Materials for diabetes therapeutics

Smart Responsive Microneedles for Controlled Drug Delivery

As an emerging technology, microneedles offer advantages such as painless administration, good biocompatibility, and ease of self-administration, so as to effectively treat various diseases, such as diabetes, wound repair, tumor treatment and so on. How to regulate the release behavior of loaded drugs in polymer microneedles is the core element of transdermal drug delivery. As an emerging on-demand drug-delivery technology, intelligent responsive microneedles can achieve local accurate release of drugs according to external stimuli or internal physiological environment changes. This review focuses on the research efforts in smart responsive polymer microneedles at home and abroad in recent years. It summarizes the response mechanisms based on various stimuli and their respective application scenarios. Utilizing innovative, responsive microneedle systems offers a convenient and precise targeted drug delivery method, holding significant research implications in transdermal drug administration. Safety and efficacy will remain the key areas of continuous efforts for research scholars in the future.

Glucose Oxidase/Egg White Protein Microparticles with a Redox Mediator for Glucose Biosensors on a Screen-Printed Electrode and a Decomposable Electrode

Glucose oxidase (GOx) is a typical model enzyme used to create biosensors. Exploring a strategy to prepare ready-to-use functional enzymatic microparticles combining GOx and food-based proteins offers compelling advantages. However, no reports exist on the integration of egg white materials to synthesize functional biorecognition particles with glucose oxidation catalytic functions for electrochemical biosensors. Here, we demonstrate functional microparticles combining egg white proteins, GOx, and 9,10-phenanthrenequinone (PQ). The egg white proteins crosslink to form three-dimensional scaffolds to accommodate GOx and redox molecules. The PQ mediator enhances electron transfer between the electrode surface and the GOx enzyme's flavin adenine dinucleotides. The functional microparticles are directly applied to the printed electrode. The performance of these microparticles is evaluated using a screen-printed carbon nanotube (CNT)-modified electrode coated with GOx/PQ/egg white protein microparticles. The analytical performance of the system exhibits a linear range of 0.125-40 mM, with a maximum current (Imax) and a Michaelis-Menten constant (Km) being 0.2 µA and 4.6 mM, respectively. Additionally, a decomposable electrode composed of CNTs and edible oil conjugated with functional enzyme microparticles is shown to undergo degradation under gastric conditions. Utilizing food-based proteins to accommodate enzymes and to create redox-active microparticles for catalyzing glucose oxidation offers advantages in developing affordable and degradable bioelectrodes. This concept holds promise for advancing biocompatible electrodes in biosensor and bioelectronics applications.

Glucose-Responsive Chitosan Nanoparticle/Poly(vinyl alcohol) Hydrogels for Sustained Insulin Release In Vivo

Stimuli-responsive hydrogels (HGs) with a controlled drug release profile are the current challenge for advanced therapeutic applications. Specifically, antidiabetic drug-loaded glucose-responsive HGs are being investigated for closed-loop insulin delivery in insulin-dependent diabetes patients. In this direction, new design principles must be exploited to create inexpensive, naturally occurring, biocompatible glucose-responsive HG materials for the future. In this work, we developed chitosan nanoparticle/poly(vinyl alcohol) (PVA) hybrid HGs (CPHGs) for controlled insulin delivery for diabetes management. In this design, PVA and chitosan nanoparticles (CNPs) are cross-linked with a glucose-responsive formylphenylboronic acid (FPBA)-based cross-linker in situ. Leveraging the structural diversity of FPBA and its pinacol ester-based cross-linkers, we fabricate six CPHGs (CPHG1-6) with more than 80% water content. Using dynamic rheological measurements, we demonstrate elastic solid-like properties of CPHG1-6, which are dramatically reduced under low-pH and high-glucose environments. An in vitro drug release assay reveals size-dependent glucose-responsive drug release from the CPHGs under physiological conditions. It is important to note that the CPHGs show appreciable self-healing and noncytotoxic properties. Promisingly, we observe a significantly slower insulin release profile from the CPHG matrix in the type-1 diabetes (T1D) rat model. We are actively pursuing scaling up of CPHGs and the in vivo safety studies for clinical trial in the near future.

Fluorescent-based biodegradable microneedle sensor array for tether-free continuous glucose monitoring with smartphone application

Continuous glucose monitoring (CGM) allows patients with diabetes to manage critical disease effectively and autonomously and prevent exacerbation. A painless, wireless, compact, and minimally invasive device that can provide CGM is essential for monitoring the health conditions of freely moving patients with diabetes. Here, we propose a glucose-responsive fluorescence-based highly sensitive biodegradable microneedle CGM system. These ultrathin and ultralight microneedle sensor arrays continuously and precisely monitored glucose concentration in the interstitial fluid with minimally invasive, pain-free, wound-free, and skin inflammation-free outcomes at various locations and thicknesses of the skin. Bioresorbability in the body without a need for device removal after use was a key characteristic of the microneedle glucose sensor. We demonstrated the potential long-term use of the bioresorbable device by applying the tether-free CGM system, thus confirming the successful detection of glucose levels based on changes in fluorescence intensity. In addition, this microneedle glucose sensor with a user-friendly designed home diagnosis system using mobile applications and portable accessories offers an advance in CGM and its applicability to other bioresorbable, wearable, and implantable monitoring device technology.

