Radial matrix constraint influences tissue contraction and promotes maturation of bi-layered skin equivalents.

Human skin equivalents (HSEs) serve as important tools for mechanistic studies with human skin cells, drug discovery, pre-clinical applications in the field of tissue engineering and for skin transplantation on skin defects. Besides the cellular and extracellular matrix (ECM) components used for HSEs, physical constraints applied on the scaffold during HSEs maturation influence tissue organization, functionality, and homogeneity. In this study, we introduce a 3D-printed culture insert that exposes bi-layered HSEs to a static radial constraint through matrix adhesion. We examine the effect of various diameters of the ring-shaped culture insert on the HSE's characteristics and compare them to state-of-the-art unconstrained and planar constrained HSEs. We show that radial matrix constraint of HSEs regulates tissue contraction, promotes fibroblast and matrix organization that is similar to human skin in vivo and improves keratinocyte differentiation, epidermal stratification, and basement membrane formation depending on the culture insert diameter. Together, these data demonstrate that the degree of HSE's contraction is an important design consideration in skin tissue engineering. Therefore, this study can help to mimic various in vivo skin conditions and to increase the control of relevant tissue properties.

Stable Ultraconcentrated and Ultradilute Colloids of CsPbX3 (X = Cl, Br) Nanocrystals Using Natural Lecithin as a Capping Ligand.

Attaining thermodynamic stability of colloids in a broad range of concentrations has long been a major thrust in the field of colloidal ligand-capped semiconductor nanocrystals (NCs). This challenge is particularly pressing for the novel NCs of cesium lead halide perovskites (CsPbX3; X = Cl, Br) owing to their highly dynamic and labile surfaces. Herein, we demonstrate that soy lecithin, a mass-produced natural phospholipid, serves as a tightly binding surface-capping ligand suited for a high-reaction yield synthesis of CsPbX3 NCs (6-10 nm) and allowing for long-term retention of the colloidal and structural integrity of CsPbX3 NCs in a broad range of concentrations-from a few ng/mL to >400 mg/mL (inorganic core mass). The high colloidal stability achieved with this long-chain zwitterionic ligand can be rationalized with the Alexander-De Gennes model that considers the increased particle-particle repulsion due to branched chains and ligand polydispersity. The versatility and immense practical utility of such colloids is showcased by the single NC spectroscopy on ultradilute samples and, conversely, by obtaining micrometer-thick, optically homogeneous dense NC films in a single spin-coating step from ultraconcentrated colloids.

Colloidal CsPbX3 (X = Cl, Br, I) Nanocrystals 2.0: Zwitterionic Capping Ligands for Improved Durability and Stability.

Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and optoelectronic applications are hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping molecules during isolation and purification. To address this issue, herein, we propose a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic molecules such as 3-(N,N-dimethyloctadecylammonio)propanesulfonate, resulting in much improved chemical durability. In particular, this class of ligands allows for the isolation of clean NCs with high photoluminescence quantum yields (PL QYs) of above 90% after four rounds of precipitation/redispersion along with much higher overall reaction yields of uniform and colloidal dispersible NCs. Densely packed films of these NCs exhibit high PL QY values and effective charge transport. Consequently, they exhibit photoconductivity and low thresholds for amplified spontaneous emission of 2 µJ cm-2 under femtosecond optical excitation and are suited for efficient light-emitting diodes.