Fabrication and in vivo osteogenesis of biomimetic poly(propylene carbonate) scaffold with nanofibrous chitosan network in macropores for bone tissue engineering.

A biomimetic poly(propylene carbonate) (PPC) porous scaffold with nanofibrous chitosan network within macropores (PPC/CSNFs) for bone tissue engineering was fabricated by a dual solid-liquid phase separation technique. PPC scaffold with interconnected solid pore wall structure was prepared by the first phase separation, which showed a high porosity of 91.9% and a good compressive modulus of 14.2 ± 0.56 MPa, respectively. By the second phase separation, nanofibrous chitosan of 50-500 nm in diameter was formed in the macropores with little influence on the pore structure and the mechanical properties of PPC scaffold. The nanofibrous chitosan content was calculated to be 9.78% by elemental analysis. After incubation in SBF for 14 days, more apatite crystals were deposited on the pore surface as well as the nanofibrous chitosan surface of PPC/CSNFs scaffold compared with PPC scaffold. The in vitro culture of bone mesenchymal stem cells showed that PPC/CSNFs scaffold exhibited a better cell viability than PPC scaffold. After implantation in rabbits for 16 weeks, the defect was entirely repaired by PPC/CSNFs scaffold, as opposed to the incomplete healing for PPC scaffold. It indicated that PPC/CSNFs scaffold showed a faster in vivo osteogenesis rate than PPC scaffold. Hereby, PPC/CSNFs scaffold will be a potential candidate for bone tissue engineering.

Poly(2-hydroxyethyl methacrylate-co-quaternary ammonium salt chitosan) hydrogel: A potential contact lens material with tear protein deposition resistance and antimicrobial activity.

Tear protein deposition resistance and antimicrobial property are two challenges of conventional poly(2-hydroxyethyl methacrylate) (pHEMA) contact lenses. In this work, we developed a poly(2-hydroxyethyl methacrylate-co-quaternary ammonium salt chitosan) hydrogel, named as p(HEMA-co-mHACC) hydrogel, using acryloyl HACC (mHACC) as a macromolecular crosslinker. With increasing the acryloyl substitution degree (14-29%) or mHACC content (2-11%), the hydrogel showed an enhanced tensile strength (432-986 kPa) and Young's modulus (360-1158 kPa), a decreased elongation at break (242-84%), and an increased visible light transmittance (0-95%). At an optimal acryloyl substitution degree of 26%, with the increase of mHACC content from 2% to 11%, p(HEMA-co-mHACC) hydrogel presented a decreased water contact angle from 84.6 to 55.3 degree, an increased equilibrium water content from 38% to 45%, and an enhanced oxygen permeability from 8.5 to 13.5 barrer. Due to the enhancement in surface hydrophilicity and electropositivity, p(HEMA-co-mHACC) hydrogel remarkably reduced the deposition of lysozyme, but little affected the adsorption of BSA, depending on the hydrophilic/hydrophobic and electrostatic interactions. The antimicrobial test against Staphylococcus aureus and Escherichia coli showed that p(HEMA-co-mHACC) hydrogel presented an 8-32 times higher germicidal ability than pHEMA hydrogel, indicative of a better antimicrobial activity. The in vitro cell culture of mouse NIH3T3 fibroblasts and immortalized human keratinocytes showed that p(HEMA-co-mHACC) hydrogel was non-toxic. Thus, p(HEMA-co-mHACC) hydrogel with tear protein deposition resistance and antimicrobial activity is a potential candidate for contact lenses.

Hydroxypropyl cellulose enhanced ionic conductive double-network hydrogels.

Ionic conductive hydrogels with both high-performance in conductivity and mechanical properties have received increasing attention due to their unique potential in artificial soft electronics. Here, a dual physically cross-linked double network (DN) hydrogel with high ionic conductivity and tensile strength was fabricated by a facile approach. Hydroxypropyl cellulose (HPC) biopolymer fibers were embedded in a poly (vinyl alcohol)­sodium alginate (PVA/SA) hydrogel, and then the prestretched PVA-HPC/SA composite hydrogel was immersed in a CaCl2 solution to prepare PVA-HPCT/SA-Ca DN hydrogels. The obtained composite hydrogel has an excellent tensile strength up to 1.4 MPa. Importantly, the synergistic effect of hydroxypropyl cellulose (HPC) and prestretching reduces the migration resistance of ions in the hydrogel, and the conductivity reaches 3.49 S/ m. In addition, these composite hydrogels are noncytotoxic, and they have a low friction coefficient and an excellent wear resistance. Therefore, PVA-HPCT/SA-Ca DN hydrogels have potential applications in nerve replacement materials and biosensors.

