non-invasive salivary glucose biosensor based on a ferrocene-chitosan (Fc-Chit) modified carbon nanotube (CNT) electrode through a simple drop-casting method. Compared with previous studies that relied mainly on trial and error for evaluation, this is the first time that dipole moment was proposed to optimize the electron-mediated Fc-Chit, demonstrating sturdy immobilization of glucose oxidase (GOx) on the electrode and improving the electron transfer process. Thus, the superior sensing sensitivity of the biosensor can achieve 119.97 μA mM-1 cm-2 in phosphate buffered saline (PBS) solution over a wide sensing range of 20-800 μM. Additionally, the biosensor exhibited high stability (retaining 95.0% after three weeks) and high specificity toward glucose in the presence of various interferents, attributed to the specific sites enabling GOx to be sturdily immobilized on the electrode. The results not only provide a facile solution for accurate and regular screening of blood glucose levels via saliva tests but also pave the way for designing enzymatic biosensors with specific enzyme immobilization through fundamental quantum calculations.

Current state of the art and future directions for implantable sensors in medical technology: Clinical needs and engineering challenges

Implantable sensors have revolutionized the way we monitor biophysical and biochemical parameters by enabling real-time closed-loop intervention or therapy. These technologies align with the new era of healthcare known as healthcare 5.0, which encompasses smart disease control and detection, virtual care, intelligent health management, smart monitoring, and decision-making. This review explores the diverse biomedical applications of implantable temperature, mechanical, electrophysiological, optical, and electrochemical sensors. We delve into the engineering principles that serve as the foundation for their development. We also address the challenges faced by researchers and designers in bridging the gap between implantable sensor research and their clinical adoption by emphasizing the importance of careful consideration of clinical requirements and engineering challenges. We highlight the need for future research to explore issues such as long-term performance, biocompatibility, and power sources, as well as the potential for implantable sensors to transform healthcare across multiple disciplines. It is evident that implantable sensors have immense potential in the field of medical technology. However, the gap between research and clinical adoption remains wide, and there are still major obstacles to overcome before they can become a widely adopted part of medical practice.

Tunable Non-Enzymatic Glucose Electrochemical Sensing Based on the Ni/Co Bimetallic MOFs

Constructing high-performance glucose sensors is of great significance for the prevention and diagnosis of diabetes, and the key is to develop new sensitive materials. In this paper, a series of Ni2Co1-L MOFs (L = H2BPDC: 4,4'-biphenyldicarboxylic acid; H2NDC: 2,6-naphthalenedicarboxylic acid; H2BDC: 1,4-benzenedicarboxylic acid) were synthesized by a room temperature stirring method. The effects of metal centers and ligands on the structure, compositions, electrochemical properties of the obtained Ni2Co1-L MOFs were characterized, indicating the successful preparation of layered MOFs with different sizes, stacking degrees, electrochemical active areas, numbers of exposed active sites, and glucose catalytic activity. Among them, Ni2Co1-BDC exhibits a relatively thin and homogeneous plate-like morphology, and the Ni2Co1-BDC modified glassy carbon electrode (Ni2Co1-BDC/GCE) has the highest electrochemical performance. Furthermore, the mechanism of the enhanced glucose oxidation signal was investigated. It was shown that glucose has a higher electron transfer capacity and a larger apparent catalytic rate constant on the Ni2Co1-BDC/GCE surface. Therefore, tunable non-enzymatic glucose electrochemical sensing was carried out by regulating the metal centers and ligands. As a result, a high-sensitivity enzyme-free glucose sensing platform was successfully constructed based on the Ni2Co1-BDC/GCE, which has a wide linear range of 0.5-2899.5 μM, a low detection limit of 0.29 μM (S/N = 3), and a high sensitivity of 3925.3 μA mM-1 cm-2. Much more importantly, it was also successfully applied to the determination of glucose in human serum with satisfactory results, demonstrating its potential for glucose detection in real samples.

