Quantitative analysis and degradation mechanisms of different protein degradation methods.

The abrasive debris produced by wear test of artificial joints in vitro is encapsulated by proteins in serum lubricants, which hinder the characterization of debris analysis. One of the key issues of isolating wear debris from serum is degrading the proteins wrapping the wear debris. In this article, the proteins in calf serum were degraded by a strong alkali, a strong acid, and an enzyme. The residual concentration of proteins in calf serum was detected by UV absorption. Quantitative analysis of protein degradation and the protein degradation rate was proposed, following treatment with different degradation reagents and different incubation times. The results showed that when 10 mL of 25% volume calf serum was added with 40 mL of NaOH and incubated at 65°C for 24 h, the protein degradation rate reached a maximum of 95.52%. The protein degradation rate in the solution ranged from 31.86% to 71.64% when a different volume of 37% HCl was added and incubated at 60°C. The highest protein degradation rate was 94.98% in the protease degradation solution. When the protein degradation rate is less than 70%, the particles were coated by protein. When the protein degradation rate was more than 95%, there was no protein coating around the particles. The three protein degradation methods have different processes and protein degradation rates. A suitable method for protein degradation can be selected according to these practical applications.

The antibacterial and wear-resistant nano-ZnO/PEEK composites were constructed by a simple two-step method.

Although the polyether ether ketone (PEEK) has excellent comprehensive properties, its non-antibacterial and low wear-resistant limit the wide application in the field of artificial joint materials. In this paper, Nano-ZnO was generated in situ on the surface of PEEK powder by one-step hydrothermal method, which improved the binding force of Nano-ZnO and PEEK matrix. Then the PEEK-based nanocomposites were prepared by melt blending with the synthesized Nano-ZnO-PEEK powders and PEEK powders. The microstructure, mechanical, biological and tribological properties of PEEK-based nanocomposites were studied. The results showed that the compressive strength of PEEK-based nanocomposites can reach up to 319.2 ± 2.4 MPa. Both PEEK and PEEK-based nanocomposites were non-toxic to cells. Meanwhile, PEEK-based nanocomposites showed good antibacterial activity against E.coli and Staphylococcus aureus, and the antibacterial activity was better with the increase of Nano-ZnO content. In addition, when the Nano-ZnO content was 5%, the wear rate of PEEK-based nanocomposites was about 68% lower than that of pure PEEK materials. Thus, PEEK-based nanocomposites has a dual function of good antibacterial property and excellent wear resistance.

Fretting stimulation enhances bone growth at the interface between hydroxyapatite coating and bone.

Biologically fixed arthroplasty is limited in its development by the long postoperative recovery time and the low quality of solidity of the fixed interface in the short postoperative period. Therefore, fretting stimulation is used to accelerate the combination between bone tissue and the biological fixation interface of artificial joint prostheses. The effects of different compression loads and tangential micro-motion amplitude on the growth rate of bone tissue and the firm quality of fixation interface were studied by using two kinds of micro-motion stimuli: compression and tangential micro-motion. The mechanism of micro-motion stimulation to promote bone growth at the fixation interface was revealed. The results of binding force detection of biological fixation interface and bone tissue section staining showed that the bone tissue and hydroxyapatite coating interface had the most tendency to produce new bone tissue under compression load of 4 N. In the tangential fretting environment, the tangential fretting amplitude of ± 40 µm and the normal load of 7.5 N were the most conducive to bone growth, making the combination of bone tissue and titanium alloy prosthesis coated with hydroxyapatite more firm. The study is important for accelerating the integration and shortening the rehabilitation time after artificial joint replacement.

3D printed chitosan-gelatine hydrogel coating on titanium alloy surface as biological fixation interface of artificial joint prosthesis.

To improve the fixation of the prosthesis-bone interface and to prevent postoperative infection, a novel antimicrobial hydrogel coating is designed as the biological fixation interface of the artificial joint prosthesis. Antimicrobial chitosan (CS) and gelatine (GT) were used as bioinks to print a CS-GT hydrogel coating with reticulated porous structure on the titanium alloy substrate by 3D printing technology. The experimental results show that the 7CS-10GT hydrogel coating has a macro-grid structure and honeycomb micro-network structure, excellent hydrophilicity (35.64°), high mechanical strength (elastic modulus 0.92 MPa) and high bonding strength (3.36 MPa) with the titanium alloy substrate. In addition, the antimicrobial effect of 7CS-10GT hydrogel against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) is enhanced after immersion in nano­silver. Moreover, the 7CS-10GT hydrogel displays good cell compatibility and supports proliferation of NIH-3 T3 cells. In summary, the 3D printed CS-GT antimicrobial hydrogel coating provides an ideal microenvironment for cell adhesion and bone growth due to the dual-scale porous network structure, good hydrophilicity and biocompatibility, thus promoting rapid fixation of the bone interface. This technology opens a new possibility for this biological fixation interface in artificial joint replacement.

