Hongping Zhang

Silver Nanoparticles and Growth Factors Incorporated Hydroxyapatite Coatings on Metallic Implant Surfaces for Enhancement of Osteoinductivity and Antibacterial Properties

Research on incorporation of both growth factors and silver (Ag) into hydroxyapatite (HA) coatings on metallic implant surfaces for enhancing osteoinductivity and antibacterial properties is a challenging work. Generally, Ag nanoparticles are easy to agglomerate and lead to a large increase in local Ag concentration, which could potentially affect cell activity. On the other hand, growth factors immobilization requires mild processing conditions so as to maintain their activities. In this study, bone morphology protein-2 (BMP-2) and Ag nanoparticle contained HA coatings were prepared on Ti surfaces by combining electrochemical deposition (ED) of Ag and electrostatic immobilization of BMP-2. During the ED process, chitosan (CS) was selected as the stabilizing agent to chelate Ag ions and generate Ag nanoparticles that are uniformly distributed in the coatings. CS also reduces Ag toxicity while retaining its antibacterial activity. Afterwards, a BMP/heparin solution was absorbed on the CS/Ag/HA coatings. Consequently, BMP-2 was immobilized on the coatings by the electrostatic attraction between CS, heparin, and BMP-2. Sustained release of BMP-2 and Ag ions from HA coatings was successfully demonstrated for a long period. Results of antibacterial tests indicate that the CS/Ag/HA coatings have high antibacterial properties against both Staphylococcus epidermidis and Escherichia coli. Osteoblasts (OB) culture reveals that the CS/Ag/HA coatings exhibit good biocompatibility. Bone marrow stromal cells (BMSCs) culture indicates that the BMP/CS/Ag/HA coatings have good osteoinductivity and promote the differentiation of BMSCs. Ti bars with BMP/CS/Ag/HA coatings were implanted into the femur of rabbits to evaluate the osteoinductivity of the coatings. Results indicate that BMP/CS/Ag/HA coatings favor bone formation in vivo. In summary, this study presents a convenient and effective method for the incorporation of growth factors and antibacterial agents into HA coatings. This method can be utilized to modify a variety of metallic implant surfaces.

Mussel-Inspired Adhesive and Tough Hydrogel Based on Nanoclay Confined Dopamine Polymerization

Adhesive hydrogels are attractive biomaterials for various applications, such as electronic skin, wound dressing, and wearable devices. However, fabricating a hydrogel with both adequate adhesiveness and excellent mechanical properties remains a challenge. Inspired by the adhesion mechanism of mussels, we used a two-step process to develop an adhesive and tough polydopamine-clay-polyacrylamide (PDA-clay-PAM) hydrogel. Dopamine was intercalated into clay nanosheets and limitedly oxidized between the layers, resulting in PDA-intercalated clay nanosheets containing free catechol groups. Acrylamide monomers were then added and in situ polymerized to form the hydrogel. Unlike previous single-use adhesive hydrogels, our hydrogel showed repeatable and durable adhesiveness. It adhered directly on human skin without causing an inflammatory response and was easily removed without causing damage. The adhesiveness of this hydrogel was attributed to the presence of enough free catechol groups in the hydrogel, which were created by controlling the oxidation process of the PDA in the confined nanolayers of clay. This mimicked the adhesion mechanism of the mussels, which maintain a high concentration of catechol groups in the confined nanospace of their byssal plaque. The hydrogel also displayed superior toughness, which resulted from nanoreinforcement by clay and PDA-induced cooperative interactions with the hydrogel networks. Moreover, the hydrogel favored cell attachment and proliferation, owning to the high cell affinity of PDA. Rat full-thickness skin defect experiments demonstrated that the hydrogel was an excellent dressing. This free-standing, adhesive, tough, and biocompatible hydrogel may be more convenient for surgical applications than adhesives that involve in situ gelation and extra agents.

Biomimetic Mineralized Hierarchical Graphene Oxide/Chitosan Scaffolds with Adsorbability for Immobilization of Nanoparticles for Biomedical Applications

