Injectable and Thermosensitive Hydrogel Containing Liraglutide as a Long-Acting Antidiabetic System

Development of 1 Month Sustained-Release Microspheres Containing Liraglutide for Type 2 Diabetes Treatment

Liraglutide has been extensively applied in the treatment of type 2 diabetes mellitus (T2DM), but its 11-15 h half-life resulted in daily administration, which led to poor patient compliance. This study aimed to solve this problem by developing liraglutide-loaded microspheres with a 1 month sustained release prepared by the W1/O/W2 method combined with the premix membrane emulsification technique to improve therapeutic efficacy. Remarkably, we found that the amphiphilic properties of liraglutide successfully reduced the oil-water interfacial tension, resulting in a stable primary emulsion and decreasing the level of drug leakage into the external water phase. As a result, exceptional drug loading (>8%) and encapsulation efficiency (>85%) of microspheres were achieved. Furthermore, the uniformity in microsphere size facilitated an in-depth exploration of the structural characteristics of liraglutide-loaded microspheres. The results indicated that the dimensions of the internal cavities of the microspheres were significantly influenced by the size of the inner water droplets in the primary emulsion. A denser and more uniform cavity structure decreased the initial burst release, improving the release process of liraglutide from the microspheres. To evaluate the release behavior of liraglutide from microspheres, a set of in vitro release assays and in vivo pharmacodynamics were performed. The liraglutide-loaded microspheres effectively decreased fasting blood glucose (FBG) levels and hemoglobin A1c (HbA1c) levels while enhancing the pancreatic and hepatic functions in db/db mice. In conclusion, liraglutide sustained-release microspheres showed the potential for future clinical applications in the management of T2DM and provided an effective therapeutic approach to overcoming patient compliance issues.

Long-Acting Gel Formulations: Advancing Drug Delivery across Diverse Therapeutic Areas

This multifaceted landscape of long-acting gels in diverse medical fields, aims to enhance therapeutic outcomes through localized treatment and controlled drug release. The objective involves advancements spanning cancer treatment, immunotherapy, diabetes management, neuroendocrine disorders, ophthalmic applications, contraception, HIV/AIDS treatment, chronic diseases, wound care, and antimicrobial treatments. It explores the potential of long-acting gels to offer sustained and extended drug release, targeted therapy, and innovative administration routes while addressing limitations such as scalability challenges and regulatory hurdles. Future directions focus on personalized therapies, biodegradability, combination therapies, interdisciplinary innovation, regulatory considerations, and patient-centric development. This comprehensive review highlights the pivotal role of long-acting gels in transforming therapeutic approaches and improving patient outcomes across various medical conditions.

Thermosensitive Triblock Copolymer for Slow-Release Lubricants under Ocular Conditions

The ocular environment is crucial for a biological lubrication system. An unstable condition of tear film may cause a series of ocular diseases due to serious friction, such as dry eye syndrome, which has drawn extensive attention nowadays. In this study, an in vitro biocompatible superlubricity system, containing thermogelling copolymers (PCGA-PEG-PCGA) and slow-release lubricant (PEG 300/Tween 80), was constructed. First, the sol-gel transition temperature and gel strength of PCGA-PEG-PCGA were adjusted based on the ocular environment by regulating the length of PCGA blocks. Furthermore, the copolymer hydrogel exhibited a reliable slow-release property within 10 days and showed low cytotoxicity. Then, the superlubricity (coefficient of friction of approximately 0.005) was achieved with its released PEG 300/Tween 80 aqueous solution at the sliding velocity range of 1-100 mm s-1 and pressure range of 10-22 kPa. However, the lubrication behaviors varied, while PEG 300 chains and Tween 80 micelles were demonstrated to form a multilayer and a single layer adsorption structure on the sliding surface, respectively. On the whole, the composite lubrication systems, especially the one composed of Tween 80, showed excellent tribological properties owing to the stable slow-release and full hydration effects under ocular conditions, which hold great potential for improving ocular lubrication and maintaining human visual health.

Hydrogel-based Drug Delivery System in Diabetes Management

BACKGROUND

It is estimated that there are over 200 million people living with diabetes mellitus (DM) all over the world. It is a metabolic condition caused by decreased insulin action or secretion. Diabetes Mellitus is also known as Type 2 Diabetes Mellitus. Type 1 diabetes mellitus and type 2 diabetes mellitus are the two most common types of DM. Treatment for type 1 diabetes often consists of insulin replacement therapy, while treatment for type 2 diabetes typically consists of oral hypoglycemics.

OBJECTIVES

Conventional dosing schedules for the vast majority of these medications come with a number of drawbacks, the most common of which are frequent dosing, a short half-life, and low bioavailability. Thus, innovative and regulated oral hypoglycemic medication delivery methods have been developed to reduce the limitations of standard dose forms.

METHODS

The studies and reviews published under the title were looked up in several databases (including PubMed, Elsevier, and Google Scholar).

RESULTS

Hydrogels made from biopolymers are three-dimensional polymeric networks that can be physically or chemically crosslinked. These networks are based on natural polymers and have an inherent hydrophilic quality because of the functional groups they contain. They have a very high affinity for biological fluids in addition to a high water content, softness, flexibility, permeability, and biocompatibility. The fact that these features are similar to those of a wide variety of soft living tissues paves the way for several potentials in the field of biomedicine. In this sense, hydrogels offer excellent platforms for the transport of medications and the controlled release of those drugs. Additionally, biopolymer-based hydrogels can be put as coatings on medical implants in order to improve the biocompatibility of the implants and to prevent medical diseases.

CONCLUSION

The current review focuses on the most recent advancements made in the field of using biopolymeric hydrogels that are physically and chemically crosslinked, in addition to hydrogel coatings, for the purpose of providing sustained drug release of oral hypoglycemics and avoiding problems that are associated with the traditional dosage forms of oral hypoglycemics.