Electro-responsive silk fibroin microneedles for controlled release of insulin

To date, very limited work has been done on convenient and active control of insulin release. Herein, we report an electro-responsive insulin delivery system based on thiolated silk fibroin. The disulfide cross-linking points in TSF were reduced and broken to form sulfhydryl groups under electrification, which led to the increase of microneedle swelling degree and promoted insulin release. After power failure, the sulfhydryl group is oxidised to form disulfide bond crosslinking point again, resulting in the reduction of microneedle swelling degree and thus the reduction of release rate. The insulin loaded in the electro-responsive insulin delivery system showed good reversible electroresponsive release performance. The addition of graphene reduced the microneedle resistance and increased the drug release rate under current conditions. In vivo studies on type 1 diabetic mice show that electro-responsive insulin delivery system effectively controls the blood glucose before and after feeding by switching on and off the power supply, and this blood glucose control can be maintained within the safe range (100-200 mg/dL) for a long time (11h). Such electrically responsive delivery microneedles show potential for integration with glucose signal monitoring and are expected to build closed-loop insulin delivery systems.

A Nanoparticle Ink Allowing the High Precision Visualization of Tissue Engineered Scaffolds by MRI

Hydrogels are widely used as cell scaffolds in several biomedical applications. Once implanted in vivo, cell scaffolds must often be visualized, and monitored overtime. However, cell scaffolds appear poorly contrasted in most biomedical imaging modalities such as magnetic resonance imaging (MRI). MRI is the imaging technique of choice for high-resolution visualization of low-density, water-rich tissues. Attempts to enhance hydrogel contrast in MRI are performed with "negative" contrast agents that produce several image artifacts impeding the delineation of the implant's contours. In this study, a magnetic ink based on ultra-small iron oxide nanoparticles (USPIONs; <5 nm diameter cores) is developed and integrated into biocompatible alginate hydrogel used in cell scaffolding applications. Relaxometric properties of the magnetic hydrogel are measured, as well as biocompatibility and MR-visibility (T₁ -weighted mode; in vitro and in vivo). A 2-week MR follow-up study is performed in the mouse model, demonstrating no image artifacts, and the retention of "positive" contrast overtime, which allows very precise delineation of tissue grafts with MRI. Finally, a 3D-contouring procedure developed to facilitate graft delineation and geometrical conformity assessment is applied on an inverted template alginate pore network. This proof-of-concept establishes the possibility to reveal precisely engineered hydrogel structures using this USPIONs ink high-visibility approach.

Characterization of Cyclic Olefin Copolymers for Insulin Reservoir in an Artificial Pancreas

Type-1 diabetes is one of the most prevalent metabolic disorders worldwide. It results in a significant lack of insulin production by the pancreas and the ensuing hyperglycemia, which needs to be regulated through a tailored administration of insulin throughout the day. Recent studies have shown great advancements in developing an implantable artificial pancreas. However, some improvements are still required, including the optimal biomaterials and technologies to produce the implantable insulin reservoir. Here, we discuss the employment of two types of cyclic olefin copolymers (Topas 5013L-10 and Topas 8007S-04) for an insulin reservoir fabrication. After a preliminary thermomechanical analysis, Topas 8007S-04 was selected as the best material to fabricate a 3D-printed insulin reservoir due to its higher strength and lower glass transition temperature (Tg). Fiber deposition modeling was used to manufacture a reservoir-like structure, which was employed to assess the ability of the material to prevent insulin aggregation. Although the surface texture presents a localized roughness, the ultraviolet analysis did not detect any significant insulin aggregation over a timeframe of 14 days. These interesting results make Topas 8007S-04 cyclic olefin copolymer a potential candidate biomaterial for fabricating structural components in an implantable artificial pancreas.

Nonmetallic N/C Nanozyme Performs Continuous Consumption of Glu for Inhibition of Colorectal Cancer Cells

Colorectal cancer (CRC) is the third leading cause of cancer-related mortality. 5-Fluorouracil (5-FU) is the first choice for treatment of CRC, but it cannot avoid the negative effects from local high glucose (Glu) in tumor. Recently, 5-FU therapy has been combined with other treatment modalities for CRC synergistic therapy. Although these combination therapy strategies are more effective in cancer therapy, the toxicity side effects to the liver and cause metabolic acidosis still exist. Herein, we report an emerging amorphous honeycomb-like nitrogen-doped carbon (N/C) nanozyme with nicotinamide adenine dinucleotide (NADH) oxidase and catalase (CAT) activity and cascade it with natural glucose dehydrogenase (GDH) to realize NAD⁺ regeneration and further hyperglycemia management. In this case, by the coupling of N/C nanozyme with natural GDH to form a N/C-GDH system, the electron transfer route can switch from Glu to a common but limited electron receptor, i.e., NAD⁺ to ubiquitous large amounts of oxygen, achieving the purpose of sustainable consumption of Glu under NAD⁺ circulation and regeneration, and importantly escaping the generation of toxic H₂O₂. The combination of the N/C-GDH system and 5-FU on CRC cells was investigated to assess their synergistic bioeffects. Notably, our results showed that the N/C-GDH system and 5-FU in combination significantly suppress the proliferation of human colon cancer cells (HCT-116) by reducing the sugar level and induced apoptosis compared with either material or drug used alone. This work expands the nanozymes in blood Glu management as well as the promising cancer cell inhibition and provides the possibility of nonmetallic nanomaterials in the realization of effective treatment of cancer.

Microneedle Patches Loaded with Nanovesicles for Glucose Transporter-Mediated Insulin Delivery

Glucose-responsive insulin delivery systems that mimic insulin secretion activity in the pancreas show great potential to improve clinical therapeutic outcomes for people with type 1 and advanced type 2 diabetes. Here, we report a glucose-responsive insulin delivery microneedle (MN) array patch that is loaded with red blood cell (RBC) vesicles or liposome nanoparticles containing glucose transporters (GLUTs) bound with glucosamine-modified insulin (Glu-Insulin). In hyperglycemic conditions, high concentrations of glucose in interstitial fluid can replace Glu-Insulin via a competitive interaction with GLUT, leading to a quick release of Glu-Insulin and subsequent regulation of blood glucose (BG) levels in vivo. To prolong the effective glucose-responsive insulin release from MNs, additional free Glu-Insulin, which serves as "stored insulin", is loaded after RBC vesicles or liposome nanoparticles bound with Glu-Insulin. In the streptozotocin (STZ)-induced type 1 diabetic mouse model, this smart GLUT-based insulin patch can effectively control BG levels without causing hypoglycemia.

