Showing papers by "Jason A. Burdick published in 2020"

Hydrogel microparticles for biomedical applications.

Abstract: Hydrogel microparticles (HMPs) are promising for biomedical applications, ranging from the therapeutic delivery of cells and drugs to the production of scaffolds for tissue repair and bioinks for 3D printing. Biologics (cells and drugs) can be encapsulated into HMPs of predefined shapes and sizes using a variety of fabrication techniques (batch emulsion, microfluidics, lithography, electrohydrodynamic (EHD) spraying and mechanical fragmentation). HMPs can be formulated in suspensions to deliver therapeutics, as aggregates of particles (granular hydrogels) to form microporous scaffolds that promote cell infiltration or embedded within a bulk hydrogel to obtain multiscale behaviours. HMP suspensions and granular hydrogels can be injected for minimally invasive delivery of biologics, and they exhibit modular properties when comprised of mixtures of distinct HMP populations. In this Review, we discuss the fabrication techniques that are available for fabricating HMPs, as well as the multiscale behaviours of HMP systems and their functional properties, highlighting their advantages over traditional bulk hydrogels. Furthermore, we discuss applications of HMPs in the fields of cell delivery, drug delivery, scaffold design and biofabrication.

The bioprinting roadmap

Abstract: This bioprinting roadmap features salient advances in selected applications of the technique and highlights the status of current developments and challenges, as well as envisioned advances in science and technology, to address the challenges to the young and evolving technique. The topics covered in this roadmap encompass the broad spectrum of bioprinting; from cell expansion and novel bioink development to cell/stem cell printing, from organoid-based tissue organization to bioprinting of human-scale tissue structures, and from building cell/tissue/organ-on-a-chip to biomanufacturing of multicellular engineered living systems. The emerging application of printing-in-space and an overview of bioprinting technologies are also included in this roadmap. Due to the rapid pace of methodological advancements in bioprinting techniques and wide-ranging applications, the direction in which the field should advance is not immediately clear. This bioprinting roadmap addresses this unmet need by providing a comprehensive summary and recommendations useful to experienced researchers and newcomers to the field.

Fundamentals and Applications of Photo-Cross-Linking in Bioprinting.

Abstract: This review provides a detailed overview of the rapidly advancing field of biofabrication, particularly with regards to the use of photo-cross-linking (i.e., light-based) techniques. The major emphasis of this review is on the fundamentals of photo-cross-linking and key criteria identified for the successful design and implementation of photo-cross-linked bioinks and bioresins in extrusion-based and lithography-based bioprinting. The general mechanisms associated with photo-cross-linking (e.g., free-radical chain polymerization, thiol-ene, photomediated redox) of natural and synthetic materials are described to inform bioink and bioresin design, which includes the selection of polymers, functional group modifications, photoinitiators, and light sources that enable facile and cytocompatible photo-cross-linking. Depending on material selection and the bioprinting technique of interest, we describe the specific bioink or bioresin properties and criteria that must be achieved to ensure optimal printability and utility. Finally, examples of current state-of-the-art applications of light-based bioprinting for in vitro tissue models, tissue engineering, and regenerative medicine are provided to further motivate future opportunities within the bioprinting landscape that are facilitated with light.

Expanding and optimizing 3D bioprinting capabilities using complementary network bioinks

Abstract: A major challenge in three-dimensional (3D) bioprinting is the limited number of bioinks that fulfill the physicochemical requirements of printing while also providing a desirable environment for encapsulated cells. Here, we address this limitation by temporarily stabilizing bioinks with a complementary thermo-reversible gelatin network. This strategy enables the effective printing of biomaterials that would typically not meet printing requirements, with instrument parameters and structural output largely independent of the base biomaterial. This approach is demonstrated across a library of photocrosslinkable bioinks derived from natural and synthetic polymers, including gelatin, hyaluronic acid, chondroitin sulfate, dextran, alginate, chitosan, heparin, and poly(ethylene glycol). A range of complex and heterogeneous structures are printed, including soft hydrogel constructs supporting the 3D culture of astrocytes. This highly generalizable methodology expands the palette of available bioinks, allowing the biofabrication of constructs optimized to meet the biological requirements of cell culture and tissue engineering.