Stimuli-bioresponsive hydrogels as new generation materials for implantable, wearable, and disposable biosensors for medical diagnostics: Principles, opportunities, and challenges

Hydrogels are excellent water-swollen polymeric materials for use in wearable, implantable, and disposable biosensors. Hydrogels have unique properties such as low cost, ease of preparation, transparency, rapid response to external conditions, biocompatibility and self-adhesion to the skin, flexibility, and strain sensitivity, making them ideal for use in biosensor platforms. This review provides a detailed overview of advanced applications of stimuli-responsive hydrogels in biosensor platforms, from hydrogel synthesis and functionalization for bioreceptor immobilization to several important diagnostic applications. Emphasis is placed on recent advances in the fabrication of ultrasensitive fluorescent and electrically conductive hydrogels and their applications in wearable, implantable, and disposable biosensors for quantitative measurements. Design, modification, and assembly techniques of fluorescent, ionically conductive, and electrically conductive hydrogels to improve performance will be addressed. The advantages and performance improvements of immobilizing bioreceptors (e.g., antibodies, enzymes, and aptamers), and incorporating fluorescent and electrically conductive nanomaterials are described, as are their limitations. Potential applications of hydrogels in implantable, wearable, disposable portable biosensors for quantitative detection of the various bioanalytes (ions, molecules, drugs, proteins, and biomarkers) are discussed. Finally, the global market for hydrogel-based biosensors and future challenges and prospects are discussed in detail.

Stimuli-Responsive and Antibacterial Cellulose-Chitosan Hydrogels Containing Polydiacetylene Nanosheets

Herein, we report a stimuli-responsive hydrogel with inhibitory activity against Escherichia coli prepared by chemical crosslinking of carboxymethyl chitosan (CMCs) and hydroxyethyl cellulose (HEC). The hydrogels were prepared by esterification of chitosan (Cs) with monochloroacetic acid to produce CMCs which were then chemically crosslinked to HEC using citric acid as the crosslinking agent. To impart a stimuli responsiveness property to the hydrogels, polydiacetylene-zinc oxide (PDA-ZnO) nanosheets were synthesized in situ during the crosslinking reaction followed by photopolymerization of the resultant composite. To achieve this, ZnO was anchored on carboxylic groups in 10,12-pentacosadiynoic acid (PCDA) layers to restrict the movement of the alkyl portion of PCDA during crosslinking CMCs and HEC hydrogels. This was followed by irradiating the composite with UV radiation to photopolymerize the PCDA to PDA within the hydrogel matrix so as to impart thermal and pH responsiveness to the hydrogel. From the results obtained, the prepared hydrogel had a pH-dependent swelling capacity as it absorbed more water in acidic media as compared to basic media. The incorporation of PDA-ZnO resulted in a thermochromic composite responsive to pH evidenced by a visible colour transition from pale purple to pale pink. Upon swelling, PDA-ZnO-CMCs-HEC hydrogels had significant inhibitory activity against E. coli attributed to the slow release of the ZnO nanoparticles as compared to CMCs-HEC hydrogels. In conclusion, the developed hydrogel was found to have stimuli-responsive properties and inhibitory activity against E. coli attributed to zinc nanoparticles.

Enhanced terahertz sensitivity for glucose detection with a hydrogel platform embedded with Au nanoparticles

We presented a strategy for enhancing the sensitivity of terahertz glucose sensing with a hydrogel platform pre-embedded with Au nanoparticles. Physiological-level glucose solutions ranging from 0 to 0.8 mg/mL were measured and the extracted absorption coefficients can be clearly distinguished compared to traditional terahertz time domain spectroscopy performed directly on aqueous solutions. Further, Isotherm models were applied to successfully describe the relationship between the absorption coefficient and the glucose concentration (R²= 0.9977). Finally, the origin of the sensitivity enhancement was investigated and verified to be the pH change induced by the catalysis of Au nanoparticles to glucose oxidation.

