An injectable and tumor-specific responsive hydrogel with tissue-adhesive and nanomedicine-releasing abilities for precise locoregional chemotherapy

Boronate Ester Hydrogels for Biomedical Applications: Challenges and Opportunities

Boronate ester (BE) hydrogels are increasingly used for biomedical applications. The dynamic nature of these molecular networks enables bond rearrangement, which is associated with viscoelasticity, injectability, printability, and self-healing, among other properties. BEs are also sensitive to pH, redox reactions, and the presence of sugars, which is useful for the design of stimuli-responsive materials. Together, BE hydrogels are interesting scaffolds for use in drug delivery, 3D cell culture, and biofabrication. However, designing stable BE hydrogels at physiological pH (≈7.4) remains a challenge, which is hindering their development and biomedical application. In this context, advanced chemical insights into BE chemistry are being used to design new molecular solutions for material fabrication. This review article summarizes the state of the art in BE hydrogel design for biomedical applications with a focus on the materials chemistry of this class of materials. First, we discuss updated knowledge in BE chemistry including details on the molecular mechanisms associated with BE formation and breakage. Then, we discuss BE hydrogel formation at physiological pH, with an overview of the main systems reported to date along with new perspectives. A last section covers several prominent biomedical applications of BE hydrogels, including drug delivery, 3D cell culture, and bioprinting, with critical insights on the design relevance, limitations and potential.

Recent research progress on tumour-specific responsive hydrogels

Most existing hydrogels, even recently developed injectable hydrogels that undergo a reversible sol-gel phase transition in response to external stimuli, are designed to gel immediately before or after implantation/injection to prevent the free diffusion of materials and drugs; however, the property of immediate gelation leads to a very weak tumour-targeting ability, limiting their application in anticancer therapy. Therefore, the development of tumour-specific responsive hydrogels for anticancer therapy is imperative because tumour-specific responses improve their tumour-targeting efficacy, increase therapeutic effects, and decrease toxicity and side effects. In this review, we introduce the following three types of tumour-responsive hydrogels: (1) hydrogels that gel specifically at the tumour site; (2) hydrogels that decompose specifically at the tumour site; and (3) hydrogels that react specifically with tumours. For each type, their compositions, the mechanisms of tumour-specific responsiveness and their applications in anticancer treatment are comprehensively discussed.

In situ forming an injectable hyaluronic acid hydrogel for drug delivery and synergistic tumor therapy

Stimulus-responsive injectable hydrogel has the key characteristics of in situ drug-loading ability and the controlled drug release, enabling efficient delivery and precise release of chemotherapy drugs at the tumor site, thereby being used as a local drug delivery system for sustained tumor treatment. This article designed a smart responsive injectable hydrogel loaded with anti-tumor drugs and nanoparticles to achieve efficient and specific synergistic treatment of tumors. Hyaluronic acid (HA) hydrogel obtained by cross-linking HA-SH (HS) and HA-Tyr (HT) through horseradish peroxidase (HRP), and doxorubicin hydrochloride (DOX) and folic acid-polyethylene glycol-amine (FA-PEG-NH2) modified PDA (denoted as PPF) were encapsulated to construct the HS/HT@PPF/D hydrogel. The hydrogel had good biocompatibility, injectability, and could respond to multiple stimuli at the tumor site, thereby achieving controlled drug release. At the same time, PPF gave it excellent photothermal efficiency, photothermal stability and tumor targeting. In vitro and in vivo experimental results showed that the HS/HT@PPF/D hydrogel combined with near-infrared laser irradiation could significantly improve its anti-tumor effect and could almost eliminate the entire tumor mass without obvious adverse reactions. The HS/HT@PPF/D hydrogel could achieve multi-stimulus-responsive drug delivery and be used for precise chemo-photothermal synergistic tumor treatment, thus providing a new platform for local synergistic tumor treatment.

Recent Advances in the Degradability and Applications of Tissue Adhesives Based on Biodegradable Polymers

In clinical practice, tissue adhesives have emerged as an alternative tool for wound treatments due to their advantages in ease of use, rapid application, less pain, and minimal tissue damage. Since most tissue adhesives are designed for internal use or wound treatments, the biodegradation of adhesives is important. To endow tissue adhesives with biodegradability, in the past few decades, various biodegradable polymers, either natural polymers (such as chitosan, hyaluronic acid, gelatin, chondroitin sulfate, starch, sodium alginate, glucans, pectin, functional proteins, and peptides) or synthetic polymers (such as poly(lactic acid), polyurethanes, polycaprolactone, and poly(lactic-co-glycolic acid)), have been utilized to develop novel biodegradable tissue adhesives. Incorporated biodegradable polymers are degraded in vivo with time under specific conditions, leading to the destruction of the structure and the further degradation of tissue adhesives. In this review, we first summarize the strategies of utilizing biodegradable polymers to develop tissue adhesives. Furthermore, we provide a symmetric overview of the biodegradable polymers used for tissue adhesives, with a specific focus on the degradability and applications of these tissue adhesives. Additionally, the challenges and perspectives of biodegradable polymer-based tissue adhesives are discussed. We expect that this review can provide new inspirations for the design of novel biodegradable tissue adhesives for biomedical applications.

