Progress in material design for biomedical applications

Biomaterials that interface with biological systems are used to deliver drugs safely and efficiently; to prevent, detect, and treat disease; to assist the body as it heals; and to engineer functional tissues outside of the body for organ replacement. The field has evolved beyond selecting materials that were originally designed for other applications with a primary focus on properties that enabled restoration of function and mitigation of acute pathology. Biomaterials are now designed rationally with controlled structure and dynamic functionality to integrate with biological complexity and perform tailored, high-level functions in the body. The transition has been from permissive to promoting biomaterials that are no longer bioinert but bioactive. This perspective surveys recent developments in the field of polymeric and soft biomaterials with a specific emphasis on advances in nano- to macroscale control, static to dynamic functionality, and biocomplex materials.National Institutes of Health. National Heart, Lung, and Blood Institute (Ruth L. Kirschstein National Research Service Award (F32HL1220090)

Surface-Enforced Alignment of Reprogrammable Liquid Crystalline Elastomers

Liquid crystalline elastomers (LCEs) are stimuli-responsive materials capable of undergoing large deformations. The thermomechanical response of LCEs is attributable to the coupling of polymer network properties and disruption of order between liquid crystalline mesogens. Complex deformations have been realized in LCEs by either programming the nematic director via surface-enforced alignment or localized mechanical deformation in materials incorporating dynamic covalent chemistries. Here, the preparation of LCEs via thiol-Michael addition reaction is reported that are amenable to surface-enforced alignment. Afforded by the thiol-Michael addition reaction, dynamic covalent bonds are uniquely incorporated in chemistries subject to surface-enforce alignment. Accordingly, LCEs prepared with complex director profiles are able to be programmed and reprogrammed by (re)activating the dynamic covalent chemistry to realize distinctive shape transformations. &nbsp;</p

Cover Image Defining the Cardiac Fibroblast Secretome in a Fibrotic Microenvironment

Background Cardiac fibroblasts (CFs) have the ability to sense stiffness changes and respond to biochemical cues to modulate their states as either quiescent or activated myofibroblasts. Given the potential for secretion of bioactive molecules to modulate the cardiac microenvironment, we sought to determine how the CF secretome changes with matrix stiffness and biochemical cues and how this affects cardiac myocytes via paracrine signaling. Methods and Results Myofibroblast activation was modulated in vitro by combining stiffness cues with TGF&beta;1 (transforming growth factor &beta; 1) treatment using engineered poly (ethylene glycol) hydrogels, and in vivo with isoproterenol treatment. Stiffness, TGF&beta;1, and isoproterenol treatment increased AKT (protein kinase B) phosphorylation, indicating that this pathway may be central to myofibroblast activation regardless of the treatment. Although activation of AKT was shared, different activating cues had distinct effects on downstream cytokine secretion, indicating that not all activated myofibroblasts share the same secretome. To test the effect of cytokines present in the CF secretome on paracrine signaling, neonatal rat ventricular cardiomyocytes were treated with CF conditioned media. Conditioned media from myofibroblasts cultured on stiff substrates and activated by TGF&beta;1 caused hypertrophy, and one of the cytokines in that media was insulin growth factor 1, which is a known mediator of cardiac myocyte hypertrophy. Conclusions Culturing CFs on stiff substrates, treating with TGF&beta;1, and in vivo treatment with isoproterenol all caused myofibroblast activation. Each cue had distinct effects on the secretome or genes encoding the secretome, but only the secretome of activated myofibroblasts on stiff substrates treated with TGF&beta;1 caused myocyte hypertrophy, most likely through insulin growth factor 1.</p

Cardiac Fibroblasts Mediate a Sexually Dimorphic Fibrotic Response to beta-Adrenergic Stimulation

Background Biological sex is an important modifier of cardiovascular disease and women generally have better outcomes compared with men. However, the contribution of cardiac fibroblasts (CFs) to this sexual dimorphism is relatively unexplored. Methods and Results Isoproterenol (ISO) was administered to rats as a model for chronic &beta;‐adrenergic receptor (&beta;‐AR)‐mediated cardiovascular disease. ISO‐treated males had higher mortality than females and also developed fibrosis whereas females did not. Gonadectomy did not abrogate this sex difference. To determine the cellular contribution to this phenotype, CFs were studied. CFs from both sexes had increased proliferation in vivo in response to ISO, but CFs from female hearts proliferated more than male cells. In addition, male CFs were significantly more activated to myofibroblasts by ISO. To investigate potential regulatory mechanisms for the sexually dimorphic fibrotic response, &beta;‐AR mRNA and PKA (protein kinase A) activity were measured. In response to ISO treatment, male CFs increased expression of &beta;1‐ and &beta;2‐ARs, whereas expression of both receptors decreased in female CFs. Moreover, ISO‐treated male CFs had higher PKA activity relative to vehicle controls, whereas ISO did not activate PKA in female CFs. Conclusions Chronic in vivo &beta;‐AR stimulation causes fibrosis in male but not female rat hearts. Male CFs are more activated than female CFs, consistent with elevated fibrosis in male rat hearts and may be caused by higher &beta;‐AR expression and PKA activation in male CFs. Taken together, our data suggest that CFs play a substantial role in mediating sex differences observed after cardiac injury. </div

Photo-expansion microscopy enables super-resolution imaging of cells embedded in 3D hydrogels

Hydrogels are extensively used as tunable, biomimetic 3D cell culture matrices, but optically deep, high-resolution images are often difficult to obtain, limiting nanoscale quantification of cell-matrix interactions and outside-in signaling. Herein, we present photopolymerized hydrogels for expansion microscopy (PhotoExM) that enable optical clearance and tunable 4.6-6.7x homogenous expansion of not only monolayer cell cultures and tissue sections, but cells embedded within hydrogels. The PhotoExM formulation relies on a rapid photoinitiated thiol/acrylate mixed-mode polymerization that is not inhibited by oxygen and decouples monomer diffusion from polymerization, which is particularly beneficial when expanding cells embedded within hydrogels. Using this technology, we visualize human mesenchymal stem cells (hMSCs) and their interactions with nascently deposited proteins at &lt;120 nm resolution when cultured in proteolytically-degradable synthetic PEG hydrogels. Results support the notion that focal adhesion maturation requires cellular fibronectin deposition; nuclear deformation precedes cellular spreading; and hMSCs display cell-surface metalloproteinases for matrix remodeling.&nbsp;</p