A systematic study on the effects of the structure of block copolymers of PEG and poly(ε-caprolactone-co-glycolic acid) on their temperature-responsive sol-to-gel transition behavior

Poly(L-lysine)-block-poly(ethylene glycol)-block-poly(L-lysine) triblock copolymers for the preparation of flower micelles and their irreversible hydrogel formation

Poly(L-lysine)-block-poly(ethylene glycol)-block-poly(L-lysine) (PLys-block-PEG-block-PLys) triblock copolymers formed polyion complex (PIC) with poly(acrylic acid) (PAAc) or sodium poly(styrenesulfonate) (PSS), leading to the formation of flower micelle-type nanoparticles (NanoLys/PAAc or NanoLys/PSS) with tens of nanometers size in water at a polymer concentration of 10 mg/mL. The flower micelles exhibited irreversible temperature-driven sol-gel transitions at physiological ionic strength, even at low polymer concentrations such as 40 mg/mL, making them promising candidates for injectable hydrogel applications. Rheological studies showed that the chain length of PLys segments and the choice of polyanions significantly impacted irreversible hydrogel formation, with PSS being superior to PAAc for the formation. The incorporation of silica gel nanoparticles into the PIC flower micelles also resulted in irreversible gelation phenomena. The highest storage modulus exceeded 10 kPa after gelation, which is sufficient for practical applications. This study demonstrates the potential of these PIC-based hydrogels as biomaterials with tunable properties for biomedical applications.

Diverse Strategies to Develop Poly(ethylene glycol)-Polyester Thermogels for Modulating the Release of Antibodies

In this work, we present basic research on developing thermogel carriers containing high amounts of model antibody immunoglobulin G (IgG) with potential use as injectable molecules. The quantities of IgG loaded into the gel were varied to evaluate the possibility of tuning the dose release. The gel materials were based on blends of thermoresponsive and degradable ABA-type block copolymers composed of poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA) or poly(lactide-co-caprolactone)-b-poly(ethylene glycol)-b-(lactide-co-caprolactone) (PLCL-PEG-PLCL). Primarily, the gels with various amounts of IgG were obtained via thermogelation, where the only factor inducing gel formation was the change in temperature. Next, to control the gels' mechanical properties, degradation rate, and the extent of antibody release, we have tested two approaches. The first one involved the synergistic physical and chemical crosslinking of the copolymers. To achieve this, the hydroxyl groups located at the ends of the PLGA-PEG-PLGA chain were modified into acrylate groups. In this case, the thermogelation was accompanied by chemical crosslinking through the Michael addition reaction. Such an approach increased the dynamic mechanical properties of the gels and simultaneously prolonged their decomposition time. An alternative solution was to suspend crosslinked PEG-polyester nanoparticles loaded with IgG in a PLGA-PEG-PLGA gelling copolymer. We observed that loading IgG into thermogels lowered the gelation temperature (TGEL) value and increased the storage modulus of the gels, as compared with gels without IgG. The prepared gel materials were able to release the IgG from 8 up to 80 days, depending on the gel formulation and on the amount of loaded IgG. The results revealed that additional, chemical crosslinking of the thermogels and also suspension of particles in the polymer matrix substantially extended the duration of IgG release. With proper matching of the gel composition, environmental conditions, and the type and amount of active substances, antibody-containing thermogels can serve as effective IgG delivery materials.

Development of immune cell delivery system using biodegradable injectable polymers for cancer immunotherapy

Immune cell delivery using injectable hydrogel attracts much attention for improving its therapeutic effect. Specifically, dendritic cells (DCs) are the trigger cells for immune responses, and DC vaccines are studied for improving cancer immunotherapy. Hydrogel-assisted cell delivery is expected to enhance the viability of the implanted cells. We recently reported temperature-responsive biodegradable injectable polymer (IP) formulation utilizing poly(ε-caprolactone-co-glycolide)-b-poly(ethylene glycol)(PEG)-b-poly(ε-caprolactone-co-glycolide) (tri-PCG). Tri-PCG-based IP was reported to exhibit immediate sol-to-gel transition in response to temperature increase, in vivo biodegradability, and excellent biocompatibility. In this study, tri-PCG-based IP was applied to DC delivery. IP encapsulated live DCs, and the DCs incorporated ovalbumin (OVA) as a model antigen and CpG-DNA (oligo DNA with adjuvant effect) in IP hydrogel. Results suggested that DCs encapsulated in IP hydrogel internalized OVA and CpG-DNA and DCs were maturated to present antigens to T cells. Moreover, subcutaneously injected tri-PCG-based IP prolonged the retention period of cell accumulation at injected sites. Tri-PCG IP hydrogel could release matured DCs as the degradation of the hydrogel progressed. Tri-PCG IP formulation improved treatment efficacy of OVA transfected mouse lymphoma (E.G7-OVA) tumor. Hence, tri-PCG IP is a promising platform for immune cell delivery.