Recent Advances in Engineering Carriers for siRNA Delivery

RNA interference (RNAi) technology has been a promising treatment strategy for combating intractable diseases. However, the applications of RNAi in clinical are hampered by extracellular and intracellular barriers. To overcome these barriers, various siRNA delivery systems have been developed in the past two decades. The first approved RNAi therapeutic, Patisiran (ONPATTRO) using lipids as the carrier, for the treatment of amyloidosis is one of the most important milestones. This has greatly encouraged researchers to work on creating new functional siRNA carriers. In this review, the recent advances in siRNA carriers consisting of lipids, polymers, and polymer-modified inorganic particles for cancer therapy are summarized. Representative examples are presented to show the structural design of the carriers in order to overcome the delivery hurdles associated with RNAi therapies. Finally, the existing challenges and future perspective for developing RNAi as a clinical modality will be discussed and proposed. It is believed that the addressed contributions in this review will promote the development of siRNA delivery systems for future clinical applications.

Liposome-camouflaged iodinated mesoporous silica nanoparticles with high loading capacity, high hemodynamic stability, high biocompatibility and high radiopacity

Due to their low osmolality and high tolerability, the highly water-soluble nonionic iodinated contrast agents, such as Ioversol (IV), are widely used as clinical agents for CT imaging. However, their clinical applications still are severely limited by the rapid renal excretion, serious adverse effects especially contrast-induced nephropathy and inefficient targetability. Various nanocarriers have demonstrated tremendous potential for achieving high imaging efficiency and low side effects. However, few nanoparticulate contrast agents can simultaneously integrate the desirable functions for imaging, including high loading capacity of iodine, high structure stability for systemic circulation, high biocompatibility and high radiopacity. Herein, we designed and prepared a kind of new radiopaque liposome-camouflaged iodinated mesoporous silica nanoparticles (OIV-MSNs@Liposomes) as contrast agents in CT imaging. Their composition, structure, morphology, biocompatibility and physicochemical properties as well as in vitro radiopacity were investigated in detail. The results indicated that OIV-MSNs@Liposomes can integrate their individual advantages of liposomes and MSNs, thus exhibiting great potential for use in the CT imaging. Considering the simple preparation process and readily available starting materials as well as enhanced biosafety and high performance in X-ray attenuation, the strategy reported here offers a versatile route to efficiently deliver highly water-soluble nonionic iodinated contrast agents for enhanced CT imaging, which are unattainable by traditional means.

Synthesis of Multifunctional Mn3O4-Ag2S Janus Nanoparticles for Enhanced T1-Magnetic Resonance Imaging and Photo-Induced Tumor Therapy

The global burden of cancer is increasing rapidly, and nanomedicine offers promising prospects for enhancing the life expectancy of cancer patients. Janus nanoparticles (JNPs) have garnered considerable attention due to their asymmetric geometry, enabling multifunctionality in drug delivery and theranostics. However, achieving precise control over the self-assembly of JNPs in solution at the nanoscale level poses significant challenges. Herein, a low-temperature reversed-phase microemulsion system was used to obtain homogenous Mn3O4-Ag2S JNPs, which showed significant potential in cancer theranostics. Structural characterization revealed that the Ag2S (5-10 nm) part was uniformly deposited on a specific surface of Mn3O4 to form a Mn3O4-Ag2S Janus morphology. Compared to the single-component Mn3O4 and Ag2S particles, the fabricated Mn3O4-Ag2S JNPs exhibited satisfactory biocompatibility and therapeutic performance. Novel diagnostic and therapeutic nanoplatforms can be guided using the magnetic component in JNPs, which is revealed as an excellent T1 contrast enhancement agent in magnetic resonance imaging (MRI) with multiple functions, such as photo-induced regulation of the tumor microenvironment via producing reactive oxygen species and second near-infrared region (NIR-II) photothermal excitation for in vitro tumor-killing effects. The prime antibacterial and promising theranostics results demonstrate the extensive potential of the designed photo-responsive Mn3O4-Ag2S JNPs for biomedical applications.

Current research trends of nanomedicines

Owing to the inherent shortcomings of traditional therapeutic drugs in terms of inadequate therapeutic efficacy and toxicity in clinical treatment, nanomedicine designs have received widespread attention with significantly improved efficacy and reduced non-target side effects. Nanomedicines hold tremendous theranostic potential for treating, monitoring, diagnosing, and controlling various diseases and are attracting an unfathomable amount of input of research resources. Against the backdrop of an exponentially growing number of publications, it is imperative to help the audience get a panorama image of the research activities in the field of nanomedicines. Herein, this review elaborates on the development trends of nanomedicines, emerging nanocarriers, in vivo fate and safety of nanomedicines, and their extensive applications. Moreover, the potential challenges and the obstacles hindering the clinical translation of nanomedicines are also discussed. The elaboration on various aspects of the research trends of nanomedicines may help enlighten the readers and set the route for future endeavors.

NIR- and pH-responsive injectable nanocomposite alginate-graft-dopamine hydrogel for melanoma suppression and wound repair

Surgical excision, chemotherapy, and radiotherapy are the main approaches used for treating melanoma. Unfortunately, surgical excision usually inevitably causes large area skin defects. In addition, chemotherapy and radiotherapy are often accompanied by adverse reactions and multi-drug resistance. To overcome these limitations, a near-infrared (NIR)- and pH-responsive injectable nanocomposite hydrogel was developed using sodium alginate-graft-dopamine (SD) and biomimetic polydopamine-Fe(III)-doxorubicin nanoparticles (PFD NPs) for treating melanoma and promoting skin regeneration. Firstly, the SD/PFD hydrogel can precisely deliver anti-cancer agents to the tumor site to reduce its loss and off-target toxicity. Then, PFD can convert light into heat energy under NIR irradiation to kill cancer cells. Meanwhile, doxorubicin can be administered continuously and controllably by NIR- and pH-responsive. Additionally, the SD/PFD hydrogel can also relieve tumor hypoxia by decomposing endogenous hydrogen peroxide (H₂O₂) into oxygen (O₂). Therefore, photothermal, chemotherapy, and nanozyme synergetic therapy resulted in the tumor suppression. Specifically, the SA-based hydrogel can kill bacteria, scavenge reactive oxygen species, promote the proliferation and migration of cells, and significantly accelerate skin regeneration. Therefore, this study provides a safe and effective strategy for melanoma treatment and wound repair.

