Covalent binding modes between BMP-2-derived peptides and graphene in 3D scaffolds determine their osteoinductivity and capacity for calvarial defect repair in vivo.

Covalent introduction of bioactive molecules is one of main strategies to significantly enhance the biological activities of bone repair materials. In this study, three most-commonly used chemical groups were respectively introduced on graphene (GP), followed by covalent binding with bone morphogenetic protein-2 (BMP-2) -derived peptides, ensuring that the same molar mass of peptides was bound to different functionalized GP (f-GP). Then the same amount of composites composed of different f-GP and peptides were respectively compounded with poly (lactic-co-glycolic acid) to fabricate 3D scaffolds. In vivo study demonstrated that the scaffolds containing ammonized GP covalently bound with the peptides through amide binding could reach best efficiency of promoting ectopic bone regeneration and repairing calvarial defect probably because the most positive charges on the peptide chain and surface of the ammonized GP could absorb more specific proteins in vivo and have better interactions with them, thereby differentiating most inducible cells into osteogenic cells. Our results indicate that the performances of scaffolds containing covalently bound bioactive molecules can be controlled by the covalent binding mode, and that our prepared scaffold containing ammonized GP covalently bound with the BMP-2-derived peptides through amide binding possess inspiring potential applicable prospects for bone tissue regeneration and engineering.

[Advantages and challenges of carbon nanotubes as bone repair materials].

With the in-depth research on bone repair process, and the progress in bone repair materials preparation and characterization, a variety of artificial bone substitutes have been fully developed in the treatment of bone related diseases such as bone defects. However, the current various natural or synthetic biomaterials are still unable to achieve the structure and properties of natural bone. Carbon nanotubes (CNTs) have provided a new direction for the development of new materials in the field of bone repair due to their excellent structural stability, mechanical properties, and functional group modifiability. Moreover, CNTs and their composites have broad prospects in the design of bone repair materials and as drug delivery carriers. This paper describes the advantages of CNTs related to bone tissue regeneration from the aspects of morphology, chemistry, mechanics, electromagnetism, and biosafety, as well as the application of CNTs in drug delivery carriers and reinforcement components of scaffold materials. In addition, the potential problems and prospects of CNTs in bone regenerative medicine are discussed.

[Experimental study on repairing rabbit skull defect with bone morphogenetic protein 2 peptide/functionalized carbon nanotube composite].

OBJECTIVE: To observe and compare the effects of peptides on the repair of rabbit skull defects through two different binding modes of non-covalent and covalent, and the combination of carboxyl (-COOH) and amino (-NH 2) groups with materials. METHODS: Twenty-one 3-month-old male ordinary New Zealand white rabbits were numbered 1 to 42 on the left and right parietal bones. They were divided into 5 groups using a random number table, the control group (group A, 6 sides) and the material group 1, 2, 3, 4 (respectively group B, C, D, E, 9 sides in each group). All animals were prepared with 12-mm-diameter skull defect models, and bone morphogenetic protein 2 (BMP-2) non-covalently bound multiwalled carbon nanotubes (MWCNT)-COOH+poly ( L-lactide) (PLLA), BMP-2 non-covalently bound MWCNT-NH 2+PLLA, BMP-2 covalently bound MWCNT-COOH+PLLA, and BMP-2 covalently bound MWCNT-NH 2+PLLA were implanted into the defects of groups B, C, D, and E, respectively. At 4, 8, and 12 weeks after operation, the samples were taken for CT scanning and three-dimensional reconstruction, the ratio of bone tissue regeneration volume to total volume and bone mineral density were measured, and the histological observation of HE staining and Masson trichrome staining were performed to quantitatively analyze the volume ratio of new bone tissue. RESULTS: CT scanning and three-dimensional reconstruction showed that with the extension of time, the defects in groups A-E were filled gradually, and the defect in group E was completely filled at 12 weeks after operation. HE staining and Masson trichrome staining showed that the volume of new bone tissue in each group gradually increased with time, and regenerated mature bone tissue appeared in groups D and E at 12 weeks after operation. Quantitative analysis showed that at 4, 8, and 12 weeks after operation, the ratio of bone tissue regeneration volume to total volume, bone mineral density, and the volume ratio of new bone tissue increased gradually over time; and at each time point, the above indexes increased gradually from group A to group E, and the differences between groups were significant ( P<0.05). CONCLUSION: Through covalent binding and using -NH 2 to bound peptides with materials, the best bone repair effect can be achieved.

