Mixing a sol and a precipitate of block copolymers with different block ratios leads to an injectable hydrogel

Thermosensitive Hydrogels for Periodontal Regeneration: A Systematic Review of the Evidence

OBJECTIVES

Thermosensitive hydrogels are now among the most commonly used biomaterials in tissue engineering. Due to their unique characteristics, this review aimed to evaluate the suitability of thermosensitive hydrogels in periodontal regeneration.

MATERIAL AND METHODS

PubMed, Scopus, and Web of Science databases were searched until March 25, 2024, to retrieve relevant articles. The eligibility criteria for the included studies were determined by the designed PICO elements. Results from each included study were extracted, focusing on the three main areas: thermosensitivity, cellular characteristics, and in vivo characteristics.

RESULTS

Nineteen studies were included in our study. The thermosensitivity assessment of the hydrogels indicated a range of sol-gel transition times from 40 s to 20 min based on the type of polymers and the fabrication process. The cellular characterization was assessed based on three main cellular behaviors: cellular viability/proliferation, differentiation, and migration. The in vivo characterization was performed based on two main approaches: radiographic and histologic evaluation.

CONCLUSIONS

The results indicated that the addition of bioactive agents could enhance the in vivo efficacy of thermosensitive hydrogels in periodontal regeneration through three main areas: antimicrobial, anti-inflammatory, and regenerative effects.

Application of Injectable Hydrogels as Delivery Systems in Osteoarthritis and Rheumatoid Arthritis

Osteoarthritis and rheumatoid arthritis, though etiologically distinct, are both inflammatory joint diseases that cause progressive joint injury, chronic pain, and loss of function. Therefore, long-term treatment with a focus on relieving symptoms is needed. At present, the primary treatment for arthritis is drug therapy, both oral and intravenous. Although significant progress has been achieved for these treatment methods in alleviating symptoms, certain prominent drawbacks such as the substantial side effects and limited absorption of medications call for an urgent need for improved drug delivery methods. Injected hydrogels can be used as a delivery system to deliver drugs to the joint cavity in a controlled manner and continuously release them, thereby enhancing drug retention in the joint cavity to improve therapeutic effectiveness, which is attributed to the desirable attributes of the delivery system such as low immunogenicity, good biodegradability and biocompatibility. This review summarizes the types of injectable hydrogels and analyzes their applications as delivery systems in arthritis treatment. We also explored how hydrogels counteract inflammation, bone and cartilage degradation, and oxidative stress, while promoting joint cartilage regeneration in the treatment of osteoarthritis (OA) and rheumatoid arthritis (RA). This review also highlights new approaches to developing injectable hydrogels as delivery systems for OA and RA.

Recent advances in regenerative biomaterials

Nowadays, biomaterials have evolved from the inert supports or functional substitutes to the bioactive materials able to trigger or promote the regenerative potential of tissues. The interdisciplinary progress has broadened the definition of 'biomaterials', and a typical new insight is the concept of tissue induction biomaterials. The term 'regenerative biomaterials' and thus the contents of this article are relevant to yet beyond tissue induction biomaterials. This review summarizes the recent progress of medical materials including metals, ceramics, hydrogels, other polymers and bio-derived materials. As the application aspects are concerned, this article introduces regenerative biomaterials for bone and cartilage regeneration, cardiovascular repair, 3D bioprinting, wound healing and medical cosmetology. Cell-biomaterial interactions are highlighted. Since the global pandemic of coronavirus disease 2019, the review particularly mentions biomaterials for public health emergency. In the last section, perspectives are suggested: (i) creation of new materials is the source of innovation; (ii) modification of existing materials is an effective strategy for performance improvement; (iii) biomaterial degradation and tissue regeneration are required to be harmonious with each other; (iv) host responses can significantly influence the clinical outcomes; (v) the long-term outcomes should be paid more attention to; (vi) the noninvasive approaches for monitoring in vivo dynamic evolution are required to be developed; (vii) public health emergencies call for more research and development of biomaterials; and (viii) clinical translation needs to be pushed forward in a full-chain way. In the future, more new insights are expected to be shed into the brilliant field-regenerative biomaterials.

Thermosensitive vancomycin@PLGA-PEG-PLGA/HA hydrogel as an all-in-one treatment for osteomyelitis

Osteomyelitis is a difficult-to-treat infectious disease. Treatment, which includes controlling the infection and removing necrotic tissues, is challenging. Considering the side effects and drug resistance of systemic antibiotics, local drug delivery systems are being explored. Antibiotic-loaded bone cement is the main treatment strategy; however, it has several disadvantages. Thus, based on its thermosensitive gelation properties, poly(D, L-lactide-co-glycolide)-poly(ethylene glycol)-poly(D, L-lactide-co-glycolide) (PLGA-PEG-PLGA) copolymer was used as a sustained-release drug carrier by calibrating its synthesis parameters. We prepared and characterized vancomycin@PLGA-PEG-PLGA/hydroxyapatite (HA) thermosensitive hydrogel with an LA/GA ratio of 15:1. The rheological characteristics, sol-gel phase-transition properties, and critical micelle concentration value of the PLGA-PEG-PLGA/HA complex confirmed that it undergoes a temperature-sensitive sol-gel phase transition. Furthermore, the HA in the composite increased the storage modulus of the system. FT-IR, XRD, and TEM findings showed that HA could be dispersed uniformly in the PLGA-PEG-PLGA polymer. Moreover, HA neutralized acidity during polymer degradation, improving in vitro cytocompatibility. In vitro and in vivo antibacterial experiments showed that the composite sustained-release system exhibited good bone repair characteristics owing to its efficacy in infection treatment. Therefore, vancomycin@PLGA-PEG-PLGA/HA allows sustained release of antibiotics and promotes bone tissue repair, showing potential for wide clinical applicability.

