Adequate blood supply and thorough innervation are essential to the survival of tissue-engineered bones. Though great progress has been created in the application of bone tissue engineering technology to bone defect repair, many challenges remain, such as insufficient vascularisation and deficient innervation in newly regenerated bone. In the present study, we addressed these challenges by manipulating the bone regeneration microenvironment in terms of vascularisation and innervation. We used a novel injectable thermosensitive liposome-hydrogel composite scaffold as a sustained-release carrier for basic fibroblast growth factor (bFGF, which promotes angiogenesis and neurogenic differentiation) and dexamethasone (Dex, which promotes osteogenic differentiation). In vitro biological assessment demonstrated that the composite scaffold had sufficient cell compatibility; it enhanced the capacity for angiogenesis in human umbilical vein endothelial cells, and the capacity for neurogenic/osteogenic differentiation in human bone marrow mesenchymal stem cells. Moreover, the introduction of bFGF/Dex liposome-hydrogel composite scaffold to bone defect sites significantly improved vascularisation and innervated bone regeneration properties in a rabbit cranial defect model. Based on our findings, the regeneration of sufficiently vascularised and innervated bone tissue through a sustained-release scaffold with excellent injectability and body temperature sensitivity represents a promising tactic towards bone defect repair.

New clinical strategies for treating severe bone and cartilage injuries are required, especially for use in combination with implant procedures. For this purpose, p(VCL-co-HEMA) thermosensitive hydrogels have been activated with icariin-loaded nanoparticles to be used as bone-cell-harvesting platforms. Supercritical CO2-SAS technology has been applied to encapsulate icariin, a small molecule that is involved in osteoblastic differentiation. Thus, physical-chemical analysis, including swelling and transmittance, showed the impact of HEMA groups in hydrogel composition. Moreover, icariin (ICA) release from p(VCL-co-HEMA) platforms, including pVCL@ICA nanoparticles, has been studied to evaluate their efficacy in relevant conditions. Finally, the thermosensitive hydrogels\' cell compatibility, transplant efficiency, and bone differentiation capacity were tested. This study identifies the optimal formulations for icariin-activated hydrogels for both control and HEMA formulations. Using this technique, osteoblastic sheets that were rich in collagen type I were successfully transplanted and recultivated, maintaining an optimal extracellular matrix (ECM) composition. These findings suggest a new cell-sheet-based therapy for bone regeneration purposes using customized and NP-activated pVCL-based cell platforms.

Dimethyl fumarate (DMF) is a drug that is orally administered for the treatment of relapsing-remitting multiple sclerosis. However, DMF causes gastrointestinal side effects and flushing in 43 % of patients, which significantly contributes to treatment discontinuation. To reduce side effects and increase patient compliance, the aim of this study was to develop a thermosensitive chitosan/glycerophosphate hydrogel for the nasal administration of DMF. A binary system of DMF with hydroxypropyl-β-cyclodextrin (HP-β-CD) was made and included in the hydrogel precursor solution. The precursor solution (drug content, DMF stability, thermogelling properties, viscosity), and the resulting thermosensitive hydrogel (mucoadhesion, in vitro DMF permeation) were characterized. HP-β-CD was able to interact with DMF and improve its water solubility. The leader thermosensitive nasal solution, G1 solution, was loaded with approximately 92 % DMF, which remained stable for 21 days. The G1 solution formed a hydrogel in approximately 2-1 min; it had a pH of 6.8 ± 0.06 and caused no significant change in the osmolality of the simulated nasal medium. The G1 hydrogel showed good mucoadhesive properties and released DMF that permeated in vitro in a controlled manner. As a result, G1 is a potential new approach to exploit the intranasal administration of DMF for treating multiple sclerosis.

Injectable hydrogels are promising for bone tissue engineering due to their minimally invasive application and adaptability to irregular defects. This study presents the development of pluronic grafted silk fibroin (PF-127-g-SF), a temperature-sensitive graft copolymer synthesized from SF and modified PF-127 via a carbodiimide coupling reaction. The PF-127-g-SF copolymer exhibited a higher sol-gel transition temperature (34 °C at 16 % w/v) compared to PF-127 (23 °C), making it suitable for injectable applications. It also showed improved flexibility and strength, with a yielding point increase from <10 % to nearly 30 %. Unlike PF-127 gel, which degrades within 72 h in aqueous media, the PF-127-g-SF copolymer maintained a stable gel structure for over two weeks due to its robust crosslinked hydrogel network. Incorporating hydroxyapatite nanoparticles (n-HA) into the hydrogel reduced pore size and decreased swelling and degradation rates, extending structural stability to four weeks. Increasing n-HA concentration from 0 % to 20 % reduced porosity from 80 % to 66 %. Rheological studies indicated that n-HA enhanced the scaffold\'s strength and mechanical properties without altering gelation temperature. Cellular studies with MG-63 cells showed that n-HA concentration influenced cell viability and mineralization, highlighting the scaffold\'s potential in bone tissue engineering.