Applications of Graphene and Its Derivatives in Bone Repair: Advantages for Promoting Bone Formation and Providing Real-Time Detection, Challenges and Future Prospects.

During continuous innovation in the preparation, characterization and application of various bone repair materials for several decades, nanomaterials have exhibited many unique advantages. As a kind of representative two-dimensional nanomaterials, graphene and its derivatives (GDs) such as graphene oxide and reduced graphene oxide have shown promising potential for the application in bone repair based on their excellent mechanical properties, electrical conductivity, large specific surface area (SSA) and atomic structure stability. Herein, we reviewed the updated application of them in bone repair in order to present, as comprehensively, as possible, their specific advantages, challenges and current solutions. Firstly, how their advantages have been utilized in bone repair materials with improved bone formation ability was discussed. Especially, the effects of further functionalization or modification were emphasized. Then, the signaling pathways involved in GDs-induced osteogenic differentiation of stem cells and immunomodulatory mechanism of GDs-induced bone regeneration were discussed. On the other hand, their applications as contrast agents in the field of bone repair were summarized. In addition, we also reviewed the progress and related principles of the effects of GDs parameters on cytotoxicity and residues. At last, the future research was prospected.

Applications of materials for dural reconstruction in pre-clinical and clinical studies: Advantages and drawbacks, efficacy, and selections.

The dura mater provides a barrier to protect the tissue underneath and cerebrospinal fluid. However, dural defects normally cause cerebrospinal fluid leakage and other complications, such as wound infections, meningitis, etc. Therefore, the reconstruction of dura mater has important clinical significance. Current dural reconstruction materials include: homologous, acellular, natural, synthetic, and composite materials. This review comprehensively summarizes the characteristics and efficacy of these dural substitutes, especially in clinical applications, including the advantages and drawbacks of those from different sources, the host tissue response in pre-clinical studies and clinical practice, and the comparison of these materials across different surgical procedures. Furthermore, the selections of materials for different surgical procedures are highlighted. Finally, the challenges and future perspectives in the development of ideal dural repair materials are discussed.

Arsenic trioxide encapsulated liposomes prepared via copper acetate gradient loading method and its antitumor efficiency.

In this study, arsenic trioxide (ATO) was encapsulated in liposomes via copper acetate (Cu(OAc)2) gradients and high entrapment efficiency of over 80% was obtained. The average particle size and the zeta-potential of the liposomes were detected to be 115.1 ±â€¯29.1 nm and -21.97 ±â€¯0.6 mV, respectively. The TEM images showed rod-like precipitates in the inner aqueous phase, which was supposed be due to the formation of insoluble ATO-Cu complex. The in vitro drug release of ATO-Cu liposomes exhibited a sustained release over 72 h, and the release rates decreased with the increase of the pH of release media. Pharmacokinetic and tissue distribution studies of ATO liposomes showed significantly reduced plasma clearance rate, increased AUC0-12 h and T1/2, and improved tumor distribution of As compared to iv administration of ATO solution. The anti-tumor effect of ATO loaded liposomes to S180 tumor-bearing mice was significantly improved with a tumor inhibition rate of 61.2%, meanwhile the toxicity of encapsulated ATO was greatly decreased. In conclusion, ATO can be effectively encapsulated into liposomes by remote loading method via Cu(OAc)2 gradients; the co-administration of ATO and Cu(II) via liposomal formulation may find wide applications in the treatment of various tumors.

Influence of the mechanical properties of biomaterials on degradability, cell behaviors and signaling pathways: current progress and challenges.

The development of suitable biomaterials with the ability to improve repair and regeneration of human tissues is continuously in progress, and mechanical properties of biomaterials play a critical role in their success in the clinical setting. Both biomaterial degradability and signaling cascades of cell interactions with biomaterials are significantly influenced by the mechanical properties of biomaterials, determining the final repair effect of bio-implants. Actually, the mechanical properties of biomaterials play a critical role in designing and developing medical material products both in research and in practice. Currently, advances in mechanics have provided new possibilities for researchers to investigate and modulate both the substrates and cell behaviors with respect to material perfection in tissue engineering. Achieving convenient and accurate approaches for producing different types of biomaterials is now possible by applying computerized methods. In this review, we have systematically clarified the influence of several selected mechanical properties of biomaterials (including stress/strain, elasticity/stiffness and certain time-dependent mechanical properties) on biomaterial degradability, cell behaviors and signaling pathways. Furthermore, the mechanical design targets and approaches for optimizing the mechanical properties of biomaterials, as well as the challenges and prospects are elaborated. This review will certainly bring up new ideas and possibilities for the field of tissue engineering and regenerative biomaterials.

