Human Cell-Derived Matrix Composite Hydrogels with Diverse Composition for Use in Vasculature-on-chip Models

Microphysiological and organ-on-chip platforms seek to address critical gaps in human disease models and drug development that underlie poor rates of clinical success for novel interventions. While the fabrication technology and model cells used to synthesize organs-on-chip have advanced considerably, most platforms rely on animal-derived or synthetic extracellular matrix as a cell substrate, limiting mimicry of human physiology and precluding use in modeling diseases in which matrix dynamics play a role in pathogenesis. Here, the development of human cell-derived matrix (hCDM) composite hydrogels for use in 3D microphysiologic models of the vasculature is reported. hCDM composite hydrogels are derived from human donor fibroblasts and maintain a complex milieu of basement membrane, proteoglycans, and nonfibrillar matrix components. The use of hCDM composite hydrogels as 2D and 3D cell culture substrates is demonstrated, and hCDM composite hydrogels are patterned to form engineered human microvessels. Interestingly, hCDM composite hydrogels are enriched in proteins associated with vascular morphogenesis as determined by mass spectrometry, and functional analysis demonstrates proangiogenic signatures in human endothelial cells cultured in these hydrogels. In conclusion, this study suggests that human donor-derived hCDM composite hydrogels could address technical gaps in human organs-on-chip development and serve as substrates to promote vascularization.

Characterization and biological evaluation of a novel flavonoid-collagen antioxidant hydrogel with cytoprotective properties

Reactive oxygen species (ROS) play a critical and important role during wound healing but excess ROS at the wound site can lead to cellular damage and sub-optimal healing. Minimizing oxidative damage to the wound site and any supplemental therapeutic cells can be achieved by delivering exogenous antioxidants. Collagen hydrogels are ideal wound care materials due to their biocompatibility, high water content, and porous, three-dimensional architecture. Yet, they lack the inherent antioxidant activity that could help mitigate excess ROS at a wound site. This work formulates and evaluates the in vitro biocompatibility and antioxidant capabilities of collagen-fibroblast hydrogels combined with the polyphenolic antioxidant luteolin. Collagen solutions mixed with luteolin readily assembled into robust hydrogels with increasing gel strength due to increasing concentrations of luteolin. SEM images confirmed a mean pore size of 2.2 μm and a drastically different macromolecular ultrastructure with extensive fine crosslinking relative to collagen. Adequate cell viability and metabolic activity of dermal fibroblasts cultured within the gels were measured across all formulations, resulting in higher antioxidant activity and more than double the protection to cells from oxidative damage than traditional collagen hydrogels. Given these results, luteolin-collagen hydrogels demonstrate the potential for superior wound-healing properties when compared to collagen alone.

Low-dose intrapulmonary drug delivery device for studies on next-generation therapeutics in mice

Although nebulizers have been developed for delivery of small molecules in human patients, no tunable device has been purpose-built for targeted delivery of modern large molecule and temperature-sensitive therapeutics to mice. Mice are used most of all species in biomedical research and have the highest number of induced models for human-relevant diseases and transgene models. Regulatory approval of large molecule therapeutics, including antibody therapies and modified RNA highlight the need for quantifiable dose delivery in mice to model human delivery, proof-of-concept studies, efficacy, and dose-response. To this end, we developed and characterized a tunable nebulization system composed of an ultrasonic transducer equipped with a mesh nebulizer fitted with a silicone restrictor plate modification to control the nebulization rate. We have identified the elements of design that influence the most critical factors to targeted delivery to the deep lungs of BALB/c mice. By comparing an in silico model of the mouse lung with experimental data, we were able to optimize and confirm the targeted delivery of over 99% of the initial volume to the deep portions of the mouse lung. The resulting nebulizer system provides targeted lung delivery efficiency far exceeding conventional nebulizers preventing waste of expensive biologics and large molecules during proof-of-concept and pre-clinical experiments involving mice. (Word Count =207).

