Kristi Anseth

Phototunable Viscoelasticity in Hydrogels Through Thioester Exchange

Anonymous — Wed, 26 Feb 2020 20:16:11 +0000

Phototunable Viscoelasticity in Hydrogels Through Thioester Exchange Anonymous (not verified) Wed, 02/26/2020 - 13:16

Mechanical cues are delivered to resident cells by the extracellular matrix and play an important role in directing cell processes, ranging from embryonic development and cancer metastasis to stem cell differentiation. Recently, cellular responses to viscoelastic and elastic mechanical cues have been studied; however, questions remain as to how cells identify and transduce these cues differently. We present a synthetic cell culture substrate with viscoelastic properties based on thioester exchange chemistry that can be modulated in situ with the photoinitiated thiol-ene ‘click’ reaction. With this method, stress relaxation in thioester hydrogels with an average relaxation time of 740,000 s can be switched off in the presence of cells without change to the elastic modulus. NIH 3T3 fibroblasts, cultured for 48 h on viscoelastic compared to elastic thioester substrates, displayed increased cell area (660–560 μm²) and increased nuclear to cytoplasmic YAP/TAZ ratios (2.4 to 2.2) when cultured on elastic compared to viscoelastic hydrogels, respectively. Next, when the viscoelasticity was switched off after 24 h, the fibroblasts responded to this change and exhibited an average cell area of 540 μm², and nuclear to cytoplasmic YAP/TAZ ratio of 2.1, approaching that of the control elastic gels. Phototunable viscoelastic thioester hydrogels provide a tunable materials system to investigate time-dependent cellular responses to viscoelasticity and should prove useful for understanding the dynamics of mechanoresponsive cellular pathways.

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Anseth earns international recognition with L’Oreal-UNESCO For Women in Science award

Anonymous — Tue, 18 Feb 2020 17:21:16 +0000

Anseth earns international recognition with L’Oreal-UNESCO For Women in Science award Anonymous (not verified) Tue, 02/18/2020 - 10:21

Jonathan Raab

ŷ��ڱ��Ƶ Boulder Professor Kristi Anseth has received one of the most prestigious recognitions in the life sciences: a L’Oreal-UNESCO For Women in Science award.

Anseth, a distinguished professor and Tisone professor in the Department of Chemical and Biological Engineering, is being recognized for her “outstanding contribution in converging engineering and biology to develop innovative biomaterials that help tissue regeneration and drug delivery,” according to UNESCO.

She is one of only five women in the world, and the only recipient in North America, to receive the recognition this year.

“I am tremendously honored and feel so very fortunate to be part of the broader University of ŷ��ڱ��Ƶ community,” Anseth said. “However, I must first acknowledge that this is a shared honor. I have the pleasure of mentoring an amazing group of undergraduate students, graduate students and postdoctoral associates in my laboratory, and these individuals have contributed tremendously to the basis for this recognition. I am so thankful to them for their dedication and ŷ��ڱ��Ƶ’s commitment to supporting not only the education of these individuals but their transition to future leaders.”

Anseth said she’s eagerly anticipating the opportunity to celebrate women scientists and engineers and to play a more visible role for the next generation. The mother of a 12-year-old daughter, Anseth said she hopes her daughter’s generation is inspired to pursue careers in STEM and that girls see no bounds to their possible careers.

She also commended her colleagues in the Department of Chemical and Biological Engineering and the BIoFrontiers Institute for their support.

“I am fortunate to work in an environment with such brilliant colleagues who work tirelessly to advance our fields and educate students to develop technologies and ideas for supporting the well-being of people, society and the planet,” Anseth said.

Anseth, who is also the associate director of the BioFrontiers Institute, has a long and storied career in applying the principles of chemical engineering to the biomaterials field, authoring over 330 papers of extensive, highly impactful research and earning numerous awards and recognitions. She is one of only a handful of individuals worldwide elected to all three national academies: the National Academy of Engineering, the National Academy of Medicine and the National Academy of Sciences. She also has been elected to the American Academy of Arts and Sciences, the National Academy of Inventors and the International Academy of Medical and Biological Engineering.