Biomimetic SIS-based biocomposites with improved biodegradability, antibacterial activity and angiogenesis for abdominal wall repair.

Small intestinal submucosa (SIS) is a widely concerned acellular material for reconstructing tissue defects, but during the restoration of abdominal wall, it has been restricted due to the fast degradation causing poor long-term mechanical properties, the infection caused by bacteria contamination, and insufficient neovascularization post-operation. In this study, we developed a biomimetic SIS-based biocomposite (CS/ES-SIS) for abdominal wall repair, in which chitosan (CS) and elastin (ES) electrospun nanofibers were used to improve the biodegradability, antibacterial activity, and angiogenesis. The CS/ES-SIS composites were examined through a series of testing experiments, especially in vitro degradation was assessed by a constant deformation loading device and the micromechanical properties during enzymatic degradation under biomechanical environment were measured by nanoindentation. In vitro antibacterial test and cytocompatibility, and in vivo biocompatibility, neovascularisation and tissue regeneration were also investigated. The main research results as follows: (1) After 7 days enzymatic degradation under biomechanical environment, the degradation rate of CS/ES-SIS composites was slower than that of SIS by about 24.5%. Moreover, the CS/ES-SIS composites could better maintain the stability of microstructure and micromechanical properties compared with SIS. (2) The antibacterial rates of CS/ES-SIS composites against E. coli and S. aureus were respectively 98.87% and 98.26% while the SIS demonstrated no obvious antibacterial capacity. (3) The CS/ES-SIS composites supported the viability and proliferation of fibroblast cell L929. In vivo studies showed that the CS/ES-SIS composites could promote tissue regeneration upon implantation without serious inflammatory reaction. Additionally, the vascular number in the CS/ES-SIS composites was as 1.69 times as that in the SIS at 4 weeks. Collectively, all the findings suggested that the newly developed CS/ES-SIS composites might be promising and attractive candidates for applications of abdominal wall repair.

Terminal Group Modification of Carbon Nanotubes Determines Covalently Bound Osteogenic Peptide Performance.

Osteogenic peptides are often introduced to improve biological activities and the osteogenic ability of artificial bone materials as an effective approach. Covalent bindings between the peptide and the host material can increase the molecular interactions and make the functionalized surface more stable. However, covalent bindings through different functional groups can bring different effects on the overall bioactivities. In this study, carboxyl and amino groups were respectively introduced onto carbon nanotubes, a nanoreinforcement for synthetic scaffold materials, which were subsequently covalently attached to the RGD/BMP-2 osteogenic peptide. MC3T3-E1 cells were cultured on scaffolds containing peptide-modified carbon nanotubes. The results showed that the peptide through the amino group binding could promote cell functions more effectively than those through carboxyl groups. The mechanism may be that the amino group could bring more positive charges to carbon nanotube surfaces, which further led to differences in the peptide conformation, protein adsorption, and targeting osteogenic effects. Our results provided an effective way of improving the bioactivities of artificial bone materials by chemically binding osteogenic peptides.

Incorporation of multi-walled carbon nanotubes to PMMA bone cement improves cytocompatibility and osseointegration.

Acrylic bone cement (ABC) has been used as a grouting agent in joint replacement surgery for over 50 years. In particular, ABC is irreplaceable for high-load joint replacement such as total hip joint replacements (THJRs) and total knee joint replacements because of its excellent mechanical properties. However, the bioactivity of ABC needs to be improved. In this study, we attempted to enhance cytocompatibility and osseointegration of polymethyl methacrylate (PMMA) bone cement via the incorporation of multi-walled carbon nanotube (MWCNT) powders. The results of in vitro rat bone marrow mesenchymal stem cells (rBMSCs) culture on the specimens of PMMA containing different levels of MWCNT loading demonstrated that MWCNT addition improved cell adhesion and proliferation. Furthermore, it was shown from both gene and protein expression levels that MWCNT addition promoted the osteogenic differentiation. For the animal model study, PMMA specimens at different levels of MWCNT loading were implanted into a New Zealand rabbit bone defect model. The results showed that new bone formation occurred inside the bone cement and the integration between the bone cement and bone tissue were significantly enhanced with an increase in MWCNT loading level at 12 weeks post-surgery. Moreover, when the loading of MWCNT was only 1 wt%, the bone ingrowth ratio was up to 42.2% at 12 weeks, and a large number of osteoblasts congregated and new bone formed within the bone cement. In conclusion, cytocompatibility and osseointegration of the bone cements can be controlled by adjusting the MWCNT loading. The whole collection of the present results suggests that MWCNT-incorporated PMMA bone cement may have promise for use in certain orthopedic applications.