Scalable and High-Throughput In Vitro Vibratory Platform for Vocal Fold Tissue Engineering Applications

The vocal folds (VFs) are constantly exposed to mechanical stimulation leading to changes in biomechanical properties, structure, and composition. The development of long-term strategies for VF treatment depends on the characterization of related cells, biomaterials, or engineered tissues in a controlled mechanical environment. Our aim was to design, develop, and characterize a scalable and high-throughput platform that mimics the mechanical microenvironment of the VFs in vitro. The platform consists of a 24-well plate fitted with a flexible membrane atop a waveguide equipped with piezoelectric speakers which allows for cells to be exposed to various phonatory stimuli. The displacements of the flexible membrane were characterized via Laser Doppler Vibrometry (LDV). Human VF fibroblasts and mesenchymal stem cells were seeded, exposed to various vibratory regimes, and the expression of pro-fibrotic and pro-inflammatory genes was analyzed. Compared to current bioreactor designs, the platform developed in this study can incorporate commercial assay formats ranging from 6- to 96-well plates which represents a significant improvement in scalability. This platform is modular and allows for tunable frequency regimes.

Towards a standardized multi-tissue decellularization protocol for the derivation of extracellular matrix materials

The goal of tissue decellularization is to efficiently remove unwanted cellular components, such as DNA and cellular debris, while retaining the complex structural and molecular milieu within the extracellular matrix (ECM). Decellularization protocols to date are centered on customized tissue-specific and lab-specific protocols that involve consecutive manual steps which results in variable and protocol-specific ECM material. The differences that result from the inconsistent protocols between decellularized ECMs affect consistency across batches, limit comparisons between results obtained from different laboratories, and could limit the transferability of the material for consistent laboratory or clinical use. The present study is the first proof-of-concept towards the development of a standardized protocol that can be used to derive multiple ECM biomaterials (powders and hydrogels) via a previously established automated system. The automated decellularization method developed by our group was used due to its short decellularization time (4 hours) and its ability to reduce batch-to-batch variability. The ECM obtained using this first iteration of a unified protocol was able to produce ECM hydrogels from skin, lung, muscle, tendons, cartilage, and laryngeal tissues. All hydrogels formed in this study were cytocompatible and showed gelation and rheological properties consistent with previous ECM hydrogels. The ECMs also showed unique proteomic composition. The present study represents the first step towards developing standardized protocols that can be used on multiple tissues in a fast, scalable, and reproducible manner.

High-Axial-Aspect Tannic Acid Microparticles Facilitate Gelation and Injectability of Collagen-Based Hydrogels

Injectable collagen-based hydrogels offer great promise for tissue engineering and regeneration, but their use is limited by poor mechanical strength. Herein, we incorporate tannic acid (TA) to tailor the rheology of the corresponding hydrogels while simultaneously adding the therapeutic benefits inherent to this polyphenolic component. TA in the solution form and needle-shaped TA microparticles are combined with collagen and the respective systems studied for their time-dependent sol-gel transitions (from storage to body temperatures, 4-37 °C) as a function of TA concentration. Compared to systems incorporating TA microparticles, those with dissolved TA, applied at a similar concentration, generate a less significant enhancement of the elastic modulus. Premature gelation at a low temperature and associated colloidal arrest of the system are proposed as a main factor explaining this limited performance. A higher yield stress (elastic stress method) is determined for systems loaded with TA microparticles compared to the system with dissolved TA. These results are interpreted in terms of the underlying interactions of TA with collagen, as probed by spectroscopy and isothermal titration calorimetry. Importantly, hydrogels containing TA microparticles show high cell viability (human dermal fibroblasts) and comparative cellular activity relative to the collagen-only hydrogel. Overall, composite hydrogels incorporating TA microparticles demonstrate a new, simple, and better-performance alternative to cell culturing and difficult implantation scenarios.

Donor Age and Time in Culture Affect Dermal Fibroblast Contraction in an In Vitro Hydrogel Model