“Professor Anseth has proven time and again, through her stellar career of research and achievement, as well as her teaching and mentoring, that she is a world-class scientist and engineer,” said Keith Molenar, interim dean of the College of Engineering and Applied Science. “The L’Oreal-UNESCO For Women in Science awards recognize the best of the best, and she is absolutely deserving of that honor. We’re proud that she calls the ŷ��ڱ��Ƶ Boulder College of Engineering and Applied Science home, as she brings immeasurable value to the research and education happening here.”

“Kristi Anseth has been a leader in cutting-edge biomaterials research for over two decades,” said Charles Musgrave, chair of the Department of Chemical and Biological Engineering. “Her work in the tissue engineering and drug delivery fields has led to the development of key technologies that will have an incredible impact on regenerative medicine and drug delivery. I can’t think of anyone more deserving of this award than her. My colleagues and I are proud of her many accomplishments.”

Anseth earned her doctoral degree in chemical engineering from ŷ��ڱ��Ƶ Boulder in 1994 and joined the faculty shortly thereafter, focusing her research on developing biomaterials for medical applications.

Rob Davis, dean emeritus of the College of Engineering and Applied Science and Tisone endowed chair in the Department of Chemical and Biological Engineering, nominated Anseth for the award. He cited her unparalleled research accomplishments in biotechnology and cell biology and the translation of her technologies into medical products, including in-situ-forming materials for enhanced bone regeneration, hydrogels for chondrocyte delivery and more.

He also emphasized her dedication to her students, recalling his first observation of her after she completed her PhD. She had volunteered to teach an 8 a.m. undergraduate course, winning over the sleepy and skeptical students with her enthusiasm and passion for the material.

Support for the nomination also came from other distinguished leaders in academia, including professors Paula T. Hammond and Robert Langer of MIT, Provost David A. Tirrell and Professor Mark E. Davis of the California Institute of Technology, and Professor Nicholas A. Peppas of the University of Texas at Austin.

The international For Women in Science awards, now in their 22nd year, recognize the accomplishments of women who work in the biotechnology, ecology, epigenetics, epidemiology and infectiology research fields. The L’Oreal Foundation and UNESCO bestow five of these awards each year, recognizing one researcher each from Africa and the Arab States, the Asia-Pacific region, Europe, Latin America and North America. Fifteen additional “Rising Talents” are recognized from these regions as well.

Anseth and the other awardees will be honored at a ceremony March 12 at UNESCO Headquarters in Paris. Each award recipient will receive €100,000 (about $109,000). The awards seek to increase the representation and awareness of women in science and their achievements to inspire more women to consider careers in the sciences.

The late Deborah Jin, a professor of physics and JILA fellow at ŷ��ڱ��Ƶ Boulder, also received the award in 2012.

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Relaxation of Extracellular Matrix Forces Directs Crypt Formation and Architecture in Intestinal Organoids

Anonymous — Fri, 31 Jan 2020 21:04:49 +0000

Relaxation of Extracellular Matrix Forces Directs Crypt Formation and Architecture in Intestinal Organoids Anonymous (not verified) Fri, 01/31/2020 - 14:04

