A modular approach to 3D-printed bilayer composite scaffolds for osteochondral tissue engineering.

Prolonged osteochondral tissue engineering damage can result in osteoarthritis and decreased quality of life. Multiphasic scaffolds, where different layers model different microenvironments, are a promising treatment approach, yet stable joining between layers during fabrication remains challenging. To overcome this problem, in this study, a bilayer scaffold for osteochondral tissue regeneration was fabricated using 3D printing technology which containing a layer of PCL/hydroxyapatite (HA) nanoparticles and another layer of PCL/gelatin with various concentrations of fibrin (10, 20 and 30 wt.%). These printed scaffolds were evaluated with SEM (Scanning Electron Microscopy), FTIR (Fourier Transform Infrared Spectroscopy) and mechanical properties. The results showed that the porous scaffolds fabricated with pore size of 210-255 µm. Following, the ductility increased with the further addition of fibrin in bilayer composites which showed these composites scaffolds are suitable for the cartilage part of osteochondral. Also, the contact angle results demonstrated the incorporation of fibrin in bilayer scaffolds based on PCL matrix, can lead to a decrease in contact angle and result in the improvement of hydrophilicity that confirmed by increasing the degradation rate of scaffolds containing further fibrin percentage. The bioactivity study of bilayer scaffolds indicated that both fibrin and hydroxyapatite can significantly improve the cell attachment on fabricated scaffolds. The MTT assay, DAPI and Alizarin red tests of bilayer composite scaffolds showed that samples containing 30% fibrin have the more biocompatibility than that of samples with 10 and 20% fibrin which indicated the potential of this bilayer scaffold for osteochondral tissue regeneration.

Poly(lactic-co-glycolic acid)(PLGA)/TiO2 nanotube bioactive composite as a novel scaffold for bone tissue engineering: In vitro and in vivo studies.

The aim of this study was to synthesize and characterize novel three-dimensional porous scaffolds made of poly (lactic-co-glycolic acid)/TiO2 nanotube (TNT) composite microspheres for bone tissue engineering applications. The incorporation of TNT greatly increases mechanical properties of PLGA/TNT microsphere-sintered scaffold. The experimental results exhibit that the PLGA/0.5 wt% TNT scaffold sintered at 100 °C for 3 h showed the best mechanical properties and a proper pore structure for tissue engineering. Biodegradation test ascertained that the weight of both PLGA and PLGA/PLGA/0.5 wt% TiO2 nanotube composites slightly reduced during the first 4 weeks following immersion in SBF solution. Moreover, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay and alkaline phosphatase activity (ALP activity) results represent increased cell viability for PLGA/0.5%TNT composite scaffold in comparison to the control group. In vivo studies show the amount of bone formation for PLGA/TNT was approximately twice of pure PLGA. Vivid histologic images of the newly generated bone on the implants further supported our test results. Eventually, a mathematical model showed that both PLGA and PLGA/TNT scaffolds' mechanical properties follow an exponential trend with time as their degradation occurs. By a three-dimensional finite element model, a more monotonous distribution of stress was present in the scaffold due to the presence of TNT with a reduction in maximum stress on bone.

Enhancing Mechanical and Biological Properties of Zinc Phosphate Dental Cement with Akermanite and Hardystonite Nanoparticles: A Synthesis and Characterization Study.

This study investigates the potential of incorporating akermanite and hardystonite nanoparticles (NPs) into commercially available zinc phosphate cement. Akermanite and hardystonite NPs were synthesized through a mechanical route and characterized using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The NPs were then added to the cement at a concentration of 5 wt%, and the physical and biological properties of the resulting composite were evaluated. The results showed that the incorporation of NPs led to a significant reduction in porosity (from 12.4% to 5.6%) and a notable improvement in compressive strength (from 90 to 120 MPa) compared to the control group. MTT assay revealed that the cement containing NPs exhibited no significant toxicity and even promoted cell growth and proliferation. Specifically, cell viability increased by 15%, and cell proliferation rate increased by 20% compared to the control group. These findings suggest that the designed cement has suitable mechanical and biological properties, making it a promising material for dental and orthopedic applications.