Current cellular hydrogel-based skin grafts composed of human dermal fibroblasts and a hydrogel scaffold tend to minimize contraction of full-thickness skin wounds and support skin regeneration. However, there has been no comparison between the sources of the dermal fibroblast used. Products using human adult or neonatal foreskin dermal fibroblasts are often expanded in vitro and used after multiple passages without a clear understanding of the effects of this initial production step on the quality and reproducibility of the cellular behavior. Based on the known effects of 2D tissue culture expansion on cellular proliferation and gene expression, we hypothesized that differences in donor age and time in culture may influence cellular properties and contractile behavior in a fibroblast-populated collagen matrix. Using porcine skin as a model based on its similarity to human skin in structure and wound healing properties, we isolated porcine dermal fibroblasts of three different donor ages for use in a 2D proliferation assay and in a 3D cell-populated collagen matrix contractility assay. In 2D cell culture, doubling time remained relatively consistent between all age groups from passage 1 to 6. In the contractility assays, fetal and neonatal groups contracted faster and generated more contractile force than the adult group at passage 1 in vitro. However, after five passages in culture, there was no difference in contractility between ages. These results show how cellular responses in a hydrogel scaffold differ based on donor age and time in culture in vitro, and suggest that consistency in the cellular component of bioengineered skin products could be beneficial in the biomanufacturing of consistent, reliable skin grafts and graft in vivo models. Future research and therapies using bioengineered skin grafts should consider how results may vary based on donor age and time in culture before seeding. Impact statement Little is known about the impact of donor cell age and time in culture on the contraction of cellular, hydrogel-based skin grafts. These results show how cellular phenotypes of porcine fibroblasts differ based on donor age and time in culture. This information is beneficial when addressing important inconsistencies in biomanufacturing of bioengineered skin grafts and in vitro models. These findings are relevant to research and therapies using bioengineered skin graft models and the results can be used to increase reproducibility and consistency during the production of bioengineered skin constructs. The information from this study can be extrapolated to future in vivo studies using human dermal fibroblasts in an in vivo model to help determine the best donor age and time in culture for optimal wound healing outcomes or more reproducible in vitro testing constructs.

Bioreactors for Vocal Fold Tissue Engineering

It is estimated that almost one-third of the United States population will be affected by a vocal fold (VF) disorder during their lifespan. Promising therapies to treat VF injury and scarring are mostly centered on VF tissue engineering strategies such as the injection of engineered biomaterials and cell therapy. VF tissue engineering, however, is a challenging field as the biomechanical properties, structure, and composition of the VF tissue change upon exposure to mechanical stimulation. As a result, the development of long-term VF treatment strategies relies on the characterization of engineered tissues under a controlled mechanical environment. In this review, we highlight the importance of bioreactors as a powerful tool for VF tissue engineering with a focus on the current state of the art of bioreactors designed to mimic phonation in vitro. We discuss the influence of the phonatory environment on the development, function, injury, and healing of the VF tissue and its importance for the development of efficient therapeutic strategies. A concise and comprehensive overview of bioreactor designs, principles, operating parameters, and scalability are presented. An in-depth analysis of VF bioreactor data to date reveals that mechanical stimulation significantly influences cell viability and the expression of proinflammatory and profibrotic genes in vitro. Although the precision and accuracy of bioreactors contribute to generating reliable results, diverse gene expression profiles across the literature suggest that future efforts should focus on the standardization of bioreactor parameters to enable direct comparisons between studies. Impact statement We present a comprehensive review of bioreactors for vocal fold (VF) tissue engineering with a focus on the influence of the phonatory environment on the development, function, injury, and healing of the VFs and the importance of mimicking phonation on engineered VF tissues in vitro. Furthermore, we put forward a strong argument for the continued development of bioreactors in this area with an emphasis on the standardization of bioreactor designs, principles, operating parameters, and oscillatory regimes to enable comparisons between studies.