Phyto-phospholipid complexes (phytosomes): A novel strategy to improve the bioavailability of active constituents.

Although active constituents extracted from plants show robust in vitro pharmacological effects, low in vivo absorption greatly limits the widespread application of these compounds. A strategy of using phyto-phospholipid complexes represents a promising approach to increase the oral bioavailability of active constituents, which is consist of ''label-friendly" phospholipids and active constituents. Hydrogen bond interactions between active constituents and phospholipids enable phospholipid complexes as an integral part. This review provides an update on four important issues related to phyto-phospholipid complexes: active constituents, phospholipids, solvents, and stoichiometric ratios. We also discuss recent progress in research on the preparation, characterization, structural verification, and increased bioavailability of phyto-phospholipid complexes.

The use of bioactive peptides to modify materials for bone tissue repair.

It has been well recognized that the modification of biomaterials with appropriate bioactive peptides could further enhance their functions. Especially, it has been shown that peptide-modified bone repair materials could promote new bone formation more efficiently compared with conventional ones. The purpose of this article is to give a general review of recent studies on bioactive peptide-modified materials for bone tissue repair. Firstly, the main peptides for inducing bone regeneration and commonly used methods to prepare peptide-modified bone repair materials are introduced. Then, current in vitro and in vivo research progress of peptide-modified composites used as potential bone repair materials are reviewed and discussed. Generally speaking, the recent related studies have fully suggested that the modification of bone repair materials with osteogenic-related peptides provide promising strategies for the development of bioactive materials and substrates for enhanced bone regeneration and the therapy of bone tissue diseases. Furthermore, we have proposed some research trends in the conclusion and perspectives part.

Mixed Surfactant Solutions for the Dispersion of Multiwalled Carbon Nanotubes and the Study of Their Antibacterial Activity.

The dispersibility of mixed surfactant-modified multiwalled carbon nanotubes (MWNTs) and their effect on antibacterial activity were examined. The ratio of 9:1 between sodium dodecyl benzene-sulfate (SDBS) and hexadecyltrimethylammonium bromide (CTAB) showed the highest dispersing power for MWNTs. The use of mixed surfactants enabled the MWNTs to form a stable dispersion at a lower total surfactant concentration than their concentrations when used alone. UV-vis spectroscopy, transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) were used to characterize the dispersion of MWNTs in the aqueous phase. The results indicated that the surfactant molecules had been successfully adsorbed onto the surface of the MWNTs. The mixed surfactant-modified MWNTs exhibited a strong antibacterial activity and concentration dependence to Staphylococcus aureus (S. aureus). Based on the considerations of the cost and environmental impact, the use of mixed surfactants (SDBS-CTAB) should be more favorable for the stable dispersion of MWNTs and the improvement of antibacterial activity than the use of a single surfactant.

Fabrication and characterization of gold nanoparticle-loaded TiO2 nanotube arrays for medical implants.

Au nanoparticles (AuNPs) are successfully assembled on TiO2 nanotube (TN) arrays through electrochemical deposition technology to improve the surface characteristics of TN arrays as an implant material. The loading amount of AuNPs can be controlled by adjusting the deposition time of electrochemical deposition. The effect of the amount of the loaded AuNPs on surface roughness and surface energy is systematically investigated on the basis of various characterizations. Results show that the increase in the loading amount of AuNPs on the TN arrays can increase surface roughness and decrease surface energy. Potentiodynamic polarization tests indicate that AuNP-modified TNs possess a higher corrosion resistance than unmodified TNs. Corrosion resistance increases as the amount of the loaded AuNP increases. In vitro cell culture tests are performed on the basis of cell morphology observations and MTT assays. Osteoblast cell adhesion and proliferation ability on the AuNP-modified TN surface are greater than those on the unmodified TN surface. The sample fabricated at the deposition time of 90 s exhibits an optimum cell performance. This work can provide a new platform to develop the surface chemistry of TN arrays and to fabricate titanium-based implant materials to enhance bioactivity.