A review of recent research and development on GLP-1 receptor agonists-sustained-release microspheres

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are increasingly used in treating type 2 diabetes (T2D). However, owing to their limited oral bioavailability, most commercially available GLP-1 RAs are administered through frequent subcutaneous injections, which may result in poor patient compliance during clinical treatment. To improve patients' compliance, sustained-release GLP-1 RA-loaded microspheres have been explored. This review is an overview of recent progress and research in GLP-1 RA-loaded microspheres. First, the fabrication methods of GLP-1 RA-loaded microspheres including the coacervation method, emulsion-solvent evaporation method based on agitation, premix membrane emulsification technology, spray drying, microfluidic droplet technology, and supercritical fluid technology are summarized. Next, the strategies for maintaining GLP-1 RAs' stability and activity in microspheres by adding additives and PEGylation are reviewed. Finally, the effect of particle size, drug distribution, the internal structure of microspheres, and the hydrogel/microsphere composite strategy on improved release behavior is summarized.

Current Role and Potential of Polymeric Biomaterials in Clinical Obesity Treatment

The rise of obesity and associated fatal diseases has taken a massive toll worldwide. Despite the existing pharmaceuticals and bariatric surgeries, these approaches manifest limited efficacy or accompany various side effects. Therefore, researchers seek to facilitate the prolonged and specific delivery of therapeutics. Or else, to mimic the essential part of "gastric bypass" by physically blocking excessive absorption via less invasive methods. To achieve these goals, polymeric biomaterials have gained tremendous interest recently. They are known for synthesizing hydrogels, microneedle patches, mucoadhesive coatings, polymer conjugates, and so forth. In this Review, we provide insights into the current studies of polymeric biomaterials in the prevention and treatment of obesity, inspiring future improvements in this regime of study.

The recent advancement in the PLGA-based thermo-sensitive hydrogel for smart drug delivery

To date, hydrogels have opened new prospects for potential applications for drug delivery. The thermo-sensitive hydrogels have the great potential to provide more effective and controllable release of therapeutic/bioactive agents in response to changes in temperature. PLGA is a safe FDA-approved copolymer with good biocompatibility and biodegradability. Recently, PLGA-based formulation have attracted a lot of interest for thermo-sensitive hydrogels. Thermo-sensitive PLGA-based hydrogels provide the delivery system with good spatial and temporal control, and have been widely applied in drug delivery. This review is focused on the recent progression of the thermo-sensitive and biodegradable PLGA-based hydrogels that have been reported for smart drug delivery to the different organs. Eventually, future perspectives and challenges of thermo-sensitive PLGA-based hydrogels are discussed briefly.

An antioxidant and antibacterial polydopamine-modified thermo-sensitive hydrogel dressing for Staphylococcus aureus-infected wound healing

Bacteria-infected wound healing is a complex and chronic process that poses a great threat to human health. A thermo-sensitive hydrogel that undergoes a sol-gel transition at body temperature is an attractive wound dressing for healing acceleration and infection prevention. In this paper, we present a thermo-sensitive and reactive oxygen species (ROS)-scavenging hydrogel based on polydopamine modified poly(ε-caprolactone-co-glycolide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-glycolide) (PDA/P2) triblock copolymer. The PDA/P2 solution at a concentration of 30 wt% could form a gel at 34-38 °C. The ROS-scavenging ability of PDA/P2 was demonstrated by DPPH and ABTS assays and intracellular ROS downregulation in RAW264.7 cells. Furthermore, silver nanoparticles were encapsulated in the hydrogel (PDA/P2-4@Ag gel) to provide antibacterial activity against E. coli and S. aureus. An in vivo S. aureus-infected rat model demonstrated that the PDA/P2-4@Ag hydrogel dressing could promote wound healing via inhibiting bacterial growth, alleviating the inflammatory response, and inducing angiogenesis and collagen deposition. This study provides a new strategy to prepare temperature-sensitive hydrogel-based multifunctional wound dressings.

Injectable PTHF-based thermogelling polyurethane implants for long-term intraocular application

BACKGROUND

Hydrogels show great potential to be used for intraocular applications due to their high-water content and similarity to the native vitreous. Injectable thermosensitive hydrogels through a small-bore needle can be used as a delivery system for drugs or a tamponading substitute to treat posterior eye diseases with clear clinical potential. However, none of the currently available thermosensitive hydrogels can provide intraocular support for up to 3 months or more.

METHOD

In this study, an injectable polytetrahydrofuran (PTHF)-based thermosensitive hydrogel was synthesized by polyurethane reaction. We examined the injectability, rheological properties, microstructure, cytotoxicity, and in vivo compatibility and stability of the hydrogels in rabbit eyes.

RESULTS

We found that the PTHF block type and PTHF component ratio could modulate thermogelation properties of the polyurethane polymers. The PTHF-based hydrogel implants retained normal retinal structure and function. Incorporating bioinert PTHF generated highly biocompatible and more stable thermogels in the vitreous cavity, with gel networks and the presence of polymer still observed after 3 months when other thermogels would have been completely cleared. Moreover, despite lacking hydrolytically cleavable linkages, the polymers could be most naturally removed from the native vitreous by bio-erosion without additional surgical interventions.

CONCLUSION

Our findings suggest the potential of incorporating hydrophobic bioinert blocks to enhance the in vivo stability of supramolecularly associated hydrogels for long-term intraocular applications.

Nanomaterials based on thermosensitive polymer in biomedical field

The progress of nanotechnology enables us to make use of the special properties of materials on the nanoscale and open up many new fields of biomedical research. Among them, thermosensitive nanomaterials stand out in many biomedical fields because of their “intelligent” behavior in response to temperature changes. However, this article mainly reviews the research progress of thermosensitive nanomaterials, which are popular in biomedical applications in recent years. Here, we simply classify the thermally responsive nanomaterials according to the types of polymers, focusing on the mechanisms of action and their advantages and potential. Finally, we deeply investigate the applications of thermosensitive nanomaterials in drug delivery, tissue engineering, sensing analysis, cell culture, 3D printing, and other fields and probe the current challenges and future development prospects of thermosensitive nanomaterials.