Hydrogel Nanoarchitectonics: An Evolving Paradigm for Ultrasensitive Biosensing

The integration of nanoarchitectonics and hydrogel into conventional biosensing platforms offers the opportunities to design physically and chemically controlled and optimized soft structures with superior biocompatibility, better immobilization of biomolecules, and specific and sensitive biosensor design. The physical and chemical properties of 3D hydrogel structures can be modified by integrating with nanostructures. Such modifications can enhance their responsiveness to mechanical, optical, thermal, magnetic, and electric stimuli, which in turn can enhance the practicality of biosensors in clinical settings. This review describes the synthesis and kinetics of gel networks and exploitation of nanostructure-integrated hydrogels in biosensing. With an emphasis on different integration strategies of hydrogel with nanostructures, this review highlights the importance of hydrogel nanostructures as one of the most favorable candidates for developing ultrasensitive biosensors. Moreover, hydrogel nanoarchitectonics are also portrayed as a promising candidate for fabricating next-generation robust biosensors.

Real-Time Monitoring of Blood Parameters in the Intensive Care Unit: State-of-the-Art and Perspectives

The number of patients in intensive care units has increased over the past years. Critically ill patients are treated with a real time support of the instruments that offer monitoring of relevant blood parameters. These parameters include blood gases, lactate, and glucose, as well as pH and temperature. Considering the COVID-19 pandemic, continuous management of dynamic deteriorating parameters in patients is more relevant than ever before. This narrative review aims to summarize the currently available literature regarding real-time monitoring of blood parameters in intensive care. Both, invasive and non-invasive methods are described in detail and discussed in terms of general advantages and disadvantages particularly in context of their use in different medical fields but especially in critical care. The objective is to explicate both, well-known and frequently used as well as relatively unknown devices. Furtehrmore, potential future direction in research and development of realtime sensor systems are discussed. Therefore, the discussion section provides a brief description of current developments in biosensing with special emphasis on their technical implementation. In connection with these developments, the authors focus on different electrochemical approaches to invasive and non-invasive measurements in vivo.

Comparison of SERS pH probe responses after microencapsulation within hydrogel matrices

SIGNIFICANCE

Personalized medicine requires the tracking of an individual's metabolite levels over time to detect anomalies and evaluate the body's response to medications. Implanted sensors offer effective means to continuously monitor specific metabolite levels, provided they are accurate, stable over long time periods, and do no harm.

AIM

Four types of hydrogel embedded with pH-sensitive sensors were evaluated for their accuracy, sensitivity, reversibility, longevity, dynamic response, and consistency in static versus dynamic conditions and long-term storage.

APPROACH

Raman spectroscopy was first used to calibrate the intensity of pH-sensitive peaks of the Raman-active hydrogel sensors in a static pH environment. The dynamic response was then assessed for hydrogels exposed to changing pH conditions within a flow cell. Finally, the static pH response after 5 months of storage was determined.

RESULTS

All four types of hydrogels allowed the surface-enhanced Raman spectroscopy (SERS) sensors to respond to the pH level of the local environment without introducing interfering signals, resulting in consistent calibration curves. When the pH level changed, the probes in the gels were slow to reach steady-state, requiring several hours, and response times were found to vary among hydrogels. Only one type, poly(2-hydroxyethyl methacrylate) (pHEMA), lasted five months without significant degradation of dynamic range.

CONCLUSIONS

While all hydrogels appear to be viable candidates as biocompatible hosts for the SERS sensing chemistry, pHEMA was found to be most functionally stable over the long interval tested. Poly(ethylene glycol) hydrogels exhibit the most rapid response to changing pH. Since these two gel types are covalently cross-linked and do not generally degrade, they both offer advantages over sodium alginate for use as implants.

Long-Term Continuous Glucose Monitoring Using a Fluorescence-Based Biocompatible Hydrogel Glucose Sensor

Fluorescence-based hydrogel glucose sensors with boronic acid-based glucose recognition are promising regarding their potential to improve continuous glucose monitoring by facilitating long-lasting accuracy. However, these sensors typically become encapsulated after implantation, and the dynamic range decreases following long-term implantation and use. Herein, a four-arm polyethylene glycol (PEG) hydrogel is developed with an immobilized glucose-responsive fluorescence dye (GF-PEG-gel); this hydrogel is effective in mitigating foreign body reactions (FBRs) that hinder stable glucose responses in vivo. The GF-PEG-gel attached to an implantable device successfully traces blood glucose concentrations in diabetic model rats for 45 days. A pig experiment shows that the device measures the glucose concentration with an equivalent accuracy to that required for clinically available settings.