Xixun Yu

Modification of collagen with a natural derived cross-linker, alginate dialdehyde

The interaction between collagen and a natural derived cross-linker alginate dialdehyde (ADA) was investigated. Fourier transform infrared (FTIR) spectroscopy and the circular dichroism (CD) measurements indicate that the structure integrity of collagen is still maintained after the ADA treatment, while the differential scanning calorimetry (DSC) study suggests that ADA could promote collagen-ADA membranes thermostability compared to pure collagen. And the atomic force microscopy (AFM) of cross-linked collagen reveals a denser network structure. Besides, the water contact angle test indicates that the hydrophilic property of collagen-ADA membrane is promoted, which is favorable for cells attachment and proliferation. Meanwhile, the cytocompatibility results imply that not only no extra cytotoxicity is introduced into the collagen-ADA membrane after ADA treatment, but also collagen-ADA membrane facilitates cells proliferation when the content of ADA is less than 20%. In conclusion, our study reveals that ADA stabilizes collagen as a cross-linker and preserves its triple helical structure.

Preparation of chitosan/silk fibroin blending membrane fixed with alginate dialdehyde for wound dressing

The objective of this work was to prepare chitosan/silk fibroin (CS/SF) blending membranes crosslinked with alginate dialdehyde (ADA) as wound dressings and to evaluate the physical properties and biocompatibility of the membranes. The morphology of membrane was observed by scanning electron microscopy (SEM) which showed that the well consistency of these two compositions. Further, the stability, water absorption and water vapor permeability of the ADA fixed CS/SF membranes could meet the needs of wound dressing. Furthermore, the biocompatibility of ADA fixed membranes was investigated by MTT assays and SEM in vitro, and the membranes were found to promote the cell attachment and proliferation. These results suggest that ADA fixed CS/SF blending membranes with a suitable ratio could be a promising candidate for wound healing applications.

The study on the degradation and mineralization mechanism of ion-doped calcium polyphosphate in vitro.

Doping with different trace elements can significantly change the original degradability, mineralization, and biological properties of bone repair material. According to the fundamental research on prepared calcium polyphosphate (CPP) as a bone repair material by our group, this article began further exploration on the effect of doping different trace elements (K, Na, Mg, Zn, Sr) into CPP on its degradability and mineralization soaking in simulated body fluids. The results indicated that doped elements significantly changed the lattice parameters and cell volume of crystal, resulted in different types of crystal defect and surface charge distribution, and consequently changed the original degradability and mineralization of CPP. The conclusion is that doped ions with relatively smaller ionic radius and equivalent positive charge compared with Ca(2+) can greatly promote the degradability and mineralization of CPP, whereas doped ions with equivalent ionic radius and diverse positive charges compared with Ca(2+) provide less contribution on promoting the degradability and mineralization or even counteract.

Acceleration of segmental bone regeneration in a rabbit model by strontium-doped calcium polyphosphate scaffold through stimulating VEGF and bFGF secretion from osteoblasts.

The development of suitable bioactive three-dimensional scaffold for the promotion of bone regeneration is critical in bone tissue engineering. The purpose of this study was to investigate in vivo osteogenesis of the porous strontium-doped calcium polyphosphate (SCPP) scaffolds for bone repair, as well as the relationship between osteogenic properties of SCPP scaffolds and the secretion of bFGF and VEGF from osteoblasts stimulated by SCPP. Besides, the advantages of scaffolds seeded with mesenchymal stem cells (MSCs) for bone repair were also studied. Firstly, the bone repair evaluation of scaffolds was performed on a rabbit segmental bony defects model over a period of 16 weeks by histology combined with X-ray microradiography. And then, in order to avoid the influence from the other factors such as hypoxia which emerge in vivo study and affect the secretion of VEGF and bFGF from host cells, human osteoblast-like cells (MG63) were seeded to SCPP, CPP and HA scaffolds in vitro to determine the ability of these scaffolds to stimulate the secretion of angiogenic growth factors (VEGF and bFGF) from MG63 and further explore the reason for the better osteogenic properties of SCPP scaffolds. The histological and X-ray microradiographic results showed that the SCPP scaffolds presented better osteogenic potential than CPP and HA scaffolds, when combined with MSCs, the SCPP scaffolds could further accelerate the bone repair. And the amounts of VEGF measured by ELISA assay in SCPP, CPP and HA groups after cultured for 7 days were about 364.989 pg/mL, 244.035 pg/mL and 232.785 pg/mL, respectively. Accordingly, the amounts of bFGF were about 27.085 pg/mL, 15.727 pg/mL and 8.326 pg/mL. The results revealed that the SCPP scaffolds significantly enhanced the bFGF and VEGF secretion compared with other scaffolds. The results presented in vivo and in vitro study demonstrated that the SCPP could accelerate bone formation through stimulating the secretion of VEGF and bFGF from osteoblasts, making it attractive for bone regeneration.

