Signal molecules-calcium phosphate coprecipitation and its biomedical application as a functional coating

Clinical Trial for the Safety and Feasibility of Pedicle Screws Coated with a Fibroblast Growth Factor-2-Apatite Composite Layer for Posterior Cervical Fusion Surgery

To solve the instrument loosening problem, we developed a fibroblast growth factor-2-calcium phosphate composite layer as a novel coating material to improve screw fixation strength. The primary aim of the present study was to demonstrate the safety and feasibility of screws coated with the FGF-2-calcium phosphate composite layer for posterior instrumented surgery of the cervical spine. The trial design was a single-arm, open-label, safety and feasibility study. Patients receiving fusion of the cervical spine from C2 (or C3) to C7 (or T1) were recruited. The primary endpoint to confirm safety was any screw-related adverse events. Seven patients who underwent posterior fusion surgery of the cervical spine were enrolled in the present study. The coated pedicle screws were inserted bilaterally into the lowest instrumented vertebrae. There was only one severe adverse event unrelated with the coated screw. Three out of the fourteen coated screws showed loosening. The present results prove the safety and feasibility of pedicle screws coated with the FGF-2-calcium phosphate composite layer for fusion surgery in the cervical spine. This is the first step to apply this novel surface coating in the field of spine surgery.

Laser-assisted biomineralization on human dentin for tooth surface functionalization

A technique for tooth surface modification with biocompatible calcium phosphate (CaP) has huge potential in dental applications. Recently, we achieved a facile and area-specific CaP coating on artificial materials by a laser-assisted biomimetic process (LAB process), which consists of pulsed laser irradiation in a supersaturated CaP solution. In this study, we induced the rapid biomineralization on the surface of human dentin by using the LAB process. A human dentin substrate was immersed in a supersaturated CaP solution, then its surface was irradiated with weak pulsed laser light for 30 min (LAB process). Ultrastructural analyses revealed that the pristine substrate had a demineralized collagenous layer on its surface due to the previous EDTA surface cleaning. After the LAB process, this collagenous layer disappeared and was replaced with a submicron-thick hydroxyapatite layer. We believe that the laser irradiation induced pseudo-biomineralization through the laser ablation of the collagenous layer, followed by CaP nucleation and growth at the dentin-liquid interface. The mineralized layer on the dentin substrate consisted of needle-like hydroxyapatite nanocrystals, whose c-axes were weakly oriented along the direction perpendicular to the substrate surface. This LAB process would offer a new tool enabling tooth surface modification and functionalization through the in situ pseudo-biomineralization.

Enhanced osteogenic differentiation of human mesenchymal stem cells on Ti surfaces with electrochemical nanopattern formation

Titanium (Ti) and its alloys are mainly used for dental and orthopedic applications due to their excellent biocompatibility and mechanical properties. However, their intrinsic bioinertness often quotes as a common complaint for biomedical applications. Herein, we produced nanopattern Ti surfaces with 10 nm nanopores in 120 nm dimples by electrochemical nanopattern formation (ENF), and evaluated the osteogenic differentiation of human mesenchymal stem cells (hMSCs) on the nanopattern Ti surfaces. The ENF surfaces were obtained by removing the TiO₂ nanotube (NT) layers prepared by an anodization process. To determine the in vitro effects of the ENF surface, cell proliferation assay, alkaline phosphatase activity assay, alizarin red staining, western blotting, and immunocytochemistry were performed. Atomic force microscopy and scanning electron microscopy analysis show that the ENF surface has an ultrafine surface roughness with highly aligned nanoporous morphology. hMSCs on ENF surfaces exhibit increased proliferation and enhanced osteogenic differentiation as compared to the ordered TiO₂ nanotubular and compact TiO₂ surfaces. Surface modification with the ENF process is a promising technique for fabricating osteointegrative implant materials with a highly bioactive, rigid and purified nano surfaces.