Smart/stimuli-responsive hydrogels: Cutting-edge platforms for tissue engineering and other biomedical applications

Recently, biomedicine and tissue regeneration have emerged as great advances that impacted the spectrum of healthcare. This left the door open for further improvement of their applications to revitalize the impaired tissues. Hence, restoring their functions. The implementation of therapeutic protocols that merge biomimetic scaffolds, bioactive molecules, and cells plays a pivotal role in this track. Smart/stimuli-responsive hydrogels are remarkable three-dimensional (3D) bioscaffolds intended for tissue engineering and other biomedical purposes. They can simulate the physicochemical, mechanical, and biological characters of the innate tissues. Also, they provide the aqueous conditions for cell growth, support 3D conformation, provide mechanical stability for the cells, and serve as potent delivery matrices for bioactive molecules. Many natural and artificial polymers were broadly utilized to design these intelligent platforms with novel advanced characteristics and tailored functionalities that fit such applications. In the present review, we highlighted the different types of smart/stimuli-responsive hydrogels with emphasis on their synthesis scheme. Besides, the mechanisms of their responsiveness to different stimuli were elaborated. Their potential for tissue engineering applications was discussed. Furthermore, their exploitation in other biomedical applications as targeted drug delivery, smart biosensors, actuators, 3D and 4D printing, and 3D cell culture were outlined. In addition, we threw light on smart self-healing hydrogels and their applications in biomedicine. Eventually, we presented their future perceptions in biomedical and tissue regeneration applications. Conclusively, current progress in the design of smart/stimuli-responsive hydrogels enhances their prospective to function as intelligent, and sophisticated systems in different biomedical applications.

Self-assembled di- and tripeptide gels for the passive entrapment and pH-responsive, sustained release of an antidiabetic drug, glimepiride

Diabetes is a global epidemic that poses a severe challenge to public health. The characteristic features of this disease are hyperglycemia and deterioration of the function of pancreatic β-cells, which...

PEG-based thermosensitive and biodegradable hydrogels

Injectable thermosensitive hydrogels are free-flowing polymer solutions at low or room temperature, making them easy to encapsulate the therapeutic payload or cells via simply mixing. Upon injection into the body, in situ forming hydrogels triggered by body temperature can act as drug-releasing reservoirs or cell-growing scaffolds. Finally, the hydrogels are eliminated from the administration sites after they accomplish their missions as depots or scaffolds. This review outlines the recent progress of poly(ethylene glycol) (PEG)-based biodegradable thermosensitive hydrogels, especially those composed of PEG-polyester copolymers, PEG-polypeptide copolymers and poly(organophosphazene)s. The material design, performance regulation, thermogelation and degradation mechanisms, and corresponding applications in the biomedical field are summarized and discussed. A perspective on the future thermosensitive hydrogels is also highlighted. STATEMENT OF SIGNIFICANCE: Thermosensitive hydrogels undergoing reversible sol-to-gel phase transitions in response to temperature variations are a class of promising biomaterials that can serve as minimally invasive injectable systems for various biomedical applications. Hydrophilic PEG is a main component in the design and fabrication of thermoresponsive hydrogels due to its excellent biocompatibility. By incorporating hydrophobic segments, such as polyesters and polypeptides, into PEG-based systems, biodegradable and thermosensitive hydrogels with adjustable properties in vitro and in vivo have been developed and have recently become a research hotspot of biomaterials. The summary and discussion on molecular design, performance regulation, thermogelation and degradation mechanisms, and biomedical applications of PEG-based thermosensitive hydrogels may offer a demonstration of blueprint for designing new thermogelling systems and expanding their application scope.

Sustained Release Systems for Delivery of Therapeutic Peptide/Protein

Peptide/protein therapeutics have been significantly applied in the clinical treatment of various diseases such as cancer, diabetes, etc. owing to their high biocompatibility, specificity, and therapeutic efficacy. However, due to their immunogenicity, instability stemming from its complex tertiary and quaternary structure, vulnerability to enzyme degradation, and rapid renal clearance, the clinical application of protein/peptide therapeutics is significantly confined. Though nanotechnology has been demonstrated to prevent enzyme degradation of the protein therapeutics and thus enhance the half-life, issues such as initial burst release and uncontrollable release kinetics are still unsolved. Moreover, the traditional administration method results in poor patient compliance, limiting the clinical application of protein/peptide therapeutics. Exploiting the sustained-release formulations for more controllable delivery of protein/peptide therapeutics to decrease the frequency of injection and enhance patient compliance is thus greatly meaningful. In this review, we comprehensively summarize the substantial advancements of protein/peptide sustained-release systems in the past decades. In addition, the advantages and disadvantages of all these sustained-release systems in clinical application together with their future challenges are also discussed in this review.

Long-Acting Formulations: A Promising Approach for the Treatment of Chronic Diseases

Medication and patient adherence are the two main aspects of any successful treatment of chronic disease. Even though diseases and its treatment existed for several hundred years, the treatment optimization for a given patient is still a researcher question for scientists. There are differences in treatment duration, prognostic signs and symptoms between patient to patient. Hence, designing ideal formulation to suit individual patient is a challenging task. The conventional formulations like oral solids and liquids gives a partial or incomplete treatment because the patient needs to follow the daily pills for a longer time. In such cases, the long-acting formulations will have better patient compliances as drug will be released for a longer duration. Many such approaches are under the clinical investigation. The favorable pharmacokinetic and pharmacodynamic relationships, will be promising option for the treatment of chronic diseases. In this review, we have highlighted the importance of long-acting formulations in the treatment of chronic diseases and the advent of newer formulation technologies.

Poly ethylene glycol (PEG)-Related controllable and sustainable antidiabetic drug delivery systems

Diabetes mellitus is one of the most challenging threats to global public health. To improve the therapy efficacy of antidiabetic drugs, numerous drug delivery systems have been developed. Polyethylene glycol (PEG) is a polymeric family sharing the same skeleton but with different molecular weights which is considered as a promising material for drug delivery. In the delivery of antidiabetic drugs, PEG captures much attention in the designing and preparation of sustainable and controllable release systems due to its unique features including hydrophilicity, biocompatibility and biodegradability. Due to the unique architecture, PEG molecules are also able to shelter delivery systems to decrease their immunogenicity and avoid undesirable enzymolysis. PEG has been applied in plenty of delivery systems such as micelles, vesicles, nanoparticles and hydrogels. In this review, we summarized several commonly used PEG-contained antidiabetic drug delivery systems and emphasized the advantages of stimuli-responsive function in these sustainable and controllable formations.

