Zhipeng Gu

In vitro study on the degradation of lithium-doped hydroxyapatite for bone tissue engineering scaffold

Li-doped hydroxyapatite (LiHA) which is prepared through introducing low dose of Li into hydroxyapatite (HA) has been increasingly studied as a bone tissue-engineered scaffold. The degradation properties play a crucial role in the success of long-term implantation of a bone tissue-engineered construct. Herein, the in vitro degradation behaviors of LiHA scaffolds via two approaches were investigated in this study: solution-mediated degradation and osteoblast-mediated degradation. In solution-mediated degradation, after being immersed in simulated body fluid (SBF) for some time, some characteristics of these scaffolds (such as release of ionized lithium and phosphate, pH change, mechanical properties, cytocompatibility and SEM surface characterization) were systematically tested. A similar procedure was also employed to research the degradation behaviors of LiHA scaffolds in osteoblast-mediated degradation. The results suggested that the degradation in SBF and degradation in culture medium with cell existed distinguishing mechanisms. LiHA scaffolds were degraded via a hydrolytic mechanism when they were soaked in SBF. Upon degradation, an apatite precipitation (layer) was formed on the surfaces of scaffolds. While a biological mechanism was presented for the degradation of scaffolds in cell-mediated degradation. Compared with pure HA, LiHA scaffolds had a better effect on the growth of osteoblast cells, meanwhile, the release amount of PO4(3-) in a degradation medium indicated that osteoblasts could accelerate the degradation of LiHA due to the more physiological activities of osteoblast. According to the results from compressive strength test, doping Li into HA could enhance the strength of HA. Moreover, the results from MTT assay and SEM observation showed that the degradation products of LiHA scaffolds were beneficial to the proliferation of osteoblasts. The results of this research can provide the theoretical basis for the clinical application of LiHA scaffolds.

Polymeric nanoparticles for colon cancer therapy: overview and perspectives

Colorectal cancer (CRC) is the third-most common malignant tumour and is associated with high morbidity and mortality worldwide. This review summarizes the recent progress in the development of polymeric nanoparticle systems for colon cancer therapy.

Effects of strontium-doped calcium polyphosphate on angiogenic growth factors expression of co-culturing system in vitro and of host cell in vivo

Efforts to induce angiogenesis have been dedicated to developing novel strategies to fabricate an ideal scaffold for bone tissue engineering. In order to mimic the environment of the repair process in vivo, this study was performed to investigate the effect of strontium-doped calcium polyphosphate (SCPP) on angiogenesis-related behaviors of umbilical vein endothelial cells and osteoblasts co-cultured in vitro. The results indicate that, compared with those in calcium polyphosphate (CPP) and hydroxyapatite (HA) group, cells attached and spread better with a significantly improved cell proliferation in SCPP group. More importantly, in vitro co-culture demonstrated a significant improvement in the VEGF and bFGF expression levels in SCPP groups. The results also demonstrated that SCPP could effectively enhance VEGF and bFGF expression from host cell in vivo and thereby inducing angiogenesis in implanted scaffolds. SCPP could be used as a potential material with stimulating angiogenesis, which would provide a novel thought for resolving the problem of angiogenesis in bone tissue engineering.

Feasibility study of the naturally occurring dialdehyde carboxymethyl cellulose for biological tissue fixation.

The aim of this study was to evaluate the crosslinking effect of dialdehyde carboxymethyl cellulose (DCMC) on decellularized porcine aortas. Before implanted, biological tissues must be chemically modified to avoid rapid enzymatic degradation and serious immune response. To overcome limitations like high cytotoxicity and susceptibility to calcification caused by glutaraldehyde (GA), a traditional crosslinking reagent, dialdehyde carboxymethyl cellulose (DCMC) was employed to fix biological tissues. The crosslinking characteristics and cytotoxicity of aortas fixed by DCMC were all investigated. The results indicated that DCMC-fixation significantly increased the mechanical strength and the capacity of enzymatic hydrolytic resistance of tissues. The histological examination showed that the microcosmic structures of tissues were all preserved well after DCMC fixation. In addition, the data obtained from MTT assay confirmed that the cytotoxicity of DCMC-fixed tissues was significantly lower than glutaraldehyde-fixed counterparts. In a word, the present study demonstrated DCMC might be an effective crosslinking reagent for biological tissue fixation with low cytotoxicity.