Laser-assisted wet coating of calcium phosphate for surface-functionalization of PEEK

Calcium phosphate (CaP) coating is an effective method for surface-functionalization of bioinert materials and for production of osteoconductive implants. Recently, we developed a laser-assisted biomimetic process (LAB process) for facile and area-specific CaP coating. In this study, the LAB process was applied to chemically stable and mechanically durable poly(etheretherketone) (PEEK), which has become widely used as an orthopedic and dental implant material. The LAB process was carried out by irradiating pulsed Nd:YAG laser light (355 nm) onto a PEEK substrate that was immersed in supersaturated CaP solution. The CaP coating applicability depended on laser fluence, i.e., CaP successfully formed on PEEK surface after the LAB process at 2 W/cm2. Further increase in laser fluence did not result in the successful formation. At the optimal fluence of 2 W/cm2, the laser-irradiated PEEK surface was modified and heated to induce heterogeneous CaP precipitation within 10 min in CaP solution, followed by further CaP growth over the irradiation time (tested up to 30 min). The LAB process improved the cytocompatibility of PEEK surface with osteoblastic MC3T3-E1 cells. Furthermore, the LAB-processed CaP-coated PEEK substrate formed a dense hydroxyapatite layer on its surface in the simulated body fluid, suggesting the osteoconductivity of this material. The present LAB process can be a useful new tool to produce osteoconductive PEEK-based implants.

Hollow boron nitride nanospheres as boron reservoir for prostate cancer treatment

High global incidence of prostate cancer has led to a focus on prevention and treatment strategies to reduce the impact of this disease in public health. Boron compounds are increasingly recognized as preventative and chemotherapeutic agents. However, systemic administration of soluble boron compounds is hampered by their short half-life and low effectiveness. Here we report on hollow boron nitride (BN) spheres with controlled crystallinity and boron release that decrease cell viability and increase prostate cancer cell apoptosis. In vivo experiments on subcutaneous tumour mouse models treated with BN spheres demonstrated significant suppression of tumour growth. An orthotopic tumour growth model was also utilized and further confirmed the in vivo anti-cancer efficacy of BN spheres. Moreover, the administration of hollow BN spheres with paclitaxel leads to synergetic effects in the suppression of tumour growth. The work demonstrates that hollow BN spheres may function as a new agent for prostate cancer treatment.

Use of soluble boron compounds in prostate cancer therapy is hampered by their short half-life time and low effectiveness. Here, the authors show that boron nitride nanospheres with controlled boron release can reduce proliferation of prostate cancer cells and inhibit tumour growth in animal models.

Rod-shaped and fluorine-substituted hydroxyapatite free of molecular immunopotentiators stimulates anti-cancer immunity in vivo

Rod-shaped and fluorine-substituted hydroxyapatite nanoparticles significantly increased the cellular uptake of a model antigen by BMDCs, improved antigen presentation, stimulated immune-related cytokine secretion, and enhanced the anti-cancer immunity.

Physicochemical fabrication of calcium phosphate-based thin layers and nanospheres using laser processing in solutions

We achieved simple and rapid fabrication of calcium phosphate (CaP)-based thin layers and nanospheres by laser processing in supersaturated solutions.

Zn- and Mg- containing tricalcium phosphates-based adjuvants for cancer immunotherapy

Zn-, and Mg-containing tricalcium phosphates (TCPs) loaded with a hydrothermal extract of a human tubercle bacillus (HTB) were prepared by immersing Zn-TCP and Mg-TCP in HTB-containing supersaturated calcium phosphate solutions. The in vitro and in vivo immunogenic activities of the HTB-loaded Zn-, and Mg-TCPs (Zn-Ap-HTB and Mg-Ap-HTB, respectively) were evaluated as potential immunopotentiating adjuvants for cancer immunotherapy. The Zn-Ap-HTB and Mg-Ap-HTB adjuvants showed no obvious cytotoxicity and more effectively stimulated granulocyte-macrophage colony-stimulating factor (GM-CSF) secretion by macrophage-like cells than unprocessed HTB or HTB-loaded TCP (T-Ap-HTB) in vitro. Zn-Ap-HTB and Mg-Ap-HTB mixed with liquid-nitrogen-treated tumor tissue markedly inhibited the in vivo development of rechallenged Lewis lung carcinoma (LLC) cells compared with T-Ap-HTB and the unprocessed HTB mixed liquid-nitrogen-treated tumor tissue. Zn-Ap-HTB and Mg-Ap-HTB contributed to eliciting potent systemic antitumor immunity in vivo.

