Glucose-responsive microgels integrated with enzyme nanocapsules for closed-loop insulin delivery

Chitosan-Based Nanomaterials for Drug Delivery

This review discusses different forms of nanomaterials generated from chitosan and its derivatives for controlled drug delivery. Nanomaterials are drug carriers with multiple features, including target delivery triggered by environmental, pH, thermal responses, enhanced biocompatibility, and the ability to cross the blood-brain barrier. Chitosan (CS), a natural polysaccharide largely obtained from marine crustaceans, is a promising drug delivery vector for therapeutics and diagnostics, owing to its biocompatibility, biodegradability, low toxicity, and structural variability. This review describes various approaches to obtain novel CS derivatives, including their distinct advantages, as well as different forms of nanomaterials recently developed from CS. The advanced applications of CS-based nanomaterials are presented here in terms of their specific functions. Recent studies have proven that nanotechnology combined with CS and its derivatives could potentially circumvent obstacles in the transport of drugs thereby improving the drug efficacy. CS-based nanomaterials have been shown to be highly effective in targeted drug therapy.

Nitrilotriacetic Acid-Functionalized Glucose-Responsive Complex Micelles for the Efficient Encapsulation and Self-Regulated Release of Insulin

Insulin plays a significant role in diabetes treatment. Although a huge number of insulin-loaded, glucose-responsive nanocarriers have been developed in past decades, most of them showed a lower loading capacity and efficiency due to the weak interaction between insulin and nanocarriers. In this work, a novel insulin-encapsulated glucose-responsive polymeric complex micelle (CM) is devised, showing (i) enhanced insulin-loading efficiency owing to the zinc ions' chelation by nitrilotriacetic acid (NTA) groups of NTA-functioned glycopolymer and the histidine imidazole of insulin, (ii) the glucose-triggered pulse release of insulin, and (iii) long stability under physiological conditions. This CM was fabricated by the self-assembly of block copolymer PEG- b-P(Asp- co-AspPBA) and glycopolymer P(Asp- co-AspGA- co-AspNTA), resulting in complex micelles with a PEG shell and a cross-linked core composed of phenylboronic acid (PBA)/glucose complexations. Notably, the modified nitrilotriacetic acid (NTA) groups of CM could specifically bind insulin via chelated zinc ions, thus enhancing the loading efficacy of insulin compared to that of nonmodified CM. The dynamic PBA/glucose complexation core of CM dissociates under the trigger of high glucose concentration (>2 g/L) while being quite stable in low glucose concentrations (<2 g/L), as demonstrated by the pulse release of insulin in vitro. Finally, in a murine model of type 1 diabetes, NTA-modified complex micelles loading an insulin (NTA-CM-INS) group exhibited a long hypoglycemic effect which is superior to that of free insulin in the PBS (PBS-INS) group and insulin-loaded complex micelles without an NTA modification (CM-INS) group. This long-term effect benefited from Zn(II) chelation by NTA-modified complex micelles and could avoid hypoglycemia caused by the burst release of insulin. Taken together, this constitutes a highly effective way to encapsulate insulin and release insulin via an on-demand manner for blood glucose control in diabetes.

Glucose-Responsive Metal-Organic-Framework Nanoparticles Act as "Smart" Sense-and-Treat Carriers

Zeolitic Zn²⁺-imidazolate cross-linked framework nanoparticles, ZIF-8 NMOFs, are used as "smart" glucose-responsive carriers for the controlled release of drugs. The ZIF-8 NMOFs are loaded with the respective drug and glucose oxidase (GOx), and the GOx-mediated aerobic oxidation of glucose yields gluconic acid and H₂O₂. The acidification of the NMOFs' microenvironment leads to the degradation of the nanoparticles and the release of the loaded drugs. In one sense-and-treat system, GOx and insulin are loaded in the NMOFs. In the presence of glucose, the nanoparticles are unlocked, resulting in the release of insulin. The release of insulin is controlled by the concentration of glucose. In the second sense-and-treat system, the NMOFs are loaded with the antivascular endothelial growth factor aptamer (VEGF aptamer) and GOx. In the presence of glucose, the ZIF-8 NMOFs are degraded, leading to the release of the VEGF aptamer, which acts as a potential inhibitor of the angiogenetic regeneration of blood vessels by VEGF. As calcination of the VEGF-generated blood vessels leads to blindness of diabetic patients, the functional NMOFs might act as "smart" materials for the treatment of macular diseases. The potential cytotoxicity of the NMOFs originated from the GOx-generated H₂O₂ is resolved by the co-immobilization of the H₂O₂-scavanger catalase in the NMOFs.