In Vitro Evaluation of Antibacterial, Antioxidant, and Antidiabetic Activities and Glucose Uptake through 2-NBDG by Hep-2 Liver Cancer Cells Treated with Green Synthesized Silver Nanoparticles

The alarming rise in diabetes owing to drug resistance necessitates the implementation of prompt countermeasures in the treatment module of diabetes. Due to their unique physicochemical features, silver nanoparticles may have potential applications in the medical and pharmaceutical industries. Silver nanoparticles (AgNPs) were synthesized from the culture filtrate of Salmonella enterica (ATCC-14028). UV-Vis spectrophotometry, FTIR, SEM, and energy dispersive X-rays were used in the characterization of the nanoparticles. Transmission electron microscopy (TEM) revealed that AgNPs are spherical and highly scattered and vary in size from 7.18 nm to 13.24 nm. AgNP stability and protein loss were confirmed by thermogravimetric analysis (TGA) at different temperatures. The AgNPs had excellent antibacterial activity and a strong synergistic effect against methicillin-resistant bacteria Staphylococcus aureus (MRSA) ATCC-4330 and Streptococcus epidermis (MRSE) ATCC-51625. The DPPH experiment revealed that the AgNPs had high antioxidant activity. The antidiabetic assay revealed that these AgNPs had an IC50 for alpha-amylase of 428.60 μg/ml and an IC50 for alpha-glucosidase of 562.02 μg/ml. Flow cytometry analysis of Hep-2 cells treated with AgNPs (40 μg/ml) revealed higher expression of 2-NBDG glucose absorption (uptake) compared to control metformin. These AgNPs have promising antidiabetic properties and could be used in pharmaceuticals and biomedical industries.

Comprehensive Review on Wearable Sweat-Glucose Sensors for Continuous Glucose Monitoring

The incidence of diabetes is increasing at an alarming rate, and regular glucose monitoring is critical in order to manage diabetes. Currently, glucose in the body is measured by an invasive method of blood sugar testing. Blood glucose (BG) monitoring devices measure the amount of sugar in a small sample of blood, usually drawn from pricking the fingertip, and placed on a disposable test strip. Therefore, there is a need for non-invasive continuous glucose monitoring, which is possible using a sweat sensor-based approach. As sweat sensors have garnered much interest in recent years, this study attempts to summarize recent developments in non-invasive continuous glucose monitoring using sweat sensors based on different approaches with an emphasis on the devices that can potentially be integrated into a wearable platform. Numerous research entities have been developing wearable sensors for continuous blood glucose monitoring, however, there are no commercially viable, non-invasive glucose monitors on the market at the moment. This review article provides the state-of-the-art in sweat glucose monitoring, particularly keeping in sight the prospect of its commercialization. The challenges relating to sweat collection, sweat sample degradation, person to person sweat amount variation, various detection methods, and their glucose detection sensitivity, and also the commercial viability are thoroughly covered.

Repurposing Pinacol Esters of Boronic Acids for Tuning Viscoelastic Properties of Glucose-responsive Polymer Hydrogels: Effects on Insulin Release Kinetics

In the era of the diabetes pandemic, Injectable hydrogels (HGs) capable of releasing the desired amount of insulin under hyperglycemic conditions will significantly advance smart insulin development. Several smart boronic...

Recent Advances of Biomedical Materials for Prevention of Post-ESD Esophageal Stricture

Esophageal stricture commonly occurs in patients that have suffered from endoscopic submucosal dissection (ESD), and it makes swallowing difficult for patients, significantly reducing their life qualities. So far, the prevention strategies applied in clinical practice for post-ESD esophageal stricture usually bring various inevitable complications, which drastically counteract their effectiveness. Nowadays, with the widespread investigation and application of biomedical materials, lots of novel approaches have been devised in terms of the prevention of esophageal stricture. Biomedical polymers and biomedical-derived materials are the most used biomedical materials to prevent esophageal stricture after ESD. Both of biomedical polymers and biomedical-derived materials possess great physicochemical properties such as biocompatibility and biodegradability. Moreover, some biomedical polymers can be used as scaffolds to promote cell growth, and biomedical-derived materials have biological functions similar to natural organisms, so they are important in tissue engineering. In this review, we have summarized the current approaches for preventing esophageal stricture and put emphasis on the discussion of the roles biomedical polymers and biomedical-derived materials acted in esophageal stricture prevention. Meanwhile, we proposed several potential methods that may be highly rational and feasible in esophageal stricture prevention based on other researches associated with biomedical materials. This review is expected to offer a significant inspiration from biomedical materials to explore more effective, safer, and more economical strategies to manage post-ESD esophageal stricture.