The inhibitory effect of strontium-doped calcium polyphosphate particles on cytokines from macrophages and osteoblasts leading to aseptic loosening in vitro

Aseptic loosening is a common cause of joint implant failure in humans. In order to enhance implant stability, we need to develop a new material that not only promotes the wear resistance of components of an artificial joint, but also possesses the pharmaceutical efficacy of protecting patients against aseptic loosening. Strontium-doped calcium polyphosphate (SCPP) has been found to have this potential ability. The goal of this study is to respectively quantify the levels of TNF-α (for macrophages), receptor activator of NF-kB ligand (RANKL) and osteoprotegerin (OPG) (for osteoblasts) when osteoblasts and macrophages are challenged with various particles (including SCPP). In this study, the osteoblasts ROS 17/2.8 and macrophages RAW 264.7 were challenged with various wear particles (8% SCPP, the molar percentage of Sr in SCPP is 8%, UHMWPE, hydroxyapatite (HA) and CPP). The secretion of TNF-α (from RAW 264.7), OPG and RANKL protein (from ROS 17/2.8) was analyzed by ELISA. The OPG and RANKL mRNA from ROS 17/2.8 was detected by RT-PCR. The data of ELISA indicated that the amount of TNF-α challenged with 8% SCPP particles was more than three-fold lower than that of all other test groups. The ratio of OPG/RANKL in the 8% SCPP group was significantly increased compared to that of all other test groups. The results of OPG and RANKL mRNA expression showed the same tendency as the ELISA results. In general, this study showed that 8% SCPP particles can inhibit the expression of TNF-α and RANKL, promote the expression of OPG so that SCPP can inhibit bone resorption and promote bone formation, and then inhibit aseptic loosening. Thus SCPP could be a promising material for the construction of artificial joints.

pH-sensitive ternary nanoparticles for nonviral gene delivery

PEGylation, which is reversed after the therapeutic agent reaches the target cell, presents attractive features for drug, protein or gene delivery. Herein, a tumor acidity-responsive PEGylated anionic polymer was synthesized for bioreversible surface shielding of DNA complexes. The pH-sensitive and non-pH-sensitive ternary nanoparticles were respectively fabricated by introducing tumor acidity-responsive PEGylated anionic polymer and its corresponding pH stable analog to the surface of positively charged PEI25K/DNA complexes via electrostatic interaction. We show clear evidence that introducing the PEGylated anionic polymer to the surface of a nanoparticle markedly reduces its nonspecific interactions with protein. We further demonstrate that the pH-sensitive ternary nanoparticle versus non-pH-sensitive analog is capable of reversing its surface charge from neutral to positive at the slightly acidic tumor extracellular microenvironment to facilitate the delivery of DNA. Such delivery system with the ability to deshield the PEG layer at the target tissues has remarkable potential in gene delivery.

Strontium-doped calcium polyphosphate/ultrahigh molecular weight polyethylene composites: A new class of artificial joint components with enhanced biological efficacy to aseptic loosening

To enhance implant stability and prolong the service life of artificial joint component, a new approach was proposed to improve the wear resistance of artificial joint component and endow artificial joint component with the biological efficacy of resistance to aseptic loosening. Strontium calcium polyphosphate (SCPP) were interfused in ultrahigh molecular weight polyethylene (UHMWPE) by a combination of liquid nitrogen ball-milling and flat-panel curing process to prepare the SCPP/UHMWPE composites. The micro-structure, mechanical characterization, tribological characterization and bioactivities of various SCPP/UHMWPE composites were investigated. The results suggested that this method could statistically improve the wear resistance of UHMWPE resulting from a good SCPP particle dispersion. Moreover, it is also observed that the SCPP/UHMWPE composites-wear particles could promote the production of OPG by osteoblasts and decrease the production of RANKL by osteoblasts, and then increase the OPG/RANKL ratio. This indicated that the SCPP/UHMWPE composites had potential efficacy to prevent and treat aseptic loosening. Above all, the SCPP/UHMWPE composites with a suitable SCPP content would be the promising materials for fabricating artificial joint component with ability to resist aseptic loosening.