Highly Selective and Sensitive Detection of Pb2+ in Aqueous Solution Using Tetra(4-pyridyl)porphyrin-Functionalized Thermosensitive Ionic Microgels

Tetra(4-pyridyl)porphyrin (TPyP)-functionalized thermosensitive ionic microgels (TPyP5-MGs) were synthesized by a two-step quaternization method. The obtained TPyP5-MGs have a hydrodynamic radius of about 189 nm with uniform size distribution and exhibit thermosensitive character. The TPyP5-MG microgel suspensions can optically respond to trace Pb²⁺ ions in aqueous solution with high sensitivity and selectivity over the interference of other 19 species of metal ions (Yb³⁺, Gd³⁺, Ce³⁺, La³⁺, Bi³⁺, Ba²⁺, Zn²⁺, Ni²⁺, Co²⁺, Mn²⁺, Cr³⁺, K⁺, Na⁺, Li⁺, Al³⁺, Cu²⁺, Ag⁺, Cd²⁺, and Fe³⁺) by using UV-visible spectroscopy. The sensitivity of TPyP5-MGs toward Pb²⁺ can be further improved by increasing the solution temperature. The limit of detection for TPyP5-MG microgel suspensions in the detection of Pb²⁺ in aqueous solution at 50 °C is about 25.2 nM, which can be further improved to be 5.9 nM by using the method of higher order derivative spectrophotometry and is much lower than the U. S. EPA standard for the safety limit of Pb²⁺ ions in drinking water. It is further demonstrated that the TPyP5-MG microgel suspensions have a potential application in the detection of Pb²⁺ in real world samples, which give consistent results with those obtained by elemental analysis.

Encapsulation of Biological Agents in Hydrogels for Therapeutic Applications

Hydrogels are materials specially suited for encapsulation of biological elements. Their large water content provides an environment compatible with most biological molecules. Their crosslinked nature also provides an ideal material for the protection of encapsulated biological elements against degradation and/or immune recognition. This makes them attractive not only for controlled drug delivery of proteins, but they can also be used to encapsulate cells that can have therapeutic applications. Thus, hydrogels can be used to create systems that will deliver required therapies in a controlled manner by either encapsulation of proteins or even cells that produce molecules that will be released from these systems. Here, an overview of hydrogel encapsulation strategies of biological elements ranging from molecules to cells is discussed, with special emphasis on therapeutic applications.

One-pot synthesis of a metal-organic framework-based drug carrier for intelligent glucose-responsive insulin delivery

We have developed a glucose-responsive metal-organic framework (MOF)-based insulin delivery nanosystem via a one-pot process. The system relies on the MOF response to glucose stimulation and this can promote insulin delivery. This nanosystem was successfully applied for glucose-responsive and self-regulated insulin release.

Treatment of type 2 diabetes: future approaches

INTRODUCTION OR BACKGROUND

Type 2 diabetes, which accounts for ~90% of all diabetes, is a heterogeneous and progressive disease with a variety of causative and potentiating factors. The hyperglycaemia of type 2 diabetes is often inadequately controlled, hence the need for a wider selection of glucose-lowering treatments.

SOURCES OF DATA

Medline, PubMed, Web of Science and Google Scholar.

AREAS OF AGREEMENT

Early, effective and sustained control of blood glucose defers the onset and reduces the severity of microvascular and neuropathic complications of type 2 diabetes and helps to reduce the risk of cardiovascular (CV) complications.

AREAS OF CONTROVERSY

Newer glucose-lowering agents require extensive long-term studies to confirm CV safety. The positioning of newer agents within therapeutic algorithms varies.

GROWING POINTS

In addition to their glucose-lowering efficacy, some new glucose-lowering agents may act independently to reduce CV and renal complications.

AREAS TIMELY FOR DEVELOPING RESEARCH

Studies of potential new glucose-lowering agents offer the opportunity to safely improve glycaemic control with prolonged efficacy and greater opportunity for therapeutic individualisation.

