Holography is a technique that is used to display objects or scenes in three dimensions. Such three-dimensional (3D) images, or holograms, can be seen with the unassisted eye and are very similar to how humans see the actual environment surrounding them. The concept of 3D telepresence, a real-time dynamic hologram depicting a scene occurring in a different location, has attracted considerable public interest since it was depicted in the original Star Wars film in 1977. However, the lack of sufficient computational power to produce realistic computer-generated holograms and the absence of large-area and dynamically updatable holographic recording media have prevented realization of the concept. Here we use a holographic stereographic technique and a photorefractive polymer material as the recording medium to demonstrate a holographic display that can refresh images every two seconds. A 50 Hz nanosecond pulsed laser is used to write the holographic pixels. Multicoloured holographic 3D images are produced by using angular multiplexing, and the full parallax display employs spatial multiplexing. 3D telepresence is demonstrated by taking multiple images from one location and transmitting the information via Ethernet to another location where the hologram is printed with the quasi-real-time dynamic 3D display. Further improvements could bring applications in telemedicine, prototyping, advertising, updatable 3D maps and entertainment.

Holographic three-dimensional (3D) displays provide realistic images without the need for special eyewear, making them valuable tools for applications that require situational awareness, such as medical, industrial and military imaging. Currently commercially available holographic 3D displays use photopolymers that lack image-updating capability, resulting in restricted use and high cost. Photorefractive polymers are dynamic holographic recording materials that allow updating of images and have a wide range of applications, including optical correlation, imaging through scattering media and optical communication. To be suitable for 3D displays, photorefractive polymers need to have nearly 100% diffraction efficiency, fast writing time, hours of image persistence, rapid erasure, and large area-a combination of properties that has not been shown before. Here, we report an updatable holographic 3D display based on photorefractive polymers with such properties, capable of recording and displaying new images every few minutes. This is the largest photorefractive 3D display to date (4 x 4 inches in size); it can be recorded within a few minutes, viewed for several hours without the need for refreshing, and can be completely erased and updated with new images when desired.

BackgroundMesenchymal stem cells (MSCs) possess intrinsic regeneration capacity as part of the repair process in response to injury, such as fracture or other tissue injury. Bone marrow and adipose tissue are the major sources of MSCs. However, which cell type is more effective and suitable for cell therapy remains to be answered. The intrinsic molecular mechanism supporting the assertion has also been lacking.MethodsHuman bone marrow-derived MSCs (BMSCs) and adipose tissue-derived MSCs (ATSCs) were isolated from bone marrow and adipose tissue obtained after total hip arthroplasty. ATSCs and BMSCs were incubated in standard growth medium. Trilineage differentiation including osteogenesis, adipogenesis, and chondrogenesis was performed by addition of relevant induction mediums. The expression levels of trilineage differentiation marker genes were evaluated by quantitative RT-PCR. The methylation status of CpG sites of Runx2, PPARγ, and Sox9 promoters were checked by bisulfite sequencing. In addition, ectopic bone formation and calvarial bone critical defect models were used to evaluate the bone regeneration ability of ATSCs and BMSCs in vivo.ResultsThe results showed that BMSCs possessed stronger osteogenic and lower adipogenic differentiation potentials compared to ATSCs. There was no significant difference in the chondrogenic differentiation potential. The CpG sites of Runx2 promoter in BMSCs were hypomethylated, while in ATSCs they were hypermethylated. The CpG sites of PPARγ promoter in ATSCs were hypomethylated, while in BMSCs they were hypermethylated. The methylation status of Sox9 promoter in BMSCs was only slightly lower than that in ATSCs.ConclusionsThe epigenetic memory obtained from either bone marrow or adipose tissue favored MSC differentiation along an osteoblastic or adipocytic lineage. The methylation status of the main transcription factors controlling MSC fate contributes to the differential differentiation capacities of different source-derived MSCs.Electronic supplementary materialThe online version of this article (doi:10.1186/s13287-017-0716-x) contains supplementary material, which is available to authorized users.

This paper describes the synthesis and characterization of self-assembled second-order nonlinear optical multilayer materials containing the high-hyperpolarizability [(aminophenyl)azo]pyridinium chromophore. The chromophoric multilayers are assembled on clean glass or single-crystal silicon substrates via the following iterative reaction sequence:  (1) treatment with 4-ClCH2C6H4SiCl3, 3-BrC3H6SiCl3, or 3-IC3H6SiCl3 to afford a self-assembled coupling layer; (2) quaternization of 4-[[4-[N,N-bis(hydroxylethyl)amino]phenyl]azo]pyridine in a “topotactic” fashion to generate an [(aminophenyl)azo]pyridinium chromophore layer; (3) cross-linking with octachlorotrisiloxane to afford a capping layer (which also regenerates surface hydroxyl groups for subsequent layer deposition). The new chromophore precursor 4-[[4-[N,N-bis(hydroxylethyl)-amino]phenyl]azo]pyridine was synthesized by diazotization of 4-aminopyridine followed by coupling with N-phenyldiethanolamine and has been characterized by elemental analysis, mass spectrometry, and infrared, UV−vis, and NMR spectroscopies. The chromophoric multilayers have been characterized by X-ray photoelectron and transmission optical spectroscopies, spectroscopic ellipsometry, X-ray reflectivity, advancing contact angle measurements, and polarized second harmonic generation (SHG). The excellent structural regularity of the chromophoric multilayers is indicated by the linear dependence of the [(aminophenyl)azo]pyridinium chromophore longitudinal HOMO → LUMO charge-transfer excitation absorbance at 572 nm and the ellipsometry- and X-ray reflectivity-derived multilayer thicknesses on the number of assembled trilayers, while the uniform polar order of the stacked chromophoric multilayers is evidenced by the quadratic dependence of the second harmonic generation intensities on the number of trilayers. The [(aminophenyl)azo]pyridinium multilayers are photochemically stable, have very high structural regularities, and exhibit a second-order nonlinear optical susceptibility (χ(2)) of ∼3.6 × 10-7 esu (∼150 pm/V) at a fundamental wavelength of 1064 nm. Finally, atomic force microscopy reveals that the surfaces of the self-assembled multilayers are very smooth (root mean square roughness = 12 Å for a 10 trilayer sample), undoubtedly reflecting the high three-dimensional structural regularities of the individual layers.