Wearable Glucose Monitoring and Implantable Drug Delivery Systems for Diabetes Management

The global cost of diabetes care exceeds $1 trillion each year with more than $327 billion being spent in the United States alone. Despite some of the advances in diabetes care including continuous glucose monitoring systems and insulin pumps, the technology associated with managing diabetes has largely remained unchanged over the past several decades. With the rise of wearable electronics and novel functional materials, the field is well-poised for the next generation of closed-loop diabetes care. Wearable glucose sensors implanted within diverse platforms including skin or on-tooth tattoos, skin-mounted patches, eyeglasses, contact lenses, fabrics, mouthguards, and pacifiers have enabled noninvasive, unobtrusive, and real-time analysis of glucose excursions in ambulatory care settings. These wearable glucose sensors can be integrated with implantable drug delivery systems, including an insulin pump, glucose responsive insulin release implant, and islets transplantation, to form self-regulating closed-loop systems. This review article encompasses the emerging trends and latest innovations of wearable glucose monitoring and implantable insulin delivery technologies for diabetes management with a focus on their advanced materials and construction. Perspectives on the current unmet challenges of these strategies are also discussed to motivate future technological development toward improved patient care in diabetes management.

A review of biosensor technology and algorithms for glucose monitoring

Diabetes mellitus (DM) has become a serious illness in the whole world. Until now, there is no effective cure for patients with DM. It is well known that the glucose level is one key factor to determine the progress of DM. It is also an important reference to carry out the accurate and timely treatment for patients with DM. In this article, the related biosensors technology that can be utilized to identify and predict glucose level are reviewed in detail, including the algorithms that can help to achieve numerical value of glucose level. Firstly, the biosensor technology based on the physiological fluids are illustrated, including blood, sweat, interstitial fluid, ocular fluid, and other available fluids. Secondly, the algorithms for achieving numerical value of glucose level are investigated, including the physiological model-based method and the machine learning-based method. Finally, the future development trend and challenges of glucose level monitoring are given and the conclusions are drawn.

Modulating the foreign body response of implants for diabetes treatment

Diabetes Mellitus is a group of diseases characterized by high blood glucose levels due to patients' inability to produce sufficient insulin. Current interventions often require implants that can detect and correct high blood glucose levels with minimal patient intervention. However, these implantable technologies have not reached their full potential in vivo due to the foreign body response and subsequent development of fibrosis. Therefore, for long-term function of implants, modulating the initial immune response is crucial in preventing the activation and progression of the immune cascade. This review discusses the different molecular mechanisms and cellular interactions involved in the activation and progression of foreign body response (FBR) and fibrosis, specifically for implants used in diabetes. We also highlight the various strategies and techniques that have been used for immunomodulation and prevention of fibrosis. We investigate how these general strategies have been applied to implants used for the treatment of diabetes, offering insights on how these devices can be further modified to circumvent FBR and fibrosis.

NANO-BIOTECHNOLOGY AND ITS INNOVATIVE PERSPECTIVE IN DIABETES MANAGEMENT

Diabetes occurs due to the imbalance of glucose in the body known as glucose homeostasis, thus leading to metabolic changes in the body. The two stages hypoglycemia or hyperglycemia classify diabetes into various categories. Various bio-nanotechnological approaches are coupled up with nano particulates, polymers, liposome, various gold plated and solid lipid particulates, regulating transcellular transport, non specific cellular uptake, and paracellular transport, leading to oral, trans-dermal , pulmonary, buccal , nasal , specific gene oriented administration to avoid the patient's non compliance with the parental routes of administration. Phytochemicals are emerging strategies for the future prospects of diabetes management.

A step towards glucose control with a novel nanomagnetic-insulin for diabetes care

Massive efforts have been devoted to insulin delivery for diabetes care. Achieving a long-term tight-regulated blood glucose level with a low risk of hypoglycemia remains a great challenge. In this study we propose a novel strategy to efficiently regulate insulin action after insulin is injected or released into patient body aiming to achieve better glycemic control, which is achieved by the administration of insulin-conjugated magnetic nanoparticles (MNPs-Ins). We show that the locomotion of MNPs-Ins can be controlled to reach a target site on an in vitro microfluidic platform, which may open a way to modulate the physiological effect of insulin in a remote-control manner. Most importantly, the in vivo blood glucose regulation of the MNPs-Ins was performed on diabetic mice to understand the glycemic control performance. The results showed that the MNPs-Ins can achieve a better glycemic control with longer effective drug duration while not causing hypoglycemia and a magnetic-modulated hypoglycemic dynamics. Moreover, the in vivo histochemistry experiments confirmed the good biocompatibility of MNPs-Ins. Along with our on-going research on the possibility of the recycle and reuse of the MNPs-Ins, the finding presented in this paper may manifest a fascinating potential in insulin delivery in the near future.

Can nanoparticles and nano‒protein interactions bring a bright future for insulin delivery?

Insulin therapy plays an essential role in the treatment of diabetes mellitus. However, frequent injections required to effectively control the glycemic levels lead to substantial inconvenience and low patient compliance. In order to improve insulin delivery, many efforts have been made, such as developing the nanoparticles (NPs)-based release systems and oral insulin. Although some improvements have been achieved, the ultimate results are still unsatisfying and none of insulin-loaded NPs systems have been approved for clinical use so far. Recently, nano‒protein interactions and protein corona formation have drawn much attention due to their negative influence on the in vivo fate of NPs systems. As the other side of a coin, such interactions can also be used for constructing advanced drug delivery systems. Herein, we aim to provide an insight into the advance and flaws of various NPs-based insulin delivery systems. Particularly, an interesting discussion on nano‒protein interactions and its potentials for developing novel insulin delivery systems is initiated.

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Insulin therapy plays essential roles in treating diabetes.

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Optimizing insulin delivery enhances insulin therapy.

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Nanoparticles are promising systems for delivery of insulin.

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Nano-protein interactions influence the delivery of nanoparticles.

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Nano-protein interactions can be used for advanced delivery of insulin.