Intracranial In Situ Thermosensitive Hydrogel Delivery of Temozolomide Accomplished by PLGA–PEG–PLGA Triblock Copolymer Blending for GBM Treatment

Glioblastoma (GBM) recurrence after surgical excision has grown to be a formidable obstacle to conquer. In this research, biodegradable thermosensitive triblock copolymer, poly(D, L–lactic acid–co–glycolic acid)–b–poly(ethylene glycol)–b–poly(D, L–lactic acid–co–glycolic acid (PLGA–PEG–PLGA) was utilized as the drug delivery system, loading with micronized temozolomide(micro-TMZ) to form an in situ drug–gel depot inside the resection cavity. The rheology studies revealed the viscoelastic profile of hydrogel under various conditions. To examine the molecular characteristics that affect gelation temperature, ¹H–NMR, inverse gated decoupling ¹³C–NMR, and GPC were utilized. Cryo-SEM and XRD were intended to disclose the appearance of the hydrogel and the micro-TMZ existence state. We worked out how to blend polymers to modify the gelation point (T_gel) and fit the correlation between T_gel and other dependent variables using linear regression. To simulate hydrogel dissolution in cerebrospinal fluid, a membraneless dissolution approach was used. In vitro, micro-TMZ@PLGA–PEG–PLGA hydrogel exhibited Korsmeyer–Peppas and zero–order release kinetics in response to varying drug loading, and in vivo, it suppressed GBM recurrence at an astoundingly high rate. Micro-TMZ@PLGA–PEG–PLGA demonstrates a safer and more effective form of chemotherapy than intraperitoneal TMZ injection, resulting in a spectacular survival rate (40%, n = 10) that is much more than intraperitoneal TMZ injection (22%, n = 9). By proving the viability and efficacy of micro-TMZ@PLGA–PEG–PLGA hydrogel, our research established a novel chemotherapeutic strategy for treating GBM recurrence.

Thermosensitive Hydrogels and Advances in Their Application in Disease Therapy

Thermosensitive hydrogels, having unique sol–gel transition properties, have recently received special research attention. These hydrogels exhibit a phase transition near body temperature. This feature is the key to their applications in human medicine. In addition, hydrogels can quickly gel at the application site with simple temperature stimulation and without additional organic solvents, cross-linking agents, or external equipment, and the loaded drugs can be retained locally to improve the local drug concentration and avoid unexpected toxicity or side effects caused by systemic administration. All of these features have led to thermosensitive hydrogels being some of the most promising and practical drug delivery systems. In this paper, we review thermosensitive hydrogel materials with biomedical application potential, including natural and synthetic materials. We describe their structural characteristics and gelation mechanism and briefly summarize the mechanism of drug release from thermosensitive hydrogels. Our focus in this review was to summarize the application of thermosensitive hydrogels in disease treatment, including the postoperative recurrence of tumors, the delivery of vaccines, the prevention of postoperative adhesions, the treatment of nervous system diseases via nasal brain targeting, wound healing, and osteoarthritis treatment.

Nano-hydroxyapatite-evoked immune response synchronized with controllable immune adjuvant release for strengthening melanoma-specific growth inhibition

Concerns about the potential systematic toxicity limit the extensive application of traditional therapeutic drugs for melanoma therapy, nano-hydroxyapatite (nHA) with good biocompatibility and anti-tumor ability could be an alternative choice. In this study, nHA was employed as an anti-tumor biomaterial due to its tumor-specific toxicity. Meanwhile, granulocyte-macrophage colony-stimulating factor (GM-CSF) served as the immune adjuvant to activate the immune response. The delivery platform was fabricated by co-encapsulation of both nHA and GM-CSF into a biocompatible thermosensitive PLGA-PEG-PLGA hydrogel. The results showed that the bio-activities of nHA and GM-CSF could be well-maintained within the hydrogel. Interestingly, the addition of nHA could attenuate the burst release of GM-CSF due to possible protein absorption capacity of nHA, which is beneficial for GM-CSF sustainable release at the tumor site, achieving boosted and prolonged anti-tumor immunity. The in vitro and in vivo data demonstrated that nHA/GM-CSF hydrogel exhibited greater potency to inhibit tumor growth via enhanced CD8⁺ T-cell response compared with hydrogel and nHA hydrogel groups, contributed by the synergistic effects of nHA and GM-CSF. Overall, the strategy combining nHA and immune adjuvant shows great promise, which largely broadens the choice of combinational therapies for melanoma. STATEMENT OF SIGNIFICANCE: Nano-hydroxyapatite (nHA) has been confirmed to specifically inhibit melanoma tumor growth and induce immune response. However, its antitumor efficiency and immunity-evoking capacity are limited. In this study, granulocyte-macrophage colony-stimulating factor (GM-CSF) was introduced to serve as the immune adjuvant. Both of them were encapsulated into a biocompatible thermosensitive PLGA-PEG-PLGA hydrogel. The addition of nHA could attenuate the burst release of GM-CSF due to the interaction with nHA, which is beneficial for GM-CSF sustainable release at tumor site, achieving boosted and prolonged anti-tumor immunity. Anti-tumor immune response could be activated due to the release of tumor-associated antigen and tumor debris induced by the specifically tumor inhibition effect of nHA and GM-CSF. The combination of nHA and GM-CSF could play synergistic inhibiting effect on tumor growth via boosting and prolonging anti-tumor immunity.

