The human amniotic membrane (hAM) is a collagen-based extracellular matrix derived from the human placenta. It is a readily available, inexpensive, and naturally biocompatible material. Over the past decade, the development of tissue engineering and regenerative medicine, along with new decellularization protocols, has recast this simple biomaterial as a tunable matrix for cellularized tissue engineered constructs. Thanks to its biocompatibility, decellularized hAM is now commonly used in a broad range of medical fields. New preparation techniques and composite scaffold strategies have also emerged as ways to tune the properties of this scaffold. The current state of understanding about the hAM as a biomaterial is summarized in this review. We examine the processing techniques available for the hAM, addressing their effect on the mechanical properties, biodegradation, and cellular response of processed scaffolds. The latest in vitro applications, in vivo studies, clinical trials, and commercially available products based on the hAM are reported, organized by medical field. We also look at the possible alterations to the hAM to tune its properties, either through composite materials incorporating decellularized hAM, chemical cross-linking, or innovative layering and tissue preparation strategies. Overall, this review compiles the current literature about the myriad capabilities of the human amniotic membrane, providing a much-needed update on this biomaterial.
It is becoming more apparent in tissue engineering applications that fine temporal control of multiple therapeutics is desirable to modulate progenitor cell fate and function. Herein, the independent temporal control of the co‐delivery of miR‐148b and miR‐21 mimic plasmonic nanoparticle conjugates to induce osteogenic differentiation of human adipose stem cells (hASCs), in a de novo fashion, is described. By applying a thermally labile retro‐Diels–Alder caging and linkage chemistry, these miRNAs can be triggered to de‐cage serially with discrete control of activation times. The method relies on illumination of the nanoparticles at their resonant wavelengths to generate sufficient local heating and trigger the untethering of the Diels–Alder cycloadduct. Characterization of the photothermal release using fluorophore‐tagged miRNA mimics in vitro is carried out with fluorescence measurements, second harmonic generation, and confocal imaging. Osteogenesis of hASCs from the sequential co‐delivery of miR‐21 and miR‐148b mimics is assessed using xylenol orange and alizarin red staining of deposited minerals, and quantitative polymerase chain reaction for gene expression of osteogenic markers. The results demonstrate that sequential miRNA mimic activation results in upregulation of osteogenic markers and mineralization relative to miR‐148b alone, and co‐activation of miR‐148b and miR‐21 at the same time.
The mechanical properties of soft materials are critically important for a wide range of applications ranging from packaging to biomedical purposes. We have constructed a simple mechanical testing apparatus using off-the-shelf materials and open-source software for a total cost of less than $100. The device consists of a wooden frame supporting a central loading apparatus attached via drawer slides. To perform a mechanical test, a sample is secured within two custom-made 3D-printed clamps affixed to brackets on the base of the frame and the load cell. The extension force is applied by the user pulling on a rope, moving the central loading apparatus up (thereby stretching the sample) while recording the force (measured by a load cell) and the displacement (measured by an ultrasonic sensor). The load cell and ultrasonic sensor are linked to an Arduino microcontroller connected to a laptop through a USB port for data acquisition and analysis. This instrument was easy to assemble and enabled students to better grasp the meaning of tensile testing while promoting experimentation with electronics, computer programming, and mechanical design. Because of its low cost and ease of use, this Arduino-based uniaxial tensile tester can be an ideal device to introduce the concepts of mechanical properties, among other concepts, to students in numerous fields.
Cardiovascular mechanical stresses trigger physiological and pathological cellular reactions including secretion of Transforming Growth Factor β1 ubiquitously in a latent form (LTGF-β1). While complex shear stresses can activate LTGF-β1, the mechanisms underlying LTGF-β1 activation remain unclear. We hypothesized that different types of shear stress differentially activate LTGF-β1. We designed a custom-built cone-and-plate device to generate steady shear (SS) forces, which are physiologic, or oscillatory shear (OSS) forces characteristic of pathologic states, by abruptly changing rotation directions. We then measured LTGF-β1 activation in platelet releasates. We modeled and measured flow profile changes between SS and OSS by computational fluid dynamics (CFD) simulations. We found a spike in shear rate during abrupt changes in rotation direction. OSS activated TGF-β1 levels significantly more than SS at all shear rates. OSS altered oxidation of free thiols to form more high molecular weight protein complex(es) than SS, a potential mechanism of shear-dependent LTGF-β1 activation. Increasing viscosity in platelet releasates produced higher shear stress and higher LTGF-β1 activation. OSS-generated active TGF-β1 stimulated higher pSmad2 signaling and endothelial to mesenchymal transition (EndoMT)-related genes PAI-1, collagen, and periostin expression in endothelial cells. Overall, our data suggest variable TGF-β1 activation and signaling occurs with competing blood flow patterns in the vasculature to generate complex shear stress, which activates higher levels of TGF-β1 to drive vascular remodeling.
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