Glucose-Responsive Microspheres as a Smart Drug Delivery System for Controlled Release of Insulin

BACKGROUND AND OBJECTIVES

Diabetes mellitus, a disease of glucose regulation, has become one of the most common medical problems in the world. At present, alternative therapy for diabetes has, to a large extent, been widely concerned with the improvement of treatment efficacy. The aims of this study were to characterize and evaluate the surface morphology of the novel glucose-responsive injectable microspheres containing insulin, along with their in vitro release and in vivo efficacy.

METHODS

In this study, glucose-responsive microspheres as an emerging smart drug delivery system for controlled release of insulin were developed by an improved water-in-oil-in-water (W/O/W) double emulsion preparation method. Here, methoxypolyethylene glycol-hydrazone-4-methoxypolyethylene glycol benzoate (mPEG-Hz-mPEG4AB) was synthesized as a pH-responsive carrier.

RESULTS

The microspheres had a good spherical structure with a particle size of 5 ~ 10 μm. Approximately 61% of insulin was released in 15 h under a high glucose environment but was barely released within the normal glucose range in in vitro studies. After a subcutaneous injection of insulin microspheres in rats, blood glucose levels rapidly decreased within 2 h and could be maintained for 2 days in the normal range. Histopathological evaluation indicated that the microspheres were almost non-irritating.

CONCLUSIONS

The pH-responsive mPEG-Hz-mPEG4AB could be used as an efficient insulin microsphere carrier, and the optimized microspheres had good morphology and sustained hypoglycemic effect.

Triggered Release of Loads from Microcapsule-in-Microcapsule Hydrogel Microcarriers: En-Route to an "Artificial Pancreas"

A method to assemble stimuli-responsive nucleic acid-based hydrogel-stabilized microcapsule-in-microcapsule systems is introduced. An inner aqueous compartment stabilized by a stimuli-responsive hydrogel-layer (∼150 nm) provides the inner microcapsule (diameter ∼2.5 μm). The inner microcapsule is separated from an outer aqueous compartment stabilized by an outer stimuli-responsive hydrogel layer (thickness of ∼150 nm) that yields the microcapsule-in-microcapsule system. Different loads, e.g., tetramethyl rhodamine-dextran (TMR-D) and CdSe/ZnS quantum dots (QDs), are loaded in the inner and outer aqueous compartments. The hydrogel layers exist in a higher stiffness state that prevents inter-reservoir or leakage of the loads from the respective aqueous compartments. Subjecting the inner hydrogel layer to Zn2+-ions and/or the outer hydrogel layer to acidic pH or crown ether leads to the triggered separation of the bridging units associated with the respective hydrogel layers. This results in the hydrogel layers of lower stiffness allowing either the mixing of the loads occupying the two aqueous compartments, the guided release of the load from the outer aqueous compartment, or the release of the loads from the two aqueous compartments. In addition, a pH-responsive microcapsule-in-microcapsule system is loaded with glucose oxidase (GOx) in the inner aqueous compartment and insulin in the outer aqueous compartment. Glucose permeates across the two hydrogel layers resulting in the GOx catalyzed aerobic oxidation of glucose to gluconic acid. The acidification of the microcapsule-in-microcapsule system leads to the triggered unlocking of the outer, pH-responsive hydrogel layer and to the release of insulin. The pH-stimulated release of insulin is controlled by the concentration of glucose. While at normal glucose levels, the release of insulin is practically prohibited, the dose-controlled release of insulin in the entire diabetic range  is demonstrated. Also, switchable ON/OFF release of insulin is achieved highlighting an autonomous glucose-responsive microdevice operating as an "artificial pancreas" for the release of insulin.

Synthesis and Applications of Hydrogels in Cancer Therapy

Hydrogels are water-insoluble, hydrophilic, cross-linked, three-dimensional networks of polymer chains having the ability to swell and absorb water but do not dissolve in it, that comprise the major difference between gels and hydrogels. The mechanical strength, physical integrity and solubility are offered by the crosslinks. The different applications of hydrogels can be derived based on the methods of their synthesis, response to different stimuli, and their different kinds. Hydrogels are highly biocompatible and have properties similar to human tissues that make it suitable to be used in various biomedical applications, including drug delivery and tissue engineering. The role of hydrogels in cancer therapy is highly emerging in recent years. In the present review, we highlighted different methods of synthesis of hydrogels and their classification based on different parameters. Distinctive applications of hydrogels in the treatment of cancer are also discussed.

Biomaterials for stem cell engineering and biomanufacturing

Recent years have witnessed the expansion of tissue failures and diseases. The uprising of regenerative medicine converges the sight onto stem cell-biomaterial based therapy. Tissue engineering and regenerative medicine proposes the strategy of constructing spatially, mechanically, chemically and biologically designed biomaterials for stem cells to grow and differentiate. Therefore, this paper summarized the basic properties of embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) and adult stem cells. The properties of frequently used biomaterials were also described in terms of natural and synthetic origins. Particularly, the combination of stem cells and biomaterials for tissue repair applications was reviewed in terms of nervous, cardiovascular, pancreatic, hematopoietic and musculoskeletal system. Finally, stem-cell-related biomanufacturing was envisioned and the novel biofabrication technologies were discussed, enlightening a promising route for the future advancement of large-scale stem cell-biomaterial based therapeutic manufacturing.

