A Mixed Thermosensitive Hydrogel System for Sustained Delivery of Tacrolimus for Immunosuppressive Therapy.

Tacrolimus is an immunosuppressive agent for acute rejection after allotransplantation. However, the low aqueous solubility of tacrolimus poses difficulties in formulating an injection dosage. Polypeptide thermosensitive hydrogels can maintain a sustained release depot to deliver tacrolimus. The copolymers, which consist of poloxamer and poly(l-alanine) with l-lysine segments at both ends (P-Lys-Ala-PLX), are able to carry tacrolimus in an in situ gelled form with acceptable biocompatibility, biodegradability, and low gelling concentrations from 3 to 7 wt %. By adding Pluronic F-127 to formulate a mixed hydrogel system, the drug release rate can be adjusted to maintain suitable drug levels in animals with transplants. Under this formulation, the in vitro release of tacrolimus was stable for more than 100 days, while in vivo release of tacrolimus in mouse model showed that rejection from skin allotransplantation was prevented for at least three weeks with one single administration. Using these mixed hydrogel systems for sustaining delivery of tacrolimus demonstrates advancement in immunosuppressive therapy.

Incorporation of surface-modified hydroxyapatite into poly(methyl methacrylate) to improve biological activity and bone ingrowth.

Poly(methyl methacrylate) (PMMA) is the most frequently used bone void filler in orthopedic surgery. However, the interface between the PMMA-based cement and adjacent bone tissue is typically weak as PMMA bone cement is inherently bioinert and not ideal for bone ingrowth. The present study aims to improve the affinity between the polymer and ceramic interphases. By surface modifying nano-sized hydroxyapatite (nHAP) with ethylene glycol and poly(ɛ-caprolactone) (PCL) sequentially via a two-step ring opening reaction, affinity was improved between the polymer and ceramic interphases of PCL-grafted ethylene glycol-HAP (gHAP) in PMMA. Due to better affinity, the compressive strength of gHAP/PMMA was significantly enhanced compared with nHAP/PMMA. Furthermore, PMMA with 20 wt.% gHAP promoted pre-osteoblast cell proliferation in vitro and showed the best osteogenic activity between the composites tested in vivo. Taken together, gHAP/PMMA not only improves the interfacial adhesion between the nanoparticles and cement, but also increases the biological activity and affinity between the osteoblast cells and PMMA composite cement. These results show that gHAP and its use in polymer/bioceramic composite has great potential to improve the functionality of PMMA cement.

In vitro and in vivo co-culture of chondrocytes and bone marrow stem cells in photocrosslinked PCL-PEG-PCL hydrogels enhances cartilage formation.

Chondrocytes (CH) and bone marrow stem cells (BMSCs) are sources that can be used in cartilage tissue engineering. Co-culture of CHs and BMSCs is a promising strategy for promoting chondrogenic differentiation. In this study, articular CHs and BMSCs were encapsulated in PCL-PEG-PCL photocrosslinked hydrogels for 4 weeks. Various ratios of CH:BMSC co-cultures were investigated to identify the optimal ratio for cartilage formation. The results thus obtained revealed that co-culturing CHs and BMSCs in hydrogels provides an appropriate in vitro microenvironment for chondrogenic differentiation and cartilage matrix production. Co-culture with a 1:4 CH:BMSC ratio significantly increased the synthesis of GAGs and collagen. In vivo cartilage regeneration was evaluated using a co-culture system in rabbit models. The co-culture system exhibited a hyaline chondrocyte phenotype with excellent regeneration, resembling the morphology of native cartilage. This finding suggests that the co-culture of these two cell types promotes cartilage regeneration and that the system, including the hydrogel scaffold, has potential in cartilage tissue engineering. Copyright © 2013 John Wiley & Sons, Ltd.