Laser-assisted calcium phosphate deposition on polymer substrates in supersaturated solutions

Calcium phosphate (CaP) deposition was induced on optically semitransparent polymers irradiated with laser in a supersaturated CaP solution, but not on a transparent polymer.

Particle-size-dependent toxicity and immunogenic activity of mesoporous silica-based adjuvants for tumor immunotherapy

Conventionally used adjuvants alone are insufficient for triggering cell-mediated immunity, although they have been successfully developed to elicit protective antibody responses in some vaccines. Here, with the aim of eliciting cell-mediated immunity, pathogen-associated molecular patterns (PAMPs) were immobilized with apatite within the pores and on the surface of mesoporous silica (MS) with particle sizes from 30 to 200nm to prepare novel MS-Ap-PAMP adjuvants, which showed cell-mediated anti-tumor immunity that was markedly improved compared to commercial alum adjuvant in vitro and in vivo. The toxicity and antitumor immunity of the MS-Ap-PAMP adjuvants were evaluated in vitro and in vivo. MS with a particle size of 200nm showed minimum in vitro cytotoxicity to NIH3T3 cells, particularly at concentrations no higher than 100μgml(-1). In particular, apatite precipitation within the pores and on the surface of MS decreased the in vitro cytotoxicity of MS particles. The MS-Ap-PAMP adjuvants showed the maximum in vitro immunogenic activity among original culture medium, PAMP and alum-PAMP. Moreover, injection of the MS-Ap-PAMP adjuvant in combination with liquid-nitrogen-treated tumor tissue (derived from Lewis lung carcinoma cells) into C57BL/6 mice markedly inhibited in vivo tumor recurrence and the development of rechallenged tumor compared to those with commercial alum adjuvant. The MS-Ap-PAMP adjuvant contributed to the elicitation of a potent systemic antitumor immunity without obvious toxicity in vivo.

Tissue-engineered endothelial cell layers on surface-modified Ti for inhibiting in vitro platelet adhesion

A tissue-engineered endothelial layer was prepared by culturing endothelial cells on a fibroblast growth factor-2 (FGF-2)-l-ascorbic acid phosphate magnesium salt n-hydrate (AsMg)-apatite (Ap) coated titanium plate. The FGF-2-AsMg-Ap coated Ti plate was prepared by immersing a Ti plate in supersaturated calcium phosphate solutions supplemented with FGF-2 and AsMg. The FGF-2-AsMg-Ap layer on the Ti plate accelerated proliferation of human umbilical vein endothelial cells (HUVECs), and showed slightly higher, but not statistically significant, nitric oxide release from HUVECs than on as-prepared Ti. The endothelial layer maintained proper function of the endothelial cells and markedly inhibited in vitro platelet adhesion. The tissue-engineered endothelial layer formed on the FGF-2-AsMg-Ap layer is promising for ameliorating platelet activation and thrombus formation on cardiovascular implants.