Preparation, in vitro and in vivo evaluation of PLGA/Chitosan based nano-complex as a novel insulin delivery formulation

The smart self-regulated drug delivery systems for insulin administration are desirable to achieve glycemic control, and decrease the long-term micro- and macro vascular complications. In this study, we developed an injectable nano-complex formulation for closed-loop insulin delivery after subcutaneous administration and release of insulin in response to increased blood glucose levels. The nano-complex was prepared by mixing oppositely charged chitosan and PLGA nanoparticles. PLGA nanoparticles were prepared using double-emulsion solvent diffusion method, and were loaded with glucose oxidase (GOx) and catalase (CAT) enzymes. These negatively charged particles decrease micro-environmental pH, by gluconic acid production in the glucose molecules presence. Positively charged chitosan nanoparticles were prepared using ionic gelation method, and were loaded with insulin. These nanoparticles (NPs) released insulin by dissociation in acidic pH caused by the GOx activity. Following in vitro studies, in vivo evaluation of nano-complex formulations in streptozocin induced diabetic rats showed significant glycemic regulation up to 98 h after subcutaneous administration.

Nanotechnology Advanced Strategies for the Management of Diabetes Mellitus

Background:

Medications currently available for the management of diabetes mellitus are inconvenient and have some limitations. Thus, investigations for novel approaches are needed to deliver and target antidiabetics safely to the site of action.

Objective:

The present review emphasizes the limitations of conventional antidiabetics and provides the recent progresses of nanotechnology in the treatment of diabetes mellitus with a special highlight on the novel nanocarriers methodologies employed as antidiabetic drug delivery systems.

Methods:

The potential nanocarriers employed for the treatment of diabetes comprise liposomes, niosomes, self-nanoemulsifying drug delivery systems, polymeric nanoparticles, gold nanoparticles, dendrimers and micelles. Herbal nanomedicine has also emerged to be a promising way for adequate delivery of herbal compounds. Other nanotechnology approaches involve the usage of oral insulin, inhalable insulin, artificial pancreas, and nanopump.

Results:

Nanocarriers have proved to lead a successful delivery of antidiabetic medications, aiming at drug targeting for enhanced efficacy and safety.

Conclusion:

These innovative generations of drug delivery systems have important benefits over conventionally existing ones. The future of nanotechnology in the management of diabetes is still open with several prospects and will be of pronounced significance.

Toward Dosing Precision and Insulin Stability in an Artificial Pancreas System

A fully implantable artificial pancreas (AP) still represents the holy grail for diabetes treatment. The quest for efficient miniaturized implantable insulin pumps, able to accurately regulate the blood glucose profile and to keep insulin stability, is still persistent. This work describes the design and testing of a microinjection system connected to a variable volume insulin reservoir devised to favor insulin stability during storage. The design, the constitutive materials, and the related fabrication techniques were selected to favor insulin stability by avoiding—or at least limiting—hormone aggregation. We compared substrates made of nylon 6 and Teflon, provided with different surface roughness values due to the employed fabrication procedures (i.e., standard machining and spray deposition). Insulin stability was tested in a worst case condition for 14 days, and pumping system reliability and repeatability in dosing were tested over an entire reservoir emptying cycle. We found that nylon 6 guarantees a higher insulin stability than Teflon and that independent of the material used, larger roughness determines a higher amount of insulin aggregates. A dedicated rotary pump featured by a 1-μL delivery resolution was developed and connected through a proper gear mechanism to a variable volume air-tight insulin reservoir. The microinjection system was also able to operate in a reverse mode to enable the refilling of the implanted reservoir. The developed system represents a fundamental building block toward the development of a fully implantable AP and could be advantageously integrated even in different implantable drug delivery apparatus (e.g., for pain management).

Glucose-Responsive Microneedle Patches for Diabetes Treatment

Antidiabetic therapeutics, including insulin as well as glucagon-like peptide 1 (GLP-1) and its analogs, are essential for people with diabetes to regulate their blood glucose levels. Nevertheless, conventional treatments based on hypodermic administration is commonly associated with poor blood glucose control, a lack of patient compliance, and a high risk of hypoglycemia. Closed-loop drug delivery strategies, also known as self-regulated administration, which can intelligently govern the drug release kinetics in response to the fluctuation in blood glucose levels, show tremendous promise in diabetes therapy. In the meantime, the advances in the development and use of microneedle (MN)-array patches for transdermal drug delivery offer an alternative method to conventional hypodermic administration. Hence, glucose-responsive MN-array patches for the treatment of diabetes have attracted increasing attentions in recent years. This review summarizes recent advances in glucose-responsive MN-array patch systems. Their opportunities and challenges for clinical translation are also discussed.

Evaluation of encapsulating and microporous nondegradable hydrogel scaffold designs on islet engraftment in rodent models of diabetes

Islet transplantation is a promising therapeutic option for type 1 diabetes mellitus, yet the current delivery into the hepatic portal vasculature is limited by poor engraftment. Biomaterials have been used as a means to promote engraftment and function at extrahepatic sites, with strategies being categorized as encapsulation or microporous scaffolds that can either isolate or integrate islets with the host tissue, respectively. Although these approaches are typically studied separately using distinct material platforms, herein, we developed nondegradable polyethylene glycol (PEG)-based hydrogels for islet encapsulation or as microporous scaffolds for islet seeding to compare the initial engraftment and function of islets in syngeneic diabetic mice. Normoglycemia was restored with transplantation of islets within either encapsulating or microporous hydrogels containing 700 islet equivalents (IEQ), with transplantation on microporous hydrogels producing lower blood glucose levels at earlier times. A glucose challenge test at 1 month after transplant indicated that encapsulated islets had a delay in glucose-stimulated insulin secretion, whereas microporous hydrogels restored normoglycemia in times consistent with native pancreata. Encapsulated islets remained isolated from the host tissue, whereas the microporous scaffolds allowed for revascularization of the islets after transplant. Finally, we compared the inflammatory response after transplantation for the two systems and noted that microporous hydrogels had a substantially increased presence of neutrophils. Collectively, these findings suggest that both encapsulation and microporous PEG scaffold designs allow for stable engraftment of syngeneic islets and the ability to restore normoglycemia, yet the architecture influences islet function and responsiveness after transplantation.