Long-Acting Release Microspheres Containing Novel GLP-1 Analog as an Antidiabetic System

Glucagon-like peptide 1 (GLP-1) has recently received significant attention as an efficacious way to treat diabetes mellitus. However, the short half-life of the peptide limits its clinical application in diabetes. In our previous study, a novel GLP-1 analog (PGLP-1) with a longer half-life was synthesized and evaluated. Herein, we prepared the PGLP-1-loaded poly(d,l-lactide- co-glycolide) microspheres to achieve long-term effects on blood glucose control. The incorporation of zinc ion into the formulation can effectively decrease the initial burst release, and a uniform drug distribution was obtained, in contrast to native PGLP-1 encapsulated microspheres. We demonstrated that the solubility of the drug encapsulated in microspheres played an important role in in vitro release behavior and drug distribution inside the microspheres. The Zn-PGLP-1 microspheres had a prominent acute glucose reduction effect in the healthy mice. A hypoglycemic effect was observed in the streptozotocin (STZ) induced diabetic mice through a 6-week treatment of Zn-PGLP-1-loaded microspheres. Meanwhile, the administration of Zn-PGLP-1 microspheres led to the β-cell protection and stimulation of insulin secretion. The novel GLP-1 analog-loaded sustained microspheres may greatly improve patient compliance along with a desirable safety feature.

Advances in Biomaterials for Drug Delivery

Advances in biomaterials for drug delivery are enabling significant progress in biology and medicine. Multidisciplinary collaborations between physical scientists, engineers, biologists, and clinicians generate innovative strategies and materials to treat a range of diseases. Specifically, recent advances include major breakthroughs in materials for cancer immunotherapy, autoimmune diseases, and genome editing. Here, strategies for the design and implementation of biomaterials for drug delivery are reviewed. A brief history of the biomaterials field is first established, and then commentary on RNA delivery, responsive materials development, and immunomodulation are provided. Current challenges associated with these areas as well as opportunities to address long-standing problems in biology and medicine are discussed throughout.

MnO2 Motor: A Prospective Cancer-Starving Therapy Promoter

Here, a tumor-targeted MnO₂ motor nanosystem (designed as MG/HA) was constructed by the assembly of glucose oxidase (GOD), manganese dioxide (MnO₂), and glycoprotein CD44-targeting polymer hyaluronic acid (HA) to elevate cancer-starving therapy efficacy in solid tumor. Upon the specific uptake of MG/HA by CD44 overexpressed cancer cells, GOD catalyzed the oxidation of glucose into gluconic acid and hydrogen peroxide (H₂O₂) accompanying the consumption of oxygen (O₂). Meanwhile, MnO₂ would react with H₂O₂ and acid to generate O₂, which is in turn supplied to the glucose-depletion process, running like a loop. As a result, MnO₂ is displayed as a motor to promote the rate of glucose depletion that contributed to the starving therapy. In contrast to G/HA, MG/HA could not only achieve effective glucose consumption to depress cancer progression, but also alleviate hypoxia and reduce the expression of Glut1 to inhibit the metabolism for further restraining the tumor aggressiveness and metastasis. The concept of MnO₂ motor shows a promising prospect to overcome the restriction of the starving therapy.

Responsive triggering systems for delivery in chronic wound healing

Non-communicable diseases including cancer, cardiovascular disease, diabetes, and neuropathy are chronic in nature. Treatment of these diseases with traditional delivery systems is limited due to lack of site-specificity, non-spatiotemporal release and insufficient doses. Numerous responsive delivery systems which respond to both physiological and external stimuli have been reported in the literature. However, effective strategies incorporating a multifactorial approach are required to control these complex wounds. This can be achieved by fabricating spatiotemporal release systems, multimodal systems or dual/multi-stimuli responsive delivery systems loaded with one or more bioactive components. Critically, these next generation stimuli responsive delivery systems that are at present not feasible are required to treat chronic wounds. This review provides a critical assessment of recent developments in the field of responsive delivery systems, highlighting their limitations and providing a perspective on how these challenges can be overcome.

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.

Nanomedicine for obesity treatment

Obesity, as a chronic condition, has been a serious public health issue over the last decades both in the affluent Western world and developing countries. As reported, the risk of several serious diseases increases with weight gain, including type 2 diabetes, coronary heart disease, cancer, and respiratory diseases. In addition to lifestyle modifications, pharmacotherapy has become an important strategy to control weight gain. However, most of the anti-obesity drugs often show poor outcome for weight-loss and cause severe adverse effects. This review surveys recent advances in nanomedicine as an emerging strategy for obesity treatment with an emphasis on the enhanced therapeutic efficiency and minimized side effects. The insights for future development are also discussed.