DPD simulations on morphologies and structures of blank PLGA-b-PEG-b-PLGA polymeric micelles and docetaxel-loaded PLGA-b-PEG-b-PLGA polymeric micelles

Dissipative particle dynamics (DPD) simulation was used to study the morphologies and structures of blank (no drug) poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) (PLGA-b-PEG-b-PLGA) polymeric micelles and the docetaxel (Dtx)-loaded PLGA-b-PEG-b-PLGA polymeric micelles. We focused on the influences of PLGA-b-PEG-b-PLGA copolymer concentration, composition, Dtx drug content and the shear rate on morphologies and structures of the micelles. Our simulations show that the PLGA-b-PEG-b-PLGA copolymers in the aqueous solutions could aggregate and form blank micelles while Dtx drug and PLGA-b-PEG-b-PLGA could aggregate and form drug-loaded micelles. Under different PLGA-b-PEG-b-PLGA concentrations and drug content, the blank and drug-loaded micelles are observed as spherical, onionlike, columnar, and lamellar structures. The onionlike structures are comprised of the PEG hydrophilic core, the PLGA hydrophobic middle layer, and the PEG hydrophilic shell. As the structure of micelles varies from a spherical core-shell structure to a core-middle layer-shell onionlike structure, the distribution of the Dtx drugs diffuses from the core to the PLGA middle layer of the aggregate. In addition, the drug release process of the Dtx-loaded micelles under shear flow is also simulated. And the results show that the spherical micelles turn into a columnar structure under a shear rate from 0.2 to 3.4. When the shear rate increases to 3.5, the Dtx drugs released gradually increase until all are released with time evolution. These findings illustrate the dependence of the structural morphologies on the detailed molecular parameters of PLGA-b-PEG-b-PLGA and Dtx.

A Micro-Environment Regulator for Filling the Clinical Treatment Gap after a Glioblastoma Operation

The rapid postoperative recurrence and short survival time of glioblastoma (GBM) patients necessitate immediate and effective postoperative treatment. Herein, an immediate and mild postoperative local treatment strategy is developed that regulates the postoperative microenvironment and delays GBM recurrence. Briefly, an injectable hydrogel system (imGEL) loaded with Zn(II)₂ -AMD3100 (AMD-Zn) and CpG oligonucleotide nanoparticles (CpG NPs) is injected into the operation cavity, with long-term function to block the recruitment of microglia/ macrophages and activate cytotoxic T cells. The finding indicated that the imGEL can regulate the immune microenvironment, inhibit GBM recurrence, and gain valuable time for subsequent adjuvant clinical chemotherapy.

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.

Recent advances in PLGA-based biomaterials for bone tissue regeneration

Bone regeneration is an interdisciplinary complex lesson, including but not limited to materials science, biomechanics, immunology, and biology. Having witnessed impressive progress in the past decades in the development of bone substitutes; however, it must be said that the most suitable biomaterial for bone regeneration remains an area of intense debate. Since its discovery, poly (lactic-co-glycolic acid) (PLGA) has been widely used in bone tissue engineering due to its good biocompatibility and adjustable biodegradability. This review systematically covers the past and the most recent advances in developing PLGA-based bone regeneration materials. Taking the different application forms of PLGA-based materials as the starting point, we describe each form's specific application and its corresponding advantages and disadvantages with many examples. We focus on the progress of electrospun nanofibrous scaffolds, three-dimensional (3D) printed scaffolds, microspheres/nanoparticles, hydrogels, multiphasic scaffolds, and stents prepared by other traditional and emerging methods. Finally, we briefly discuss the current limitations and future directions of PLGA-based bone repair materials. STATEMENT OF SIGNIFICANCE: As a key synthetic biopolymer in bone tissue engineering application, the progress of PLGA-based bone substitute is impressive. In this review, we summarized the past and the most recent advances in the development of PLGA-based bone regeneration materials. According to the typical application forms and corresponding crafts of PLGA-based substitutes, we described the development of electrospinning nanofibrous scaffolds, 3D printed scaffolds, microspheres/nanoparticles, hydrogels, multiphasic scaffolds and scaffolds fabricated by other manufacturing process. Finally, we briefly discussed the current limitations and proposed the newly strategy for the design and fabrication of PLGA-based bone materials or devices.

Exploration of possible cell chirality using material techniques of surface patterning

Consistent left-right (LR) asymmetry or chirality is critical for embryonic development and function maintenance. While chirality on either molecular or organism level has been well established, that on the cellular level has remained an open question for a long time. Although it remains unclear whether chirality exists universally on the cellular level, valuable efforts have recently been made to explore this fundamental topic pertinent to both cell biology and biomaterial science. The development of material fabrication techniques, surface patterning, in particular, has afforded a unique platform to study cell-material interactions. By using patterning techniques, chirality on the cellular level has been examined for cell clusters and single cells in vitro in well-designed experiments. In this review, we first introduce typical fabrication techniques of surface patterning suitable for cell studies and then summarize the main aspects of preliminary evidence of cell chirality on patterned surfaces to date. We finally indicate the limitations of the studies conducted thus far and describe the perspectives of future research in this challenging field. STATEMENT OF SIGNIFICANCE: While both biomacromolecules and organisms can exhibit chirality, it is not yet conclusive whether a cell has left-right (LR) asymmetry. It is important yet challenging to study and reveal the possible existence of cell chirality. By using the technique of surface patterning, the recent decade has witnessed progress in the exploration of possible cell chirality within cell clusters and single cells. Herein, some important preliminary evidence of cell chirality is collected and analyzed. The open questions and perspectives are also described to promote further investigations of cell chirality in biomaterials.