Mast Cell-Biomaterial Interactions and Tissue Repair

Tissue engineers often use biomaterials to provide structural support along with mechanical and chemical signals to modulate the wound healing process. Biomaterials that are implanted into the body interact with a heterogeneous and dynamic inflammatory environment that is present at the site of injury. Whether synthetically derived, naturally derived, or a combination of both, it is important to assess biomaterials for their ability to modulate inflammation to understand their potential clinical use. One important, but underexplored cell in the context of biomaterials is the mast cell (MC). MCs are granulocytic leukocytes that engage in a variety of events in both the innate and adaptive immune systems. Although highly recognized for their roles in allergic reactions, MCs play an important role in wound healing by recognizing antigens through pattern recognition receptors and the high-affinity immunoglobulin E receptor (FceRI) and releasing granules that affect cell recruitment, fibrosis, extracellular matrix deposition, angiogenesis, and vasculogenesis. MCs also mediate the foreign body response, contributing to the incorporation or rejection of implants. Studies of MC-biomaterial interactions can aid in the elucidation of MC roles during the host tissue response and tissue repair. This review is designed for those in the tissue engineering and biomaterial fields who are interested in exploring the role MCs may play in wound-biomaterial interactions and wound healing. With this review, we hope to inspire more research in the MC-biomaterial space to accelerate the design and construction of optimized implants. Impact statement Mast cells (MCs) are highly specialized inflammatory cells that have crucial, but not fully understood, roles in wound healing and tissue repair. Upon stimulation, they recognize foreign antigens and release granules that help orchestrate the inflammatory response after tissue damage or biomaterial implantation. This review summarizes the current use of MCs in biomaterial research along with literature from the past decade focusing on MC interactions with materials used for tissue repair and regeneration. Studying MC-biomaterial interactions will help (i) further understand the process of inflammation and (ii) design biomaterials and tissue-engineered constructs for optimal repair and regeneration.

Monitoring decellularization via absorbance spectroscopy during the derivation of extracellular matrix scaffolds

Extracellular matrix (ECM) is a complex structure composed of bioactive molecules representative of the local tissue microenvironment. Decellularized ECM biomaterials harness these biomolecules for regenerative medicine applications. One potential therapeutic application is the use of vocal fold (VF) specific ECM to restore the VFs after injury. ECM scaffolds are derived through a process of decellularization, which aims to remove unwanted immunogenic biomolecules (e.g. DNA) while preserving the composition of the ECM. The effectiveness of the decellularization is typically assessed at the end by quantifying ECM attributes such as final dsDNA content. However, batch-to-batch variability in ECM manufacturing remains a significant challenge for the standardization, cost-effectiveness, and scale-up process. The limited number of tools available for in-process control heavily restricts the uncovering of the correlations between decellularization process parameters and ECM attributes. In this study, we developed a technique applicable to both the classical batch method and semi-continuous decellularization systems to trace the decellularization of two laryngeal tissues in real-time. We hypothesize that monitoring the bioreactor’s effluent absorbance at 260 nm as a function of time will provide a representative DNA release profile from the tissue and thus allow for process optimization. The DNA release profiles were obtained for laryngeal tissues and were successfully used to optimize the derivation of VF lamina propria-ECM (auVF-ECM) hydrogels. This hydrogel had comparable rheological properties to commonly used biomaterials to treat VF injuries. Also, the auVF-ECM hydrogel promoted the down-regulation of CCR7 by THP-1 macrophages upon lipopolysaccharide stimulation in vitro suggesting some anti-inflammatory properties. The results show that absorbance profiles are a good representation of DNA removal during the decellularization process thus providing an important tool to optimize future protocols.

Extracellular Matrix Hydrogels Promote Expression of Muscle-Tendon Junction Proteins

Muscle and tendon injuries are prevalent and range from minor sprains and strains to traumatic, debilitating injuries. However, the interactions between these tissues during injury and recovery remain unclear. Three-dimensional tissue models that incorporate both tissues and a physiologically relevant junction between muscle and tendon may help understand how the two tissues interact. Here, we use tissue specific extracellular matrix (ECM) derived from muscle and tendon to determine how cells of each tissue interact with the microenvironment of the opposite tissue resulting in junction specific features. ECM materials were derived from the Achilles tendon and gastrocnemius muscle, decellularized, and processed to form tissue specific pre-hydrogel digests. ECM materials were unique in respect to protein composition and included many types of ECM proteins, not just collagens. After digestion and gelation, ECM hydrogels had similar complex viscosities which were less than type I collagen hydrogels at the same concentration. C2C12 myoblasts and tendon fibroblasts were cultured in tissue-specific ECM conditioned media or encapsulated in tissue-specific ECM hydrogels to determine cell-matrix interactions and the effects on a muscle-tendon junction marker, paxillin. ECM conditioned media had only a minor effect on upregulation of paxillin in cells cultured in monolayer. However, cells cultured within ECM hydrogels had 50-70% higher paxillin expression than cells cultured in type I collagen hydrogels. Contraction of the ECM hydrogels varied by the type of ECM used. Subsequent experiments with varying density of type I collagen (and thus contraction) showed no correlation between paxillin expression and the amount of gel contraction, suggesting that a constituent of the ECM was the driver of paxillin expression in the ECM hydrogels. In addition, the extracellular matrix protein type XXII collagen had similar expression patterns as paxillin, with smaller effect sizes. Using tissue specific ECM allowed for the de-construction of the cell-matrix interactions similar to muscle-tendon junctions to study the expression of MTJ specific proteins.

