Studies of Attosecond Time Delay and Superheavy Elements in Atomic Photoionization

This research consists of two distinct but related elements in the realm of atomic photoionization. The first was to explore the photoionization in superheavy elements. Employing the fully Relativistic Random Phase Approximation (RRPA), we calculated the photoionization cross sections for the Oganesson (Og), the heaviest element, since the influence of relativity becomes more significant as the atomic number increases. The results revealed the importance of relativistic interactions along with the predominant influence of interchannel coupling on the photoionization cross sections. Encouraged by the ability of the RRPA to deal with the combination of relativistic and many-body correlation effects, we proceeded to investigate the angle-dependent time delay in the photoionization process using the RRPA. Specifically, we investigated the time delay in argon. The matrix elements calculated using RRPA were used to calculate the phases of the various photoionization amplitudes, and the energy derivative of these phases provided us with the time delay information. We computed a weighted average of the time delays associated with dipole and quadrupole components, averaged over photoelectron spin and orientation of the residual ion, considering different transitions involved in the photoionization process. Time delay in photoionization exhibits angular dependence, a phenomenon explored in previous calculations considering only dipole transitions. In the nonrelativistic dipole approximation, time delay for atomic ns-states is angle-independent. However, incorporating relativistic effects, such as spin-flip transitions and non-dipole (quadrupole) effects, introduces angular dependence to the time delay. This is especially prominent when dominant dipole photoionization channels (without spin-flip) vanish at specific angles due to angular momentum geometry. In these instances, quadrupole and spin-flip transitions dominate. When the dipole amplitude vanishes, time delay results from a combination of spin-flip dipole and quadrupole time delays. Relativistic expressions have been formulated to delineate the conditions where quadrupole and/or spin-flip channels influence the time delay. We focus on the 3s subshell in argon to highlight the complex effects of spin-flip and quadrupole transitions. Of particular interest is the presence of a significant Cooper minimum in the cross section, leading to notably long time delays. Our goal is to explore these dynamics and understand the intricate processes in photoionization

Micro- and nanoengineering approaches to control stem cell-biomaterial interactions.

As our population ages, there is a greater need for a suitable supply of engineered tissues to address a range of debilitating ailments. Stem cell based therapies are envisioned to meet this emerging need. Despite significant progress in controlling stem cell differentiation, it is still difficult to engineer human tissue constructs for transplantation. Recent advances in micro- and nanofabrication techniques have enabled the design of more biomimetic biomaterials that may be used to direct the fate of stem cells. These biomaterials could have a significant impact on the next generation of stem cell based therapies. Here, we highlight the recent progress made by micro- and nanoengineering techniques in the biomaterials field in the context of directing stem cell differentiation. Particular attention is given to the effect of surface topography, chemistry, mechanics and micro- and nanopatterns on the differentiation of embryonic, mesenchymal and neural stem cells

Fiber-based tissue engineering: Progress, challenges, and opportunities.

Tissue engineering aims to improve the function of diseased or damaged organs by creating biological substitutes. To fabricate a functional tissue, the engineered construct should mimic the physiological environment including its structural, topographical, and mechanical properties. Moreover, the construct should facilitate nutrients and oxygen diffusion as well as removal of metabolic waste during tissue regeneration. In the last decade, fiber-based techniques such as weaving, knitting, braiding, as well as electrospinning, and direct writing have emerged as promising platforms for making 3D tissue constructs that can address the abovementioned challenges. Here, we critically review the techniques used to form cell-free and cell-laden fibers and to assemble them into scaffolds. We compare their mechanical properties, morphological features and biological activity. We discuss current challenges and future opportunities of fiber-based tissue engineering (FBTE) for use in research and clinical practice

Emerging micro- and nanotechnologies in cancer diagnosis and therapy

Understanding the mechanism of cancer cell metastasis is crucial for targeted cancer diagnosis and research. But this process is still not fully understood mainly because of lack of in vitro cell culture models that precisely mimic the physiological complexities of cancer cell intravascular flows, invasion, adhesion, metastasis, angiogenesis and migration to specific sites. Micro- and nanoscale technologies offer a promising tool for such purpose.National Institutes of Health (U.S.) (Grant 1R01CA139070

Modular microporous hydrogels formed from microgel beads with orthogonal thermo-chemical responsivity: Microfluidic fabrication and characterization.

Despite the significant advances in designing injectable bulk hydrogels, the inability to control the pore interconnectivity and decoupling it from the matrix stiffness has tremendously limited the applicability of stiff, flowable hydrogels for 3D cellular engineering, e.g., in hard tissue engineering. To overcome this persistent challenge, here, we introduce a universal method to convert thermosensitive macromolecules with chemically-crosslinkable moieties into annealable building blocks, forming 3D microporous beaded scaffolds in a bottom-up approach. In particular, we show gelatin methacryloyl (GelMA), a widely used biomaterial in tissue engineering, may be converted into physically-crosslinked microbeads using a facile microfluidic approach, followed by flow of the microbead suspension and chemical crosslinking in situ to fabricate microporous beaded GelMA (B-GelMA) scaffolds with interconnected pores, promoting cell functionality and rapid (within minutes) 3D seeding in stiff scaffolds, which are otherwise impossible in the bulk gel counterparts. This novel approach may set the stage for the next generation modular hydrogels with orthogonal porosity and stiffness made up of a broad range of natural and synthetic biomaterials. •This method combines well-known flow focusing microfluidic devices with facile post-processing steps to fabricate microporous scaffolds.•Temperature-driven physical crosslinking of the microbeads enables the facile purification of gel building blocks without further chemical reactions.•This method provides a simple approach to fabricate microporous scaffolds, which overcomes some of the challenges of newly emerging beaded scaffolds, including oxygen-mediated impaired crosslinking