(Macro)molecular self-assembly for hydrogel drug delivery

Hydrogels prepared via self-assembly offer scalable and tunable platforms for drug delivery applications. Molecular-scale self-assembly leverages an interplay of attractive and repulsive forces; drugs and other active molecules can be incorporated into such materials by partitioning in hydrophobic domains, affinity-mediated binding, or covalent integration. Peptides have been widely used as building blocks for self-assembly due to facile synthesis, ease of modification with bioactive molecules, and precise molecular-scale control over material properties through tunable interactions. Additional opportunities are manifest in stimuli-responsive self-assembly for more precise drug action. Hydrogels can likewise be fabricated from macromolecular self-assembly, with both synthetic polymers and biopolymers used to prepare materials with controlled mechanical properties and tunable drug release. These include clinical approaches for solubilization and delivery of hydrophobic drugs. To further enhance mechanical properties of hydrogels prepared through self-assembly, recent work has integrated self-assembly motifs with polymeric networks. For example, double-network hydrogels capture the beneficial properties of both self-assembled and covalent networks. The expanding ability to fabricate complex and precise materials, coupled with an improved understanding of biology, will lead to new classes of hydrogels specifically tailored for drug delivery applications.

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.

In vivo biocompatibility and efficacy of dexamethasone-loaded PLGA-PEG-PLGA thermogel in an alkali-burn induced corneal neovascularization disease model

Challenges of ophthalmic drug delivery arise not only from the limited solubility of hydrophobic therapeutics, but also the restricted permeability and fast clearance of drugs due to the complex anatomy and physiology of eyes. Excellent biocompatibility of a thermosensitive polymer, PLGA-PEG-PLGA (1800-1500-1800, LA:GA ratio = 3:1), as an ophthalmic delivery system was demonstrated in our previous work. In this study, delivery of dexamethasone using this thermogel via a single subconjunctival injection for prolonged treatment was evaluated with corneal neovascularization using an alkali-burn diseased model in rat. Solubility of dexamethasone in the polymeric solution was increased by 5.2-fold and the resulting drug-loaded solution formed in situ rigid gel at body temperature. Prolonged in vitro release of dexamethasone from the gel structure was noted. Dexamethasone gel formulation was demonstrated to be more effective in reducing the burn stimulus and neovascularization in the rat diseased model. The findings suggest the PLGA-PEG-PLGA in situ gelling system can be applied for ophthalmic drug delivery to achieve sustained drug release and improved efficacy.

Structures and Applications of Thermoresponsive Hydrogels and Nanocomposite-Hydrogels Based on Copolymers with Poly (Ethylene Glycol) and Poly (Lactide-Co-Glycolide) Blocks

Thermoresponsive hydrogels showing biocompatibility and degradability have been under intense investigation for biomedical applications, especially hydrogels composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(lactic acid-co-glycolic acid) (PLGA) as first-line materials. Even though various aspects such as gelation behavior, degradation behavior, drug-release behavior, and composition effect have been studied for 20 years since the first report of these hydrogels, there are still many outputs on parameters affecting their gelation, structure, and application. In this review, the current trends of research on linear block copolymers composed of PEG and PLGA during the last 5 years (2014-2019) are summarized. In detail, this review stresses newly found parameters affecting thermoresponsive gelation, findings from structural analysis by simulation, small-angle neutron scattering (SANS), etc., progress in biomedical applications including drug delivery systems and regeneration medicine, and nanocomposites composed of block copolymers with PEG and PLGA and nanomaterials (laponite).

Self-Healable, Fast Responsive Poly(ω-Pentadecalactone) Thermogelling System for Effective Liver Cancer Therapy

A polyurethane based thermogelling system comprising poly(ω-pentadecalactone) (PPDL), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG), termed as PDEP, was synthesized. The incorporation of PPDL lowers critical micelle concentration (CMC) as well as critical gelation concentration (CGC) of the novel copolymers compared to commercial Pluronic® F127. The thermogels showed excellent thermal stability at high temperature up to 80°C, fast response to temperature change in a time frame of less than second, as well as remarkable self-healing properties after being broken at high strain. In vitro drug release studies using docetaxel (DTX) and cell uptake studies using doxorubicin (DOX) show high potential of the hydrogel as drug reservoir for sustainable release profile of payloads, while the in vivo anti-tumor evaluation using mice model of hepatocellular carcinoma further demonstrated the significant inhibition on the growth of tumor. Together with its excellent biocompatibility in different organs, the novel PDPE thermogelling copolymers reported in this work could potentially be utilized as in situ-forming hydrogels for liver cancer therapy.

Smart injectable biogels based on hyaluronic acid bioconjugates finely substituted with poly(β-amino ester urethane) for cancer therapy

In situ-forming injectable biogels (IBGs) have been developed for the programmed delivery of potent chemotherapeutic drugs.

