Modulation of Stiffness-Dependent Macrophage Inflammatory Responses by Collagen Deposition.

Macrophages are innate immune cells that interact with complex extracellular matrix environments, which have varied stiffness, composition, and structure, and such interactions can lead to the modulation of cellular activity. Collagen is often used in the culture of immune cells, but the effects of substrate functionalization conditions are not typically considered. Here, we show that the solvent system used to attach collagen onto a hydrogel surface affects its surface distribution and organization, and this can modulate the responses of macrophages subsequently cultured on these surfaces in terms of their inflammatory activation and expression of adhesion and mechanosensitive molecules. Collagen was solubilized in either acetic acid (Col-AA) or N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid (HEPES) (Col-HEP) solutions and conjugated onto soft and stiff polyacrylamide (PA) hydrogel surfaces. Bone marrow-derived macrophages cultured under standard conditions (pH 7.4) on the Col-HEP-derived surfaces exhibited stiffness-dependent inflammatory activation; in contrast, the macrophages cultured on Col-AA-derived surfaces expressed high levels of inflammatory cytokines and genes, irrespective of the hydrogel stiffness. Among the collagen receptors that were examined, leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) was the most highly expressed, and knockdown of the Lair-1 gene enhanced the secretion of inflammatory cytokines. We found that the collagen distribution was more homogeneous on Col-AA surfaces but formed aggregates on Col-HEP surfaces. The macrophages cultured on Col-AA PA hydrogels were more evenly spread, expressed higher levels of vinculin, and exerted higher traction forces compared to those of cells on Col-HEP. These macrophages on Col-AA also had higher nuclear-to-cytoplasmic ratios of yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), key molecules that control inflammation and sense substrate stiffness. Our results highlight that seemingly slight variations in substrate deposition for immunobiology studies can alter critical immune responses, and this is important to elucidate in the broader context of immunomodulatory biomaterial design.

Biophysical regulation of macrophages in health and disease.

Macrophages perform critical functions for homeostasis and immune defense in tissues throughout the body. These innate immune cells are capable of recognizing and clearing dead cells and pathogens, and orchestrating inflammatory and healing processes that occur in response to injury. In addition, macrophages are involved in the progression of many inflammatory diseases including cardiovascular disease, fibrosis, and cancer. Although it has long been known that macrophages respond dynamically to biochemical signals in their microenvironment, the role of biophysical cues has only recently emerged. Furthermore, many diseases that involve macrophages are also characterized by changes to the tissue biophysical environment. This review will discuss current knowledge about the effects of biophysical cues including matrix stiffness, material topography, and applied mechanical forces, on macrophage behavior. We will also describe the role of molecules that are known to be important for mechanotransduction, including adhesion molecules, ion channels, as well as nuclear mediators such as transcription factors, scaffolding proteins, and epigenetic regulators. Together, this review will illustrate a developing role of biophysical cues in macrophage biology, and also speculate upon molecular targets that may potentially be exploited therapeutically to treat disease.

Design and evaluation of cryodevice, an easy to use apparatus for maintenance of optimum temperature during cryoglobulin assay.

INTRODUCTION: Maintenance of temperature during collection and transport of blood is an important pre-requisite for cryoglobulin assays. In this manuscript, we describe 'cryodevice', a low-cost device for transportation and/or incubation of vials of whole blood at 37°C. Such a device would reduce false negatives in cryoglobulin assays. METHOD: The 'cryodevice' takes the embodiment of a portable, light, insulated water bath, which can be used as an incubator in a plugged-in state, or as a transport container after it is set up and disconnected from the power supply. The design of the cryodevice is described here, with focus on its construction and electronic control circuit. Computer simulations and in vitro trials were performed to study the temperature drop in the blood samples placed in the device. Subsequently, the cryodevice was also used with actual patient blood samples. RESULTS: Thermal simulations and in vitro testing of the cryodevice predicted that the design would meet the temperature maintenance goals. When the cryodevice was put in to use for screening 45 patient blood samples, it helped identify positive cryoglobulinemia in three of the samples. CONCLUSION: The description of the cryodevice envisions enabling the construction of a low-cost device in resource-limited healthcare settings in India created with locally available resources. On testing, the device was found to be satisfactory in performance and is expected to bring down incidences of false negatives in cryoglobulin tests.