Magnitude-dependent and inversely-related osteogenic/chondrogenic differentiation of human mesenchymal stem cells under dynamic compressive strain.

Biomechanical forces have been shown to significantly affect tissue development, morphogenesis, pathogenesis and healing, especially in orthopaedic tissues. Such biological processes are critically related to the differentiation of human mesenchymal stem cells (hMSCs). However, the mechanistic details regarding how mechanical forces direct MSC differentiation and subsequent tissue formation are still elusive. Electrospun three-dimensional scaffolds were used to culture and subject hMSCs to various magnitudes of dynamic compressive strains at 5, 10, 15 or 20% (ε = 0.05, 0.10, 0.15, 0.20) at a frequency of 1 Hz for 2 h daily for up to 28 days in osteogenic media. Gene expression of chondrogenic markers (ACAN, COL2A1, SOX9) and glycosaminoglycan (GAG) synthesis were upregulated in response to the increased magnitudes of compressive strain, whereas osteogenic markers (COL1A1, SPARC, RUNX2) and calcium deposition had noticeable decreases by compressive loading in a magnitude-dependent manner. Dynamic mechanical analysis showed enhanced viscoelastic modulus with respect to the increased dynamic strain peaking at 15%, which coincides with the maximal GAG synthesis. Furthermore, polarization-sensitive optical coherence tomography revealed that mechanical loading enhanced the alignment of extracellular matrix to the greatest level by 15% strain as well. Overall, we show that the degree of differentiation of hMSCs towards osteogenic or chondrogenic lineage is inversely related, and it depends on the magnitude of dynamic compressive strain. These results demonstrate that multiphenotypic differentiation of hMSCs can be controlled by varying the strain regimens, providing a novel strategy to modulate differentiation specification and tissue morphogenesis. Copyright © 2016 John Wiley & Sons, Ltd.

Collagen denaturation can be quantified in burned human skin using polarization-sensitive optical coherence tomography.

Quantifiable prognostic indicators are of considerable practical value following thermal injury. Collagen is a major component of the skin, and is known to undergo denaturation at the elevated temperatures associated with burns. The purpose of this study was to determine whether a recently developed, non-invasive imaging technique could detect and quantify collagen denaturation in burned human skin. Polarization-sensitive optical coherence tomography (PS-OCT) imaging was used to quantify collagen birefringence in normal human skin, and in skin excised from burn patients. Images were acquired and displayed in 1s, and demonstrated qualitative differences between normal and partial-thickness burned human skin. Birefringence loss due to thermal denaturation of collagen was quantified, with mean phase retardation rates for samples of 26 normal and 26 burned skin sites determined to be 0.401 +/- 0.020 and 0.249 +/- 0.017 degrees /microm, respectively (mean +/- S.E.M.), with this difference in sample means shown to be statistically significant (P < 0.000001). Analysis of the accuracy of the technique indicated that PS-OCT measurements may be made with resolution sufficient to distinguish between burns of varying severity. In conclusion, PS-OCT is capable of imaging and quantifying collagen denaturation in burned human skin, providing a new parameter against which post-injury outcome may be compared.

Birefringence measurements in human skin using polarization-sensitive optical coherence tomography.

Optical coherence tomography enables cross-sectional imaging of tissue structure to depths of around 1.5 mm, at high-resolution and in real time. Incorporation of polarization sensitivity (PS) provides an additional contrast mechanism which is complementary to images mapping backscattered intensity only. We present here polarization-sensitive optical coherence tomography (OCT) images of human skin in vivo, demonstrating the ability of the technique to visualize and quantify the birefringent properties of skin. Variation in normal skin birefringence according to anatomical location is demonstrated, and discussed in relation to collagen distribution at each location. From measurements on a sample of five human volunteers, mean double-pass phase retardation rates of 0.340+/-0.143, 0.250+/-0.076, and 0.592+/-0.142 deg/microm were obtained for the dorsal hand, temple, and lower back regions, respectively. We demonstrate how averaging the Stokes parameters of backscattered light over a range of axial and lateral dimensions results in a reduction of speckle-induced noise. Examples of PS-OCT images from skin sites following wound healing and repair are also presented and discussed.

Simultaneous intensity, birefringence, and flow measurements with high-speed fiber-based optical coherence tomography.

We demonstrate that tissue structure, birefringence, and blood flow can be imaged simultaneously by use of techniques of polarization-sensitive optical coherence tomography and phase-resolved optical Doppler tomography. An efficient data-acquisition procedure is implemented that optimizes the concurrent processing and display of all three image types. Images of in vivo human skin acquired with a high-speed fiber-based system are presented.