Intestinal organoid protocols rely on the use of extracellular scaffolds, typically Matrigel, and upon switching from growth to differentiation promoting media, a symmetry breaking event takes place. During this stage, the first bud like structures analogous to crypts protrude from the central body and differentiation ensues. While organoids provide unparalleled architectural and functional complexity, this sophistication is also responsible for the high variability and lack of reproducibility of uniform crypt‐villus structures. If function follows form in organoids, such structural variability carries potential limitations for translational applications (e.g., drug screening). Consequently, there is interest in developing synthetic biomaterials to direct organoid growth and differentiation. It has been hypothesized that synthetic scaffold softening is necessary for crypt development, and these mechanical requirements raise the question, what compressive forces and subsequent relaxation are necessary for organoid maturation? To that end, allyl sulfide hydrogels are employed as a synthetic extracellular matrix mimic, but with photocleavable bonds that temporally regulate the material's bulk modulus. By varying the extent of matrix softening, it is demonstrated that crypt formation, size, and number per colony are functions of matrix softening. An understanding of the mechanical dependence of crypt architecture is necessary to instruct homogenous, reproducible organoids for clinical applications.

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Porous bio-click microgel scaffolds control hMSC interactions and promote their secretory properties

Anonymous — Tue, 31 Dec 2019 18:59:51 +0000

Porous bio-click microgel scaffolds control hMSC interactions and promote their secretory properties Anonymous (not verified) Tue, 12/31/2019 - 11:59

Human mesenchymal stem/stromal cells (hMSCs) are known to secrete numerous cytokines that signal to endogenous cells and aid in tissue regeneration. However, the role that biomaterial scaffolds can play in controlling hMSC secretory properties has been less explored. Here, microgels were co-assembled with hMSCs using three different microgel populations, with large (190 ± 100  μm), medium (110 ± 60  μm), and small (13±6  μm) diameters, to create distinct porous environments that influenced hMSC clustering. Cells embedded in large diameter microgel networks resided in large clusters (∼40 cells), compared to small clusters (∼6 cells) observed in networks using medium diameter microgels and primarily single cells in small diameter microgel networks. Using a cytokine microarray, an overall increase in secretion was observed in scaffolds that promoted hMSC clustering, with over 60% of the measured cytokines most elevated in the large diameter microgel networks. N-cadherin interactions were identified as partially mediating these differences, so the microgel formulations were modified with an N-cadherin epitope, HAVDI, to mimic cell-cell interactions. Results revealed increased secretory properties for hMSCs in HAVDI functionalized scaffolds, even the non-clustered cells in small diameter microgel networks. Together, these results demonstrate opportunities for microgel-based scaffold systems for hMSC delivery and tailoring of porous materials properties to promote their secretory potential.

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Designing Microgels for Cell Culture and Controlled Assembly of Tissue Microenvironments

Anonymous — Tue, 31 Dec 2019 17:47:41 +0000

Designing Microgels for Cell Culture and Controlled Assembly of Tissue Microenvironments Anonymous (not verified) Tue, 12/31/2019 - 10:47

Micrometer‐sized hydrogels, termed microgels, are emerging as multifunctional platforms that can recapitulate tissue heterogeneity in engineered cell microenvironments. The microgels can function as either individual cell culture units or can be assembled into larger scaffolds. In this manner, individual microgels can be customized for single or multicell coculture applications, or heterogeneous populations can be used as building blocks to create microporous assembled scaffolds that more closely mimic tissue heterogeneities. The inherent versatility of these materials allows user‐defined control of the microenvironments, from the order of singly encapsulated cells to entire 3D cell scaffolds. These hydrogel scaffolds are promising for moving towards personalized medicine approaches and recapitulating the multifaceted microenvironments that exist in vivo.

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Thiol‐ene hydrogels for local delivery of PTH for bone regeneration in critical size defects

Anonymous — Fri, 22 Nov 2019 18:30:38 +0000

Thiol‐ene hydrogels for local delivery of PTH for bone regeneration in critical size defects Anonymous (not verified) Fri, 11/22/2019 - 11:30