The influence of spatial distribution on add-on therapy of designed Ca-Alg/CS MEMs system

To improve the efficacy and reduce the systemic toxicity of the diabetes mellitus, herewith, we developed a novel microparticles-embedded microcapsules (MEMs) system, synthesized from calcium alginate/chitosan (Ca-Alg/CS), by emulsion gelation using a high voltage electrostatic droplet generator. In our study, we selected two antidiabetic drugs insulin (INS) and metformin (MET) as model drugs to investigate different spatial distribution appropriate of MEMs system. Characterization based on particle size and morphology, encapsulation efficiency and drug loading, as well as drug delivery properties were carried out on the MEMs system. Typical multi-chamber structure was shown by SEM and the optical spectra. The average diameters of microparticles and Ca-Alg/CS MEMs were 2100 nm and 410 μm, respectively. Insulin and MET were embedded into MEMs via electrostatic reaction according to FT-IR spectra. Moreover, drug loading and encapsulation efficiency of INS were higher than that of MET in this system when drugs were loaded alone or together. More importantly, this system has potential for orderly drug release and well sustained release when MET in the inner and INS in the outer space could be applied as a combination therapy for diabetes. The obtained in vivo experimental data on diabetes rats has shown that the designed MEMs system resulted in a higher hypoglycemic effect within add-on therapy.

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.

Regulated basal and bolus insulin release from glucose-responsive core-shell microspheres based on concanavalin A-sugar affinity

Individual insulin therapy considering the heterogeneity of insulin resistance between patients may bring more benefits than conventional therapy. Therefore, in glucose-responsive insulin delivery systems, more attention should be paid on further regulation of insulin release to meet individual requirements. Our study shows the feasibility of using a photo-crosslinkable shell layer to regulate basal and bolus insulin release from glucose-responsive Con A-polysaccharides network. Core-shell microspheres were fabricated through a two-step high-speed shear-emulsification method. The morphology was observed by SEM and TEM, and the core-shell structure was confirmed by the differences in chemical composition between core-shell and single-layer microspheres obtained from XPS and IR analysis. In vitro insulin release test revealed that the core-shell microspheres with or without light-irradiation could maintain corresponding bolus and basal insulin release in response to different glucose concentration but enable much lower burst release compared with single-layer microspheres without shell. Meanwhile, insulin release rate and amount could be further decreased upon light-irradiation owing to the photo-induced cycloaddition of cinnamate pendant groups of the shell material. The released insulin was proved to remain active according to fluorescence and circular dichroism analysis. The HDF cell viability assessment suggested that the core-shell microspheres possessed no in vitro cytotoxicity.

Targeted delivery of puerarin/glycyrrhetinic acid-PEG-PBLA complex attenuated liver ischemia/reperfusion injury via modulating Toll-like receptor 4/nuclear factor-κB pathway

Aim: To synthesize a puerarin nanoparticle based on glycyrrhetinic acid (GA)-PEG-PBLA and evaluate it in vivo. Materials & methods: In this study, drug nanoparticle was synthesized, characterized and assessed as puerarin delivery system. Nanoparticle GA-PEG-PBLA could combine with puerarin via hydrophobic interaction to form the compound. Puerarin could be quickly and efficiently loaded via the nanoparticle GA-PEG-PBLA at pH 7.4. Further, GA-PEG-PBLA-mediated puerarin delivery system could target for the liver that had GA receptor binding. The antiliver ischemia/reperfusion injury role of puerarin/GA-PEG-PBLA was measured in rats using free puerarin and puerarin/PEG-PBLA as the controls. Results: GA-PEG-PBLA displayed efficient loading and sustained release. Puerarin/GA-PEG-PBLA showed strengthened antiliver ischemia/reperfusion injury characteristics. Conclusion: Overall, the results show that GA-PEG-PBLA could be regarded as an underlying puerarin nanoparticle.

Polymeric microneedles for transdermal protein delivery

The intrinsic properties of therapeutic proteins generally present a major impediment for transdermal delivery, including their relatively large molecule size and susceptibility to degradation. One solution is to utilize microneedles (MNs), which are capable of painlessly traversing the stratum corneum and directly translocating protein drugs into the systematic circulation. MNs can be designed to incorporate appropriate structural materials as well as therapeutics or formulations with tailored physicochemical properties. This platform technique has been applied to deliver drugs both locally and systemically in applications ranging from vaccination to diabetes and cancer therapy. This review surveys the current design and use of polymeric MNs for transdermal protein delivery. The clinical potential and future translation of MNs are also discussed.