[Biological activity evaluation of porous HA ceramics using NH4 HCO3/PVA as pore-creating agents].

Porous HA ceramics were prepared by using NH4 HCO3/PVA as pore-formed material along with biological glass as intensifier, and these ceramics were immersed in Locke's Physiological Saline and Simulate Body Fluid (SBF). The changes of phase composition, grain size and crystallinity of porous HA ceramics before and after immersion were investigated by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The biological activity was evaluated. The porous HA ceramics showed various degrees of decomposition after immersion in the two solution systems, but there was no evident change in respect to crystallinity. Besides, the impact of different degrees of solution systems on the change of grain size and planar preferred orientation was observed. The TCP phase of the ceramics immersed in Locke's Physiological Saline decomposed and there was no crystal growth on the surface of ceramics; however, the grain size of ceramics immersed in SBF became refined in certain degree and the surface of ceramics took on the new crystal growth.

In situ reduction of silver nanoparticles by sodium alginate to obtain silver-loaded composite wound dressing with enhanced mechanical and antimicrobial property.

Wound dressings provide barrier protection during wound treatment while providing an environment suitable for wound healing. However, traditional wound dressings have disadvantages, such as easily adhering to wounds, poor barrier effects, and poor haemostasis. Therefore, it is of great significance to design a new wound dressing that does not cause further injury, has good antibacterial effect and promotes wound healing in view of the disadvantages of traditional wound dressings. In this paper, silver nanoparticles (AgNPs) were reduced by in situ reduction with sodium alginate (SA), and construct a silver-loaded PVA/SA/CMCS hydrogel antibacterial wound dressing. The properties of antibacterial hydrogel were evaluated. The results show that SA can successfully reduce AgNPs, and the particle size is small and uniform, which meets the requirements of antibacterial material. The AgNPs are evenly distributed inside the hydrogel and have stable performance. The silver-loaded hydrogel was formed uniform pores inside the material, and had excellent water absorption and water retention, which can absorb a large amount of wound exudate while maintaining a moist wound environment. The antibacterial hydrogel exhibited good mechanical properties, antibacterial activity and biocompatibility. In summary, the silver-loaded hydrogel is an ideal wound dressing.

[The appraisal of mechanical properties and friction coefficient of PVA hydro-gel].

Gelatin and hydroxyapatite were introduced to polyvinyl alcohol (PVA) hydrogel with an attempt to enhance the performances of PVA hydrogel. Through a reiterative freezing-thawing methods, three kinds of PVA composite hydrogels were prepared. The mechanical performances of these composite hydrogels with the same PVA and HA content but varying gelatin content, such as tensile strength, elasticity modulus, creep curve, relaxation curve and friction coefficient were evaluated by using a computer-controlled universal electronic mechanical testing machine and a UMT-II frictional testing machine. The additional effects of hydroxylapatite and varying gelatin on the performances of composite PVA hydro-gels were analyzed. It was found that the gelatin content directly influenced the physical performances of PVA composite hydrogels; but no linear relationship was recorded. PVA composite hydrogel containing 2wt-% gelatin gave optimal results, i.e. tensile strength of 5.5MPa, compressive elastical modulus of 1.48MPa, creeping rate of 31% in 45 minutes, stress relaxing rate of 40.3%, and the starting friction coefficient of 0.332.

Torsional friction behavior of the contact interface between the materials of an artificial knee joint replacement.

The torsional friction behavior of the materials (CoCrMo alloy and ultra-high-molecular-weight polyethylene (UHMWPE)) that are used in artificial knee joint replacement (AKJR) were investigated under dynamic loading. The torsional friction torque, wear loss and scars and stress distribution were analyzed and compared. The results show the following: (1) the friction torque declines rapidly at the beginning of the experiments, and meanwhile, the maximum normal load and the torsional angle amplitude show very little effect on the steady value; (2) the wear loss decreases with the increased torsional angle amplitude but increases with the increased maximum normal load; additionally, as the cycle times increase, the wear rate decreases, and the wear is minimal; (3) unloading and secondary loading significantly reduce the friction and wear of the materials, and thus, patients should rest after prolonged exercise to reduce wear; (4) the margins of UHMWPE and CoCrMo are worn, and the wear mechanism is abrasive wear; (5) around the center of the UHMWPE, the surface is peeled off, and the wear mechanism is fatigue wear; and (6) in terms of the compressive stress and shear stress, the calculated results from a finite element model match the experimental results well.