Nano-hydroxyapatite enhanced double network hydrogels with excellent mechanical properties for potential application in cartilage repair.

Hydrogels with desirable characteristics have been supposed to be potential materials for cartilage repair. However, the biomechanical, biotribological and biocompatible properties of hydrogels remain some crucial challenges. To address these challenges, we developed a dual physically cross-linked poly (vinyl alcohol)-(nano hydroxyapatite)/(2-hydroxypropyltrimethyl ammonium chloride chitosan) (PVA-HA/HACC-Cit) hydrogels with double-network (DN) through a simply freezing/thawing technique and an immersing process. The DN hydrogel with an optimized HA concentration exhibited outstanding fracture tensile stress (2.70 ± 0.24 MPa), toughness (14.09 ± 2.06 MJ/m3) and compressive modulus (0.88 ± 0.09 MPa). In addition, the PVA-HA/HACC-Cit DN hydrogels demonstrated remarkable anti-fatigue property, extraordinary self-recovery and energy dissipation ability due to their unique dual physically cross-linked structures. Moreover, the low friction coefficient, the predominant wear resistance property, as well as the excellent cytocompatibility were realized for the DN hydrogels because of the existence of nano-hydroxyapatite. Thus, this work puts forward a new strategy in the preparation of DN hydrogels for promising applications in cartilage repair.

An alginate/poly(N-isopropylacrylamide)-based composite hydrogel dressing with stepwise delivery of drug and growth factor for wound repair.

Anti-inflammation and angiogenesis play an essential role in wound healing. In this study, we developed a composite hydrogel dressing with stepwise delivery of diclofenac sodium (DS) and basic fibroblast growth factor (bFGF) in the inflammation stage and new tissue formation stage respectively for wound repair. Sodium alginate (SA) crosslinked by calcium ion acted as the continuous phase, and thermosensitive bFGF-loaded poly(N-isopropylacrylamide) nanogels (pNIPAM NGs, LCST1 ~33 °C) and DS-loaded p(N-isopropylacrylamide-co-acrylic acid) nanogels [p(NIPAM-co-AA) NGs, LCST2 ~40 °C] acted as the dispersed phase. The synthesized SA/bFGF@pNIPAM/DS@p(NIPAM-co-AA) hydrogel presented a desirable storage modulus of ~4500 Pa, a high water equilibrium swelling ratio of ~90, an appropriate water vapor transmission rate of ~2300 g/m2/day, and nontoxicity to human skin fibroblasts. The in vitro thermosensitive cargo delivery of this hydrogel showed that 92% of DS was sustainably delivered at 37 °C within the early three days mimicking the inflammation stage, while 80% of bFGF was controlled released at 25 °C within the later eight days mimicking new tissue formation stage. The in vivo wound healing of rats showed that this composite hydrogel presented a better healing effect with a wound contraction of 96% at 14 d, less inflammation and higher angiogenesis, than all control groups. These findings indicate SA/bFGF@pNIPAM/DS@p(NIPAM-co-AA) composite hydrogel is a potential dressing for wound repair.

Poly(2-hydroxyethyl methacrylate)/ß-cyclodextrin-hyaluronan contact lens with tear protein adsorption resistance and sustained drug delivery for ophthalmic diseases.