Glucose-lowering therapies in type 2 diabetes: Opportunities and challenges for peptides

This overview considers the opportunities and challenges that face the use of gluco-regulatory peptides to treat type 2 diabetes. New insulin analogues and formulations are being developed with pharmacokinetic properties to speed-up or prolong transfer from a subcutaneous injection site to the target tissues, or to selectively favour effects on the liver. Alternative routes of insulin administration continue to attract attention, and advances in the integration of glucose monitoring with insulin pump devices are improving miniaturised 'closed loop' artificial pancreas systems. Proof of concept has been established for non-cellular glucose-responsive insulin delivery ('smart insulins') to release insulin from implants or circulating depots in proportion to circulating glucose. The many peptides involved in blood glucose control offer diverse therapeutic opportunities. Exploitation of multiple selected receptor targets using constructs of hybrid and chimeric peptides, especially those based on glucagon and gastrointestinal hormones, has gained much credence from initial preclinical studies. Peptide templates identified from comparative endocrine studies have also provided valuable insights in this respect and indicated novel approaches to address associated conditions such as obesity and infections at the same time. Nevertheless, there are many challenges to the use of therapeutic peptides that impose on every step in the complex pathway from design and testing through to making a fully characterised therapeutic product, and optimising administration, tissue targeting and degradation. Stability of peptides and immunological uncertainties of novel structures require particular consideration as well as the need to avoid over-reduction of blood glucose into hypoglycaemia.

Fabrication of Polymer-Protein Hybrids

Rapid developments in organic chemistry and polymer chemistry promote the synthesis of polymer-protein hybrids with different structures and biofunctionalities. In this feature article, recent progress achieved in the synthesis of polymer-protein conjugates, protein-nanoparticle core-shell structures, and polymer-protein nanogels/hydrogels is briefly reviewed. The polymer-protein conjugates can be synthesized by the "grafting-to" or the "grafting-from" approach. In this article, different coupling reactions and polymerization methods used in the synthesis of bioconjugates are reviewed. Protein molecules can be immobilized on the surfaces of nanoparticles by covalent or noncovalent linkages. The specific interactions and chemical reactions employed in the synthesis of core-shell structures are discussed. Finally, a general introduction to the synthesis of environmentally responsive polymer-protein nanogels/hydrogels by chemical cross-linking reactions or molecular recognition is provided.

Tailor-Making Fluorescent Hyaluronic Acid Microgels via Combining Microfluidics and Photoclick Chemistry for Sustained and Localized Delivery of Herceptin in Tumors

Antibody therapeutics, though representing a most used biomedicine, suffers from poor in vivo stability, rapid degradation, and frequent injections. Here, we report that fluorescent hyaluronic acid microgels (HMGs) tailor-made by combining microfluidics and "tetrazole-alkene" photoclick chemistry enable sustained and localized delivery of Herceptin in ovarian tumors. HMGs were obtained with a defined size (25-50 μm), narrow size distribution, high stability, and strong green fluorescence. Notably, HMGs exhibited a remarkably high loading of proteins such as Herceptin and IgG with a loading efficiency exceeding 90% at a theoretical protein-loading content of 30 wt %. In vitro protein release experiments revealed a sustained and hyaluronidase (HAase)-dependent release of Herceptin from HMGs, in which 80.6% of Herceptin was released at 1 U/mL HAase in 10 days. The released Herceptin maintained its secondary structure and antitumor activity. In vivo imaging results demonstrated obviously better tumoral retention for Cy5-labeled Herceptin-loaded HMGs following subcutaneous (sc) injection than for the free-protein counterpart. Interestingly, sc injection of the Herceptin-loaded HMGs into SKOV-3 human ovarian tumor-bearing nude mice at a dose of 30 mg Herceptin equiv/kg induced nearly complete tumor suppression, which was significantly more effective than the sc or systemic injection of free Herceptin. These tailor-made fluorescent HMGs appeared as a robust injectable platform for sustained and localized delivery of therapeutic proteins.

The combination of endolysosomal escape and basolateral stimulation to overcome the difficulties of "easy uptake hard transcytosis" of ligand-modified nanoparticles in oral drug delivery