Biomimetic calcium phosphate mineralized graphene oxide/chitosan (GO/CS) scaffolds with hierarchical structures were developed. First, GO/CS scaffolds with large micropores (∼300 μm) showed high mechanical strength due to the electrostatic interaction between the oxygen-containing functional groups of GO and the amine groups of CS. Second, octacalcuim phosphate (OCP) with porous structures (∼1 μm) was biomimetically mineralized on the surfaces of the GO/CS scaffolds (OCP-GO/CS). The hierarchical microporous structures of OCP-GO/CS scaffolds provide a suitable environment for cell adhesion and growth. The scaffolds have exceptional adsorbability of nanoparticles. Bone morphogenetic protein-2 (BMP-2)-encapsulated bovine serum albumin (BSA) nanoparticles and Ag nanoparticles (Ag-NPs) were adsorbed in the scaffolds for enhancement of osteoinductivity and antibacterial properties, respectively. Antibacterial tests showed that the scaffolds exhibited high antibacterial properties against both Escherichia coli and Staphylococcus epidermidis. In vitro and in vivo experiments revealed that the scaffolds have good biocompatibility, enhanced bone marrow stromal cells proliferation and differentiation, and induced bone tissue regeneration. Thus, the biomimetic OCP-GO/CS scaffolds with immobilized growth factors and antibacterial agents might be excellent candidates for bone tissue engineering.

Computer simulation of biomolecule–biomaterial interactions at surfaces and interfaces

Biomaterial surfaces and interfaces are intrinsically complicated systems because they involve biomolecules, implanted biomaterials, and complex biological environments. It is difficult to understand the interaction mechanism between biomaterials and biomolecules through conventional experimental methods. Computer simulation is an effective way to study the interaction mechanism at the atomic and molecular levels. In this review, we summarized the recent studies on the interaction behaviors of biomolecules with three types of the most widely used biomaterials: hydroxyapatite (HA), titanium oxide (TiO2), and graphene(G)/graphene oxide(GO). The effects of crystal forms, crystallographic planes, surface defects, doping atoms, and water environments on biomolecules adsorption are discussed in detail. This review provides valuable theoretical guidance for biomaterial designing and surface modification.

Polydopamine Nanoparticles Modulating Stimuli-Responsive PNIPAM Hydrogels with Cell/Tissue Adhesiveness

Stimuli-responsive hydrogels can respond to stimuli by phase transformation or volume change and exhibit specific functions. Near-infrared (NIR)-responsive hydrogel is a type of stimuli-responsive hydrogel, which can be precisely controlled by altering the radiation intensity, exposure time of the light source, and irradiation sites. Here, polydopamine nanoparticles (PDA-NPs) were introduced into a poly(N-isopropylacrylamide) (PNIPAM) network to fabricate a PDA-NPs/PNIPAM hydrogel with NIR responsibility, self-healing ability, and cell/tissue adhesiveness. After incorporation of PDA-NPs into the hydrogel, the PDA-NPs/PNIPAM hydrogel showed phase transitions and volume changes in response to NIR. Thus, the hydrogel can achieve triple response effects, including pulsatile drug release, NIR-driven actuation, and NIR-assisted healing. After coating PDA-NPs onto hydrogel surfaces, the hydrogel showed improved cell affinity, good tissue adhesiveness, and growth factor/protein immobilization ability because of reactive catechol groups on PDA-NPs. The tissue adhesion strength to porcine skin was as high as 90 KPa. In vivo full-skin defect experiments demonstrated that PDA-NPs coating on the hydrogel and an immobilized growth factor had a synergistic effect on accelerating wound healing. In summary, we combined thermosensitive PNIPAM and mussel-inspired PDA-NPs to form a NIR-responsive hydrogel, which may have potential applications for chemical and physical therapies.

Biohybrid methacrylated gelatin/polyacrylamide hydrogels for cartilage repair

Articular cartilage defect repair is challenging for clinics because of the lack of self-regenerative ability of avascular tissue. Gelatin-based hydrogels are widely used in the field of tissue engineering because of their good biodegradability, excellent biocompatibility, and cell/tissue affinity. However, gelatin-based hydrogels exhibit poor thermal stability and low mechanical strength, which limit their application in cartilage repair. In this study, methacrylic anhydride (MA) was employed to modify gelatin to obtain photo-crosslinkable methacrylated gelatin (GelMA). The GelMA-based natural-synthetic polymer biohybrid hydrogel was prepared by co-polymerizing acrylamide (AM) and GelMA under ultraviolet radiation in the presence of a photo-initiator. The GelMA/PAM biohybrid hydrogel simultaneously possessed the advantages of both PAM hydrogels and GelMA hydrogels. The GelMA block provided specific biological functions for cell adhesion and proliferation, while the flexible PAM chains reinforced the brittle gelatin network and sustained the load during deformation. Compared with pure PAM hydrogel and GelMA, the GelMA/PAM biohybrid hydrogels showed enhanced compression strength (0.38 MPa) and improved elasticity (storage modulus of 1000 Pa). The GelMA/PAM biohybrid hydrogel showed a favorable degradation rate and sustained protein release. In vitro cell culture showed that the chondrocytes remained viable and proliferated on the biohybrid hydrogel, demonstrating that the biohybrid hydrogels had good cell adhesion and excellent biocompatibility. In a rabbit knee cartilage defect model, we evaluated the cartilage repair ability of the biohybrid hydrogel in vivo. In summary, this study demonstrated that hybridization of synthetic polymers considerably improves the performance and expands the application of the gelatin-based hydrogels. The biohybrid hydrogel is a good candidate material to be applied in articular cartilage tissue engineering and may have great potential in various soft tissue engineering applications.