Tumor microenvironment-labile polymer-doxorubicin conjugate thermogel combined with docetaxel for in situ synergistic chemotherapy of hepatoma

Topical chemotherapy with complementary drugs is one of the most promising strategies to achieve an effective antitumor activity. Herein, a synergistic strategy for hepatoma therapy by the combination of tumor microenvironment-sensitive polymer-doxorubicin (DOX) conjugate thermogel, containing a DNA intercalator DOX, and docetaxel (DTX), a microtubule-interfering agent, was proposed. First, cis-aconitic anhydride-functionalized DOX (CAD) and succinic anhydride-modified DOX (SAD) were conjugated onto the terminal hydroxyl groups of poly(lactide-co-glycolide)-block-poly(ethylene glycol)-block-poly(lactide-co-glycolide) (PLGA-PEG-PLGA), yielding the acid-sensitive CAD-PLGA-PEG-PLGA-CAD and the insensitive SAD-PLGA-PEG-PLGA-SAD conjugates, respectively. The prodrug aqueous solution exhibited a thermoreversible sol-gel transition between room and physiological temperature. Meantime, appropriate mechanical property, biodegradability, as well as a sustained release profile were revealed in such prodrug thermogels. More importantly, the addition of DTX to the DOX-conjugated thermogels (i.e., Gel-CAD and Gel-SAD) was verified with enhanced curative effect against tumor, where the antitumor efficacy of Gel-CAD+DTX was obviously higher than the other groups. A reliable security in vivo was also showed in the Gel-CAD+DTX group. Taken together, such combination of tumor microenvironment-labile prodrug thermogel and a complementary drug exhibited fascinating prospect for local synergistic antineoplastic therapy.

STATEMENT OF SIGNIFICANCE

Multidrug chemotherapy with synergistic effect has been proposed recently for hepatoma treatment in the clinic. However, the quick release, fast elimination, and unselectivity of multidrugs in vivo always limit their further application. To solve this problem, a synergistic combination of tumor microenvironment-sensitive polymeric doxorubicin (DOX) prodrug thermogel for DNA intercalation and a microtubule-interfering agent docetaxel (DTX) is developed in the present study for the local chemotherapy of hepatoma. Interestingly, a pH-triggered sustained release behavior, an enhanced antitumor efficacy, and a favorable security in vivo are observed in the combined dual-drug delivery platform. Therefore, effectively combining tumor microenvironment-labile polymeric prodrug thermogel with a complementary drug provides an advanced system and a promising prospect for local synergistic hepatoma chemotherapy.

Injectable Gel Constructs with Regenerative and Anti-Infective Dual Effects Based on Assembled Chitosan Microspheres

There is increasing demand for biomaterials that both assist with bone regeneration and have anti-infection qualities in clinical applications. To achieve this goal, chitosan microspheres with either positive or negative charges were fabricated and then assembled as a gel for bone healing. The positively charged chitosan microspheres (CSM; ∼35.5 μm) and negatively charged O-carboxymethyl chitosan microspheres (CMCSM; ∼13.5 μm) were loaded, respectively, with bone morphogenetic protein (BMP-2) and berberine (Bbr) via swollen encapsulation and physical adsorption without a significant change in the electric charges. The release kinetics of BMP-2 and Bbr from the microspheres were also studied in vitro. The results showed that the Bbr/CMCSM microsphere group possessed high antibacterial activity against Staphylococcus aureus; the BMP-2/CSM microsphere group also had excellent cytocompatibility and improved osteoinductivity with the assistance of BMP-2. The assembled gel group consisting of Bbr/CMCSM and BMP-2/CSM had a porous structure that allowed biological signal transfer and tissue infiltration and exhibited significantly enhanced bone reconstruction compared with that of the respective microsphere groups, which should result from the osteoconductivity of the porous structure and the osteoinduction of the BMP-2 growth factor. The oppositely charged microspheres and their assembled gel provide a promising prospect for making injectable tissue-engineered constructs with regenerative and anti-infective dual effects for biomedical applications.

Investigations of Peptide-Based Biocompatible Injectable Shape-Memory Hydrogels: Differential Biological Effects on Bacterial and Human Blood Cells

Here, we report the self-assembly of Amoc (9-anthracenemethoxycarbonyl)-capped dipeptides, which self-assemble to form injectable, self-healable, and shape-memory hydrogels with inherent antibacterial properties. Amoc-capped dipeptides self-assemble to form nanofibrillar networks, which are established by several spectroscopic and microscopic techniques. The inherent antibacterial properties of hydrogels are evaluated using two Gram-positive Staphylococcus aureus, Bacillus subtilis and three Gram-negative Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhi bacteria. These hydrogels exhibit potent antibacterial efficacy against Gram-positive and Gram-negative bacteria. The minimum inhibitory concentrations (MIC₅₀) for the hydrogels on Gram-positive bacteria are in the range of 10-200 μM hydrogelator concentrations. The biocompatibility and cytotoxicity of the hydrogels are evaluated using 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), hemolysis, and lipid peroxidation (LPO) assay on human blood cells. The hydrogels are hemocompatible and they decrease LPO values on human red blood cells probably via increased cellular stability against oxidative stress. Furthermore, MTT data show that the hydrogels are biocompatible and promote cell viability and proliferation on cultured human white blood cells. Taken together, these results may suggest that our designed injectable hydrogels could be useful to prevent localized bacterial infections.