Ligand-modified nanoparticles (NPs) are an effective tool to increase the endocytosis efficiency of drugs, but these functionalized NPs face the drawback of "easy uptake hard transcytosis" in the oral delivery of proteins and peptides. Adversely, the resulting deficiency in transcytosis has not attracted much attention. Herein, NPs modified with the low-density lipoprotein receptor (LDLR) ligand NH₂-C6-[cMPRLRGC]c-NH₂, i.e., peptide-22 (P22NPs) were fabricated to investigate strategies related to the enhancement of transcytosis. By systematically studying the intracellular trafficking of NPs, it was found that reduced transcytosis might be associated with the entrapment of P22NPs in endosomes or lysosomes and limited basolateral exocytosis. On this basis, the prevention of the endolysosomal entrapment of NPs and the acceleration of basolateral exocytosis should be considered as strategies to enhance the transcytosis of NPs. By screening chemicals that could help the endosomal/lysosomal escape of chemicals related to LDLR-mediated transcytosis, it was shown that hemagglutinin-2 (HA₂) and metformin had higher abilities to enhance the exocytosis of P22NPs. The transcytosis efficiencies of insulin loaded in P22NPs were also investigated, and a 3.2-fold increase in transcytosis was observed in comparison with free insulin. The transcytosis efficiencies of insulin could be further increased by the addition of metformin or HA₂ (3.6-fold or 4.1-fold higher than that of free insulin). Inspiringly, the simultaneous addition of the abovementioned two chemicals led to the highest transcytosis efficiency of insulin, which was up to 5.1-fold higher than that of free insulin. These results demonstrated that endolysosomal entrapment and basolateral exocytosis are two of the most important limiting steps for the "easy uptake hard transcytosis" of orally administered ligand-modified NPs. Moreover, our work provides a new point of view for the design of novel oral drug delivery systems.

Preparation and characterization of layer-by-layer hypoglycemic nanoparticles with pH-sensitivity for oral insulin delivery

We developed an insulin oral delivery system with the combination of pH-sensitive material and structure to avoid intestinal degradation.

Injectable self-assembled peptide hydrogels for glucose-mediated insulin delivery

Closed-loop glucose-responsive insulin delivery with excellent biocompatibility has the potential to improve the health and quality of life of diabetic patients.

Biomolecule-Responsive Hydrogels in Medicine

Recent advances and applications of biomolecule-responsive hydrogels, namely, glucose-responsive hydrogels, protein-responsive hydrogels, and nucleic-acid-responsive hydrogels are highlighted. However, achieving the ultimate purpose of using biomolecule-responsive hydrogels in preclinical and clinical areas is still at the very early stage and calls for more novel designing concepts and advance ideas. On the way toward the real/clinical application of biomolecule-responsive hydrogels, plenty of factors should be extensively studied and examined under both in vitro and in vivo conditions. For example, biocompatibility, biointegration, and toxicity of biomolecule-responsive hydrogels should be carefully evaluated. From the living body's point of view, biocompatibility is seriously depended on the interactions at the tissue/polymer interface. These interactions are influenced by physical nature, chemical structure, surface properties, and degradation of the materials. In addition, the developments of advanced hydrogels with tunable biological and mechanical properties which cause no/low side effects are of great importance.

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.

Microneedle-array patches loaded with dual mineralized protein/peptide particles for type 2 diabetes therapy

The delivery of therapeutic peptides for diabetes therapy is compromised by short half-lives of drugs with the consequent need for multiple daily injections that reduce patient compliance and increase treatment cost. In this study, we demonstrate a smart exendin-4 (Ex4) delivery device based on microneedle (MN)-array patches integrated with dual mineralized particles separately containing Ex4 and glucose oxidase (GOx). The dual mineralized particle-based system can specifically release Ex4 while immobilizing GOx as a result of the differential response to the microenvironment induced by biological stimuli. In this manner, the system enables glucose-responsive and closed-loop release to significantly improve Ex4 therapeutic performance. Moreover, integration of mineralized particles can enhance the mechanical strength of alginate-based MN by crosslinking to facilitate skin penetration, thus supporting painless and non-invasive transdermal administration. We believe this smart glucose-responsive Ex4 delivery holds great promise for type 2 diabetes therapy by providing safe, long-term, and on-demand Ex4 therapy.

Diabetes treatments often rely on frequent and scheduled drug administration, which reduces patient compliance and increases treatment cost. Here, the authors develop a microneedle-array patch that separately loads drug-releasing module and glucose-sensing element for on-demand, long-term diabetes therapy.

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.

In vitro and in vivo protein release and anti-ischemia/reperfusion injury properties of bone morphogenetic protein-2-loaded glycyrrhetinic acid-poly(ethylene glycol)-b-poly(l-lysine) nanoparticles