3D bioprinting of high cell-density heterogeneous tissue models through spheroid fusion within self-healing hydrogels

Abstract: Cellular models are needed to study human development and disease in vitro, including the screening of drugs for toxicity and efficacy. However, current approaches are limited in the engineering of functional tissue models with requisite cell densities and heterogeneity to appropriately model cell and tissue behaviors. Here, we develop a new bioprinting approach to transfer spheroids into self-healing support hydrogels at high resolution, which enables their patterning and fusion into high-cell density microtissues of prescribed spatial organization. As an example application, we bioprint induced pluripotent stem cell-derived cardiac microtissue models with spatially controlled cardiomyocyte and fibroblast cell ratios to replicate the structural and functional features of scarred cardiac tissue that arise following myocardial infarction, including reduced contractility and irregular electrical activity. The bioprinted in vitro model is combined with functional readouts to probe how various pro-regenerative microRNA treatment regimes influence tissue regeneration and recovery of function as a result of cardiomyocyte proliferation. This method is useful for a range of biomedical applications, including the development of precision models to mimic diseases and for the screening of drugs, particularly where high cell densities and heterogeneity are important.

Recent Advances in Enabling Technologies in 3D Printing for Precision Medicine.

Abstract: Advances in areas such as data analytics, genomics, and imaging have revealed individual patient complexities and exposed the inherent limitations of generic therapies for patient treatment. These observations have also fueled the development of precision medicine approaches, where therapies are tailored for the individual rather than the broad patient population. 3D printing is a field that intersects with precision medicine through the design of precision implants with patient-directed shapes, structures, and materials or for the development of patient-specific in vitro models that can be used for screening precision therapeutics. Toward their success, advances in 3D printing and biofabrication technologies are needed with enhanced resolution, complexity, reproducibility, and speed and that encompass a broad range of cells and materials. The overall goal of this progress report is to highlight recent advances in 3D printing technologies that are helping to enable advances important in precision medicine.

Metabolic Labeling to Probe the Spatiotemporal Accumulation of Matrix at the Chondrocyte-Hydrogel Interface.

Abstract: Hydrogels are engineered with biochemical and biophysical signals to recreate aspects of the native microenvironment and to control cellular functions such as differentiation and matrix deposition. This deposited matrix accumulates within the pericellular space and likely affects the interactions between encapsulated cells and the engineered hydrogel; however, there has been little work to study the spatiotemporal evolution of matrix at this interface. To address this, metabolic labeling is employed to visualize the temporal and spatial positioning of nascent proteins and proteoglycans deposited by chondrocytes. Within covalently crosslinked hyaluronic acid hydrogels, chondrocytes deposit nascent proteins and proteoglycans in the pericellular space within 1 d after encapsulation. The accumulation of this matrix, as measured by an increase in matrix thickness during culture, depends on the initial hydrogel crosslink density with decreased thicknesses for more crosslinked hydrogels. Encapsulated fluorescent beads are used to monitor the hydrogel location and indicate that the emerging nascent matrix physically displaces the hydrogel from the cell membrane with extended culture. These findings suggest that secreted matrix increasingly masks the presentation of engineered hydrogel cues and may have implications for the design of hydrogels in tissue engineering and regenerative medicine.

Engineered Biomaterial Platforms to Study Fibrosis.

Abstract: Many pathologic conditions lead to the development of tissue scarring and fibrosis, which are characterized by the accumulation of abnormal extracellular matrix (ECM) and changes in tissue mechanical properties. Cells within fibrotic tissues are exposed to dynamic microenvironments that may promote or prolong fibrosis, which makes it difficult to treat. Biomaterials have proved indispensable to better understand how cells sense their extracellular environment and are now being employed to study fibrosis in many tissues. As mechanical testing of tissues becomes more routine and biomaterial tools become more advanced, the impact of biophysical factors in fibrosis are beginning to be understood. Herein, fibrosis from a materials perspective is reviewed, including the role and mechanical properties of ECM components, the spatiotemporal mechanical changes that occur during fibrosis, current biomaterial systems to study fibrosis, and emerging biomaterial systems and tools that can further the understanding of fibrosis initiation and progression. This review concludes by highlighting considerations in promoting wide-spread use of biomaterials for fibrosis investigations and by suggesting future in vivo studies that it is hoped will inspire the development of even more advanced biomaterial systems.

Mechanochemical Adhesion and Plasticity in Multifiber Hydrogel Networks.