Sustained intrathecal delivery of amphotericin B using an injectable and biodegradable thermogel

Cryptococcal meningitis is a fungal infectious disease with a poor prognosis and high mortality. Amphotericin B (AMB) is the first choice for the treatment of cryptococcal meninges. The blood-brain barrier (BBB) is the major barrier for the effective delivery of drugs to the brain. In this study, AMB was incorporated in a thermosensitive gel for intrathecal injection. We first synthesized AMB-loaded thermogel, investigated its in vitro cumulative release, and in vivo neurotoxicity, and therapeutic effect. The thermosensitive gel was comprised of 25 wt% poly (lactic acid-co-glycolic acid)-poly (ethylene glycol)-poly (lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) triblock polymer aqueous solution. The AMB loaded in the thermosensitive gel (AMB in gel) had low viscosity at low temperature and resulted in the formation of a non-flowing gel at 37 °C (physiological temperature). AMB loading in gel sustained its release for 36 days and the in vitro cumulative release rate was satisfactory. Compared with the AMB solution, intrathecal administration of AMB in gel could reduce the neurovirulence of AMB and get a better treatment effect. The findings of the current study show that the injectable PLGA–PEG–PLGA thermogel is a biocompatible carrier for the delivery of drugs into the intrathecal.

Glucose-responsive hydrogel enhances the preventive effect of insulin and liraglutide on diabetic nephropathy of rats

Diabetic nephropathy (DN) is one of the most serious complications of diabetes mellitus. The combination of insulin (Ins) with liraglutide (Lir) has a greater potential for preventing DN than monotherapy. However, the renal protective effect of the combined Ins/Lir therapy is largely compromised due to their short half-lives after subcutaneous injection. Herein, a glucose-responsive hydrogel was designed in situ forming the dynamic boronic esters bonds between phenylboronic acid-grafted γ-Polyglutamic acid (PBA-PGA) and konjac glucomannan (KGM). It was hypothesized that the KGM/PBA-PGA hydrogel as the delivery vehicle of Ins/Lir would enhance the combinational effect of the latter on preventing the DN progress. Scan electronic microscopy and rheological studies showed that KGM/PBA-PGA hydrogel displayed good glucose-responsive property. Besides, the glucose-sensitive release profile of either Ins or Lir from KGM/PBA-PGA hydrogel was uniformly displayed at hyperglycemic level. Furthermore, the preventive efficacy of KGM/PBA-PGA hydrogel incorporating insulin and liraglutide (Ins/Lir-H) on DN progress was evaluated on streptozotocin-induced rats with diabetic mellitus (DM). At 6 weeks after subcutaneous injection of Ins/Lir-H, not only the morphology of kidneys was obviously recovered as shown by ultrasonography, but also the renal hemodynamics was significantly improved. Meanwhile, the 24-h urinary protein and albumin/creatinine ratio were well modulated. Inflammation and fibrosis were also largely inhibited. Besides, the glomerular NPHS-2 was obviously elevated after treatment with Ins/Lir-H. The therapeutic mechanism of Ins/Lir-H was highly associated with the alleviation of oxidative stress and activation of autophagy. Conclusively, the better preventive effect of the combined Ins/Lir via KGM/PBA-PGA hydrogel on DN progress was demonstrated as compared with their mixed solution, suggesting KGM/PBA-PGA hydrogel might be a potential vehicle of Ins/Lir to combat the progression of DN.

Alpha-beta transition induced by C18-conjugation of polyalanine and its implication in aqueous solution behavior of poly(ethylene glycol)-polyalanine block copolymers

BACKGROUND

The aqueous solution behavior of thermosensitive PEG-PA block copolymers as well as secondary structure of PA is expected to significantly change through modification of the hydrophobic PA by long chain alkyl (C18) groups with different configurations.

METHOD

Oleoyl and stearoyl (C18) groups were conjugated to poly(ethylene glycol)-poly(L-alanine) (PEG-PA; EG₄₅A₁₆) diblock copolymers to compare their conjugation effect on nano-assemblies and corresponding aqueous solution behavior of the polymers.

RESULTS

Due to the nature of a hydrophilic PEG block and a hydrophobic PA or C18-modified PA, PEG-PA, oleoyl group-conjugated PEG-PA (PEG-PAO), and stearoyl group-conjugated PEG-PA (PEG-PAS) block copolymers form micelles in water. Compared with PEG-PA, the micelle size of PEG-PAO and PEG-PAS increased. Circular dichroism and FTIR spectra of aqueous polymer solutions showed that β sheet content increased, whereas α helix content decreased by C18 modification of PEG-PA. PEG-PAS showed better performance in ice crystallization inhibition than PEG-PAO. The sol-to-gel transition temperatures of aqueous PEG-PAO solutions were 25-37 °C higher than those of aqueous PEG-PA solutions, whereas aqueous PEG-PAS solutions remained as gels in the temperature range of 0-80 °C. ¹H-NMR spectra indicated that the oleoyl groups increased core mobility, whereas stearoyl groups decreased the core mobility of the micelles in water. The difference in micromobility between PAO and PAS interfered or promoted gelation of the aqueous polymer solutions, respectively.

CONCLUSIONS

This study suggests that a hydrophobic C18-modification of polypeptide induces α helix-to-β sheet transition of the polypeptide; however, aqueous solution behaviors including ice recrystallization inhibition and gelation are significantly affected by the nature of the hydrophobic molecule.