Targeted hollow pollen silica nanoparticles for enhanced intravesical therapy of bladder cancer

Bladder cancer (BC), such as non-muscle invasive bladder cancer (NMIBC), has a significantly high recurrence rate even after intravesical therapy because traditional intravesical chemotherapeutic drugs have short retention time in the bladder and lack efficient uptake in BC cells. Pollen structure usually shows potent adhesion ability to tissue surfaces, different from traditional electronic interaction or covalent binding. 4-Carboxyphenylboric acid (CPBA) has high affinity to sialic acid residues that are overexpressed on BC cells. In the present study, hollow pollen silica (HPS) nanoparticles (NPs) were prepared and modified with CPBA to form CHPS NPs, which could be further loaded with pirarubicin (THP) to form THP@CHPS NPs. THP@CHPS NPs showed high adhesion to skin tissues and could be more efficiently internalized by a mouse bladder cancer cell line (MB49) than THP, inducing more significant apoptotic cells. After intravesical instillation into a BC mouse model through an indwelling catheter, THP@CHPS NPs could more significantly accumulate at the bladder than THP at 24 h post-instillation, and after 8 days of intravesical treatments, magnetic resonance imaging (MRI) revealed that the bladders treated with THP@CHPS NPs showed more smooth bladder lining and more reduction in size and weights than those with THP. Moreover, THP@CHPS NPs exhibited excellent biocompatibility. THP@CHPS NPs hold great potential for intravesical treatment of bladder cancer.

An injectable hydrogel based on Bi2Se3 nanosheets and hyaluronic acid for chemo-photothermal synergistic therapy

To resolve poor accumulation caused by systemic administration, injectable and responsive hydrogels are the prospective drug delivery systems for localized tumor treatment, owning to negligible invasiveness and accurate administration. Herein, an injectable hydrogel, based on dopamine (DA) crosslinked hyaluronic acid and Bi₂Se₃ nanosheets (NSs) loading with doxorubicin (DOX) coated with polydopamine (Bi₂Se₃-DOX@PDA), was developed for synergistic chem-photothermal cancer therapy. The ultrathin functional Bi₂Se₃-DOX@PDA NSs could be responsive to the weak acidic condition and photothermal effect under NIR laser irradiation, achieving controlled release of DOX. Moreover, nanocomposite hydrogel based on hyaluronic acid matrix could be precisely administrated through intratumoral injection since its injectability and self-healing capacity, remaining at injected sites for at least 12 days. Furthermore, the excellent therapeutics effect of Bi₂Se₃-DOX@PDA nanocomposite hydrogel was demonstrated on 4 T1 xenograft tumor with outstanding injectability and negligible systemic side-effect. In short, the construction of Bi₂Se₃-DOX@PDA nanocomposite hydrogel paves a prospective path for local treatment of cancers.

Evolution of nanostructured skin patches towards multifunctional wearable platforms for biomedical applications

Recent advances in the field of skin patches have promoted the development of wearable and implantable bioelectronics for long-term, continuous healthcare management and targeted therapy. However, the design of electronic skin (e-skin) patches with stretchable components is still challenging and requires an in-depth understanding of the skin-attachable substrate layer, functional biomaterials and advanced self-powered electronics. In this comprehensive review, we present the evolution of skin patches from functional nanostructured materials to multi-functional and stimuli-responsive patches towards flexible substrates and emerging biomaterials for e-skin patches, including the material selection, structure design and promising applications. Stretchable sensors and self-powered e-skin patches are also discussed, ranging from electrical stimulation for clinical procedures to continuous health monitoring and integrated systems for comprehensive healthcare management. Moreover, an integrated energy harvester with bioelectronics enables the fabrication of self-powered electronic skin patches, which can effectively solve the energy supply and overcome the drawbacks induced by bulky battery-driven devices. However, to realize the full potential offered by these advancements, several challenges must be addressed for next-generation e-skin patches. Finally, future opportunities and positive outlooks are presented on the future directions of bioelectronics. It is believed that innovative material design, structure engineering, and in-depth study of fundamental principles can foster the rapid evolution of electronic skin patches, and eventually enable self-powered close-looped bioelectronic systems to benefit mankind.

Nanoarchitecture-Integrated Hydrogel Systems toward Therapeutic Applications

Hydrogels, as one of the most feasible soft biomaterials, have gained considerable attention in therapeutic applications by virtue of their tunable properties including superior patient compliance, good biocompatibility and biodegradation, and high cargo-loading efficiency. However, hydrogel application is still limited by some challenges like inefficient encapsulation, easy leakage of loaded cargoes, and the lack of controllability. Recently, nanoarchitecture-integrated hydrogel systems were found to be therapeutics with optimized properties, extending their bioapplication. In this review, we briefly presented the category of hydrogels according to their synthetic materials and further discussed the advantages in bioapplication. Additionally, various applications of nanoarchitecture hybrid hydrogels in biomedical engineering are systematically summarized, including cancer therapy, wound healing, cardiac repair, bone regeneration, diabetes therapy, and obesity therapy. Last, the current challenges, limitations, and future perspectives in the future development of nanoarchitecture-integrated flexible hydrogels are addressed.