Abstract: The extracellular matrix (ECM) has force-responsive (i.e., mechanochemical) properties that enable adaptation to mechanical loading through changes in fibrous network structure and interfiber bonding. Imparting such properties into synthetic fibrous materials will allow reinforcement under mechanical load, the potential for material self-adhesion, and the general mimicking of ECM. Multifiber hydrogel networks are developed through the electrospinning of multiple fibrous hydrogel populations, where fibers contain complementary chemical moieties (e.g., aldehyde and hydrazide groups) that form covalent bonds within minutes when brought into contact under mechanical load. These fiber interactions lead to microscale anisotropy, as well as increased material stiffness and plastic deformation. Macroscale structures (e.g., tubes and layered scaffolds) are fabricated from these materials through interfiber bonding and adhesion when placed into contact while maintaining a microscale fibrous architecture. The design principles for engineering plasticity described can be applied to numerous material systems to introduce unique properties, from textiles to biomedical applications.

Influence of Fiber Stiffness on Meniscal Cell Migration into Dense Fibrous Networks

Abstract: Fibrous scaffolds fabricated via electrospinning are being explored to repair injuries within dense connective tissues. However, there is still much to be understood regarding the appropriate scaffold properties that best support tissue repair. In this study, the influence of the stiffness of electrospun fibers on cell invasion into fibrous scaffolds is investigated. Specifically, soft and stiff electrospun fibrous networks are fabricated from crosslinked methacrylated hyaluronic acid (MeHA), where the stiffness is altered via the extent of MeHA crosslinking. Meniscal fibrochondrocyte (MFC) adhesion and migration into fibrous networks are investigated, where the softer MeHA fibrous networks are easily deformed and densified through cellular tractions and the stiffer MeHA fibrous networks support ≈50% greater MFC invasion over weeks when placed adjacent to meniscal tissue. When the scaffolds are sandwiched between meniscal tissues and implanted subcutaneously, the stiffer MeHA fibrous networks again support enhanced cellular invasion and greater collagen deposition after 4 weeks when compared to the softer MeHA fibrous networks. These results indicate that the mechanics and deformability of fibrous networks likely alter cellular interactions and invasion, providing an important design parameter toward the engineering of scaffolds for tissue repair.

Nuclear softening expedites interstitial cell migration in fibrous networks and dense connective tissues

Abstract: Dense matrices impede interstitial cell migration and subsequent repair. We hypothesized that nuclear stiffness is a limiting factor in migration and posited that repair could be expedited by transiently decreasing nuclear stiffness. To test this, we interrogated the interstitial migratory capacity of adult meniscal cells through dense fibrous networks and adult tissue before and after nuclear softening via the application of a histone deacetylase inhibitor, Trichostatin A (TSA) or knockdown of the filamentous nuclear protein Lamin A/C. Our results show that transient softening of the nucleus improves migration through microporous membranes, electrospun fibrous matrices, and tissue sections and that nuclear properties and cell function recover after treatment. We also showed that biomaterial delivery of TSA promoted in vivo cellularization of scaffolds by endogenous cells. By addressing the inherent limitations to repair imposed by nuclear stiffness, this work defines a new strategy to promote the repair of damaged dense connective tissues.

Engineered Full-Length Fibronectin-Hyaluronic Acid Hydrogels for Stem Cell Engineering.

Abstract: Mechanical cues induce a variety of downstream effects on cells, including the regulation of stem cell behavior. Cell fate is typically characterized on biomaterial substrates where mechanical and chemical properties can be precisely tuned; however, most of these substrates do not recapitulate the biological complexity of the extracellular matrix (ECM). Here, hydrogels are engineered for mechanobiological studies using two major components of the ECM: hyaluronic acid (HA) and fibronectin (FN). Rather than typical surface chemisorption of FN to substrates, the system contains full-length FN covalently crosslinked to HA throughout the hydrogel. The control over the mechanical properties of the hydrogel independent of the concentration of FN and the ability to culture viable cells either on top or encapsulated within the hydrogels are shown. Interestingly, human mesenchymal stem cells (MSCs) experience an increase in nuclear translocation of the yes-associated protein (YAP) to the nucleus when cultured on (2D) substrates with increasing amounts of FN while maintaining constant hydrogel stiffness. However, this FN dependence on nuclear YAP translocation is not observed for MSCs encapsulated in (3D) hydrogels. This work develops complex hydrogels that recapitulate features of the ECM for the control of stem cells in both 2D and 3D environments.