Structure and mobility of nanoconfined polyamide-6,6 oligomers: application of a molecular dynamics technique with constant temperature, surface area, and parallel pressure.

A molecular dynamics simulation method with coupling to an external bath is used to simulate polyamide-6,6 trimers confined between graphite surfaces. In this simulation method, the temperature and the parallel component of pressure are kept fixed, and the distance between the confining graphite surfaces is changed to achieve equilibrium. The simulation results on the oscillatory behavior of solvation force, the number density of confined oligomers, and stepwise variation of the oligomer numbers as a function of distance between the confining graphite surfaces are reported and discussed. The hydrogen bonding in confined oligomers has also been studied in detail, and it is shown that hydrogen-bond formation depends on the layering effect and on the geometrical restrictions and reveals an oscillatory behavior like the solvation force oscillations. The autocorrelation functions for NH, CO, and end-to-end vectors are also studied, and it is concluded that the confined fluid has a considerably lower relaxation time than that of the bulk fluid, and the relaxation times for confined fluid show an oscillatory behavior with maxima corresponding to well-formed structures parallel to the surfaces. The study of local dynamics via calculating the autocorrelation functions for bins parallel to the surfaces reveals that the fluid layers close to the surfaces have higher relaxation times than the fluid in the central region. Our calculated center-of-mass diffusion coefficients also show oscillatory behavior with out-of-phase oscillations with respect to the solvation force oscillations.

Effects of incorporation of 2.5 and 5 wt% TiO2 nanotubes on fracture toughness, flexural strength, and microhardness of denture base poly methyl methacrylate (PMMA).

PURPOSE: The aim of this preliminary study was to investigate, for the first time, the effects of addition of titania nanotubes (n-TiO2) to poly methyl methacrylate (PMMA) on mechanical properties of PMMA denture base. MATERIALS AND METHODS: TiO2 nanotubes were prepared using alkaline hydrothermal process. Obtained nanotubes were assessed using FESEM-EDX, XRD, and FT-IR. For 3 experiments of this study (fracture toughness, three-point bending flexural strength, and Vickers microhardness), 135 specimens were prepared according to ISO 20795-1:2013 (n of each experiment=45). For each experiment, PMMA was mixed with 0% (control), 2.5 wt%, and 5 wt% nanotubes. From each TiO2:PMMA ratio, 15 specimens were fabricated for each experiment. Effects of n-TiO2 addition on 3 mechanical properties were assessed using Pearson, ANOVA, and Tukey tests. RESULTS: SEM images of n-TiO2 exhibited the presence of elongated tubular structures. The XRD pattern of synthesized n-TiO2 represented the anatase crystal phase of TiO2. Moderate to very strong significant positive correlations were observed between the concentration of n-TiO2 and each of the 3 physicomechanical properties of PMMA (Pearson's P value ≤.001, correlation coefficient ranging between 0.5 and 0.9). Flexural strength and hardness values of specimens modified with both 2.5 and 5 wt% n-TiO2 were significantly higher than those of control (P≤.001). Fracture toughness of samples reinforced with 5 wt% n-TiO2 (but not those of 2.5% n-TiO2) was higher than control (P=.002). CONCLUSION: Titania nanotubes were successfully introduced for the first time as a means of enhancing the hardness, flexural strength, and fracture toughness of denture base PMMA.

Efficacy of the biomaterials 3wt%-nanostrontium-hydroxyapatite-enhanced calcium phosphate cement (nanoSr-CPC) and nanoSr-CPC-incorporated simvastatin-loaded poly(lactic-co-glycolic-acid) microspheres in osteogenesis improvement: An explorative multi-phase experimental in vitro/vivo study.