A series of poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels containing cross-linked ß-cyclodextrin-hyaluronan (ß-CD-crHA), with tear protein adsorption resistance and sustained drug delivery, were developed as contact lens materials for eye diseases. ß-CD-HA was synthesized from aminated ß-CD and HA and then crosslinked within pHEMA hydrogel using polyethylenimine as a crosslinker. The synthesized ß-CD-HA was characterized by 1H NMR analysis, and ß-CD-crHA immobilized in pHEMA hydrogel was confirmed by FT-IR, SEM, and AFM analyses. The incorporation of ß-CD-crHA significantly improved the surface hydrophilicity, water uptake ability, oxygen permeability, and flexibility of pHEMA hydrogel, but did not compromise light transmission. pHEMA/ß-CD-crHA hydrogels not only decreased the tear protein adsorption because of the electrostatically mutual repulsion and the improved hydrophilicity, leading to the reduced adhesion of Staphylococcus aureus on the hydrogel surface, but also enhanced the encapsulation capacity and the sustainable delivery of diclofenac due to the formation of inclusion complexes between ß-CD and drugs. All the hydrogels were nontoxic to 3T3 mouse fibroblasts by in vitro cell viability analysis. Among these hydrogels with different ß-CD-crHA contents, pHEMA/ß-CD-crHA10 hydrogel showed the lowest water contact angle of 52 °, the highest water content of 65%, the largest Dk value of 36.4 barrer, and the optimal modulus of 1.8 MPa, as well as a good light transmission of over 90%. The in vivo conjunctivitis treatment of rabbits for 72 h indicated that drug-loaded pHEMA/ß-CD-crHA10 hydrogel presented a better therapeutic effect than both one dose administration of drug solution per day and drug-loaded pHEMA hydrogel. Thus, pHEMA/ß-CD-crHA10 hydrogel is a promising contact lens material for ophthalmic diseases. STATEMENT OF SIGNIFICANCE: Topical eye drops are currently the most popular treatment for ophthalmic diseases, but frequent dosing is necessary to acquire the desirable clinical effect at the expense of systemic side-effects. Drug-loaded contact lenses, as an alternative of eye drops, possess many good performances and show potential applications. However, the sustained drug delivery and the tear protein adsorption resistance are still challenging for contact lenses. Hence, we developed a novel pHEMA/ß-CD-crHA hydrogel by incorporating ß-CD-crHA crosslinked network into pHEMA hydrogel. Besides the improvements in surface hydrophilicity, water uptake ability, oxygen permeability, and flexibility, pHEMA/ß-CD-crHA hydrogel also reduced the adsorption of tear proteins and the adhesion of Staphylococcus aureus, enhanced the drug encapsulation, and prolonged the drug delivery, with better effect in the conjunctivitis treatment of rabbits. Thus, pHEMA/ß-CD-crHA hydrogel is a potential contact lens material for treating ophthalmic diseases.

Chitosan derivative-based double network hydrogels with high strength, high fracture toughness and tunable mechanics.

Physically cross-linked double-network (DN) hydrogels are capturing more and more attention due to their good mechanical properties and self-recovery ability. However, they usually suffer from complicated preparation process and fussy performance regulation, which severely limit their applications in many fields. Herein, we fabricated a physically cross-linked poly(vinyl alcohol)-(2-hydroxypropyltrimethyl ammonium chloride chitosan) (PVA-HACC) DN hydrogels without organic solvents or toxic cross-linking agents via a simple two-step method of freezing/thawing and immersion processing. The effects of immersion time and concentration of Na3Cit solution on the structures and mechanical properties of the hydrogels were investigated. The obtained hydrogels exhibited excellent mechanical properties including high elastic modulus (1.44 MPa), high strength (a maximal tensile fracture stresses of 4.14 MPa and a maximal compressive stresses of over 70 MPa at 98% strain), and superior fracture toughness (17.09 MJ/m3). In addition, good self-recovered property and anti-fatigue performance were realized for the hydrogels owing to the reversible HACC ionic networks. The preparation of PVA-HACC DN hydrogels offers a new guidance for the design and synthesis of environmentally friendly DN hydrogels with outstanding mechanical properties and broad application prospects.

Anti-biofouling and functionalizable bioinspired chitosan-based hydrogel coating via surface photo-immobilization.