Photoinduced reconfiguration to control the protein-binding affinity of azobenzene-cyclized peptides

The impact of next-generation biorecognition elements (ligands) will be determined by the ability to remotely control their binding activity for a target biomolecule in complex environments. Compared to conventional mechanisms for regulating binding affinity (pH, ionic strength, or chaotropic agents), light provides higher accuracy and rapidity, and is particularly suited for labile targets. In this study, we demonstrate a general method to develop azobenzene-cyclized peptide ligands with light-controlled affinity for target proteins. Light triggers a cis/trans isomerization of the azobenzene, which results in a major structural rearrangement of the cyclic peptide from a non-binding to a binding configuration. Critical to this goal are the ability to achieve efficient photo-isomerization under low light dosage and the temporal stability of both cis and trans isomers. We demonstrated our method by designing photo-switchable peptides targeting vascular cell adhesion marker 1 (VCAM1), a cell marker implicated in stem cell function. Starting from a known VCAM1-binding linear peptide, an ensemble of azobenzene-cyclized variants with selective light-controlled binding were identified by combining in silico design with experimental characterization via spectroscopy and surface plasmon resonance. Variant cycloAZOB[G-VHAKQHRN-K] featured rapid, light-controlled binding of VCAM1 (KD,trans/KD,cis ∼ 130). Biotin-cycloAZOB[G-VHAKQHRN-K] was utilized to label brain microvascular endothelial cells (BMECs), showing co-localization with anti-VCAM1 antibodies in cis configuration and negligible binding in trans configuration.

Microphysiological System for High-Throughput Computer Vision Measurement of Microtissue Contraction

The ability to measure microtissue contraction in vitro can provide important information when modeling cardiac, cardiovascular, respiratory, digestive, dermal, and skeletal tissues. However, measuring tissue contraction in vitro often requires the use of high number of cells per tissue construct along with time-consuming microscopy and image analysis. Here, we present an inexpensive, versatile, high-throughput platform to measure microtissue contraction in a 96-well plate configuration using one-step batch imaging. More specifically, optical fiber microprobes are embedded in microtissues, and contraction is measured as a function of the deflection of optical signals emitted from the end of the fibers. Signals can be measured from all the filled wells on the plate simultaneously using a digital camera. An algorithm uses pixel-based image analysis and computer vision techniques for the accurate multiwell quantification of positional changes in the optical microprobes caused by the contraction of the microtissues. Microtissue constructs containing 20,000-100,000 human ventricular cardiac fibroblasts (NHCF-V) in 6 mg/mL collagen type I showed contractile displacements ranging from 20-200 μm. This highly sensitive and versatile platform can be used for the high-throughput screening of microtissues in disease modeling, drug screening for therapeutics, physiology research, and safety pharmacology.

Transcriptome-targeted analysis of human peripheral blood-derived macrophages when cultured on biomaterial meshes

Surgical meshes are commonly used to repair defects and support soft tissues. Macrophages (Mφs) are critical cells in the wound healing process and are involved in the host response upon foreign biomaterials. There are various commercially available permanent and absorbable meshes used by surgeons for surgical interventions. Polypropylene (PP) meshes represent a permanent biomaterial that can elicit both inflammatory and anti-inflammatory responses. In contrast, poly-4-hydroxybutyrate (P4HB) based meshes are absorbable and linked to positive clinical outcomes but have a poorly characterized immune response. This study evaluated the in vitro targeted transcriptomic response of human Mφs seeded for 48 h on PP and P4HB surgical meshes. The in vitro measured response from human Mφs cultured on P4HB exhibited inflammatory and anti-inflammatory gene expression profiles typically associated with wound healing, which aligns with in vivo animal studies from literature. The work herein provides in vitro evidence for the early transcriptomic targeted signature of human Mφs upon two commonly used surgical meshes. The findings suggest a transition from an inflammatory to a non-inflammatory phenotype by P4HB as well as an upregulation of genes annotated under the pathogen response pathway.