Rheumatoid arthritis (RA), an immune-mediated inflammatory disease, is characterized by a large number of infiltrated immune cells and abnormally elevated reactive oxygen species (ROS) in the joint. Various proinflammatory factors secreted by macrophages and the elevated ROS by inflammatory cells are deeply intertwined and together contribute to joint damage. Targeted and sustained anti-inflammation and antioxidation strategies are needed for RA treatment. To alleviate the oxidative stress and target the source of inflammatory cytokines, we developed a thermosensitive injectable hydrogel, Dex-DSLip/Cro@Gel, to coordinate the targeted anti-inflammatory and antioxidation effects. Within the injectable gel, dexamethasone (Dex)-loaded liposomes (Dex-DSLip), modified with dextran sulfate (DS), target macrophages via interaction with scavenger receptor A (SR-A). Simultaneously, crocin I (Cro) is loaded in the gel with a high loading capacity. The porous structure of Dex-DSLip/Cro@Gel successfully prolongs the retention time of both drugs and sustains the release of Dex and Cro. After intra-articular injection of Dex-DSLip/Cro@Gel in RA rats, the expression of inflammatory factors in the ankle joints was significantly reduced. Joint erythema and bone erosion were markedly alleviated. Through the synergistic effects of Dex and Cro, Dex-DSLip/Cro@Gel demonstrates targeted anti-inflammatory and antioxidation effects as well as mitigated bone erosion and long-term therapeutic effects for RA. This thermosensitive injectable nanocomposite hydrogel synergizes anti-inflammatory and antioxidation effects and targets the microenvironment in the joint, offering a new approach for RA treatment.

The conventional treatment of osteomyelitis with antibiotic-loaded nondegradable polymethylmethacrylate (ATB-PMMA) beads has certain limitations, including impeded bone reconstruction and the need for secondary surgery. To overcome this challenge, this study aimed to develop and characterize an injectable vancomycin-loaded silk fibroin/methylcellulose containing calcium phosphate-based in situ thermosensitive hydrogel (VC-SF/MC-CAPs). The VC-SF/MC-CAPs solution can be easily administered at room temperature with a low injectability force of ≤30 N and a high vancomycin (VC) content of ~96%. Additionally, at physiological temperature (37 °C), the solution could transform into a rigid hydrogel within 7 minutes. In vitro drug release performed under both physiological (pH 7.4) and infection conditions (pH 4.5) revealed a prolonged release pattern of VC-SF/MC-CAPs following the Peppas-Sahlin kinetic model. In addition, the released VC from VC-SF/MC-CAPs hydrogels exhibited antibacterial activity against Staphylococcus aureus for a period exceeding 35 days, as characterized by the disk diffusion assay. Furthermore, at pH 7.4, the VC-SF/MC-CAPs demonstrated >60% degradation within 35 days. Importantly, when exposed to physiological pH conditions, CAPs are transformed into bioactive hydroxyapatite, which benefits bone formation. Therefore, VC-SF/MC-CAPs showed significant potential as a local drug delivery system for treating osteomyelitis.

Despite the remarkable advances of dermal fillers that reduce wrinkles caused by dermis thickness reduction, they still lack effective hydrogel systems that stimulate collagen generation along with injection convenience. Here, we develop a stem cell-derived extracellular vesicle (EV)-bearing thermosensitive hydrogel (EVTS-Gel) for effective in vivo collagen generation. The TS-Gel undergoes sol-gel transition at 32.6 °C, as demonstrated by the storage and loss moduli crossover. Moreover, the TS-Gel and the EVTS-Gel have comparable rheological properties. Both hydrogels are injected in a sol state; hence, they require lower injection forces than conventional hydrogel-based dermal fillers. When locally administered to mouse skin, the TS-Gel extends the retention time of EVs by 2.23 times. Based on the nature of the controlled EV release, the EVTS-Gel significantly inhibits the dermis thickness reduction caused by aging compared to the bare EV treatment for 24 weeks. After a single treatment, the collagen layer thickness of the EVTS-Gel-treated dermis becomes 2.64-fold thicker than that of the bare EV-treated dermis. Notably, the collagen generation efficacy of the bare EV is poorer than that of the EVTS-Gel of a 10× lesser dose. Overall, the EVTS-Gel shows potential as an antiaging dermal filler for in vivo collagen generation.