Carboxylmethyl konjac glucomannan conjugated polydopamine composites for Pb(II) removal

Carboxylmethyl konjac glucomannan conjugated polydopamine (CMKGM-PDA) composite was successfully prepared using a cost-effective method. CMKGM-PDA exhibited excellent adsorption performance for the removal of Pb(II) and could be a convenient agent for recovery. The Langmuir linear model was suitable for describing the adsorption process of Pb(II). The maximum adsorption capacity was 95.24mgg-1 at 298K, showing a high absorption capacity in comparison to similar absorbents. The pseudo-second order equation and intra-particle diffusion model exhibited good correlation with the adsorption kinetic. The thermodynamic values (ΔH0 > 0, ΔS0 > 0, ΔG0 < 0) indicated that the adsorption process of Pb(II) was endothermic, feasible, and spontaneous in nature. The chelation and electrostatic attraction between Pb(II) and -OH (or -NH2) groups on the CMKGM-PDA formed a possible adsorption mechanism.

Adsorption of 2,3,7,8-tetrochlorodibenzo-p-dioxins on intrinsic, defected, and Ti (N, Ag) doped graphene: a DFT study

As one of the most hazardous substances in the world, dioxins have received continuous interest in chemistry, materials, and environmental sciences. The rapid detection and capture of carcinogenic 2,3,7,8-tetrochlorodibenzo-p-dioxin (TCDD) are particularly challenging in the fields of materials and environmental sciences. In this study, density functional theory (DFT) method was applied to systematically investigate the interactions between TCDD and different types of graphene samples. The results reveal that the initial configuration of TCDD affects the interactions to a certain extent. As TCDD molecule is parallel to the graphene sheets, the interactions are the largest for all three types of graphene samples (intrinsic, defected and doped). In addition, the “TCDD” capture ability of graphene can be greatly improved by Ti doping. Our study facilitates the rational design of efficient sensors for a variety of applications in environmental science and engineering.

Band structure of graphene modulated by Ti or N dopants and applications in gas sensoring

The exploration of novel sensors for NO2 detection is particularly important in material and environmental sciences. In this work, the HOMO-LUMO gap of graphene, Ti- or N-doped graphene is investigated by DFT methods. The adsorption of NO2, NO, and O2 on Ti- or N-doped graphene of different sizes is also explored. Results reveal that the interactions between gases (NO2, NO, and O2) and Ti- or N-doped graphenes is not affected by the size of graphene. The doped Ti greatly improves the interactions between gases and graphene whereas the doped N has no effect on those interactions. The HOMO- LUMO gap of Ti-doped graphene can be modulated by adsorption of the gases. The cross effect of the NO and O2 is also investigated, and it is demonstrated that Ti-doped graphene has specific interactions with NO2. Thus, Ti-doped graphene can be a candidate for NO2 sensor materials. Furthermore, doping the graphene with Ti or N improves the sensitivity of the sheets toward NO2, which can be trapped and detected by the intrinsic graphene. Efficient sensors are rationally designed to diversify their applications in environmental science and engineering.

Electrospun Cu2ZnSnS4 microfibers with strong (112) preferred orientation: fabrication and characterization

In this study, Cu2ZnSnS4 (CZTS) microfibers were fabricated using a non-vacuum method of electrospinning following vulcanization process. CZTS fibers were obtained via the vulcanization of the electrospun precursor fibers at 500 °C (CZTS-500), 550 °C (CZTS-550), and 600 °C (CZTS-600), in sulfur ambient conditions. Samples were characterized by scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), XRD mapping scan, Raman spectrum and UV-vis absorption. Polycrystalline CZTS fibers with kesterite crystallization were formed in CZTS-500, whereas higher temperature vulcanization in CZTS-550 led to a strong preferential crystallization along CZTS [112] crystal direction around fiber surface, which is definitely confirmed by XRD mapping scan. More interestingly, the band gap value (Eg), which was 1.48 eV for CZTS-500, reduced to 1.43 eV for CZTS-550. Eg reduction may be related to lattice distortion induced by stress or strain around fiber surface, and can be beneficial for broadening optical absorption range thus increasing the efficiency of CZTS-based solar cells.