3D printing for drug manufacturing: A perspective on the future of pharmaceuticals

Since a three-dimensional (3D) printed drug was first approved by the Food and Drug Administration in 2015, there has been a growing interest in 3D printing for drug manufacturing. There are multiple 3D printing methods - including selective laser sintering, binder deposition, stereolithography, inkjet printing, extrusion-based printing, and fused deposition modeling - which are compatible with printing drug products, in addition to both polymer filaments and hydrogels as materials for drug carriers. We see the adaptability of 3D printing as a revolutionary force in the pharmaceutical industry. Release characteristics of drugs may be controlled by complex 3D printed geometries and architectures. Precise and unique doses can be engineered and fabricated via 3D printing according to individual prescriptions. On-demand printing of drug products can be implemented for drugs with limited shelf life or for patient-specific medications, offering an alternative to traditional compounding pharmacies. For these reasons, 3D printing for drug manufacturing is the future of pharmaceuticals, making personalized medicine possible while also transforming pharmacies.

α,ω-Diphenylalanine-End-Capping of PEG-PPG-PEG Polymers Changes the Micelle Morphology and Enhances Stability of the Thermogel

Pluronics F127 (P, PEG-PPG-PEG triblock copolymer) was coupled with diphenylalanine (FF) to prepare FF-end-capped Pluronics (FFPFF). With increasing temperature from 10 to 60 °C, the FFPFF self-assembled to vesicles in water. The unimer-to-vesicle transition accompanies endothermic enthalpy of 53.9 kcal/mol. Aqueous P and FFPFF solutions exhibited thermogelation in 15.0-24.0 wt %. The gel phase of FFPFF was stable up to 90 °C, whereas that of P turned into a sol again at 55-86 °C, indicating that end-capping with FF improved the gel stability against heat. In addition, the carboxylic acids of the FF end-groups can form coordination bonds with metal ions, and the gel modulus at 37 °C increased from 15-21 KPa (P) to 20-25 KPa (FFPFF) to 24-28 KPa (FFPFF-Zn), and the duration of gel against water-erosion increased from 24 h (P) to 60 h (FFPFF-Zn), leading to a useful biomaterial for sustained drug delivery. The FFPFF-Zn gels implanted in the rats' subcutaneous layer induced a mild inflammatory responses. Contrary to the previous end-capping of Pluronics by poly(lactic acid), polycarprolactone, carboxylic acid, and so on that weakened the gel stability, the diphenylalanine end-capping strengthened the stability of Pluronics gel against heat and water-erosion. This paper suggests that the control of polymer nanoassemblies directed by FF end-groups improves the mechanical properties and stability of the resulting thermogel and, thus, provides a useful drug delivery carrier with prolonged durability.

Non-invasive monitoring of in vivo degradation of a radiopaque thermoreversible hydrogel and its efficacy in preventing post-operative adhesions

In vivo behavior of hydrogel-based biomaterials is very important for rational design of hydrogels for various biomedical applications. Herein, we developed a facile method for in situ fabrication of radiopaque hydrogel. An iodinated functional diblock copolymer of poly(ethylene glycol) and aliphatic polyester was first synthesized by coupling the hydroxyl end of the diblock copolymer with 2,3,5-triiodobenzoic acid (TIB) and then a radiopaque thermoreversible hydrogel was obtained by mixing it with the virgin diblock copolymer. A concentrated aqueous solution of the copolymer blend was injectable at room temperature and spontaneously turned into an in situ hydrogel at body temperature after injection. The introduction of TIB moieties affords the capacity of X-ray opacity, enabling in vivo visualization of the hydrogel using Micro-CT. A rat model with cecum and abdominal defects was utilized to evaluate the efficacy of the radiopaque hydrogel in the prevention of post-operative adhesions, and a significant reduction of the post-operative adhesion formation was confirmed. Meanwhile, the maintenance of the radiopaque hydrogel in the abdomen after administration was non-destructively detected via Micro-CT scanning. The reconstructed three-dimensional images showed that the radiopaque hydrogel with an irregular morphology was located on the injured abdominal wall. The time-dependent profile of the volume of the radiopaque hydrogel determined by Micro-CT imaging was well consistent with the trend obtained from the dissection observation. Therefore, the radiopaque thermoreversible hydrogel can serve as a potential visualized biomedical implant and this practical mixing approach is also useful for further extension into the in vivo monitoring of other biomaterials.

STATEMENT OF SIGNIFICANCE

While a variety of biomaterials have been extensively studied, it is rare to monitor in vivo degradation and medical efficacy of a material after being implanted deeply into the body. Herein, the radiopaque thermoreversible hydrogel developed by us not only holds desirable performance on the prevention of post-operative abdominal adhesions, but also allows non-invasive monitoring of its in vivo degradation with CT imaging in a real-time, quantitative and three-dimensional manner. The methodology based on CT imaging provides important insights into the in vivo fate of the hydrogel after being deeply implanted into mammals for different biomedical applications and significantly reduces the amount of animals sacrificed.