Dual-Function Hydrogel Dressings with a Dynamic Exchange of Iron Ions and an Antibiotic Drug for Treatment of Infected Wounds

Bacterial infection is a major problem with diabetic wounds that may result in nonhealing chronic ulcers. Here, we report an approach to antibacterial hydrogel dressings for enhanced treatment of infected skin wounds. A fibrous hydrogel was derived from cellulose nanocrystals that were modified with dopamine and cross-linked with gelatin. The hydrogel was loaded with gentamicin, an antibiotic drug. Enhanced antibacterial hydrogel performance resulted from (i) a highly specific sequestration of Fe³⁺ ions (much needed by bacteria) from the wound exudate and (ii) a dynamic exchange between gentamicin released from the hydrogel and Fe³⁺ ions withdrawn from the wound exudate. Such exchange was possible due to the high value of the binding constant of Fe³⁺ ions to dopamine. The hydrogel did not affect the metabolic activity of skin-related cells and showed enhanced antibacterial performance against common wound pathogens such as S. aureus and P. aeruginosa. Furthermore, it promoted healing of infected diabetic wounds due to a synergistic antibacterial effect providing the dynamic exchange between Fe³⁺ ions and gentamicin. This work provides a strategy for the design of dual-function wound dressings, with both starving and killing bacteria and enhanced wound healing performance.

Versatile Hydrogel Dressing with Skin Adaptiveness and Mild Photothermal Antibacterial Activity for Methicillin-Resistant Staphylococcus Aureus-Infected Dynamic Wound Healing

Bacterial infection often induces chronic repair of wound healing owing to aggravated inflammation. Hydrogel dressing exhibiting intrinsic antibacterial activity may substantially reduce the use of antibiotics for infected wound management. Hence, a versatile hydrogel dressing (rGB/QCS/PDA-PAM) exhibiting skin adaptiveness on dynamic wounds and  mild photothermal antibacterial activity is developed for safe and efficient infected wound treatment. Phenylboronic acid-functionalized graphene (rGB) and oxadiazole-decorated quaternary carboxymethyl chitosan (QCS) are incorporated into a polydopamine-polyacrylamide (PDA-PAM) network with multiple covalent and noncovalent bonds, which conferred the hydrogel with flexible mechanical properties, strong tissue adhesion and excellent self-healing ability on the dynamic wounds. Moreover, the glycocalyx-mimicking phenylboronic acid on the surface of rGB enables the hydrogel to specifically capture bacteria. The enhanced membrane permeability of QCS enhanced bacterial vulnerability to photothermal therapy（PTT）, which is demonstrated by efficient mild PTT antibacteria against methicillin-resistant Staphylococcus aureus in vitro and in vivo at temperatures of <49.6 °C. Consequently, the hydrogel demonstrate accelerated tissue regeneration on MRSA-infected wound in vivo, with an intact epidermis, abundant collagen deposition and prominent angiogenesis. Therefore, rGB/QCS/PDA-PAM is a versatile hydrogel dressing exhibiting inherent antibacterial activity and has considerable potential in treating wounds infected with drug-resistant bacteria.

An injectable and pH-responsive hyaluronic acid hydrogel as metformin carrier for prevention of breast cancer recurrence

To achieve the pH-responsive release of metformin in tumor acidic microenvironment, we prepared OHA-Met by covalently grafting metformin (Met) onto oxidized hyaluronic acid (OHA) through imine bonds, and then prepared carboxymethyl chitosan (CMCS)/OHA-Met drug loaded hydrogels. The CMCS/OHA-Met hydrogels showed the in-situ injection performance. At pH = 7.4, the cumulative release rate of metformin from CMCS/OHA-Met20 hydrogel was 42.7 ± 2.6 % in 6 h, and the release tended to balance after 72 h. At pH = 5.5, the release kept constant and the cumulative release rate was 79.3 ± 4.7 % at 6 h, showing good pH-responsive behavior. Metformin induced apoptosis of MCF-7 cells through the caspase 3/PARP pathway. CMCS/OHA-Met20 hydrogel could effectively kill MCF-7 cells, while reducing the cytotoxicity of free metformin to L929 cells. In vivo breast cancer recurrence experiments showed CMCS/OHA-Met20 hydrogel could achieve local injection and pH-responsive smart drug delivery at the tumor resection site, inhibiting breast cancer recurrence. Compared with direct administration, CMCS/OHA-Met20 hydrogel reduced the metformin dosage, frequency of administration and systemic side effects.

Injectable carboxymethyl chitosan-based hydrogel for simultaneous anti-tumor recurrence and anti-bacterial applications

The postoperative recurrence has adversely affected the treatment of tumors. Besides, the potential bacterial infection at the wound site may lead to a series of tissue necrosis. Here, we developed an injectable γ-polyglutamic acid/carboxymethyl chitosan/polydopamine hydrogel (PCP) for simultaneously reducing the postoperative infection and preventing the tumor recurrence. On the one hand, the aqueous solution of carboxymethyl chitosan oxidized the dopamine into polydopamine; on the other, the carboxymethyl chitosan was cross-linked with the activated γ-polyglutamic acid to form a hydrogel. After local implantation, the PCP hydrogel effectively killed tumor cells and bacteria under 808 nm laser irradiation. In addition, carboxymethyl chitosan rendered the hydrogel with anti-bacterial properties as well as anti-tumor efficiencies. The anti-tumor recurrence and anti-bacterial efficiencies of PCP hydrogel were proved on a tumor-removed mouse model and a Staphylococcus aureus-infected mouse model, respectively. Moreover, the hydrogel has the advantages of good biocompatibility and simple preparation, and thus has potential application prospects in the prevention of tumor recurrence and wound bacterial infection.