Injectable hydrogel derived from chitosan with tunable mechanical properties via hybrid-crosslinking system

Thermo-sensitive injectable hydrogels that spontaneously react to physiological temperature have been widely studied to be used in biomedical fields. However, several challenges on their unstable structures with large-sized pores and low mechanical strength under physiological conditions must be addressed to enable their practical applications. We synthesized the hydroxybutyl methacrylated chitosan (HBC-MA) hydrogel that possesses both thermo-sensitive and photo-crosslinkable properties. The HBC-MA showed effective sol-gel transition under physiological temperature as well as a sensitive photo-crosslinkable property with visible light capable of skin penetration. The co-nonsolvency property and thermo-sensitivity of HBC-MA prevented unintended loss of the hydrogel graft after being subcutaneously injected in mice. Subsequently applied visible light on the skin beneath which the hydrogel was injected significantly improved the mechanical strength and stability of the graft. The injectable HBC-MA hydrogel developed in this study can be applicable to a wide range of biomedical fields such as drug delivery system and tissue engineering.

Thermogelling Inclusion Complex System for Fine-Tuned Osteochondral Differentiation of Mesenchymal Stem Cells

How to control osteochondral differentiation of mesenchymal stem cells at a proper stage is a key issue for articular cartilage regeneration. To solve this problem, injectable scaffolds with different chemical functional groups were designed by introducing one equivalent of α-cyclodextrin (α-CD) carboxylate and α-CD phosphate along poly(ethylene glycol)-poly(l-alanine) (PEG-L-PA) block copolymers. Dynamic light scattering, transmission electron microscopy images, and two-dimensional NMR spectra indicated that the PEG-L-PA block copolymers formed inclusion complexes with α-CD derivatives. Aqueous solutions of PEG-L-PA block copolymers (P), α-CD carboxylate/PEG-L-PA block copolymers (PCC), and α-CD phosphate/PEG-L-PA block copolymers (PCP) underwent sol-to-gel transition as the temperature increased. The storage moduli of P, PCC, and PCP gels ranged from 1000 to 1300 Pa at 37 °C. Tonsil-derived mesenchymal stem cells (TMSCs) were incorporated in situ in the gel during thermogelation of P, PCC, and PCP, which became the three-dimensional cell culture systems with different functional groups. After 21 days of incubation of TMSCs in the P, PCC, and PCP systems, the chondrogenic differentiation biomarker of type II collagen significantly increased in the P system, whereas the osteogenic biomarkers of osteocalcin and runt-related transcription factor 2 significantly increased in the PCP system. Both chondrogenic and osteogenic biomarkers were highly expressed in the PCC system. This study proved that thermogelling inclusion complex systems consisting of PEG-L-PA block copolymers and α-CD derivatives could be an excellent injectable matrix for fine-controlling osteochondral differentiation of mesenchymal stem cells.

Oral delivery of exenatide-loaded hybrid zein nanoparticles for stable blood glucose control and β-cell repair of type 2 diabetes mice

BACKGROUND

Exenatide is an insulinotropic peptide drug for type 2 diabetes treatment with low risk of hypoglycemia, and is administrated by subcutaneous injection. Oral administration is the most preferred route for lifelong treatment of diabetes, but oral delivery of peptide drug remains a significant challenge due to the absorption obstacles in gastrointestinal tract. We aimed to produce exenatide-loaded nanoparticles containing absorption enhancer, protectant and stabilizer using FDA approved inactive ingredients and easy to scale-up method, and to evaluate their long-term oral therapeutic effect in type 2 diabetes db/db mice.

RESULTS

Two types of nanoparticles, named COM NPs and DIS NPs, were fabricated using anti-solvent precipitation method. In COM NPs, the exenatide was complexed with cholic acid and phosphatidylcholine to increase the exenatide loading efficiency. In both nanoparticles, zein acted as the cement and the other ingredients were embedded in zein nanoparticles by hydrophobic interaction. Casein acted as the stabilizer. The nanoparticles had excellent lyophilization, storage and re-dispersion stability. Hypromellose phthalate protected the loaded exenatide from degradation in simulated gastric fluid. Cholic acid promoted the intestinal absorption of the loaded exenatide via bile acid transporters. The exenatide loading efficiencies of COM NPs and DIS NPs were 79.7% and 53.6%, respectively. The exenatide oral pharmacological availability of COM NPs was 18.6% and DIS NPs was 13.1%. COM NPs controlled the blood glucose level of the db/db mice well and the HbA_1c concentration significantly decreased to 6.8% during and after 7 weeks of once daily oral administration consecutively. Both DIS NPs and COM NPs oral groups substantially increased the insulin secretion by more than 60% and promoted the β-cell proliferation by more than 120% after the 7-week administration.

CONCLUSIONS

Both COM NPs and DIS NPs are promising systems for oral delivery of exenatide, and COM NPs are better in blood glucose level control than DIS NPs. Using prolamin to produce multifunctional nanoparticles for oral delivery of peptide drug by hydrophobic interaction is a simple and effective strategy.

Release rate determination from in situ gel forming PLGA implant: a novel 'shape-controlled basket in tube' method

OBJECTIVES

This study aimed to examine the impact of syringe-needle assembly differences in making implants of different shapes as well as its influence on the release kinetics and investigate the release kinetics of the in situ forming implant under various release arrangements.

METHODS

PLGA in situ forming implant was prepared in different shape and then subjected to in vitro release testing. Mathematical modelling was used to investigate drug release mechanisms.

KEY FINDINGS

The in situ forming implant was investigated for the first time how implant shapes can affect release results. It was demonstrated that implant shape differences could lead to significant variation in the release data. Here, we addressed this issue by developing a shape-controlled method to provide a consistent surface to volume ratio and, therefore, a reliable release result. Injectability in the in vitro release was discussed for the first time. Comparisons between various release methods were also evaluated. The release arrangement was found to be of great importance in release kinetics.

CONCLUSIONS

The developed 'shape-controlled basket in tube' method can provide the most reproducible release profiles by minimizing implant adhesion to the release vessels or movement without sacrificing full contact between the release medium and the implant surface.

Poly(N-Isopropyl-Acrylamide)/Poly(γ-Glutamic Acid) Thermo-Sensitive Hydrogels Loaded with Superoxide Dismutase for Wound Dressing Application

INTRODUCTION

Chronic trauma repair is an important issue affecting people's healthy lives. Thermo-sensitive hydrogel is injectable in situ and can be used to treat large-area wounds. In addition, antioxidants play important roles in promoting wound repair.