Neither allograft nor commercially available bone graft substitutes provide the same quality of bone healing as autograft. Incorporation of bioactive molecules like PTH within bone graft substitute materials may provide similar, if not better treatment options to grafting. The goal of this work was to develop a biomaterial system for the local delivery of PTH to large bone defects for promoting bone regeneration. PTH was loaded in a thiol‐ene hydrogel at several concentrations and polymerized in and around an osteoconductive poly(propylene fumarate) (PPF) scaffold. PTH was shown to be bioactive when released from the hydrogel for up to 21 days. Eighty percent of the PTH was released by day 3 with the remaining 20% released by day 14. Bone healing was quantified in rat critical size femoral defects that were treated with hydrogel/PPF and 0, 1, 3, 10, or 30 µg of PTH. Although complete osseous healing was not observed in all samples in any one treatment group, all samples in the10 µg PTH group were bridged fully by bone or a combination of bone and cartilage containing hypertrophic chondrocytes and endochondral ossification. Outcome measures indicated improved defect bridging by a combination of bony and cartilaginous tissue in the 10 μg treatment group compared to empty bone defects and defects treated with only hydrogel/PPF (i.e., without PTH). Given the tailorability of the hydrogel, future studies will investigate the effects of prolonged gradual PTH release on bone healing. Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J. Orthop. Res 00:00–00, 2019.

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Soft Materials for Studying Hard Biological Problems

Anonymous — Fri, 22 Nov 2019 18:18:40 +0000

Soft Materials for Studying Hard Biological Problems Anonymous (not verified) Fri, 11/22/2019 - 11:18

Our group focuses on the development of biomaterial matrices that can serve as advanced culture systems or in vivo delivery systems for primary cells. We exploit material chemistry as a tool to decipher how cells process signals from the extracellular matrix (ECM), and then use this information to design improved biomaterials that promote tissue regeneration. Specifically, we design synthetic ECM analogs that capture key features of the unique chemistry and physical properties of a cell’s niche—an environment that is not only tissue specific, but can be strikingly heterogeneous and dynamic. Unique to our approach is the ability to create cell-laden matrices in three-dimensional space in which the matrix properties can be changed on demand—so-called 4D biology. Here, our group has focused on the development of photochemical reactions to create tunable cell-laden matrices, for example, the thiol-ene photo-click reaction and complementary photo-clip reactions to introduce and remove biological signals from a complex milieu. These photochemical reactions not only proceed rapidly and with high specificity, but are bio-orthogonal, spatiotemporally controlled, and cytocompatible. This talk will illustrate how we leverage these and other reversible chemistries to create biologically responsive hydrogel matrices, and employ them to study the effects of matricellular signaling on diverse cellular functions and processes. For example, we exploit peptide-crosslinked PEG hydrogels to encapsulate stem cells and study how matrix density, degradability, elasticity, and adhesivity influence migration, proliferation, and differentiation. More recently, we have integrated photodegradable linkers into hydrogels and used these spatiotemporal controlled reactions to direct the growth and differentiation of stem cells into intestinal organoids.

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PEG–Anthracene Hydrogels as an On‐Demand Stiffening Matrix To Study Mechanobiology

Anonymous — Thu, 31 Oct 2019 18:01:55 +0000

PEG–Anthracene Hydrogels as an On‐Demand Stiffening Matrix To Study Mechanobiology Anonymous (not verified) Thu, 10/31/2019 - 12:01

There is a growing interest in materials that can dynamically change their properties in the presence of cells to study mechanobiology. Herein, we exploit the 365 nm light mediated [4+4] photodimerization of anthracene groups to develop cytocompatible PEG‐based hydrogels with tailorable initial moduli that can be further stiffened. A hydrogel formulation that can stiffen from 10 to 50 kPa, corresponding to the stiffness of a healthy and fibrotic heart, respectively, was prepared. This system was used to monitor the stiffness‐dependent localization of NFAT, a downstream target of intracellular calcium signaling using a reporter in live cardiac fibroblasts (CFbs). NFAT translocates to the nucleus of CFbs on stiffening hydrogels within 6 h, whereas it remains cytoplasmic when the CFbs are cultured on either 10 or 50 kPa static hydrogels. This finding demonstrates how dynamic changes in the mechanical properties of a material can reveal the kinetics of mechanoresponsive cell signaling pathways that may otherwise be missed in cells cultured on static substrates.