Crosslinking effect of dialdehyde starch (DAS) on decellularized porcine aortas for tissue engineering

Biological tissue-derived biomaterials must be chemically modified to avoid immediate degradation and immune response before being implanted in human body to replace malfunctioning organs. DAS with active aldehyde groups was employed to replace glutaraldehyde (GA), a most common synthetic crosslinking reagent in clinical practice, to fix bioprostheses for lower cytotoxicity. The aim of this research was to evaluate fixation effect of DAS. The tensile strength, crosslinking stability, cytotoxicity especially the anti-calcification capability of DAS-fixed tissues were investigated. The tensile strength and resistance to enzymatic degradation of samples were increased after DAS fixation, the values maintained stably in D-Hanks solution for several days. Meanwhile, ultrastructure of samples preserved well and the anti-calcification capability of samples were improved, the amount of positive staining points in the whole visual field of 15% DAS-fixed samples was only 0.576 times to GA-fixed ones. Moreover, both unreacted DAS and its hydrolytic products were nontoxic in cytotoxicity study. The results demonstrated DAS might be an effective crosslinking reagent to fix biological tissue-derived biomaterials in tissue engineering.

Correlation of polymeric micelle sizes and their cellular internalization in vitro and tumor targeting in vivo

In order to explore the size effect of polymeric micelles on cellular internalization and tumor targeting, chrysin modified mPEG–PCL copolymer micelles with different particle sizes were fabricated to load Nile red as fluorescence probes. Four kinds of micelles with the mean sizes of 20, 40, 80 and 120 nm and narrow size distributions were prepared. The zeta potentials of the micelles were within −2 to 0 mV. The micelles were stable at low concentration (10−3 mg mL−1) for a long time of storage. The micelles were incubated with C2C12 myoblasts and 4T1 breast cancer cells to investigate their cellular uptake. It was found that the cellular internalization of the polymeric micelles was dependent on the cell line and particle size. The cellular uptake of the micelles in 4T1 cells was much better than that in C2C12 cells, and the polymeric micelles with a size of 120 nm exhibited the strongest red fluorescence. The Nile red loaded polymeric micelles were injected in mice via their tail vein to study tumor targeting in vivo. The micelles were mainly accumulated in the liver and kidney, however, different from the results in vitro, the red fluorescence intensity in the tumor administrated with polymeric micelles with a size of 40 nm was the strongest compared with the other three particles, which implied that micelles with a size of 40 nm exhibited efficient tumor targeting. This work provides guidelines for the rational design of polymeric micelles as carriers for efficient targeted drug delivery.

Fabrication of a novel bio-inspired collagen–polydopamine hydrogel and insights into the formation mechanism for biomedical applications

The bio-inspired approach to the construction of hydrogels with both excellent biological properties and superior initiative adhesive ability to cells is a crucial intersection of the branches of biomaterials science and biotechnology. In the present work, a novel bio-inspired collagen–polydopamine (COL–PDA) hydrogel has been successfully fabricated via collagen self-assembly and the incorporation of PDA. Systematic FTIR and XRD analysis confirmed that the hydrogen bond interactions between collagen and PDA did not destroy the triple helix conformation of collagen which is mainly responsible for the good biological properties of the COL–PDA hydrogel. In comparison with a pristine collagen hydrogel, the physicochemical properties (i.e. porosity, swelling ratio and water holding capacity) of COL–PDA hydrogels could be tuned by modulating the extent of interaction between COL and PDA with the change of dopamine concentrations. The further analysis of AFM observation indicated that a higher dopamine concentration could interrupt the aggregation or self-assembly of collagen molecules into fibrils via the extensive self-polymerization process of dopamine. Furthermore, the formation of a fibrous network could also be controlled by the self-assembly of collagen through varying the dopamine concentration, thus to adjust the thermal stability, enhance the resistance ability to enzymatic degradation and further cause promoted chain entanglement and forming increased elasticity. In addition, owing to the combined biological properties of COL and PDA, fabrication of a bio-inspired COL–PDA hydrogel has significant potential for the development of novel collagen hydrogels with good biological property and initiative adhesive ability to cells in biomedical applications.