Designing Hydrogels for On-Demand Therapy

Systemic administration of therapeutic agents has been the preferred approach to treat most pathological conditions, in particular for cancer therapy. This treatment modality is associated with side effects, off-target accumulation, toxicity, and rapid renal and hepatic clearance. Multiple efforts have focused on incorporating targeting moieties into systemic therapeutic vehicles to enhance retention and minimize clearance and side effects. However, only a small percentage of the nanoparticles administered systemically accumulate at the tumor site, leading to poor therapeutic efficacy. This has prompted researchers to call the status quo treatment regimen into question and to leverage new delivery materials and alternative administration routes to improve therapeutic outcomes. Recent approaches rely on the use of local delivery platforms that circumvent the hurdles of systemic delivery. Local administration allows delivery of higher "effective" doses while enhancing therapeutic molecules' stability, minimizing side effects, clearance, and accumulation in the liver and kidneys following systemic administration. Hydrogels have proven to be highly biocompatible materials that allow for versatile design to afford sensing and therapy at the same time. Hydrogels' chemical and physical versatility can be exploited to attain disease-triggered in situ assembly and hydrogel programmed degradation and consequent drug release, and hydrogels can also serve as a biocompatible depot for local delivery of stimuli-responsive therapeutic cargo. We will focus this Account on the hydrogel platform that we have developed in our lab, based on dendrimer amine and dextran aldehyde. This hydrogel is disease-responsive and capable of sensing the microenvironment and reacting in a graded manner to diverse pathologies to render different properties, including tissue adhesion, biocompatibility, hydrogel degradation, and embedded drug release profile. We also studied the degradation kinetics of our stimuli-responsive materials in vivo and analyzed the in vitro conditions under which in vitro-in vivo correlation is attained. Identifying key parameters in the in vivo microenvironment under healthy and disease conditions was key to attaining that correlation. The adhesive capacity of our dendrimer-dextran hydrogel makes it optimal for localized and sustained release of embedded drugs. We demonstrated that it affords the delivery of a range of therapeutics to combat cancer, including nucleic acids, small molecules, and antibody drugs. As a depot for local delivery, it allows a high dose of active biomolecules to be delivered directly at the tumor site. Immunotherapy, a recently blooming area in cancer therapy, may exploit stimuli-responsive hydrogels to impart systemic effects following localized therapy. Local delivery would enable release of the proper drug dose and improve drug bioavailability where needed at the same time creating memory and exerting the therapeutic effect systemically. This Account highlights our perspective on how local and systemic therapies provided by stimuli-responsive hydrogels should be used to impart more precise, long-lasting, and potent therapeutic outcomes.

Efficacy of Poly(D,L-Lactic Acid-co-Glycolic acid)-Poly(Ethylene Glycol)-Poly(D,L-Lactic Acid-co-Glycolic Acid) Thermogel As a Barrier to Prevent Spinal Epidural Fibrosis in a Postlaminectomy Rat Model

STUDY DESIGN

Experimental animal study.

OBJECTIVE

The authors conducted a study to determine the efficacy and safety of the poly(D,L-lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(D,L-lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) thermogel to prevent peridural fibrosis in an adult rat laminectomy model.

SUMMARY OF BACKGROUND DATA

Peridural fibrosis often occurs after spinal laminectomy. It might cause persistent back and/or leg pain postoperatively and make a reoperation more difficult and dangerous. Various materials have been used to prevent epidural fibrosis, but only limited success has been achieved.

MATERIALS AND METHODS

The PLGA-PEG-PLGA thermogel was synthesized by us. Total L3 laminectomies were performed on 24 rats. The PLGA-PEG-PLGA thermogel or chitosan (CHS) gel (a positive control group) was applied to the operative sites in a blinded manner. In the control group, the L3 laminectomy was performed and the defect was irrigated with the NS solution 3 times. All the rats were killed 4 weeks after the surgery.

RESULTS

The cytotoxicity of this thermogel was evaluated in vitro and the result demonstrated that no evidence of cytotoxicity was observed. The extent of epidural fibrosis, the area of epidural fibrosis, and the density of the fibroblasts and blood vessel were evaluated histologically. There were statistical differences among the PLGA-PEG-PLGA thermogel or CHS gel group compared with the control group. Although there was no difference between the PLGA-PEG-PLGA thermogel and CHS gel, the efficiency of the PLGA-PEG-PLGA thermogel was shown to be slightly improved compared with the CHS gel.

CONCLUSIONS

The biocompatibility of the PLGA-PEG-PLGA thermogel was proven well. The application of this thermogel effectively reduced epidural scarring and prevented the subsequent adhesion to the dura mater. No side effects were noted in the rats.

Modified PLGA-PEG-PLGA thermosensitive hydrogels with suitable thermosensitivity and properties for use in a drug delivery system

PLGA-PEG-PLGA (PPP) triblock copolymer is the most widely studied thermosensitive hydrogel owing to its non-toxic, biocompatible, biodegradable, and thermosensitive properties. PPP thermosensitive hydrogels are being investigated as in situ gels because, at a low temperature, PPP solutions with drugs can be injected at the target site, and converted into a gel without surgical procedures. To meet the requirements of different therapeutic applications, PPP hydrogels with different properties need to be synthesized. The adjustable properties include the sol-gel transition temperature, gel window width, retention time and drug release time. Furthermore, thermo- and pH-, thermo- and electro-, and thermo- and photo-dual sensitive hydrogels are needed for some special therapies. Thus, this review examines the methods of modification of PPP thermosensitive hydrogels used to obtain desired drug delivery systems with appropriate physicochemical and pharmaceutical properties.