Exploration of hemocompatibility and intratumoral accumulation of paclitaxel after loco-regional administration of thermoresponsive hydrogel composed of poloxamer and xanthan gum: An application to dose-dense chemotherapy

Although paclitaxel is a front-line chemotherapeutic agent for the treatment of metastatic breast cancer, its intravenous therapy produces deleterious adverse effects. In an attempt to address the issue, the present study aimed to develop a paclitaxel loaded thermosensitive/thermoresponsive hydrogel (PTXNp-TGel) for loco-regional administration to breast tumors to provide dose-dense chemotherapy. Poloxamer and xanthan gum were used to prepare TGel by the cold method. In vitro and in vivo performance of PTXNp-TGel was compared with TGel, pure drug loaded TGel (PTX-TGel) and marketed formulation, Taxol®. The formulated PTXNp-TGel showed acceptable gelation temperature and time (37 °C and 57 s), lower viscosity at room temperature and higher viscosity at body temperature to support sol-gel transition with increasing temperature, and sustained drug release up to 21 days. Additionally, PTXNp-TGel showed negligible hemolytic toxicity as compared to PTX-TGel and Taxol®. Intratumoral administration of PTXNp-TGel produced significantly higher antitumor activity as indicated by lowest relative tumor volume (1.50) and relative antitumor proliferation rate (27.71 %) in comparison with PTX-TGel, Taxol®, and PTXNp (p < 0.05). Finally, insignificant body weight loss during the experimental period, lack of hematotoxicity, nephrotoxicity, and hepatotoxicity imply improved therapeutic performance of the locally administrated dose-dense therapy of PTXNp-TGel as compared to Taxol®.

Functional Nanoparticles for Enhanced Cancer Therapy

Cancer is the leading cause of death in people worldwide. The conventional therapeutic approach is mainly based on chemotherapy, which has a series of side effects. Compared with traditional chemotherapy drugs, nanoparticle-based delivery of anti-cancer drugs possesses a few attractive features. The application of nanotechnology in an interdisciplinary manner in the biomedical field has led to functional nanoparticles achieving much progress in cancer therapy. Nanoparticles have been involved in the diagnosis and targeted and personalized treatment of cancer. For example, different nano-drug strategies, including endogenous and exogenous stimuli-responsive, surface conjugation, and macromolecular encapsulation for nano-drug systems, have successfully prevented tumor procession. The future for functional nanoparticles is bright and promising due to the fast development of nanotechnology. However, there are still some challenges and limitations that need to be considered. Based on the above contents, the present article analyzes the progress in developing functional nanoparticles in cancer therapy. Research gaps and promising strategies for the clinical application are discussed.

Facile Construction of a Two-in-One Injectable Micelleplex-Loaded Thermogel System for the Prolonged Delivery of Plasmid DNA

Nanoparticle-hydrogel systems have recently emerged as a class of interesting hybrid materials with immense potential for several biomedical applications. Remarkably, the incorporation of nanoparticles into a hydrogel may yield synergistic benefits lacking in a singular system. However, most synthetic strategies require laborious steps to achieve the system, severely restricting the process of translational research. Herein, a facile strategy to access a two-in-one system comprising two distinct polyurethane (PU)-based micellar systems is demonstrated and applied as a novel sustained gene delivery platform, where the two PUs are synthesized similarly but with slightly different compositions. One PU forms cationic micelles that complex with plasmid DNA (pDNA), which are loaded into a thermogel formed by another PU micellar system for the prolonged release of pDNA micelleplexes. Specifically, a thermogelling multiblock PU copolymer (denoted as EPH) was synthesized via the step-growth polymerization of poly(ethylene glycol), poly(propylene glycol), and poly(3-hydroxybutyrate). By further introducing a cationic extender, 3-(dimethylamino)-1,2-propanediol, into the reaction feed, a series of cationic PUs (denoted as EPHD) with varying compositions were obtained. The EPHDs formed positively charged micelles in aqueous solutions, efficiently condensed pDNA into nano-sized micelleplexes (<200 nm) at optimized w/w ratios, and mediated transient green fluorescence protein expression in HEK293T cells at 48 h post-transfection. On the other hand, aqueous EPH solution (4 wt %) was injectable at 4 °C and rapidly gelled upon heating to 37 °C to form a stable hydrogel depot. EPHD/pDNA micelleplexes were easily loaded into EPH by mixing the solutions at 4 °C, before heating to 37 °C, leading to the resultant hydrogel system. The in vitro release study revealed that while free pDNA loaded in the thermogel was completely released in 2 weeks, the release of EPHD/pDNA micelleplexes was prolonged to at least 28 days, suggesting substantial micelleplex-hydrogel interactions. Intact, bioactive, and noncytotoxic EPHD/pDNA micelleplexes in the release media were proved by gel retardation, in vitro gene transfection, and CCK-8 cytotoxicity assay results, respectively. Collectively, this work presents a simple approach to achieving and optimizing a novel two-in-one nanoparticle-hydrogel system for the prolonged delivery of pDNA and may be promising for long-term gene delivery applications.