METHODS

The purpose of this research was to prepare a novel thermo-sensitive hydrogel-poly(N-isopropyl-acrylamide)/poly(γ-glutamic acid) (PP) loaded with superoxide dismutase (SOD) to improve the effect for trauma treatment. The micromorphology of the hydrogel was observed by scanning electron microscope and the physical properties were measured. The biocompatibility of hydrogel was evaluated by MTT experiment, and the effect of hydrogel on skin wound healing was evaluated by in vivo histological staining.

RESULTS

Gelling behavior and differential scanning calorimeter outcomes showed that the PP hydrogels possessed thermo-sensitivity at physiological temperature and the phase transformation temperature was 28.2°C. The high swelling rate and good water retention were conducive to wound healing. The activity of SOD in vitro was up to 85% at 10 h, which was advantageous to eliminate the superoxide anion. MTT assay revealed that this hydrogel possessed good biocompatibility. Dressings of PP loaded with SOD (SOD-PP) had a higher wound closure rate than other treatments in vivo in diabetic rat model.

DISCUSSION

The SOD-PP thermo-sensitive hydrogels can effectively promote wound healing and have good application prospects for wound repair.

Repair of a Meniscal Defect in a Rabbit Model Through Use of a Thermosensitive, Injectable, In Situ Crosslinked Hydrogel With Encapsulated Bone Mesenchymal Stromal Cells and Transforming Growth Factor β1

BACKGROUND

Meniscal injury repair with tissue engineering technique is promising. Among various scaffolds, the thermosensitive injectable hydrogel has recently attracted much attention.

PURPOSE

(1) Evaluate the biocompatibility of thermosensitive, injectable, in situ crosslinked hydrogel and (2) determine whether the hydrogel with or without transforming growth factor β1 (TGF-β1) could support the fibrochondrogenic differentiation of bone mesenchymal stromal cells (BMSCs) and promote the repair of a critical-sized defect in rabbit meniscus.

STUDY DESIGN

Controlled laboratory study.

METHODS

The rheological and sustained release properties of the hydrogel were demonstrated. BMSCs were isolated and cultured. Cell viability, quantitative polymerase chain reaction (qPCR), and Western blot were tested in vitro. In vivo, a critical-sized defect was introduced into the meniscus of 30 rabbits. Each defect was randomly assigned to be implanted with either phosphate-buffered saline (PBS); BMSC-laden hydrogel; or BMSC-laden, TGF-β1-incorporated hydrogel. Histological and immunohistochemical analyses were performed at 8 weeks after surgery. The Ishida scoring system was adopted to evaluate the healing quantitatively.

RESULTS

The elastic modulus of the hydrogel was about 1000 Pa. The hydrogel demonstrated a sustained-release property and could promote proliferation and induce fibrochondrogenic differentiation of BMSCs after the incorporation of TGF-β1 (P < .001). At 8 weeks after surgery, a large amount of fibrocartilaginous tissue, which was positive on safranin-O staining and expressed strong type II collagen intermingled with weak type I collagen, was observed in the defect region of the BMSC-laden, TGF-β1-incorporated hydrogel group. In the BMSC-laden hydrogel group, the defect was filled with fibrous tissue together with a small amount of fibrocartilage. The mean ± SD quantitative scores obtained for the 3 groups-PBS; BMSC-laden hydrogel; and BMSC-laden, TGF-β1-incorporated hydrogel-were 1.00, 3.20 ± 0.84, and 5.00 ± 0.71, respectively (P < .001).

CONCLUSION

The hydrogel was biocompatible and could stimulate strong fibrochondrogenic differentiation of BMSCs after the incorporation of TGF-β1. The local administration of the BMSC-laden, TGF-β1-incorporated hydrogel could promote the healing of rabbit meniscal injury.

CLINICAL RELEVANCE

This hydrogel is an alternative scaffold for meniscus tissue engineering.

Self-Assemblable Polymer Smart-Blocks for Temperature-Induced Injectable Hydrogel in Biomedical Applications

Self-assembled temperature-induced injectable hydrogels fabricated via self-assembly of polymer smart-blocks have been widely investigated as drug delivery systems and platforms for tissue regeneration. Polymer smart-blocks that can be self-assembly play an important role in fabrication of hydrogels because they can self-assemble to induce the gelation of their copolymer in aqueous solution. The self-assembly occurs in response to an external stimulus change, such as temperature, pH, glucose, ionic strength, light, magnetic field, electric field, or their combination, which results in property transformations like hydrophobicity, ionization, and conformational change. The self-assembly smart-block based copolymers exist as a solution in aqueous media at certain conditions that are suitable for mixing with bioactive molecules and/or cells. However, this solution turns into a hydrogel due to the self-assembly of the smart-blocks under exposure to an external stimulus change in vitro or injection into the living body for a controllable release of loaded bioactive molecules or serving as a biomaterial scaffold for tissue regeneration. This work reports current scenery in the development of these self-assembly smart-blocks for fabrication of temperature-induced injectable physically cross-linked hydrogels and their potential application as drug delivery systems and platforms for tissue engineering.

Mussel-Inspired Injectable Hydrogel Adhesive Formed under Mild Conditions Features Near-Native Tissue Properties

Injectable hydrogel adhesives, especially those that can strongly adhere to tissues and feature near-native tissue mechanical properties, are desirable biomaterials for tissue repair. Compared to nonadhesive injectable hydrogels for minimally invasive delivery of therapeutic agents, they can better retain the delivered agents at targeted tissue locations and provide additional local physical barriers. However, regardless of recent advances, an ideal injectable hydrogel adhesive with both proper adhesion and mechanical matching between hydrogels and tissues is yet to be demonstrated with cytocompatible and efficient in situ curing methods. Inspired by marine mussels, where different mussel foot proteins (Mfps) function cooperatively to achieve excellent wet adhesion, we herein report a dual-mode-mimicking strategy by modifying gelatin (Gel) biopolymers with a single-type thiourea-catechol (TU-Cat) functionality to mimic two types of Mfps and their mode of action. This strategy features a minor, yet impactful modification of biopolymers, which gives access to collective properties of an ideal injectable hydrogel adhesive. Specifically, with TU-Cat functionalization of only ∼0.4-1.2 mol % of total amino acid residues, the Mfp-mimetic gelatin biopolymer (Gel-TU-Cat) can be injected and cured rapidly under mild and cytocompatible conditions, giving rise to tissue adhesive hydrogels with excellent matrix ductility, proper wet adhesion, and native tissue-like stress relaxation behaviors. Such a set of properties originating from our novel dual-mode-mimicking strategy makes the injectable hydrogel adhesive a promising platform for cell delivery and tissue repair.