Cold-induced vasoconstriction is a significant contributor that leads to chilblains and hypothermia in humans. However, current animal models have limitations in replicating cold-induced acral injury due to their low sensitivity to cold. Moreover, existing in vitro vascular chips composed of endothelial cells and perfusion systems lack temperature responsiveness, failing to simulate the vasoconstriction observed under cold stress. This study presents a novel approach where a microfluidic bioreactor of vessel-on-a-chip was developed by grafting the inner microchannel surface of polydimethylsiloxane with a thermosensitive hydrogel skin composed of N-isopropyl acrylamide and gelatin methacrylamide. With a lower critical solution temperature set at 30°C, the gel layer exhibited swelling at low temperatures, reducing the flow rate inside the channel by 10% when the temperature dropped from 37°C to 4°C. This well mimicked the blood stasis observed in capillary vessels in vivo. The vessel-on-a-chip was further constructed by culturing endothelial cells on the surface of the thermosensitive hydrogel layer, and a perfused medium was introduced to the cells to provide a physiological shear stress. Notably, cold stimulation of the vessel-on-a-chip led to cell necrosis, mitochondrial membrane potential (ΔΨm) collapse, cytoskeleton disaggregation, and increased levels of reactive oxygen species. In contrast, the static culture of endothelial cells showed limited response to cold exposure. By faithfully replicating cold-induced endothelial injury, this groundbreaking thermosensitive vessel-on-a-chip technology offers promising advancements in the study of cold-induced cardiovascular diseases, including pathogenesis and therapeutic drug screening.

To develop a submucosal injection material with sustained submucosal lifting for endoscopic submucosal dissection (ESD), this study designed and prepared a novel composite thermosensitive hydrogel system with high pH chitosan-polyvinylpyrrolidone-β-glycerophosphate (HpHCS-PVP-GP). HpHCS improved the injectability of the hydrogels and retained the rapid gelation ability at low concentrations. The modification of PVP significantly improved the stability of low-temperature hydrogel precursor solutions and the integrity of hydrogels formed at 37 °C through hydrogen bonds between PVP and HpHCS. A mathematical model was established using response surface methodology (RSM) to evaluate the synergistic effect of HpHCS, GP, and PVP concentrations on gelation time. This RSM model and submucosal lifting evaluation using in vitro pig esophageal models were used to determine the optimal formula of HpHCS-PVP-GP hydrogels. Although the higher PVP concentration (5 % (w/v)) prolonged gelation time, it improved hydrogel mechanical strength, resulting in better submucosal lifting performance. The experiments of Bama mini pigs showed that the heights of the cushions elevated by the HpHCS-5%PVP-GP hydrogel remained about 80 % 1 h after injection. Repeated injections were avoided, and the hydrogel had no cytotoxicity after electric cutting. Therefore, the HpHCS-PVP-GP thermosensitive hydrogel might be a promising submucosal injection material for ESD.

Currently, an important group of biomaterials used in the research in the field of tissue engineering is thermosensitive chitosan hydrogels. Their main advantage is the possibility of introducing their precursors (sols) into the implantation site using a minimally invasive method-by injection. In this publication, the results of studies on the new chitosan structures in the form of thermosensitive hydrogels containing graphene oxide as a nanofiller are presented. These systems were prepared from chitosan lactate and chitosan chloride solutions with the use of a salt of pyrimidine nucleotide-uridine 5\'-monophosphate disodium salt-as the cross-linking agent. In order to perform the characterization of the developed hydrogels, the sol-gel transition temperature of the colloidal systems was first determined based on rheological measurements. The hydrogels were also analyzed using FTIR spectroscopy and SEM. Biological studies assessed the cytotoxicity (resazurin assay) and genotoxicity (alkaline version of the comet assay) of the nanocomposite chitosan hydrogels against normal human BJ fibroblasts. The conducted research allowed us to conclude that the developed hydrogels containing graphene oxide are an attractive material for potential use as scaffolds for the regeneration of damaged tissues.