Influence of Critical Parameters on Cytotoxicity Induced by Mesoporous Silica Nanoparticles

Mesoporous Silica Nanoparticles (MSNs) have received increasing attention in biomedical applications due to their tuneable pore size, surface area, size, surface chemistry, and thermal stability. The biocompatibility of MSNs, although generally believed to be satisfactory, is unclear. Physicochemical properties of MSNs, such as diameter size, morphology, and surface charge, control their biological interactions and toxicity. Experimental conditions also play an essential role in influencing toxicological results. Therefore, the present study includes studies from the last five years to statistically analyse the effect of various physicochemical features on MSN-induced in-vitro cytotoxicity profiles. Due to non-normally distributed data and the presence of outliers, a Kruskal–Wallis H test was conducted on different physicochemical characteristics, including diameter sizes, zeta-potential measurements, and functionalisation of MSNs, based on the viability results, and statistical differences were obtained. Subsequently, pairwise comparisons were performed using Dunn’s procedure with a Bonferroni correction for multiple comparisons. Other experimental parameters, such as type of cell line used, cell viability measurement assay, and incubation time, were also explored and analysed for statistically significant results.

Metal-organic framework-based hydrogel with structurally dynamic properties as a stimuli-responsive localized drug delivery system for cancer therapy

Metal-organic framework (MOF) is an exciting class of porous biomaterials that have been considered as a carrier to store and deliver therapeutic drugs. However, similar to other nanomaterials, the application of MOF in clinical settings is still limited because of premature diffusion of their payloads and tissue off-targeting behavior. To overcome these challenges, we designed an MOF-based hydrogel with structurally dynamic properties, i.e., self-healing and shear-thinning, as an injectable localized drug delivery platform. The drug-encapsulating MOF hydrogel is formed through a dynamic coordination bond cross-linkage between a doxorubicin-loaded MOF (MOF@DOX) particle and a homemade bisphosphonate-modified hyaluronic acid (HA-BP) polymeric binder. The HA-BP·MOF@DOX hydrogel demonstrates pH- and ATP-responsive drug release characteristic and efficiently kills cancer cells in vitro. The animal experiments reveal that the HA-BP·MOF@DOX hydrogel has enhanced capability in terms of tumor growth suppression as compared to the MOF@DOX group, which can be attributed to drug localization in hydrogel superstructure and sustained release at the tumor site. The presented injectable dynamic MOF-based hydrogel is a promising in vivo localized drug delivery system for cancer treatment. Herein, we report the self-healing and shear-thinning of MOF-based drug carrier cross-linked by coordinate bonds for the first time and provide new insights and a facile chemical strategy for designing and fabricating MOF-based biomaterials by using bisphosphonate-zinc interaction. STATEMENT OF SIGNIFICANCE: Bisphosphonate-zinc interaction is a facile chemical strategy to cross-link metal-organic framework (MOF)-based hydrogel. The presented MOF-based hydrogel demonstrates structurally dynamic properties, including smooth injectability, self-healing, and shear-thinning. The developed MOF-based hydrogel possesses pH- and ATP-responsive drug release characteristic and kills cancer cells in vitro efficiently. The dynamic MOF-based hydrogel shows enhanced in vivo anticancer activity as compared to pure MOF particles. Self-healing and shear-thinning of metal-ligand cross-linked MOF-based drug delivery system are reported for the first time, thus providing new insights for the design and fabrication of MOF-based biomaterials.

Cutting-Edge Progress in Stimuli-Responsive Bioadhesives: From Synthesis to Clinical Applications

With the advent of “intelligent” materials, the design of smart bioadhesives responding to chemical, physical, or biological stimuli has been widely developed in biomedical applications to minimize the risk of wounds reopening, chronic pain, and inflammation. Intelligent bioadhesives are free-flowing liquid solutions passing through a phase shift in the physiological environment due to stimuli such as light, temperature, pH, and electric field. They possess great merits, such as ease to access and the ability to sustained release as well as the spatial transfer of a biomolecule with reduced side effects. Tissue engineering, wound healing, drug delivery, regenerative biomedicine, cancer therapy, and other fields have benefited from smart bioadhesives. Recently, many disciplinary attempts have been performed to promote the functionality of smart bioadhesives and discover innovative compositions. However, according to our knowledge, the development of multifunctional bioadhesives for various biomedical applications has not been adequately explored. This review aims to summarize the most recent cutting-edge strategies (years 2015–2021) developed for stimuli-sensitive bioadhesives responding to external stimuli. We first focus on five primary categories of stimuli-responsive bioadhesive systems (pH, thermal, light, electric field, and biomolecules), their properties, and limitations. Following the introduction of principal criteria for smart bioadhesives, their performances are discussed, and certain smart polymeric materials employed in their creation in 2015 are studied. Finally, advantages, disadvantages, and future directions regarding smart bioadhesives for biomedical applications are surveyed.

Effect of pH on the Properties of Hydrogels Cross-Linked via Dynamic Thia-Michael Addition Bonds

Hydrogels cross-linked with dynamic covalent bonds exhibit time-dependent properties, making them an advantageous platform for applications ranging from biomaterials to self-healing networks. However, the relationship between the cross-link exchange kinetics, material properties, and stability of these platforms is not fully understood, especially upon addition of external stimuli. In this work, pH was used as a handle to manipulate cross-link exchange kinetics and control the resulting hydrogel mechanics and stability in a physiologically relevant window. Poly(ethylene glycol)-based hydrogels were cross-linked with a reversible thia-Michael addition reaction in aqueous buffer between pH 3 and pH 7. The rate constants of bond exchange and equilibrium constants were determined for each pH value, and these data were correlated with the resulting mechanical profiles of the bulk hydrogels. With increasing pH, both the forward and the reverse rate constants increased, while the equilibrium constant decreased. These changes led to faster stress relaxation and less stiff hydrogels at more basic pH values. The elevated pH values also led to an increased mass loss and a faster rate of release of an encapsulated model bovine serum albumin fluorescent protein. The connection between the kinetics, mechanics, and molecular release profiles provides important insight into the structure–property relationships of dynamic covalent hydrogels, and this system offers a promising platform for controlled release between physiologically relevant pH values.