Hydrogels For Peptide Hormones Delivery: Therapeutic And Tissue Engineering Applications

Peptides are the most abundant biological compounds in the cells that act as enzymes, hormones, structural element, and antibodies. Mostly, peptides have problems to move across the cells because of their size and poor cellular penetration. Therefore, a carrier that could transfer peptides into cells is ideal and would be effective for disease treatment. Until now, plenty of polymers, e.g., polysaccharides, polypeptides, and lipids were used in drug delivery. Hydrogels made from polysaccharides showed significant development in targeted delivery of peptide hormones because of their natural characteristics such as networks, pore sizes, sustainability, and response to external stimuli. The main aim of the present review was therefore, to gather the important usages of the hydrogels as a carrier in peptide hormone delivery and their application in tissue engineering and regenerative medicine.

Double-Network Polyurethane-Gelatin Hydrogel with Tunable Modulus for High-Resolution 3D Bioprinting

Three-dimensional (3D) bioprinting is a technology to print materials (bioink) with cells into customized tissues for regeneration or organoids for drug screening applications. Herein, a series of biodegradable polyurethane (PU)-gelatin hydrogel with tunable mechanical properties and degradation rates were developed as the bioink. The PU-gelatin hydrogel demonstrated good printability in 24-31 °C and could print a complicated structure such as the nose-shaped construct. Due to the excellent shear thinning and fast strain recovery properties, the PU-gelatin hydrogel also had long working windows for bioprinting (over 24 h), stacking ability (up to 80 layers), and feasibility for high-resolution printing (through an 80 μm nozzle). The structure stability of the PU-gelatin hydrogel was maintained by two-stage double-network formation through Ca²⁺ chelation and thermal gelation at 37 °C without any toxic cross-linking reagent. The compressive modulus of printed PU-gelatin hydrogel constructs increased in about 3-fold by the treatment of CaCl₂ solution for 15 min and enhanced further after incubation because of the thermal sensitivity of PU at 37 °C. Mesenchymal stem cells (MSCs) printed with the PU-gelatin hydrogel through the 80 μm nozzle showed good viability, high mobility, and ∼200% proliferation ratio (or an ∼300% proliferation ratio through a 200 μm nozzle) in 10 days. Furthermore, the MSC-laden PU-gelatin constructs containing small molecular drug Y27632 underwent chondrogenesis in 10 days. The novel series of PU-gelatin hydrogels with tunable modulus, long working window, convenient bioprinting process, and high-resolution printing possibilities may serve as new bioink for 3D bioprinting of various tissues.

Sustained Release Strategy Designed for Lixisenatide Delivery to Synchronously Treat Diabetes and Associated Complications

Diabetes and its complications have become a global challenge of public health. Herein, we aimed to develop a long-acting delivery system of lixisenatide (Lixi), a glucose-dependent antidiabetic peptide, based on an injectable hydrogel for the synchronous treatment of type 2 diabetes mellitus (T2DM) and associated complications. Two triblock copolymers, poly(ε-caprolactone-co-glycolic acid)-poly(ethylene glycol)-poly(ε-caprolactone-co-glycolic acid) and poly(d,l-lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(d,l-lactic acid-co-glycolic acid) possessing temperature-induced sol-gel transitions, were synthesized by us. Compared to the two single-component hydrogels, their 1/1 mixture hydrogel not only maintained the temperature-induced gelation but also exhibited a steadier degradation profile in vivo. Both in vitro and in vivo release studies demonstrated that the mixture hydrogel provided the sustained release of Lixi for up to 9 days, which was attributed to balanced electrostatic interactions between the positive charges in the peptide and the negative charges in the polymer carrier. The hypoglycemic efficacy of Lixi delivered from the mixture hydrogel after a single subcutaneous injection into diabetic db/db mice was comparable to that of twice-daily administrations of Lixi solution for up to 9 days. Furthermore, three successive administrations of the abovementioned gel system within a month significantly increased the plasma insulin level, lowered glycosylated hemoglobin, and improved the pancreatic function of the animals. These results were superior or equivalent to those of twice-daily injections of Lixi solution for 30 days, but the number of injections was markedly reduced from 60 to 3. Finally, an improvement in hyperlipidemia, augmentation of nerve fiber density, and enhancement of motor nerve conduction velocity in the gel formulation-treated db/db mice indicated that the sustained delivery of Lixi arrested and even ameliorated diabetic complications. These findings suggested that the Lixi-loaded mixture hydrogel has great potential for the treatment of T2DM with significant improvements in the health and quality of life of patients.

Injectable self-assembling hydrogel from alginate grafted by P(N-isopropylacrylamide-co-N-tert-butylacrylamide) random copolymers

Sodium alginate grafted by a thermo-responsive copolymer of N-isopropylacrylamide, enriched with the hydrophobic N-tert-butylacrylamide monomer, (P(NIPAM-co-NtBAM)-NH₂) was synthesized and its thermo- and shear-induced responsive capabilities were studied through rheology. The graft copolymer formed a 3D network through thermo-induced hydrophobic association of the thermo-responsive P(NIPAM-co-NtBAM) side chains in water. By applying the frequency-temperature superposition principle, the terminal relaxation time, τ and the shear viscosity, as a function of temperature were evaluated. Both parameters increased exponentially upon heating orders of magnitude, 15 °C above the onset of gelation (35 °C). It is shown that the thermo-induced thickening effect was mainly due to the slowdown of the P(NIPAM₉₀-co-NtBAM₁₀) associative side chains exchange dynamics. Moreover, combination of shear- and thermo-responsiveness provided excellent hydrogel injectability with instantaneous gelation at physiological temperature. The better insight of the thermo-thickening mechanism through oscillatory rheology allows precise tuning of the carbohydrate-based hydrogel properties towards potential bioapplications.