Improvement in endothelial cell adhesion and retention under physiological shear stress using a laminin-apatite composite layer on titanium

Apatite (Ap), laminin-apatite composite (L5Ap, L10Ap, L20Ap and L40Ap) and albumin-apatite (AlbAp) composite layers were prepared on titanium (Ti) using a supersaturated calcium phosphate solution supplemented with laminin (0, 5, 10, 20 and 40 μg ml(-1)) or albumin (800 μg ml(-1)). With an increase in the concentrations of laminin in the supersaturated calcium phosphate solutions, the amounts of laminin immobilized on the Ti increased. The number of human umbilical vein endothelial cells (HUVECs) adhered to the laminin-apatite composite layers were remarkably higher than those to the untreated Ti, Ap layer and AlbAp composite layer. The number of cells adhered to the L40Ap was 4.3 times the untreated Ti. Moreover, cells adhered to the laminin-apatite composite layers showed significantly higher cell retention under the physiological shear stress for 1 h and 2 h than those to the untreated Ti, Ap layer and AlbAp composite layer. The number of cells remaining on the L40Ap under the physiological shear stress for 2 h was 9.5 times that of the untreated Ti. The laminin-apatite composite layer is a promising interfacial layer for endothelialization of blood-contacting materials.

Calcium phosphate composite layers for surface-mediated gene transfer

In this review, the surface-mediated gene transfer system using calcium phosphate composite layers is described. Calcium phosphate ceramics are osteoconductive bioceramics used typically in orthopedic and dental applications. Additionally, calcium phosphate particles precipitated by a liquid-phase process have long been used as a safe and biocompatible transfection reagent in molecular biology. Recently, calcium phosphate composite layers immobilizing DNA were fabricated on the surfaces of base materials through a biomimetic process using supersaturated solutions. These composite layers possess useful characteristics of both osteoconductive bioceramics and transfection reagents; they thus provide a biocompatible surface to support cell adhesion and growth, and can stimulate the cell effectively via surface-mediated gene transfer. By modifying the fabrication conditions, physicochemical and biological properties of the composite layers can be varied. With such an approach, these composite layers can be designed to have improved affinity for cells and to exhibit increased gene transfer efficiency over that of conventional lipid transfection reagents. The composite layers with the increased gene transfer efficiency induced specific cell differentiation and tissue regeneration in vivo. These composite layers, given their good biocompatibility and the potential to control cell behavior on their surfaces, have great potential in tissue engineering applications.

Ultrasound microbubble-mediated delivery of the siRNAs targeting MDR1 reduces drug resistance of yolk sac carcinoma L2 cells

Background

MDR1 gene encoding P-glycoprotein is an ATP-dependent drug efflux transporter and related to drug resistance of yolk sac carcinoma. Ultrasound microbubble-mediated delivery has been used as a novel and effective gene delivery method. We hypothesize that small interfering RNA (siRNA) targeting MDR1 gene (siMDR1) delivery with microbubble and ultrasound can down-regulate MDR1 expression and improve responsiveness to chemotherapeutic drugs for yolk sac carcinoma in vitro.

Methods

Retroviral knockdown vector pSEB-siMDR1s containing specific siRNA sites targeting rat MDR1 coding region were constructed and sequence verified. The resultant pSEB-siMDR1 plasmids DNA were encapsulated with lipid microbubble and the DNA release were triggered by ultrasound when added to culture cells. GFP positive cells were counted by flow cytometry to determine transfection efficiency. Quantitative real-time PCR and western blot were performed to determine the mRNA and protein expression of MDR1. P-glycoprotein function and drug sensitivity were analyzed by Daunorubicin accumulation and MTT assays.

Results

Transfection efficiency of pSEB-siMDR1 DNA was significantly increased by ultrasound microbubble-mediated delivery in rat yolk sac carcinoma L2 (L2-RYC) cells. Ultrasound microbubble-mediated siMDR1s delivery effectively inhibited MDR1 expression at both mRNA and protein levels and decreased P-glycoprotein function. Silencing MDR1 led to decreased cell viability and IC₅₀ of Vincristine and Dactinomycin.

Conclusions

Our results demonstrated that ultrasound microbubble-mediated delivery of MDR1 siRNA was safe and effective in L2-RYC cells. MDR1 silencing led to decreased P-glycoprotein activity and drug resistance of L2-RYC cells, which may be explored as a novel approach of combined gene and chemotherapy for yolk sac carcinoma.