Imaging of Injectable Hydrogels Delivered into Myocardium with SPECT/CT.

Abstract: Injectable hydrogels are being widely explored for treatment after myocardial infarction (MI) through mechanical bulking or the delivery of therapeutics. Despite this interest, there have been few approaches to image hydrogels upon injection to identify their location, volume, and pattern of delivery, features that are important to understand toward clinical translation. Using a hyaluronic acid (HA) hydrogel as an example, the aim of this study is to introduce radiopacity to hydrogels by encapsulating a clinically used contrast agent (Omnipaque Iohexol, GE Healthcare) for imaging upon placement in the myocardium. Specifically, iohexol is encapsulated into shear-thinning and self-healing hydrogels formed through the mixing of HA-hydrazide and HA-aldehyde. Upon examination of a range of iohexol concentrations, a concentration of 100 mg mL-1 iohexol is deemed optimal based on the greatest contrast, while maintaining hydrogel mechanical properties and acceptable injection forces. In an acute porcine model of MI, hybrid single-photon emission computed tomography/computed tomography (SPECT/CT) perfusion imaging is performed immediately and 3-4 days after hydrogel delivery to assess radiopacity and verify the hydrogel location within the perfusion defect. Hybrid SPECT/CT imaging demonstrates excellent radiopacity of the hydrogel within the perfusion defect immediately after intramyocardial hydrogel injection, demonstrating the feasibility of this method for short-term noninvasive hydrogel monitoring.

Resorbable Pins to Enhance Scaffold Retention in a Porcine Chondral Defect Model.

Abstract: ObjectiveCartilage repair strategies have seen improvement in recent years, especially with the use of scaffolds that serve as a template for cartilage formation. However, current fixation strategi...

A Bioengineered Neuregulin-Hydrogel Therapy Reduces Scar Size and Enhances Post-Infarct Ventricular Contractility in an Ovine Large Animal Model

Abstract: The clinical efficacy of neuregulin (NRG) in the treatment of heart failure is hindered by off-target exposure due to systemic delivery. We previously encapsulated neuregulin in a hydrogel (HG) for targeted and sustained myocardial delivery, demonstrating significant induction of cardiomyocyte proliferation and preservation of post-infarct cardiac function in a murine myocardial infarction (MI) model. Here, we performed a focused evaluation of our hydrogel-encapsulated neuregulin (NRG-HG) therapy’s potential to enhance cardiac function in an ovine large animal MI model. Adult male Dorset sheep (n = 21) underwent surgical induction of MI by coronary artery ligation. The sheep were randomized to receive an intramyocardial injection of saline, HG only, NRG only, or NRG-HG circumferentially around the infarct borderzone. Eight weeks after MI, closed-chest intracardiac pressure–volume hemodynamics were assessed, followed by heart explant for infarct size analysis. Compared to each of the control groups, NRG-HG significantly augmented left ventricular ejection fraction (p = 0.006) and contractility based on the slope of the end-systolic pressure–volume relationship (p = 0.006). NRG-HG also significantly reduced infarct scar size (p = 0.002). Overall, using a bioengineered hydrogel delivery system, a one-time dose of NRG delivered intramyocardially to the infarct borderzone at the time of MI in adult sheep significantly reduces scar size and enhances ventricular contractility at 8 weeks after MI.

Compositions and methods for cardiac regeneration

Abstract: The present disclosure provides microRNA-based therapies using a hydrogel delivery system that provides regenerative approach to myocardial infarction by targeting cardiomyocytes. The hydrogel provides for local and sustained cardiac delivery of microRNAs, such miR-302 mimics that can be used to promote cardiomyocyte proliferation. Also provided are compositions suitable for local and sustained release and methods for intramyocardial gel delivery of a miRNA oligonucleotide.

Injectable hydrogels for local delivery to the heart

Abstract: The invention concerns methods of delivering a hydrogel to the heart, comprising: introducing a hydrogel composition into a subject, said hydrogel comprising components mixed prior to introduction; the introducing being performed such that the hydrogel composition resides between the epicardium and the pericardium of the subject. In some embodiments, the injection is performed using a syringe or catheter.