Dermal Extracellular Matrix-Derived Hydrogels as an In Vitro Substrate to Study Mast Cell Maturation

Mast cells (MCs) are pro-inflammatory tissue-resident immune cells that play a key role in inflammation. MCs circulate in peripheral blood as progenitors and undergo terminal differentiation in the tissue microenvironment where they can remain for many years. This in situ maturation results in tissue- and species-specific MC phenotypes, culminating in significant variability in response to environmental stimuli. There are many challenges associated with studying mature tissue-derived MCs, particularly in humans. In cases where cultured MCs are able to differentiate in two-dimensional in vitro cultures, there remains an inability for full maturation. Extracellular matrix (ECM) scaffolds provide for a more physiologically relevant environment for cells in vitro and have been shown to modulate the response of other immune cells such as T cells, monocytes, and macrophages. To improve current in vitro testing platforms of MCs and to assess future use of ECM scaffolds for MC regulation, we studied the in vitro response of human MCs cultured on decellularized porcine dermis hydrogels (dermis extracellular matrix hydrogel [dECM-H]). This study investigated the effect of dECM-H on cellular metabolic activity, cell viability, and receptor expression compared to collagen type I hydrogel (Collagen-H). Human MCs showed different metabolic activity when cultured in the dECM-H and also upregulated immunoglobulin E (IgE) receptors associated with MC maturation/activation compared to collagen type I. These results suggest an overall benefit in the long-term culture of human MCs in the dECM-H compared to Collagen-H providing important steps toward a model that is more representative of in vivo conditions. Graphical abstract [Formula: see text] Impact statement Mast cells (MCs) are difficult to culture in vitro as current culture conditions and substrates fail to promote similar phenotypic features observed in vivo. Extracellular matrix (ECM)-based biomaterials offer three-dimensional, tissue-specific environments that more closely resemble in vivo conditions. Our study explores the use of dermal ECM hydrogels for MC culture and shows significant upregulation of metabolic activity, cell viability, and gene expression of markers associated with MC maturation or activation compared to collagen type I-hydrogel and tissue culture plastic controls at 7 days. These results are among the first to describe MC behavior in response to ECM hydrogels.

Platelet-like particles improve fibrin network properties in a hemophilic model of provisional matrix structural defects

Following injury, a fibrin-rich provisional matrix is formed to stem blood loss and provide a scaffold for infiltrating cells, which rebuild the damaged tissue. Defects in fibrin network formation contribute to impaired healing outcomes, as evidenced in hemophilia. Platelet-fibrin interactions greatly influence fibrin network structure via clot contraction, which increases fibrin density over time. Previously developed hemostatic platelet-like particles (PLPs) are capable of mimicking platelet functions including binding to fibrin fibers, augmenting clotting, and inducing clot retraction. In this study, we aimed to apply PLPs within a plasma-based in vitro hemophilia B model of deficient fibrin network structure to determine the ability of PLPs to improve fibrin structure and wound healing responses within hemophilia-like abnormal fibrin network formation. PLP impact on structurally deficient clot networks was assessed via confocal microscopy, a micropost deflection model, atomic force microscopy and an in vitro wound healing model of early cell migration within a provisional fibrin matrix. PLPs improved clot network density, force generation, and stiffness, and promoted fibroblast migration within an in vitro model of early wound healing under hemophilic conditions, indicating that PLPs could provide a biomimetic platform for improving wound healing events in disease conditions that cause deficient fibrin network formation.