Here, we describe a bone morphogenetic protein-2 (BMP-2) nanocarrier based on glycyrrhetinic acid (GA)-poly(ethylene glycol) (PEG)-b-poly(l-lysine) (PLL). A protein nanocarrier was synthesized, characterized and evaluated as a BMP-2 delivery system. The designed nanocarrier was synthesized based on the ring-opening polymerization of amino acid N-carboxyanhydride. The final product was measured with ¹H nuclear magnetic resonance. GA-PEG-b-PLL nanocarrier could combine with BMP-2 through electrostatic interaction to form polyion complex (PIC) micelles. BMP-2 could be rapidly and efficiently encapsulated through the GA-PEG-b-PLL nanocarrier under physiological conditions, exhibiting efficient encapsulation and sustained release. In addition, the GA-PEG-b-PLL-mediated BMP-2 delivery system could target the liver against hepatic diseases as it has GA-binding receptors. The anti-hepatic ischemia/reperfusion injury (anti-HI/RI) effect of BMP-2/GA-PEG-b-PLL PIC micelles was investigated in rats using free BMP-2 and BMP-2/PEG-b-PLL PIC micelles as controls, and the results showed that BMP-2/GA-PEG-b-PLL PIC micelles indicated significantly enhanced anti-HI/RI property compared to BMP-2 and BMP-2/PEG-b-PLL. All results suggested that GA-PEG-b-PLL could be used as a potential BMP-2 nanocarrier.

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.

Near-Infrared-Light-Responsive Magnetic DNA Microgels for Photon- and Magneto-Manipulated Cancer Therapy

Functional DNA molecules have been introduced into polymer-based nanocarrier systems to incorporate chemotherapy drugs for cancer therapy. Here is the first report of dual-responsive microgels composed of a core of Au nanorods and a shell of magnetic ionic liquid and DNA moieties in the cross-linking network simultaneously, as effective drug delivery vectors. TEM images indicated a magnetic polymer shell has an analogous "doughnut" shape which loosely surround the AuNRs core. When irradiated with a near-infrared-light (near-IR) laser, Au nanorods are the motors which convert the light to heat, leading to the release of the encapsulated payloads with high controllability. DNA acts not only as a cross-linker agent, but also as a gatekeeper to regulate the release of drugs. The internalization study and MTT assay confirm that these core-shell DNA microgels are excellent candidates which can enhance the cytotoxicity of cancer cells controlled by near-IR laser and shield the high toxicity of chemotherapeutic agents to improve the killing efficacy of chemotherapeutic agents efficiently in due course.

Supersensitive Oxidation-Responsive Biodegradable PEG Hydrogels for Glucose-Triggered Insulin Delivery

Reactive oxygen species (ROS)-responsive polymers and hydrogels represent an emerging family of intelligent materials owing to the key functions of ROS in physiological processes or pathological diseases. Nonetheless, the weaknesses such as low sensitivity, slow response, instability, and low mechanical strength are associated with the limited ROS-responsive polymeric or supramolecular hydrogels. In this study, a novel type of oxidation-responsive degradable hydrogels was fabricated by the redox-initiated radical polymerization of a 4-arm-poly(ethylene glycol) (PEG) acrylic macromonomer that possesses a H₂O₂-cleavable phenylboronic acid linker in each of the arms. The macroscopic hydrogels have the features of good cytocompatibility, moderate mechanical strength, and fast response toward H₂O₂ of low concentration, owing to the covalently cross-linked hydrophilic PEG network and high sensitivity of the linker. They could encapsulate biomacromolecules, such as insulin and glucose oxidase (GOx), with high efficacy, affording a new glucose-responsive insulin-delivery platform on the basis of enzymatic transformation of a biochemical signal (glucose) into an oxidative stimulus (H₂O₂). Interestingly, in vitro results demonstrate that the same GOx-loaded hydrogel exhibited disparate degradation modes under different triggering molecules, that is, bulk degradation by H₂O₂ and surface erosion by glucose. Moreover, compared to the macroscopic hydrogel, the nanogel with a diameter of ∼160 nm prepared by inverse emulsion polymerization showed a much higher degradation rate even under triggering of 20 μM H₂O₂, a pathologically available concentration in vivo.

Development of glucose-responsive 'smart' insulin systems

PURPOSE OF REVIEW

The complexity of modern insulin-based therapy for type I and type II diabetes mellitus and the risks associated with excursions in blood-glucose concentration (hyperglycemia and hypoglycemia) have motivated the development of 'smart insulin' technologies (glucose-responsive insulin, GRI). Such analogs or delivery systems are entities that provide insulin activity proportional to the glycemic state of the patient without external monitoring by the patient or healthcare provider. The present review describes the relevant historical background to modern GRI technologies and highlights three distinct approaches: coupling of continuous glucose monitoring (CGM) to deliver devices (algorithm-based 'closed-loop' systems), glucose-responsive polymer encapsulation of insulin, and molecular modification of insulin itself.

RECENT FINDINGS

Recent advances in GRI research utilizing each of the three approaches are illustrated; these include newly developed algorithms for CGM-based insulin delivery systems, glucose-sensitive modifications of existing clinical analogs, newly developed hypoxia-sensitive polymer matrices, and polymer-encapsulated, stem-cell-derived pancreatic β cells.