Injectable self-healing cellulose hydrogel based on host-guest interactions and acylhydrazone bonds for sustained cancer therapy

Tumor local chemotherapy employing injectable hydrogel reservoirs is a promising platform to achieve precise drug administration. However, balanced injectability, pH-responsiveness and long-term hydrolysis resistance of self-healing hydrogels remain appealing challenges. Herein, a modular preassembly strategy combining host-guest interactions with dynamic acylhydrazone bonds, was exploited to fabricate injectable cellulose-based hydrogels (CAAs) dressed with self-healing properties, pH-responsiveness and hydrolytic degradation resistance. Attributed to the host-guest interaction between β-cyclodextrin (CD) and 1-adamantane (AD), the hydrogels exhibited injectability, self-healing properties (healing efficiency of 97.5%) and rapid recovery (< 10 min) without external stimuli in physiological environment. Moreover, the hydrogels equipped with dynamic acylhydrazone linkages underwent slow hydrolytic degradation (> 30 days) and pH-responsive behavior, endowing the hydrogels with precise spatiotemporal drug release administration. The in vivo application of CAA as a carrier was studied using doxorubicin (DOX) model drug, and the results shows that using CAA as DOX carrier not only greatly enhances the anti-tumor efficacy of DOX, but also reduced the side effects of DOX. STATEMENT OF SIGNIFICANCE: With the preassemble approach combining host-guest interactions with dynamic acylhydrazone bonds, this work demonstrated a multi-functional self-healing hydrogel as drug carrier developed by using natural polysaccharides, which offers a new avenue for the high-value utilization of biomass. The strategy demonstrated in the present work may also supply a pathway for the preparation and regulation of hydrogels as intelligent biomedicine materials.

Hyaluronic Acid-Functionalized Hollow Mesoporous Silica Nanoparticles as pH-Sensitive Nanocarriers for Cancer Chemo-Photodynamic Therapy

Hollow mesoporous silica nanoparticles (HMSNs) served as nanocarriers for transporting doxorubicin hydrochloride (DOX) and indocyanine green (ICG) and were incorporated into a pH-sensitive targeted drug delivery system (DDS). Boronate ester bonds were employed to link HMSNs and dopamine-modified hyaluronic acid (DA-HA), which acted as both the "gatekeeper" and targeting agents (HMSNs-B-HA). Well-dispersed HMSNs-B-HA with a diameter of about 170 nm was successfully constructed. The conclusion was drawn from the in vitro drug release experiment that ICG and DOX (ID) co-loaded nanoparticles (ID@HMSNs-B-HA) with high drug loading efficiency could sustain drug release under acidic conditions. More importantly, in vitro cell experiments perfectly showed that ID@HMSNs-B-HA could well inhibit murine mammary carcinoma (4T1) cells via chemotherapy combined with photodynamic therapy and accurately target 4 T1 cells. In summary, all test results sufficiently demonstrated that the prepared ID@HMSNs-B-HA was a promising nano-DDS for cancer photodynamic combined with chemotherapy.

Optimization of Mesoporous Silica Nanoparticles through Statistical Design of Experiment and the Application for the Anticancer Drug

The synthesis process or composition of mesoporous silica nanoparticles (MSNs) affects the physicochemical properties. Using these properties, MSNs were synthesized through the Box–Behnken design (BBD) among statistical experimental methods. The effect of the amounts of synthetic reagents, hexadecyl triethyl ammonium bromide (CTAB), tetraethyl orthosilicate (TEOS), and 2 N sodium hydroxide (NaOH), was studied using the reaction surface design. Surface area, particle size, and zeta potential were set as response values. The physicochemical properties of the optimized MSNs were evaluated, and the effect as a drug delivery system was evaluated by loading doxorubicin hydrochloride (DOX). Nano-sized MSNs were successfully prepared with 0.617 g of CTAB, 8.417 mL of TEOS, and 2.726 mL of 2 N NaOH and showed excellent physicochemical properties. The optimized MSNs showed negligible toxicity in MCF-7 cells. The drug release profile from DOX-loaded MSNs (MSN@DOX) showed an increased rate of release with decreasing pH of the medium, with the release profile sustained for 48 h. In the cytotoxicity test, the sustained drug release mechanism of MSN@DOX was confirmed. This study proposed a new statistical approach to the synthesis of MSNs.

Nanocomposite adhesive hydrogels: from design to application

Hydrogels may exhibit strong adhesion upon embedding nanoparticles into them forming strong/weak bonds (via the multiple physical or chemical interactions).