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Quantifying heart valve interstitial cell contractile state using highly tunable poly(ethylene glycol) hydrogels.

Anonymous — Thu, 31 Oct 2019 17:59:19 +0000

Quantifying heart valve interstitial cell contractile state using highly tunable poly(ethylene glycol) hydrogels. Anonymous (not verified) Thu, 10/31/2019 - 11:59

Valve interstitial cells (VIC) are the primary cell type residing within heart valve tissues. In many valve pathologies, VICs become activated and will subsequently profoundly remodel the valve tissue extracellular matrix (ECM). A primary indicator of VIC activation is the upregulation of α-smooth muscle actin (αSMA) stress fibers, which in turn increase VIC contractility. Thus, contractile state reflects VIC activation and ECM biosynthesis levels. In general, cell contraction studies have largely utilized two-dimensional substrates, which are a vastly different micro mechanical environment than 3D native leaflet tissue. To address this limitation, hydrogels have been a popular choice for studying cells in a three-dimensional environment due to their tunable properties and optical transparency, which allows for direct cell visualization. In the present study, we extended the use of hydrogels to study the active contractile behavior of VICs. Aortic VICs (AVIC) were encapsulated within poly(ethylene glycol) (PEG) hydrogels and were subjected to flexural-deformation tests to assess the state of AVIC contraction. Using a finite element model of the experimental setup, we determined the effective shear modulus μ of the constructs. An increase in μ resulting from AVIC active contraction was observed. Results further indicated that AVIC contraction had a more pronounced effect on μ in softer gels (72 ± 21% increase in μ within 2.5 kPa gels) and was dependent upon the availability of adhesion sites (0.5-1 mM CRGDS). The transparency of the gel allowed us to image AVICs directly within the hydrogel, where we observed a time-dependent decrease in volume (time constant τ=3.04 min) when the AVICs were induced into a hypertensive state. Our results indicated that AVIC contraction was regulated by both the intrinsic (unseeded) gel stiffness and the CRGDS peptide concentrations. This finding suggests that AVIC contractile state can be profoundly modulated through their local micro environment using modifiable PEG gels in a 3D micromechanical-emulating environment. Moving forward, this approach has the potential to be used towards delineating normal and diseased VIC biomechanical properties using highly tunable PEG biomaterials.

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Extended Exposure to Stiff Microenvironments Leads to Persistent Chromatin Remodeling in Human Mesenchymal Stem Cells

Anonymous — Thu, 31 Oct 2019 17:53:34 +0000

Extended Exposure to Stiff Microenvironments Leads to Persistent Chromatin Remodeling in Human Mesenchymal Stem Cells Anonymous (not verified) Thu, 10/31/2019 - 11:53

Bone marrow derived human mesenchymal stem cells (hMSCs) are a promising cell source for regenerative therapies; however, ex vivo expansion is often required to achieve clinically useful cells numbers. Recent results reveal that when MSCs are cultured in stiff microenvironments, their regenerative capacity can be altered in a manner that is dependent on time (e.g., a mechanical dosing analogous to a chemical one). It is hypothesized that epigenomic modifications are involved in storing these mechanical cues, regulating gene expression, and ultimately leading to a mechanical memory. Using hydrogels containing an allyl sulfide cross‐linker and a radical‐mediated addition‐fragmentation chain transfer process, in situ softened hMSC‐laden hydrogels at different time points are achieved and the effects of short‐term and long‐term mechanical dosing on epigenetic modifications in hMSCs are quantified. Results show that histone acetylation and chromatin organization adapt rapidly after softening and can be reversible or irreversible depending on time of exposure to stiff microenvironments. Furthermore, epigenetic modulators are differentially expressed depending on the culture history. Collectively, these experiments suggest that epigenetic remodeling can be persistent and might be a memory keeper.

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