Hua Wu

Galactosylated chitosan-polycaprolactone nanoparticles for hepatocyte-targeted delivery of curcumin

Galactosylated chitosan-polycaprolactone (Gal-CH-PCL) copolymers with a galactosylation degree of around 10% and varied PCL percentages less than 40 wt% were synthesized and used to produce nanoparticles for delivering curcumin. Some nanoparticles with encapsulation efficiency of 70% or higher and sizes changing from 100 to 250 nm were able to deliver curcumin in a controlled manner. PCL content in Gal-CH-PCLs was found to be a key factor for governing the release behavior of nanoparticles. Hepatocyte-targeted characteristic of nanoparticles was confirmed using human hepatocellular carcinoma (HepG2) cells. In comparison to free curcumin, curcumin-loaded Gal-CH-PCL nanoparticles well retained its anticancer activity. At an equivalent curcumin-dose of around 20 μg/mL that was found to be relatively safe to human normal liver cells, the results obtained from flow-cytometry revealed that some optimized Gal-CH-PCL nanoparticles showed more than 6-fold increasing abilities to induce the apoptosis and necrosis of HepG2 cells during 72 h treatment compared to free curcumin.

Chitosan-polycaprolactone copolymer microspheres for transforming growth factor-β1 delivery

Chitosan-polycaprolactone (CPC) copolymer microspheres loaded with transforming growth factor-β1 (TGF-β1) were fabricated with an emulsification method using sodium tripolyphosphate as crosslinker. They were found to be dense and had regular sphericity with various diameters changing from several hundred nanometers to a few micrometers. Their loading efficiency could be regulated by both the amount of crosslinker and the composition of CPCs, and some microspheres showed their loading efficiency higher than 80%. It was observed that in neutral PBS media, the composition of CPCs predominantly governed swelling behavior and release profiles of the microspheres while the effect of crosslinker on the swelling and release behavior was limited. The initial fast releases of TGF-β1 from different microspheres could be significantly decreased with increasing polycaprolactone content in CPCs, and some microspheres were able to maintain sustained releases of TGF-β1 by mainly controlling their composition. In addition, in a simulated acidic environment (pH 6.5) for cartilage lesions, release patterns of the microspheres were notably modulated by pH but some selected microspheres could still well administrate the release of TGF-β1 in a sustained way without severe burst features.

Designed composites for mimicking compressive mechanical properties of articular cartilage matrix

Collagen, chitosan-polycaprolactone (CH-PCL) copolymer with PCL content of around 40wt% and chondroitin sulfate (CS) were mixed together at various ratios to prepare collagen/CH-PCL/CS composites and the resulting composites were used to build stratified porous scaffolds that are potentially applicable for articular cartilage repair. The ternary composites were designed in such a way that collagen content in the scaffolds decreased from the top layer to the bottom layer while the content of CH-PCL and CS altered in a reversed trend in order to reach partial similarity to cartilage matrix in the composition of main components. Porous structures inside collagen/CH-PCL/CS scaffolds were constructed using a low-temperature deposition processing technique and graded average pore-size and porosity for the scaffolds were established. Such produced scaffolds were further crosslinked using 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide under optimized conditions, and the obtained scaffolds showed well-defined elastic compressive properties. Compressive modulus (E) and stress at 10% strain (σ10) of full scaffolds in wet state reached about 2.8MPa and 0.3MPa, respectively, and meanwhile, E and σ10 of layers inside hydrated scaffolds changed in a gradient-increased manner from the top layer to the bottom layer with significant differences between contiguous layers, which partially mimics compressive mechanical properties of cartilage matrix. In addition, in vitro culture of cell-scaffold constructs exhibited that scaffolds were able to well support the ingrowth and migration of seeded cells, and cells also showed relatively uniform distribution throughout the scaffolds. These results suggest that the presently developed collagen/CH-PCL/CS scaffolds have promising potential for applications in articular cartilage repair.

Mechanical properties and permeability of porous chitosan–poly(p-dioxanone)/silk fibroin conduits used for peripheral nerve repair