Zwitterionic polymer is a new generation of anti-fouling materials with its good resistance to protein and bacterial adhesion. Constructing the anti-fouling surfaces with zwitterionic polymer has been regarded as an effective approach for improving the biocompatibility and biofunctionality of clinic devices. Herein, we reported a facile approach to construct a biodegradable anti-biofouling and functionalizable hydrogel coating via photo-immobilization using commercial polyethylene terephthalate (PET) films as the substrate, based on zwitterionic glycidyl methacrylate-phosphorylcholine-chitosan (PCCs-GMA). The surface structure and physicochemical properties of zwitterionic PCCs-GMA hydrogel coating were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM) and static water contact angle measurement, and its functionalizable sites were detected by fluorescence labeling. Compared with the pristine PET and cationic chitosan - GMA and hydroxypropyltrimethyl ammonium chloride chitosan (HTCC) - GMA hydrogel coatings, zwitterionic PCCs-GMA hydrogel coating exhibited excellent biocompatibility, and significantly reduced protein adsorption for three model proteins of fibrinogen, immunoglobulin and lysozyme, repelled platelet adhesion, as well as showed a high resistance to bacterial attachment of Escherichia coli and Staphylococcus aureus and superior anti-fouling properties to MRC-5 cells. The results indicated that photo-immobilized zwitterionic PCCs-GMA hydrogel coating has perspective as a dual functional platform with integrated antifouling and further biofunctional properties for various biomedical applications.

Superior hybrid hydrogels of polyacrylamide enhanced by bacterial cellulose nanofiber clusters.

Hybrid polyacrylamide/bacterial cellulose nanofiber clusters (PAM/BC) hydrogels with high strength, toughness and recoverability were synthesized by in situ polymerization of acrylamide monomer in BC nanofiber clusters suspension. The hybrid gels exhibited an extremely large elongation at break of 2200%, and a high fracture stress of 1.35MPa. Additionally, the original length of hydrogels could be recovered after releasing the tensile force. Compressive results showed that the PAM/BC hybrid gels could reach a strain of about 99% without break, and was able to completely recover its original shape immediately after releasing the compression force. The compressive stress at 99% reached as high as 30MPa. Nearly no hysteresis in cyclic compressive tests was observed with these hybrid gels. The FT-IR, XRD and TGA analysis showed that hydrogen bonds between the PAM chains and BC nanofiber clusters mainly contributed to the superior mechanical properties of hybrid hydrogels. The cell viability results suggested that PAM/BC hybrid hydrogel was benign for biomedical application. These PAM/BC hydrogels offer a great promise as biomaterials such as bone and cartilage repair materials.

In vitro drug release and biological evaluation of biomimetic polymeric micelles self-assembled from amphiphilic deoxycholic acid-phosphorylcholine-chitosan conjugate.

Novel biomimetic amphiphilic chitosan derivative, deoxycholic acid-phosphorylcholine-chitosan conjugate (DCA-PCCs) was synthesized based on the combination of Atherton-Todd reaction for coupling phosphorylcholine (PC) and carbodiimide coupling reaction for linking deoxycholic acid (DCA) to chitosan. The chemical structure of DCA-PCCs was characterized by (1)H and (31)P nuclear magnetic resonance (NMR). The self-assembly of DCA-PCCs in water was analyzed by fluorescence measurements, dynamic laser light-scattering (DLS), zeta potential and transmission electron microscopy (TEM) technologies. The results confirmed that the amphiphilic DCA-PCCs can self-assemble to form nanosized spherical micelles with biomimetic PC shell. In vitro biological evaluation revealed that DCA-PCCs micelles had low toxicity against NIH/3T3 mouse embryonic fibroblasts as well as good hemocompatibility. Using quercetin as a hydrophobic model drug, drug loading and release study suggested that biomimetic DCA-PCCs micelles could be used as a promising nanocarrier avoiding unfavorable biological response for hydrophobic drug delivery applications.

Structure, morphology and cell affinity of poly(L-lactide) films surface-functionalized with chitosan nanofibers via a solid-liquid phase separation technique.