Multiresponsive Supramolecular Theranostic Nanoplatform Based on Pillar[5]arene and Diphenylboronic Acid Derivatives for Integrated Glucose Sensing and Insulin Delivery

A closed-loop "smart" insulin delivery system with the capability to mimic pancreatic cells will be highly desirable for diabetes treatment. This study reports a multiple stimuli-responsive insulin delivery platform based on an explicit supramolecular strategy. Self-assembled from a well-designed amphiphilic host-guest complex formed by pillar[5]arene and a diphenylboronic acid derivative and loaded with insulin and glucose oxidase, the obtained insulin-GOx-loaded supramolecular vesicles can selectively recognize glucose, accompanied by the structure disruption and efficient release of the entrapped insulin triggered by the high glucose concentration as well as the in situ generated H₂ O₂ and acid microenvironment during the GOx-promoted specific oxidation of glucose into gluconic acid. Moreover, such a "smart" supramolecular theranostic nanoplatform is able to function as both a glucose sensor and a controlled insulin delivery actuator. In vivo experiments further demonstrate that this smart supramolecular nanocarrier shows fast response to hyperglycemic circumstances and can effectively regulate the glucose levels in a mouse model of type I diabetes.

Glucose- and H2O2-Responsive Polymeric Vesicles Integrated with Microneedle Patches for Glucose-Sensitive Transcutaneous Delivery of Insulin in Diabetic Rats

Herein, a dual-responsive insulin delivery device by integrating glucose- and H₂O₂-responsive polymeric vesicles (PVs) with transcutaneous microneedles (MNs) has been designed. This novel microneedle delivery device achieves a goal of fast response, excellent biocompatibility, and painless administration. The PVs are self-assembled from a triblock copolymer including poly(ethylene glycol), poly(phenylboronic acid) (glucose-sensitive block), and poly(phenylboronic acid pinacol ester) (H₂O₂-sensitive block). After loading with insulin and glucose oxidase (GO _x), the drug-loaded PVs display a basal insulin release as well as a promoted insulin release in response to hyperglycemic states. The insulin release rate responds quickly to elevated glucose and can be further promoted by the incorporated GO _x, which will generate the H₂O₂ at high glucose levels and further break the chemical links of phenylboronic acid pinacol ester group. Finally, the transdermal delivery of insulin to the diabetic rats ((insulin + GO _x)-loaded MNs) presents an effective hypoglycemic effect compared to that of subcutaneous injection or only insulin-loaded MNs, which indicates the as-prepared MNs insulin delivery system could be of great importance for the applications in the therapy of diabetes.

Bioresponsive Microneedles with a Sheath Structure for H2 O2 and pH Cascade-Triggered Insulin Delivery

Self-regulating glucose-responsive insulin delivery systems have great potential to improve clinical outcomes and quality of life among patients with diabetes. Herein, an H2 O2 -labile and positively charged amphiphilic diblock copolymer is synthesized, which is subsequently used to form nano-sized complex micelles (NCs) with insulin and glucose oxidase of pH-tunable negative charges. Both NCs are loaded into the crosslinked core of a microneedle array patch for transcutaneous delivery. The microneedle core is additionally coated with a thin sheath structure embedding H2 O2 -scavenging enzyme to mitigate the injury of H2 O2 toward normal tissues. The resulting microneedle patch can release insulin with rapid responsiveness under hyperglycemic conditions owing to an oxidative and acidic environment because of glucose oxidation, and can therefore effectively regulate blood glucose levels within a normal range on a chemically induced type 1 diabetic mouse model with enhanced biocompatibility.

Core-Shell Microneedle Gel for Self-Regulated Insulin Delivery

A bioinspired glucose-responsive insulin delivery system for self-regulation of blood glucose levels is desirable for improving health and quality of life outcomes for patients with type 1 and advanced type 2 diabetes. Here we describe a painless core-shell microneedle array patch consisting of degradable cross-linked gel for smart insulin delivery with rapid responsiveness and excellent biocompatibility. This gel-based device can partially dissociate and subsequently release insulin when triggered by hydrogen peroxide (H2O2) generated during the oxidation of glucose by a glucose-specific enzyme covalently attached inside the gel. Importantly, the H2O2-responsive microneedles are coated with a thin-layer embedding H2O2-scavenging enzyme, thus mimicking the complementary function of enzymes in peroxisomes to protect normal tissues from injury caused by oxidative stress. Utilizing a chemically induced type 1 diabetic mouse model, we demonstrated that this smart insulin patch with a bioresponsive core and protective shell could effectively regulate the blood glucose levels within a normal range with improved biocompatibility.

An injectable particle-hydrogel hybrid system for glucose-regulatory insulin delivery

Long-term and daily subcutaneous injections of insulin for the treatment of insulin-dependent diabetic patients often lead to poor patient compliance and undesired complications. Phenylboronic acid (PBA)-based polymeric hydrogels have been widely considered as one of the most promising insulin delivery system to replace the frequent insulin injections. However, their applications are limited by clinically irrelevant glucose-responsive range, slow response rate, low tissue-adhesiveness and poor biodegradability, undesirable leakage at normoglycemic state. Herein, we report a novel implantable insulin hydrogel for glucose-regulated delivery of insulin based on a unique particle-hydrogel hybrid platform featuring fast glucose responsiveness at physiological pH, shear-thinning behavior for injection, tissue-adhesive function for long-lasting adherence, and full biodegradability for safe use. The system was thoroughly characterized both in vitro and in vivo and was demonstrated to hold these unique functions. Using streptozotocin-induced diabetic mice as a model, it was shown that a single subcutaneous injection of the insulin-loaded particle-hydrogel formulation led to quasi-steady-state blood glucose levels within the normal range for about two weeks. In addition, the preparation of the formulation only involved simple mixing and self-assembling processes, and thus it had great scalability and reproducibility for practical use. The highly feasible preparation, excellent performance, inherent biocompatibility and biodegradability make this novel composite hydrogel promising platform for diabetes therapy.