Temperature-responsive in situ nanoparticle hydrogels based on hydrophilic pendant cyclic ether modified PEG-PCL-PEG

Thermo-sensitive injectable hydrogels based on poly(ε-caprolactone)/poly(ethylene glycol) (PCL/PEG) block copolymers have attracted considerable attention for sustained drug release and tissue engineering applications. Previously, we have reported a thermo-sensitive hydrogel of P(CL-co-TOSUO)-PEG-P(CL-co-TOSUO) (PECT) triblock copolymers modified by hydrophilic cyclic ether pendant groups 1,4,8-trioxa-[4.6]spiro-9-undecanone (TOSUO). Unfortunately, the low gel modulus of PECT (only 50-70 Pa) may limit its applications. Herein, another kind of thermogelling triblock copolymer of a pendant cyclic ether-modified caprolactonic poloxamer analog, PEG-P(CL-co-TOSUO)-PEG (PECTE), was successfully prepared by control of the hydrophilicity/hydrophobicity balance and chemical compositions of the copolymers. PECTE powder could directly disperse in water to form a stable nanoparticle (NP) aqueous dispersion and underwent sol-gel-sol transition behavior at a higher concentration with the temperature increasing from ambient or lower temperatures. Significantly, the microstructure parameters (e.g., different chemical compositions of the hydrophobic block and topology) played a critical role in the phase transition behavior. Furthermore, comparison studies on PECTE and PEG-PCL-PEG (PECE) showed that the introduction of pendant cyclic ether groups into PCL blocks could avoid unexpected ahead-of-time gelling of the PECE aqueous solution. In addition, the rheological analysis of PECTE and PECT indicated that the storage modulus of the PECTE hydrogel could be 100 times greater than that of the PECT hydrogel under the same mole ratios of TOSUO/CL and lower molecular weight. Consequently, PECTE thermal hydrogel systems are believed to be promising as in situ gel-forming biomaterials for drug delivery and tissue engineering.

Controlled release of liraglutide using thermogelling polymers in treatment of diabetes

In treatment of diabetes, it is much desired in clinics and challenging in pharmaceutics and material science to set up a long-acting drug delivery system. This study was aimed at constructing a new delivery system using thermogelling PEG/polyester copolymers. Liraglutide, a fatty acid-modified antidiabetic polypeptide, was selected as the model drug. The thermogelling polymers were presented by poly(ε-caprolactone-co-glycolic acid)-poly(ethylene glycol)-poly(ε-caprolactone-co-glycolic acid) (PCGA-PEG-PCGA) and poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA). Both the copolymers were soluble in water, and their concentrated solutions underwent temperature-induced sol-gel transitions. The drug-loaded polymer solutions were injectable at room temperature and gelled in situ at body temperature. Particularly, the liraglutide-loaded PCGA-PEG-PCGA thermogel formulation exhibited a sustained drug release manner over one week in both in vitro and in vivo tests. This feature was attributed to the combined effects of an appropriate drug/polymer interaction and a high chain mobility of the carrier polymer, which facilitated the sustained diffusion of drug out of the thermogel. Finally, a single subcutaneous injection of this formulation showed a remarkably improved glucose tolerance of mice for one week. Hence, the present study not only developed a promising long-acting antidiabetic formulation, but also put forward a combined strategy for controlled delivery of polypeptide.

Safe and Efficient Colonic Endoscopic Submucosal Dissection Using an Injectable Hydrogel

Endoscopic submucosal dissection (ESD) has not yet been widely adopted in the treatment of early colonic cancers due to the greater technical difficulty involved, longer procedure time, and the increased risk of perforation. Adequate mucosal elevation by submucosal injection is crucial for en bloc resection and prevention of perforation during colonic ESD. This study is aimed to evaluate the efficacy of an injectable thermoreversible hydrogel as the colonic submucosal agent for the first time. Triblock copolymer poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) was synthesized, and its concentrated aqueous solution was injected into the colonic submucosa of living minipig and spontaneously transformed into an in situ hydrogel with adequate mucosal elevation at body temperature. Such a mucosal lifting lasted for a longer time than that created by the control group, glycerol fructose. Colonic ESD was then performed with the administration of hydrogels at various polymer concentrations or glycerol fructose. All colonic lesions were successfully resected en bloc after one single injection of the hydrogel, and repeated injections were not needed. No evidence of major hemorrhage, perforation and tissue damage were observed. Considering the injection pressure, duration of mucosal elevation and efficacy of "autodissection", the hydrogel containing 15 wt % polymer was the optimized system for colonic ESD. Consequently, the thermoreversible hydrogel is an ideal submucosal fluid that provides a durable mucosal lifting and makes colonic ESD accessible to a large extent. In particular, the efficacy of "autodissection" after one single injection of the hydrogel simplifies significantly the procedures while minimizing the complications.

Sustained intravitreal delivery of dexamethasone using an injectable and biodegradable thermogel

Delivery of therapeutic agents to posterior segment of the eyes is challenging due to the anatomy and physiology of ocular barriers and thus long-acting implantable formulations are much desired. In this study, a thermogelling system composed of two poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) triblock copolymers was developed as an injectable matrix for intravitreal drug delivery. The thermogel was prepared by mixing a sol and a precipitate of PLGA-PEG-PLGA triblock copolymers with different block ratios, among which a hydrophobic glucocorticoid, dexamethasone (DEX), was incorporated. The DEX-loaded thermogel was a low-viscous liquid at low temperature and formed a non-flowing gel at body temperature. The in vitro release rate of DEX from the thermogel could be conveniently modulated by varying the mixing ratio of the two copolymers. The long-lasting intraocular residence of the thermogel was demonstrated by intravitreal injection of a fluorescence-labeled thermogel to rabbits. Compared with a DEX suspension, the intravitreal retention time of DEX increased from a dozen hours to over 1week when being loaded in the thermogel. Additionally, intravitreal administration of the thermogel did not impair the morphology of retina and cornea. This study reveals that the injectable PLGA-PEG-PLGA thermogel is a biocompatible carrier for sustained delivery of bioactive agents into the eyes, and provides an alternative approach for treatment of posterior segment diseases.