Poly(L-lactide) films with a nano-structured surface by immobilizing chitosan nanofibers (CSNFs) for improving the cell affinity were fabricated via a solid-liquid phase separation technique. The successful grafting of CSNFs on the surface of poly(L-lactide) films was confirmed by the binding energy of N1s at 398.0 eV in the X-ray photoelectron spectroscopy and the amide I and II bands of chitosan at 1650 and 1568 cm(-1) in the Fourier transform infrared spectroscopy. Compared with the poly(L-lactide) film, the hydrophilicity was improved with a lower water contact angle of 83.3±1.9° and 75.3±2.5° for the CSNFs-grafted and CSNFs-grafted/anchored poly(L-lactide) films respectively. The scanning electron microscopy and atomic force microscopy analyses showed that the grafted CSNFs with 50-500 nm in diameter were randomly arranged on the film surface and entangled with the anchored CSNFs on the outermost layer. The 3T3 fibroblasts culture indicated cells tended to attach and stretch along the CSNFs on the film surface. The cell viability measurement revealed that among all the samples, the film with both grafted and anchored CSNFs exhibited the highest cell proliferation rate that was twice as much of the poly(L-lactide) film at 7 d. Herein, engineering a nano-structured surface by solid-liquid phase separation will be a promising tool for surface modification of biomaterials.

Preparation, characterization and cytocompatibility of polyurethane/cellulose based liquid crystal composite membranes.

Two types of polyurethane/liquid crystal (PU/LC) composite membranes with different LC contents, namely polyurethane/octyl hydroxypropyl cellulose ester (PU/OPC) and polyurethane/propyl hydroxypropyl cellulose ester (PU/PPC), were prepared and studied. The effects of surface properties on cell compatibility of the membranes were elucidated. PPC tended to assemble to independent phases in the composite membranes, while OPC formed uniformly distributed LC domains. As the introduction of LC, phase separation occurred, and the crystallization of PU was disrupted. The surface of PU/LC composite membranes showed fingerprint texture and two-phase morphology. Hydrophilicity of the two types of composite membranes exhibited a reversal tendency with the increase of LC contents. Cells seeded on the composite membranes presented favorable growth when the content of LC was over 30%, especially on PU/OPC complex. The surface morphology, phase separation between LC and PU as well as the type of LC showed significant effects on the cell behaviors.

Preparation and properties of biomimetic porous nanofibrous poly(L-lactide) scaffold with chitosan nanofiber network by a dual thermally induced phase separation technique.

A biomimetic nanofibrous poly(L-lactide) scaffold decorated by chitosan nanofiber network inside the macropores was fabricated using a dual thermally induced phase separation technique. The first phase separation was used to build a nanofibrous poly(L-lactide) scaffold with interconnected macropores, where chitosan nanofibers about 500nm in diameter were incorporated via the second phase separation. The content of nanofibrous chitosan was determined to be 5.76 in weight percentage by elemental analysis. The composite scaffold showed the highest protein adsorption of 7225±116 µg/cm(3) and the most hydroxyapatite crystal deposition in the mineralization. Compared with non-nanofibrous poly(L-lactide) scaffold, nanofibrous poly(L-lactide) scaffold exhibited a much faster degradation, but it could be restrained by the introduced chitosan nanofibers. The bone mesenchymal stem cell culture results indicated that the cells would rather attach and stretch along the chitosan nanofibers in the composite scaffold that showed the highest viability and the best cytocompatibility may be attributed to the biomimetic nanofibrous network and good cell affinity of chitosan nanofibers.

Improving the cell affinity of a poly(D,L-lactide) film modified by grafting collagen via a plasma technique.

Poly(D,L-lactide) films were surface-modified by grafting collagen via NH(3) plasma to improve cell affinity. The modified films were characterized by IR analysis, contact angle measurement, SEM analysis and collagen quantity determination. It was demonstrated that -NH(2) and collagen were incorporated into the surface of PDLLA films. The hydrophilicity of the PDLLA film increased after NH(3) plasma treatment, but decreased with further collagen modification. More collagen was incorporated into the PDLLA films by a grating method as compared to that with an anchorage treatment. L929 fibroblast cells were used to evaluate the cell affinity of the modified films and control. It was shown that PDLLA films surface-modified by grafting collagen via NH(3) plasma more efficiently enhanced the cells attachment and proliferation than those films modified by collagen anchorage or only NH(3) plasma treatment.