SUMMARY

Although GRI technologies have yet to be perfected, the recent advances across several scientific disciplines that are described in this review have provided a path towards their clinical implementation.

Glucose Oxidase-Based Glucose-Sensitive Drug Delivery for Diabetes Treatment

The glucose-sensitive drug delivery systems based on glucose oxidase (GOD), which exhibit highly promising applications in diabetes therapy, have attracted much more interest in recent years. The self-regulated drug delivery systems regulate drug release by glucose concentration automatically and continuously to control the blood glucose level (BGL) in normoglycemic state. This review covers the recent advances at the developments of GOD-based glucose-sensitive drug delivery systems and their in vivo applications for diabetes treatment. The applications of GOD-immobilized platforms, such as self-assembly layer-by-layer (LbL) films and polymer vesicles, cross-linking hydrogels and microgels, hybrid mesoporous silica nanoparticles, and microdevices fabricated with insulin reservoirs have been surveyed. The glucose-sensitive drug delivery systems based on GOD are expected to be a typical candidate for smart platforms for potential applications in diabetes therapy.

Preparation of exenatide-loaded linear poly(ethylene glycol)-brush poly(l-lysine) block copolymer: potential implications on diabetic nephropathy

The poly(ethylene glycol)-b-brush poly(l-lysine) polymer (PEG-b-(PELG50-g-PLL3)) was synthesized and evaluated as a nanocarrier for prolonging delivery of exenatide through the abdominal subcutaneous injection route. The isoelectric point of exenatide was 4.86, and exenatide could combine with PEG-b-(PELG50-g-PLL3) polymers via electrostatic interactions at pH 7.4. This polymer was a good candidate for achieving prolonged drug delivery for exenatide, considering its high molecular weight. Besides the physicochemical characterization of the polymer, in vitro and in vivo applications were researched as a sustained exenatide delivery system. In the in vitro release research, 20.16%-76.88% of total exenatide was released from the PEG-b-(PELG50-g-PLL3) polymer within 7 days. The synthesized block-brush polymers and exenatide-block-brush polymers were analyzed by nuclear magnetic resonance spectroscopy, gel permeation chromatography, transmission electron microscopy, nanoparticle size instrument, and scanning electron microscopy. The best formulation was selected for in vivo experimentation to achieve blood glucose control in diabetic rat models using free exenatide as the control. The hypoglycemic action of the formulation following subcutaneous injection in diabetic rats lasted 7 days, and the results indicated that exenatide-block-brush polymers demonstrate enhanced long-acting hypoglycemic action. Besides the hypoglycemic action, exenatide-block-brush polymers significantly alleviated diabetic nephropathy via improving renal function, decreasing oxidative stress injury, decreasing urinary albumin excretion rate, mitigating albumin/creatinine ratio, reducing blood lipids, abating kidney index, weakening apoptosis, and downregulating expression of connective tissue growth factor. All of the results suggested that PEG-b-(PELG50-g-PLL3) polymers could be used as potential exenatide nanocarriers, with efficient encapsulation and sustained release.

Boosting the Peroxidase-Like Activity of Nanostructured Nickel by Inducing Its 3+ Oxidation State in LaNiO3 Perovskite and Its Application for Biomedical Assays

Catalytic nanomaterials with intrinsic enzyme-like activities, called nanozymes, have recently attracted significant research interest due to their unique advantages relative to natural enzymes and conventional artificial enzymes. Among the nanozymes developed, particular interests have been devoted to nanozymes with peroxidase mimicking activities because of their promising applications in biosensing, bioimaging, biomedicine, etc. Till now, lots of functional nanomaterials have been used to mimic peroxidase. However, few studies have focused on the Ni-based nanomaterials for peroxidase mimics. In this work, we obtained the porous LaNiO₃ nanocubes with high peroxidase-like activity by inducing its 3+ oxidation state in LaNiO₃ perovskite and optimizing the morphology of LaNiO₃ perovskite. The peroxidase mimicking activity of the porous LaNiO₃ nanocubes with Ni³⁺ was about 58~fold and 22~fold higher than that of NiO with Ni²⁺ and Ni nanoparticles with Ni⁰. More, the porous LaNiO₃ nanocubes exhibited about 2-fold higher activity when compared with LaNiO₃ nanoparticles. Based on the superior peroxidase-like activity of porous LaNiO₃ nanocubes, facile colorimetric assays for H₂O₂, glucose, and sarcosine detection were developed. Our present work not only demonstrates a useful strategy for modulating nanozymes' activities but also provides promising bioassays for clinical diagnostics.