AIMS: The purpose of this multi-phase explorative in vivo animal/surgical and in vitro multi-test experimental study was to (1) create a 3wt%-nanostrontium hydroxyapatite-enhanced calcium phosphate cement (Sr-HA/CPC) for increasing bone formation and (2) creating a simvastatin-loaded poly(lactic-co-glycolic acid) (SIM-loaded PLGA) microspheres plus CPC composite (SIM-loaded PLGA+nanostrontium-CPC). The third goal was the extensive assessment of multiple in vitro and in vivo characteristics of the above experimental explorative products in vitro and in vivo (animal and surgical studies). METHODS AND RESULTS PERTAINING TO SR-HA/CPC: Physical and chemical properties of the prepared Sr-HA/CPC were evaluated. MTT assay and alkaline phosphatase activities, and radiological and histological examinations of Sr-HA/CPC, CPC and negative control were compared. X-ray diffraction (XRD) indicated that crystallinity of the prepared cement increased by increasing the powder-to-liquid ratio. Incorporation of Sr-HA into CPC increased MTT assay (biocompatibility) and ALP activity (P<0.05). Histomorphometry showed greater bone formation after 4weeks, after implantation of Sr-HA/CPC in 10 rats compared to implantations of CPC or empty defects in the same rats (n=30, ANOVA P<0.05). METHODS AND RESULTS PERTAINING TO SIM-LOADED PLGA MICROSPHERES+NANOSTRONTIUM-CPC COMPOSITE: After SEM assessment, the produced composite of microspheres and enhanced CPC were implanted for 8weeks in 10 rabbits, along with positive and negative controls, enhanced CPC, and enhanced CPC plus SIM (n=50). In the control group, only a small amount of bone had been regenerated (localized at the boundary of the defect); whereas, other groups showed new bone formation within and around the materials. A significant difference was found in the osteogenesis induced by the groups sham control (16.96±1.01), bone materials (32.28±4.03), nanostrontium-CPC (24.84±2.6), nanostrontium-CPC-simvastatin (40.12±3.29), and SIM-loaded PLGA+nanostrontium-CPC (44.8±6.45) (ANOVA P<0.001). All the pairwise comparisons were significant (Tukey P<0.01), except that of nanostrontium-CPC-simvastatin and SIM-loaded PLGA+nanostrontium-CPC. This confirmed the efficacy of the SIM-loaded PLGA+nanostrontium-CPC composite, and its superiority over all materials except SIM-containing nanostrontium-CPC.

Molecular dynamics simulation of water influence on local structure of nanoconfined polyamide-6,6.

Our recently developed molecular dynamics simulation method for simulating fluids confined in nanometric pores [Eslami et al. J. Chem. Phys.2008, 129, 194702] is employed to simulate nanoconfined polyamide-6,6+water in contact with graphene monolayers. In this work, a number of dry and wet polymer samples, containing 3 and 6 wt % water at 350 K, confined in pores of different sizes as well as the bulk polymer samples are simulated. It is shown that both water and polymer molecules form organized layers beside the surfaces. The effect of nanoconfinement on the hydrogen bonding in the polymer+water system is studied in detail. It is shown that addition of water to the polymer replaces a fraction of looser amide-amide hydrogen bonds with amide-water ones. The distribution of hydrogen bond lengths shows that both the polymer and water form shorter length hydrogen bonds in the confined region compared to the bulk system. The number of hydrogen bonds between polymer and water molecules is shown to depend on the pore size and on the water content. In small pores, water molecules are forced by the surfaces into the polymer layers and form strong hydrogen bonds with the amide groups, a process that increases the water solubility of the polymer in small pores. Increasing the water content in larger pores increases the number of hydrogen bonds between water molecules and causes the formation of big clusters in the central region of the pore. In simulations of to 50 ns, it is shown that such big clusters grow with of time, and hence, phase separate out from the mixture.