In vitro study in stimulating the secretion of angiogenic growth factors of strontium-doped calcium polyphosphate for bone tissue engineering

Angiogenesis of tissue-engineered bone remains a limited factor for the engineering of larger bone tissue constructs. Attempts to stimulate angiogenesis, using recombinant protein or gene transfer of angiogenic growth factors, have been proposed; however, these approaches have been associated with some problems regarding such as complex technique, expensive prices as well as safety problems and short half-life of angiogenic growth factors. This study was performed to determine the ability of strontium-doped calcium polyphosphate (SCPP) to induce angiogenesis via researching its effect on the mRNA expressions and protein secretion of VEGF and bFGF in/from cultured osteoblasts (ROS17/2.8 cells). We cultured osteoblasts with SCPP scaffolds containing various doses of strontium as well as calcium polyphosphate (CPP) scaffold. Through the detection of MTT and SEM, we have found that SCPP could promote cell proliferation and maintain their morphology. The results of RT–PCR and ELISA indicated that, compared with those in CPP group, the mRNA expression as well as protein levels of VEGF and bFGF in/from cultured osteoblasts were dose-dependent increasing in response to increasing strontium before reaching the peak in SCPP groups, and 8% SCPP showed the optimal promoting role. Therefore, SCPP containing proper dose of strontium could be served as a potential biomaterial with stimulating angiogenesis in bone tissue engineering and bone repair.

Coculture of peripheral blood-derived mesenchymal stem cells and endothelial progenitor cells on strontium-doped calcium polyphosphate scaffolds to generate vascularized engineered bone.

Vascularization of engineered bone tissue is critical for ensuring its survival after implantation and it is the primary factor limiting its clinical use. A promising approach is to prevascularize bone grafts in vitro using endothelial progenitor cells (EPC) derived from peripheral blood. Typically, EPC are added together with mesenchymal stem cells (MSC) that differentiate into osteoblasts. One problem with this approach is how to promote traditional tissue engineering bone survival with a minimally invasive method. In this study, we examined the effectiveness of administering to stimulate the release of peripheral blood stem cells and their co-culturing system for generating prevascularized engineered bone. Cells were isolated by Ficoll density gradient centrifugation and identified as EPC and MSC based on morphology, surface markers, and functional analysis. EPC and MSC were cocultured in several different ratios, and cell morphology and tube formation were assessed by microscopy. Expression of osteogenesis and vascularization markers was quantified by enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction, and histochemical and immunofluorescence staining. Increasing the proportion of EPC in the coculture system led to greater tube formation and greater expression of the endothelial cell marker CD31. An EPC:MSC ratio of 75:25 gave the highest expression of osteogenesis and angiogenesis markers. Cocultures adhered to a three-dimensional scaffold of strontium-doped calcium polyphosphate and proliferated well. Our findings show that coculturing peripheral blood-derived EPC and MSC may prove useful for generating prevascularized bone tissue for clinical use.

The accuracy of ultrasonography and magnetic resonance imaging for the diagnosis of Morton's neuroma: a systematic review

AIM To determine the accuracy of MRI versus ultrasound for Mortons neuroma. MATERIALS AND METHODS A search was undertaken for clinical studies published in any language in PubMed up to the date of December 2013. Studies assessing the accuracy of the ultrasound or MRI for the diagnosis of Mortons neuroma were included. Data were pooled for meta-analysis. Study selection, data collection, and extraction were performed independently by two authors. Meta-disc 1.4 and Revman 5.2 software were applied for statistical analysis. RESULTS The study included 12 studies; 217 patients underwent MRI and 241 underwent ultrasound examinations. There appeared greater diagnostic accuracy for ultrasound than MRI for the diagnosis of Mortons neuroma (ultrasound sensitivity 90%, specificity 88%, positive likelihood ratio 2.77, negative likelihood ratio 0.16 versus MRI sensitivity 93%, specificity 68%, positive likelihood ratio 1.89, negative likelihood ratio 0.19). CONCLUSIONS The available evidence suggests that ultrasound can provide better accuracy for the diagnosis of Mortons neuroma than MRI.

In vitro cytocompatibility evaluation of alginate dialdehyde for biological tissue fixation.

Biological tissues must be chemically fixed before they can be implanted in humans, due to the immediate degradation and presence of antigenicity of naturally derived tissues. To provide a crosslinking reagent which is cytocompatible and may prepare biocompatible fixed tissues, a novel crosslinking agent, alginate dialdehyde (ADA), was employed to fix biological tissues by our group. The study was to evaluate the cytocompatibility of ADA for biological tissue fixation. Glutaraldehyde and genipin counterparts were used as controls. The result suggested that the cytotoxicity of ADA was significantly lower than that of glutaraldehyde and genipin. Additionally, in the evaluation of cytotoxicity of fixed tissue itself and the residues, as well as the cell adhesion property, ADA-fixed tissue was significantly superior to its glutaraldehyde counterpart and comparable to its genipin counterpart. The results obtained in this study demonstrate that ADA is a cytocompatible crosslinking reagent for biological tissue fixation.

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.

In vitro enzymatic degradation of a biological tissue fixed by alginate dialdehyde.

Biological tissues must be chemically fixed before they can be implanted in humans as tissue engineering scaffolds. To provide an ideal tissue engineering scaffold material, which is biodegradable and cytocompatible, a novel crosslinking agent, alginate dialdehyde (ADA), was employed to fix biological tissues by our group. The study mainly investigated the enzymatic degradation of ADA fixed biological tissues in vitro. Glutaraldehyde, the most commonly used crosslinking agent for biological tissue fixation, was employed as a control. The results suggested that, the ADA fixation could enhance the resistance against enzymatic degradation of biological tissues effectively. Meanwhile, compared to glutaraldehyde-fixed tissues, the ADA-fixed tissues could also degrade gradually over time. Moreover, the ADA crosslinking reagent itself had a stimulatory effect on cell proliferation when at an appropriate concentration. The results obtained in this study demonstrate that ADA fixation might provide a successful example of the biodegradable scaffold materials in tissue engineering.