DNA directed self-assembly of shape-controlled hydrogels

Using DNA as programmable, sequence specific ‘glues’, shape-controlled hydrogel units are self-assembled into prescribed structures. Here we report that aggregates are produced using hydrogel cubes with edge length ranging from 30 micrometers to 1 millimeter, demonstrating assembly across scales. In a simple one-pot agitation reaction, 25 dimers are constructed in parallel from 50 distinct hydrogel cube species, demonstrating highly multiplexed assembly. Using hydrogel cuboids displaying face-specific DNA glues, diverse structures are achieved in aqueous and in interfacial agitation systems. These include dimers, extended chains, and open network structures in an aqueous system; and dimers, chains of fixed length, T-junctions, and square shapes in the interfacial system, demonstrating the versatility of the assembly system

The mechanical properties and cytotoxicity of cell-laden double-network hydrogels based on photocrosslinkable gelatin and gellan gum biomacromolecules

A major goal in the application of hydrogels for tissue engineering scaffolds, especially for load-bearing tissues such as cartilage, is to develop hydrogels with high mechanical strength. In this study, a double-network (DN) strategy was used to engineer strong hydrogels that can encapsulate cells. We improved upon previously studied double-network (DN) hydrogels by using a processing condition compatible with cell survival. The DN hydrogels were created by a two-step photocrosslinking using gellan gum methacrylate (GGMA) for the rigid and brittle first network, and gelatin methacrylamide (GelMA) for the soft and ductile second network. We controlled the degree of methacrylation of each polymer so that they obtain relevant mechanical properties as each network. The DN was formed by photocrosslinking the GGMA, diffusing GelMA into the first network, and photocrosslinking the GelMA to form the second network. The formation of the DN was examined by diffusion tests of the large GelMA molecules into the GGMA network, the resulting enhancement in the mechanical properties, and the difference in mechanical properties between GGMA/GelMA single networks (SN) and DNs. The resulting DN hydrogels exhibited the compressive failure stress of up to 6.9 MPa, which approaches the strength of cartilage. It was found that there is an optimal range of the crosslink density of the second network for high strength of DN hydrogels. DN hydrogels with a higher mass ratio of GelMA to GGMA exhibited higher strength, which shows promise in developing even stronger DN hydrogels in the future. Three dimensional (3D) encapsulation of NIH-3T3 fibroblasts and the following viability test showed the cell-compatibility of the DN formation process. Given the high strength and the ability to encapsulate cells, the DN hydrogels made from photocrosslinkable macromolecules could be useful for the regeneration of load-bearing tissues.Samsung Scholarship FoundationNational Institutes of Health (U.S.) (HL092836)National Institutes of Health (U.S.) (EB02597)National Institutes of Health (U.S.) (AR057837)National Science Foundation (U.S.) (CAREER Award DMR0847287)United States. Office of Naval Research (Young Investigator Award

Endovascular Embolization by Transcatheter Delivery of Particles: Past, Present, and Future.

Minimally invasive techniques to occlude flow within blood vessels, initially pioneered in the 1970s with autologous materials and subsequently advanced with increasingly sophisticated engineered biomaterials, are routinely performed for a variety of medical conditions. Contemporary interventional radiologists have at their disposal a wide armamentarium of occlusive agents to treat a range of disease processes through a small incision in the skin. In this review, we provide a historical perspective on endovascular embolization tools, summarize the current state-of-the-art, and highlight burgeoning technologies that promise to advance the field in the near future

A multilayered microfluidic blood vessel-like structure

There is an immense need for tissue engineered blood vessels. However, current tissue engineering approaches still lack the ability to build native blood vessel-like perfusable structures with multi-layered vascular walls. This paper demonstrated a new method to fabricate tri-layer biomimetic blood vessel-like structures on a microfluidic platform using photocrosslinkable gelatin hydrogel. The presented method enables fabrication of physiological blood vessel-like structures with mono-, bi- or tri-layer vascular walls. The diameter of the vessels, the total thickness of the vessel wall and the thickness of each individual layer of the wall were independently controlled. The developed fabrication process is a simple and rapid method, allowing the physical fabrication of the vascular structure in minutes, and the formation of a vascular endothelial cell layer inside the vessels in 3–5 days. The fabricated vascular constructs can potentially be used in numerous applications including drug screening, development of in vitro models for cardiovascular diseases and/or cancer metastasis, and study of vascular biology and mechanobiology.American University of Beirut (startup grant and University Research Board grant)National Council for Scientific Research (Lebanon)National Science Foundation (U.S.) (EFRI-1240443)Immodgel (602694)National Institutes of Health (U.S.) (EB012597, AR057837, DE021468, HL099073, AI105024, AR063745)National Institute of General Medical Sciences (U.S.) ( Award Number P20GM103638-04)King Abdulaziz City for Science and Technology (Grant No. 12-MED3096-3