Fast Automated Approach for the Derivation of Acellular Extracellular Matrix Scaffolds from Porcine Soft Tissues

Decellularized extracellular matrix (ECM) scaffolds derived from tissues and organs are complex biomaterials used in clinical and research applications. A number of decellularization protocols have been described for ECM biomaterials derivation, each adapted to a particular tissue and use, restricting comparisons among materials. One of the major sources of variability in ECM products comes from the tissue source and animal age. Although this variability could be minimized using established tissue sources, other sources arise from the decellularization process itself. Overall, current protocols require manual work and are poorly standardized with regard to the choice of reagents, the order by which they are added, and exposure times. The combination of these factors adds variability affecting the uniformity of the final product between batches. Furthermore, each protocol needs to be optimized for each tissue and tissue source making tissue-to-tissue comparisons difficult. Automation and standardization of ECM scaffold development constitute a significant improvement to current biomanufacturing techniques but remains poorly explored. This study aimed to develop a biofabrication method for fast and automated derivation of raw material for ECM hydrogel production while preserving ECM composition and controlling lot-to-lot variability. The main result was a closed semibatch bioreactor system with automated dosing of decellularization reagents capable of deriving ECM material from pretreated soft tissues. The ECM was further processed into hydrogels to demonstrate gelation and cytocompatibility. This work presents a versatile, scalable, and automated platform for the rapid production of ECM scaffolds.

An off-the-shelf artificial cardiac patch improves cardiac repair after myocardial infarction in rats and pigs

Cell therapy has been a promising strategy for cardiac repair after injury or infarction; however, low retention and engraftment of transplanted cells limit potential therapeutic efficacy. Seeding scaffold material with cells to create cardiac patches that are transplanted onto the surface of the heart can overcome these limitations. However, because patches need to be freshly prepared to maintain cell viability, long-term storage is not feasible and limits clinical applicability. Here, we developed an off-the-shelf therapeutic cardiac patch composed of a decellularized porcine myocardial extracellular matrix scaffold and synthetic cardiac stromal cells (synCSCs) generated by encapsulating secreted factors from isolated human cardiac stromal cells. This fully acellular artificial cardiac patch (artCP) maintained its potency after long-term cryopreservation. In a rat model of acute myocardial infarction, transplantation of the artCP supported cardiac recovery by reducing scarring, promoting angiomyogenesis, and boosting cardiac function. The safety and efficacy of the artCP were further confirmed in a porcine model of myocardial infarction. The artCP is a clinically feasible, easy-to-store, and cell-free alternative to myocardial repair using cell-based cardiac patches.

Porcine Vocal Fold Lamina Propria-Derived Biomaterials Modulate TGF-β1-Mediated Fibroblast Activation in Vitro

The vocal fold lamina propria (VFLP), one of the outermost layers of the vocal fold (VF), is composed of tissue-specific extracellular matrix (ECM) proteins and is highly susceptible to injury. Various biomaterials have been clinically tested to treat voice disorders (e.g., hydrogels, fat, and hyaluronic acid), but satisfactory recovery of the VF functionality remains elusive. Fibrosis or scar formation in the VF is a major challenge, and the development and refinement of novel therapeutics that promote the healing and normal function of the VF are needed. Injectable hydrogels derived from native tissues have been previously reported with major advantages over synthetic hydrogels, including constructive tissue remodeling and reduced scar tissue formation. This study aims to characterize the composition of a decellularized porcine VFLP-ECM scaffold and the cytocompatibility and potential antifibrotic properties of a hydrogel derived from VFLP-ECM. In addition, we isolated potential matrix-bound vesicles (MBVs) and macromolecules from the VFLP-ECM that also downregulated smooth muscle actin ACTA2 under transforming growth factor-beta 1 (TGF-β1) stimulation. The results provide evidence of the unique protein composition of the VFLP-ECM and the potential link between the components of the VFLP-ECM and the inhibition of TGF-β1 signaling observed in vitro when transformed into injectable forms.

Platelet-like particles dynamically stiffen fibrin matrices and improve wound healing outcomes

Native platelets perform several critical functions within the context of wound healing, including participating in initial hemostasis and interacting with fibrin at the wound site to induce clot retraction. Platelet depletion or dysfunction due to trauma or disease can inhibit robust wound healing responses. There has been a focus recently on developing synthetic, non-immunogenic platelet mimetic technologies for the purpose of augmenting hemostatic responses in cases of deficient native platelet functionality. Here we describe the application of synthetic platelet-like particles (PLPs), capable of recapitulating the deformable platelet body and fibrin specificity found in native platelets, to enhance healing outcomes. We first demonstrate PLPs mimic activated platelet morphology and induce fibrin clot retraction. During clot retraction, native platelets generate forces within a fibrin network to stiffen the fibrin matrix; therefore, we hypothesized that our PLPs will likewise be able to stiffen provisional fibrin matrices. Due to previous studies indicating that increased matrix stiffness is linked to increased cellular migration, we further hypothesize that PLP-mediated fibrin stiffening will enhance cell migration and improve healing outcomes within in vitro and in vivo models of wound healing. PLPs were found to enhance fibroblast migration in in vitro models of early wound healing and enhance healing outcomes in an in vivo murine model of wound healing. These studies demonstrate the utility of PLPs for enhancing wound repair and also provide insight into the role of native platelet-mediated clot retraction in wound healing.