Preparation and property of high strength and low friction PVA-HA/PAA composite hydrogel using annealing treatment.

PVA hydrogels have desirable characteristics for use as soft tissue substitutes. However, PVA hydrogels are not high strength enough to withstand the demanding in load-bearing environment of human. In this paper, a high strength and low friction PVA-HA/PAA composite hydrogel is obtained by freezing-thawing and annealing method. The microstructure, thermal stability, mechanical and biotribological properties of the hydrogel are studied. Annealing PVA-HA/PAA composite hydrogel has porous structure, interaction occurred between PVA, HA and PAA. HA particles are distributed in PVA matrix and played a role of diffuse strengthening and toughening. Annealing improves the crystallinity and crosslinking of the hydrogel, annealing PVA-HA/PAA composite hydrogel has good thermal stability, strength and mechanical properties. The tensile strength of annealing PVA-HA/PAA composite hydrogel can be up to 3.71 MPa. Annealing PVA-HA/PAA composite hydrogel has favorable lubricating properties, and the friction coefficient is very low.

Preparation, optimization and property of PVA-HA/PAA composite hydrogel.

PVA-HA/PAA composite hydrogel is prepared by freezing-thawing, PEG dehydration and annealing method. Orthogonal design method is used to choose the optimization combination. Results showed that HA and PVA have the maximum effect on water content. PVA and freezing-thawing cycles have the maximum effect on creep resistance and stress relaxation rate of hydrogel. Annealing temperature and freezing-thawing cycles have the maximum effect on compressive elastic modulus of hydrogel. Comparing with the water content and mechanical properties of 16 kinds of combination, PVA-HA/PAA composite hydrogel with freezing-thawing cycles of 3, annealing temperature of 120°C, PVA of 16%, HA of 2%, PAA of 4% has the optimization comprehensive properties. PVA-HA/PAA composite hydrogel has a porous network structure. There are some interactions between PVA, HA and PAA in hydrogel and the properties of hydrogel are strengthened. The annealing treatment improves the crystalline and crosslinking of hydrogel. Therefore, the annealing PVA-HA/PAA composite hydrogel has good thermostability, strength and mechanical properties. It also has good lubrication property and its friction coefficient is relative low.

Research on torsional friction behavior and fluid load support of PVA/HA composite hydrogel.

Hydrogels have been extensively studied for use as synthetic articular cartilage. This study aimed to investigate (1) the torsional friction contact state and the transformation mechanism of PVA/HA composite hydrogel against CoCrMo femoral head and (2) effects of load and torsional angle on torsional friction behavior. The finite element method was used to study fluid load support of PVA/HA composite hydrogel. Results show fluid loss increases gradually of PVA/HA composite hydrogel with torsional friction time, leading to fluid load support decreases. The contact state changes from full slip state to stick-slip mixed state. As the load increases, friction coefficient and adhesion zone increase gradually. As the torsional angle increases, friction coefficient and slip trend of the contact interface increase, resulting in the increase of the slip zone and the reduction of the adhesion zone. Fluid loss increases of PVA/HA composite hydrogel as the load and the torsional angle increase, which causes the decrease of fluid load support and the increase of friction coefficient.

[Construction and eukaryotic expression of recombinant plasmid encoding fusion protein of goat complement C3d and foot-and-mouth disease virus VP1].

We constructed a recombinant plasmid encoding VP1 gene of O type foot-and-mouth disease virus fused to a molecular adjuvant, goat complement C3d gene. The goat C3d gene was cloned and three copies were tandem-linked with the linker (G4S)2 sequence. VP1 gene of O type foot-and-mouth disease virus was linked to three tandem repeats of C3d through the linker sequence and cloned into pUC19 to obtain the recombinant plasmid pUC19-VP1-C3d3. The VP1-C3d3 fusion gene was then subcloned into the eukaryotic vector pcDNA3.1(+) that had been modified to contain the tissue plasminogen activator (tPA) leader sequence to obtain pcDNA3.1-tPA-VP1-C3d3. HeLa cells were transfected with pcDNA3.1-tPA-VP1-C3d3 by Lipofectamine 2000. Indirect immunofluorescent assay and Western blot assay showed that VP1-C3d3 fusion gene was successfully expressed in HeLa cells. The fusion protein with the expected size 133 kD could be secreted outside the cells. This study laid a good foundation to further research on the novel vaccine against foot-and-mouth disease virus by using goat C3d as a molecular adjuvant to enhance the immunogenicity of VP1.