Non-Anticoagulant Heparin Prodrug Loaded Biodegradable and Injectable Thermoresponsive Hydrogels for Enhanced Anti-Metastasis Therapy

Metastasis is a pathogenic spread of cancer cells from the primary site to surrounding tissues and distant organs, making it one of the primary challenges for effective cancer treatment and the major cause of cancer mortality. Heparin-based biomaterials exhibit significant inhibition of cancer cell metastasis. In this study, a non-anticoagulate heparin prodrug is developed for metastasis treatment with a localized treatment system using temperature sensitive, injectable, and biodegradable (poly-(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) polymeric hydrogel. The drug molecule (heparin) is conjugated with the polymer via esterification, and its sustained release is ensured by hydrolysis and polymeric biodegradation. An aqueous solution of the polymer could be used as an injectable solution at below 25 °C and it achieves gel formation at 37 °C. The anti-metastasis effect of the hydrogels is investigated both in vitro and in vivo. The results demonstrated that local administration of injectable heparin-loaded hydrogels effectively promote an inhibitory effect on cancer metastasis.

Prolonged Drug-Releasing Fibers Attenuate Alzheimer's Disease-like Pathogenesis

Delivering drugs and agents to the brain is a huge challenge, especially for chronic neurodegenerative disorders, such as Alzheimer's disease (AD). For this, prolonged and sustained release methods to increase brain uptake represent an impacting concept. The bioresorbable polymer poly-lactic acid (PLA) has high potential for medical implants; at the same time, glucagon-like peptide-1 (GLP-1) analogues have considerable neuroprotective attributes and represent a therapeutic strategy for AD. Here, a biodevice is produced by electrospinning PLA with a GLP-1 analogue (liraglutide, LG), coated with a thin layer of gelatin. The biodevice is subcutaneously implanted in a transgenic mouse model of AD and LG is released for 14 days in mice serum. After 4 weeks of implantation, crucial hallmarks of the AD are highly diminished: hippocampal senile amyloid β plaque load and neuroinflammatory markers. Furthermore, neurogenesis is enhanced in the subventricular zone, an important neurogenic niche in the brain. The designed biodevice holds great promise for being an affordable candidate to act as a prolonged drug provider, promoting LG mission through increasing its lifetime, constituting a relevant approach for old and impaired brain.

Thermogel Loaded with Low-Dose Paclitaxel as a Facile Coating to Alleviate Periprosthetic Fibrous Capsule Formation

Medical-grade silicones as implants have been utilized for decades. However, the postoperative complications, such as capsular formation and contracture, have not yet been fully controlled and resolved. The aim of the present study is to elucidate whether the capsular formation can be alleviated by local and sustained delivery of low-dose paclitaxel (PTX) during the critical phase after the insertion of silicone implants. A biocompatible and thermogelling poly(lactic acid- co-glycolic acid)- b-poly(ethylene glycol)- b-poly(lactic acid- co-glycolic acid) triblock copolymer was synthesized by us. The micelles formed by the amphiphilic polymers in water could act as a reservoir for the solubilization of PTX, a very hydrophobic drug. The concentrated polymer aqueous solution containing PTX exhibited a sol-gel transition upon heating and formed a thermogel depot at body temperature. In vitro release tests demonstrated that the entrapped microgram-level PTX displayed a sustained release manner up to 57 days without a significant initial burst effect. Customized silicone implants coated with the PTX-loaded thermogels at various drug concentrations were inserted into the pockets of the subpanniculus carnosus plane of rats. The histological observations performed 1 month postoperation showed that the sustained release of PTX with an appropriate dose significantly reduced the peri-implant capsule thickness, production and deposition of collagen, and expression of contracture-mediating factors compared with bare silicone implants. More importantly, such an optimum dose had an excellent repeatability for the suppression of the capsular formation. Therefore, this study provides a strategic foothold regarding the sustained release of low-dose PTX to alleviate fibrotic capsule formation after implantation, and the microgram-level PTX-loaded thermogel holds great potential as an "all-purpose antifibrosis coating" for veiling the surfaces of various implantable medical devices.

Enzymatically cross-linked hydrogels based on a linear poly(ethylene glycol) analogue for controlled protein release and 3D cell culture

Injectable and enzyme-mediated cross-linked hydrogels are promising biomedical materials. However, although poly(ethylene glycol) (PEG) is a popular basic component of synthetic hydrogels, only a few PEG-based enzymatically cross-linked hydrogels have been developed based on branched PEG. Compared with branched PEG, linear PEGs with different molecular weights are readily available and low-cost, while the poor capacity for post-polymerization modifications of linear PEG limited its application on a greater scale. Herein, a linear PEG-based analogue functionalized with multiple phenolic hydroxyl moieties, PEGDA-DTT-HPA, was designed and synthesized via Michael-type polyaddition combined with Steglich esterification. Environmentally friendly hydrogels composed of PEGDA-DTT-HPA were facilely formed under the catalysis of horseradish peroxidase (HRP) in the presence of hydrogen peroxide (H₂O₂). The gelation time and mechanical strengths of hydrogels were found to be adjusted independently by altering the concentrations of HRP and H₂O₂, respectively. The hydrogels were further demonstrated as protein drug and cell carriers using bovine serum albumin (BSA) and lentivirus-mediated LifeAct-EGFP overexpressed human mesenchymal stem cells (hMSCs-LifeAct-EGFP), respectively. The BSA-loaded hydrogel systems exhibited a sustained drug release over 3 weeks; the encapsulated hMSCs showed good viability over all time points assessed. Consequently, the current study opens new avenues for the design of PEG-based injectable hydrogels and the PEGDA-DTT-HPA hydrogel has great potential for applications in drug delivery, 3D cell culture and tissue regeneration.