A robust hybrid nanozyme@hydrogel platform as a biomimetic cascade bioreactor for combination antitumor therapy

The development of highly effective and minimally invasive approaches for cancer treatment is the ultimate goal. Herein, an injectable hybrid hydrogel as a biomimetic cascade bioreactor is designed for combination antitumor therapy by providing spatiotemporally-controlled and long-term delivery of therapeutic agents. This hybrid nanozyme@hydrogel (hPB@gellan) is doped with Prussian blue (PB) nanoparticles via the in situ nanoprecipitation method in the polysaccharide gellan matrix. The obtained PB nanoparticles have a small size of 10 nm and play dual roles as a photothermal agent with a photothermal conversion efficiency of 59.6% and as a nanozyme to decompose hydrogen peroxide into oxygen. By incorporating glucose oxidase (GOD) into the hybrid hydrogel, a cascade bioreactor is formed for PB-promoted glucose consumption. Owing to its shear-thinning and self-recovery properties, the hybrid hydrogel is locally administered into tumors, and shows long-term resistance against body clearance and metabolism. The in vivo antitumor results demonstrate that the tumors in the group of combined photothermal and starvation therapy (GOD/hPB@gellan + NIR) are greatly eliminated with a tumor suppression rate of 99.7% 22 days after the treatment. The outstanding antitumor performance is attributed to the main attack by NIR-triggered hyperthermia and the holding attack by GOD-mediated starvation from the catalytic bioreactor of the hybrid hydrogel. Taking into consideration the advantages of biosafety, simple synthetic approaches and facile manipulation in treatment, the hybrid hydrogel has great potential for clinical translation.

Multi-transformable nanocarrier with tumor extracellular acidity-activated charge reversal, size reduction and ligand reemergence for in vitro efficient doxorubicin loading and delivery

Various nanoparticles as drug delivery system provide significant improvements in the cancer treatment. However, their clinical success remains elusive in large part due to their inability to overcome both systemic and tumor tissue barriers. The nanosystems with nanoproperty-transformability (surface, size, stability and target) hold great promise for achieving enhanced delivery efficacy. However, currently available systems that are mainly polymer-based assemblies usually suffer from the intrinsic drawbacks of poor stability, premature leakage and low drug loading as well as limited transformability. In this study, we designed a facile strategy to build a novel multi-transformable MSNs@GO nanosystem for efficient doxorubicin (DOX) loading and delivery. This novel nanosystem was well characterized and investigated in vitro. The results indicated that the MSNs@GO can realize a very high drug loading ability due to the large pore surface area of MSNs and the demonstrated donor-acceptor (boron‑nitrogen) coordination interactions between phenylboronic acid-containing nanocarriers and electron donor-containing DOX. More importantly, the novel nanocarriers can simultaneously achieve charge reversal, size reduction and ligand reemergence by shielding/deshielding transition via acid-cleavable dynamic boronate bonds under in vitro simulated acidic microenvironment of tumor tissues, opening a new avenue for improving delivery efficiency of chemotherapeutics.

Stimuli-Responsive Hydrogels for Local Post-Surgical Drug Delivery

Currently, surgical operations, followed by systemic drug delivery, are the prevailing treatment modality for most diseases, including cancers and trauma-based injuries. Although effective to some extent, the side effects of surgery include inflammation, pain, a lower rate of tissue regeneration, disease recurrence, and the non-specific toxicity of chemotherapies, which remain significant clinical challenges. The localized delivery of therapeutics has recently emerged as an alternative to systemic therapy, which not only allows the delivery of higher doses of therapeutic agents to the surgical site, but also enables overcoming post-surgical complications, such as infections, inflammations, and pain. Due to the limitations of the current drug delivery systems, and an increasing clinical need for disease-specific drug release systems, hydrogels have attracted considerable interest, due to their unique properties, including a high capacity for drug loading, as well as a sustained release profile. Hydrogels can be used as local drug performance carriers as a means for diminishing the side effects of current systemic drug delivery methods and are suitable for the majority of surgery-based injuries. This work summarizes recent advances in hydrogel-based drug delivery systems (DDSs), including formulations such as implantable, injectable, and sprayable hydrogels, with a particular emphasis on stimuli-responsive materials. Moreover, clinical applications and future opportunities for this type of post-surgery treatment are also highlighted.

Stimuli-responsive release and efficient siRNA delivery in non-small cell lung cancer by a poly(l-histidine)-based multifunctional nanoplatform

Small interfering RNA (siRNA) has extensive potential for the treatment of non-small cell lung cancer (NSCLC). While both cationic lipids and polymers have demonstrated promise to facilitate siRNA encapsulation, they can also hamper cytosolic siRNA release and induce severe cytotoxicity. To address these issues, a unique polymer hybrid nanoparticle (NP) nanoplatform was developed for multistage siRNA delivery based on both pH-responsive and endo/lysosomal escape characteristics, which was formed via a combination of an electrostatic interactions between the copolymer methoxy poly(ethylene glycol)-poly(l-histidine)-poly(sulfadimethoxine) (mPEG-PHis-PSD, shortened to PHD), dendritic poly-l-lysine (PLL) and PLK1 siRNA (shortened to siPLK1). The biological composition of the proton sponge effect polymer of the PHis chain, which was in position to make efficient endo/lysosomal escape, and the pH-responsive polymer of the PSD fragment, which could accelerate the release of siPLK1. In the present study, the NP illustrated excellent physiochemical properties and rapid endo/lysosomal escape in vitro. Besides this, compared with the PD/PLL/siRNA formulation, the PHD/PLL/siRNA NP indicated higher cellular uptake, and higher cell cytotoxicity in vitro. The in vivo results demonstrated that the PHD/PLL/siRNA NP exhibited the strongest tumor growth inhibition rate and ideal safety compared with the control and other siPLK1-treated formulations, which can be mainly attributed to pH-induced instantaneous dissociation and efficient endo/lysosomal escape arising from the PHD copolymer. Consequently, the above evidence indicates that the PHD/PLL/siRNA NP is a favorable gene delivery system and provides a potential strategy for siRNA delivery.