Some poly(p-dioxanone) (PDO) homopolymers were first synthesized and the selected PDO was conjugated onto chitosan using a group-protecting method to produce chitosan-poly(p-dioxanone) (CH-PDO) copolymers with various PDO percentages changing from around 30 to 60 wt%. The CH-PDO with the PDO content of around 42 wt% was used to blend with prescribed amounts of silk fibroin (SF) to build porous single-lumen conduits that are intended to be used for long-gap peripheral nerve repair. Some genipin-crosslinked CH-PDO/SF conduits were endowed with an average porosity of around 60% in their porous wall, and with changed pore-sizes varying from around 10 to ca. 70 μm using optimized processing conditions. After being degraded in a PBS medium containing a certain amount of lysozyme for various periods up to 8 weeks, some optimal CH-PDO/SF conduits were able to retain their compressive load and deformation recovery at around 59 N/m and 73% in wet state, respectively. In addition, the achieved CH-PDO/SF conduits allowed the permeation of nutritional molecules with various molecular weights while showing a certain ability to prevent cells from infiltrating through the conduit wall. Cell culture confirmed that the optimized CH-PDO/SF conduits were able well supported the growth of rat glioma C6 cells. These results suggest that presently developed CH-PDO/SF conduits have promising potential for long-gap peripheral nerve repair.

Injectable hydrogels embedded with alginate microspheres for controlled delivery of bone morphogenetic protein-2.

Some delivery carriers with injectable characteristics were built using the thermosensitive chitosan/dextran-polylactide/glycerophosphate hydrogel and selected alginate microspheres for the controllable release of bone morphogenetic protein-2 (BMP-2). BMP-2 was first loaded into the microspheres with an average size of around 20 μm and the resulting microspheres were then embedded into the gel in order to achieve well-controlled BMP-2 release. The microsphere-embedded gels show their incipient gelation temperature at around 32 °C and pH at about 7.1. Some gels had their elastic modulus close to 1400 Pa and the ratio of elastic modulus to viscous modulus at around 34, revealing that they behaved like mechanically strong gels. Optimized microsphere-embedded gels were found to be able to administer the BMP-2 release without significant initial burst release in an approximately linear manner over a period of time longer than four weeks. The release rate and the released amount of BMP-2 from these gels could be regulated individually or cooperatively by the initial BMP-2 load and the dextran-polylactide content in the gels. Measurements of the BMP-2 induced alkaline phosphatase activity in C2C12 cells confirmed that C2C12 cells responded to BMP-2 in a dose-dependent way and the released BMP-2 from the microsphere-embedded gels well retained their bioactivity. In vivo assessment of some gels revealed that the released BMP-2 maintained its osteogenesis functions.

Multi-tubule conduit-filler constructs loaded with gradient-distributed growth factors for neural tissue engineering applications

Chitosan/silk fibroin/glycerophosphate gels were loaded with nerve growth factor (NGF) and further processed into multi-tubule fillers. NGF was loaded into the fillers in such a way so that a NGF gradient was established longitudinally along the filler length. A type of poly(lactide-co-glycolide)(PLGA)/chitosan(CH) porous conduit was fabricated using a pre-crosslinking method. The filler was fully filled into the lumen of conduits to build multi-tubule conduit-filler constructs that are intended for long-gap peripheral nerve repair. In vitro degradation in a lysozyme-contained medium revealed that constructs had degradation-tolerant features and the optimized multi-tubule filler was capable of maintaining its multi-tubules unblocked for around 10-week. After being degraded for various periods up to 8 weeks, the optimal conduit-filler constructs showed confirmative ability to retain their compressive load, deformation recovery and tensile strength at about 80N/m, 75% and 15N/cm2 in wet state, respectively. The constructs were able to administer NGF release and to maintain persistent NGF gradients longitudinally distributed inside the PLGA/CH conduit for about 6 weeks or even longer. The PC12 cell neurite extension assay confirmed that the presently developed multi-tubule conduit-filler constructs were reliable for effectively preserving the bioactivity of released NGF.

Establishment of nerve growth factor gradients on aligned chitosan-polylactide /alginate fibers for neural tissue engineering applications

Nerve conduits containing aligned fibrous fillers with gradiently distributed signal molecules are essential for long-gap nerve repair. This study was to develop an approach for establishing nerve growth factor (NGF) gradients onto the aligned chitosan-polylactide (CH-PLA) fibers. CH-PLA containing 37wt% of PLA was spun into fibers using a wet-spinning technique. CH-PLA fibers showed much higher wet-state tensile strength, enhanced degradation tolerance and significantly lower swelling degree in comparison to chitosan fibers. The CH-PLA fibers with diameters from 40 to 60μm were selected and segmentally coated in bundles using NGF-contained alginate solutions to establish NGF gradients lengthwise along fibers. The diameter of resulting NGF-loaded CH-PLA/alginate fibers was well controlled within a range between 60 and 120μm. Calcium ion crosslinked alginate coating layers on fibers showed abilities to administer the sustainable NGF release in a gradient distribution manner for at least 5 weeks. NGF-induced neurite outgrowth of PC12 cells confirmed that bioactivity of NGF released from fibers was well retained.