Thermosensitive In Situ Gels for Joint Disorders: Pharmaceutical Considerations in Intra-Articular Delivery

Intra-articular hydrogel formulation prolongs the in vivo stability of Toll-like receptor antagonistic peptides for rheumatoid arthritis treatment

Rheumatoid arthritis (RA) is an autoimmune disease characterized by systemic inflammation that primarily affects joint tissue and requires frequent medication. Recently, we developed cyclic phage-display-derived inhibitory peptides (CPs), which act as Toll-like Receptor 4 antagonists. These CPs exhibited therapeutic efficacy against joint diseases by alleviating inflammatory factors. Nonetheless, CP exhibits in vivo instability and a short half-life. Therefore, this study sought to improve the in vivo stability of CP, thereby reducing the frequency of CP administration through the development of an injectable hydrogel depot formulation. To improve in vivo stability, CP was chemically conjugated to hyaluronic acid (HA-CP) and subsequently mixed into a temperature-sensitive hydrogel [methoxy polyethylene glycol-b-poly(ε-caprolactone)-ran-poly(lactide) (PC)] as an injectable depot (PC+(HA-CP)). For comparison, CP was physically mixed with HA and PC (PC+(HA+CP)). Both PC+(HA-CP) and PC+(HA+CP) were found to rapidly form depots upon injection into the joint space. Cell viability assays confirmed the non-toxic nature of PC+(HA-CP) and PC+(HA+CP), whereas both formulations exhibited inhibition of inflammatory factors. Furthermore, PC+(HA-CP) retained CP for a longer duration compared to PC+(HA+CP) in the presence of hyaluronidase and within the RA joint space. Following intra-articular injection, both the PC+(HA-CP) and PC+(HA+CP) depots exhibited reductions in RA symptoms, cartilage regeneration, and suppression of pro-inflammatory cytokine levels. Specifically, by extending the in vivo retention of CP, PC+(HA-CP) demonstrated superior RA treatment efficacy compared to PC+(HA+CP). In conclusion, intra-articular injection of PC+(HA-CP) was validated as an effective strategy for treating RA, owing to its ability to prolong the in vivo retention of CP. This approach holds promise for improving RA management and patient outcomes.

Thermosensitive black phosphorus hydrogel loaded with silver sulfadiazine promotes skin wound healing

Wounds can lead to skin and soft tissue damage and their improper management may lead to the growth of pathogenic bacteria at the site of injury. Identifying better ways to promote wound healing is a major unmet need and biomedical materials with the ability to promote wound healing are urgently needed. Here, we report a thermosensitive black phosphorus hydrogel composed of black phosphorus nano-loaded drug silver sulfadiazine (SSD) and chitosan thermosensitive hydrogel for wound healing. The hydrogel has temperature-sensitive properties and enables the continuous release of SSD under near-infrared irradiation to achieve synergistic photothermal and antibacterial treatment. Additionally, it exerts antibacterial effects on Staphylococcus aureus. In a rat skin injury model, it promotes collagen deposition, boosts neovascularization, and suppresses inflammatory markers. In summary, the excellent thermosensitivity, biocompatibility, and wound-healing-promoting qualities of the reported thermosensitive hydrogel make it suitable as an ideal wound dressing in the clinic.

Polymeric in situ forming depots for long-acting drug delivery systems

Polymeric in situ forming depots have emerged as highly promising drug delivery systems for long-acting applications. Their effectiveness is attributed to essential characteristics such as biocompatibility, biodegradability, and the ability to form a stable gel or solid upon injection. Moreover, they provide added versatility by complementing existing polymeric drug delivery systems like micro- and nanoparticles. The formulation's low viscosity facilitates manufacturing unit operations and enhances delivery efficiency, as it can be easily administered via hypodermic needles. The release mechanism of drugs from these systems can be predetermined using various functional polymers. To enable unique depot design, numerous strategies involving physiological and chemical stimuli have been explored. Important assessment criteria for in situ forming depots include biocompatibility, gel strength and syringeability, texture, biodegradation, release profile, and sterility. This review focuses on the fabrication approaches, key evaluation parameters, and pharmaceutical applications of in situ forming depots, considering perspectives from academia and industry. Additionally, insights about the future prospects of this technology are discussed.

Ultrasound-responsive hyaluronic acid hydrogel of hydrocortisone to treat osteoarthritis

One of the practical ways to manage the disease flares of arthritis is using an intra-articular depot formulation of glucocorticoids. Hydrogels, as controllable drug delivery systems, are hydrophilic polymers with distinctive properties, such as remarkable water capacity and biocompatibility. This study aimed to design an injectable thermo-ultrasound-triggered drug carrier based on Pluronic® F-127, hyaluronic acid, and gelatin. The in situ hydrogel loaded by hydrocortison was developed and D-optimal design was used to formulate the process. The optimized hydrogel was combined with four different surfactants to better regulate the release rate. In situ gels composed of the hydrocortisone-loaded hydrogel and hydrocortisone-loaded mixed-micelle hydrogel were characterized. The hydrocortisone-loaded hydrogel and selected hydrocortisone-loaded mixed-micelle hydrogel showed a spherical shape and were nano-sized with a unique thermo-responsive nature able to prolong drug release. The ultrasound-triggered release study showed that drug release was time-dependent. By inducing osteoarthritis in a rat model, behavioral tests and histopathological analyses were carried out on the hydrocortisone-loaded hydrogel and a particular hydrocortisone-loaded mixed-micelle hydrogel. In vivo results showed that the selected hydrocortisone-loaded mixed-micelle hydrogel improved the status of the disease. Results highlighted the potential of ultrasound-responsive in situ-forming hydrogels as hopeful formulas for efficient treatment of arthritis.