STATEMENT OF SIGNIFICANCE

Phenylboronic acid (PBA)-based polymeric hydrogels have been widely considered as one of the most promising insulin delivery system to replace the frequent insulin injections. However, these hydrogels, mostly based on a variety of PBA-containing acrylamide monomers, are still far from clinical reality. Building upon a unique particle-hydrogel hybrid platform, herein we report a novel implantable insulin storage and delivery system with multifunctionalities including fast glucose-sensitiveness at physiological pH, shear-thinning behavior for injection, tissue-adhesive function for long-lasting adherence, biodegradable materials for safe use and well-controlled insulin release. These unique functions were demonstrated through research both in vitro and in vivo. In addition, the preparation of the formulation was simple, and thus it had great scalability and reproducibility for practical use.

Advances in bioresponsive closed-loop drug delivery systems

Controlled drug delivery systems are able to improve efficacy and safety of therapeutics by optimizing the duration and kinetics of release. Among them, closed-loop delivery strategies, also known as self-regulated administration, have proven to be a practical tool for homeostatic regulation, by tuning drug release as a function of biosignals relevant to physiological and pathological processes. A typical example is glucose-responsive insulin delivery system, which can mimic the pancreatic beta cells to release insulin with a proper dose at a proper time point by responding to plasma glucose levels. Similar self-regulated systems are also important in the treatment of other diseases including thrombosis and bacterial infection. In this review, we survey the recent advances in bioresponsive closed-loop drug delivery systems, including glucose-responsive, enzyme-activated, and other biosignal-mediated delivery systems. We also discuss the future opportunities and challenges in this field.

Rational Design of Glucose-Responsive Insulin Using Pharmacokinetic Modeling

A glucose responsive insulin (GRI) is a therapeutic that modulates its potency, concentration, or dosing of insulin in relation to a patient's dynamic glucose concentration, thereby approximating aspects of a normally functioning pancreas. Current GRI design lacks a theoretical basis on which to base fundamental design parameters such as glucose reactivity, dissociation constant or potency, and in vivo efficacy. In this work, an approach to mathematically model the relevant parameter space for effective GRIs is induced, and design rules for linking GRI performance to therapeutic benefit are developed. Well-developed pharmacokinetic models of human glucose and insulin metabolism coupled to a kinetic model representation of a freely circulating GRI are used to determine the desired kinetic parameters and dosing for optimal glycemic control. The model examines a subcutaneous dose of GRI with kinetic parameters in an optimal range that results in successful glycemic control within prescribed constraints over a 24 h period. Additionally, it is demonstrated that the modeling approach can find GRI parameters that enable stable glucose levels that persist through a skipped meal. The results provide a framework for exploring the parameter space of GRIs, potentially without extensive, iterative in vivo animal testing.

Glucose-responsive insulin release: Analysis of mechanisms, formulations, and evaluation criteria

Diabetes mellitus has become one of the biggest medical challenges affecting millions of people globally. Alternative treatments for diabetes are currently being intensively investigated to improve the treatment efficacy and life qualities for diabetic patients. Glucose-responsive insulin release (GRIR) systems have exhibited tremendous potential to improve the normal glycemic control and to reduce the incidence of hyperglycemia and hypoglycemia, which further reduces potential complications in diabetic patients. In a given GRIR drug formulation, accuracy, response time, and reversibility of the GRIR functions are three key features enabling potential seamless control of blood glucose level. Nevertheless, there is significant challenge preventing current GRIR formulations from achieving them. This review article analyzes the most updated literature and provides insights on the impact of GRIR mechanisms, and formulations on these key features, and the relevant in vitro and in vivo evaluation methods to test these functions.

Glucose Sensing for Diabetes Monitoring: Recent Developments

This review highlights recent advances towards non-invasive and continuous glucose monitoring devices, with a particular focus placed on monitoring glucose concentrations in alternative physiological fluids to blood.

A glucose-sensitive block glycopolymer hydrogel based on dynamic boronic ester bonds for insulin delivery

Hydrogels are good candidates to satisfy many needs for functional and tunable biomaterials. How to precisely control the gel structure and functions is crucial for the construction of sophisticated soft biomaterials comprising the hydrogels, which facilitates the impact of the surrounding environment on a unique biological function occurring. Here, glucose-responsive hydrogels comprised of 3-acrylamidophenyl boronic acid copolymerized with 2-lactobionamidoethyl methacrylate (p(APBA-b-LAMA)) were synthesized, and further evaluated as carriers for insulin delivery. The formation of (p(APBA-b-LAMA)) hydrogel was based on dynamic covalent bond using the association of boronic acid with diols. P(APBA-b-LAMA) hydrogel with the typical porous structure showed a rapid increase in equilibrium of swelling, which was up to 1856% after incubation with aqueous solution. Using insulin as a model protein therapeutic, p(APBA-b-LAMA) hydrogel exhibited high drug loading capability up to 15.6%, and also displayed glucose-dependent insulin release under physiological conditions. Additionally, the viability of NIH3T3 cells was more than 90% after treated with p(APBA-b-LAMA) hydrogel, indicating that the hydrogel had no cytotoxicity. Consequently, the novel p(APBA-b-LAMA) hydrogel has a practical application for diabetes treatment.