Mesenchymal Stem Cell/Red Blood Cell-Inspired Nanoparticle Therapy in Mice with Carbon Tetrachloride-Induced Acute Liver Failure

Acute liver failure is a critical condition characterized by global hepatocyte death and often time needs a liver transplantation. Such treatment is largely limited by donor organ shortage. Stem cell therapy offers a promising option to patients with acute liver failure. Yet, therapeutic efficacy and feasibility are hindered by delivery route and storage instability of live cell products. We fabricated a nanoparticle that carries the beneficial regenerative factors from mesenchymal stem cells and further coated it with the membranes of red blood cells to increase blood stability. Unlike uncoated nanoparticles, these particles promote liver cell proliferation in vitro and have lower internalization by macrophage cells. After intravenous delivery, these artificial stem cell analogs are able to remain in the liver and mitigate carbon tetrachloride-induced liver failure in a mouse model, as gauged by histology and liver function test. Our technology provides an innovative and off-the-shelf strategy to treat liver failure.

Contributions of bone morphogenetic proteins in cardiac repair cells in three-dimensional in vitro models and angiogenesis

One of the main efforts in myocardial tissue engineering is towards designing cardiac tissues able to rescue the reduction in heart function once implanted at the site of myocardial infarction. To date, the efficiency of this approach in preclinical applications is limited in part by our incomplete understanding of the inflammatory environment known to be present at the site of myocardial infarct and by poor vascularization. It was recently reported that polarized macrophages known to be present at the site of myocardial infarction secrete bone morphogenetic proteins (BMPs)-2 and -4 causing changes in the expression of cardiac proteins in a 2D in vitro model. Here, these findings were extended towards cardiac tissues composed of human embryonic stem cell derived cardiomyocytes embedded in collagen gel. By preconditioning cardiac tissues with BMPs, constructs were obtained with enhanced expression of cardiac markers. Additionally, after BMP preconditioning, the resulting cardiac-tissues were able to sustain diffusion of the BMPs with the added benefit of supporting human umbilical vein endothelial cell tube formation. Here, a model is proposed of cardiac tissues preconditioned with BMPs that results in stimulation of cardiomyocyte function and diffusion of BMPs able to support angiogenesis. This platform represents a step towards the validation of more complex bioengineered constructs for in vivo applications.

Directed Differentiation of Human Pluripotent Stem Cells to Microglia

Microglia, the immune cells of the brain, are crucial to proper development and maintenance of the CNS, and their involvement in numerous neurological disorders is increasingly being recognized. To improve our understanding of human microglial biology, we devised a chemically defined protocol to generate human microglia from pluripotent stem cells. Myeloid progenitors expressing CD14/CX3CR1 were generated within 30 days of differentiation from both embryonic and induced pluripotent stem cells (iPSCs). Further differentiation of the progenitors resulted in ramified microglia with highly motile processes, expressing typical microglial markers. Analyses of gene expression and cytokine release showed close similarities between iPSC-derived (iPSC-MG) and human primary microglia as well as clear distinctions from macrophages. iPSC-MG were able to phagocytose and responded to ADP by producing intracellular Ca²⁺ transients, whereas macrophages lacked such response. The differentiation protocol was highly reproducible across several pluripotent stem cell lines.

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Efficient protocol to generate human microglia from PSCs

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iPSC-derived microglia have ramified morphology and motile processes

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Expression and cytokine profiles of iPSC-derived microglia resemble primary microglia

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iPSC-derived microglia can phagocytose beads and respond to ADP

Tissue Engineering Strategies for Myocardial Regeneration: Acellular Versus Cellular Scaffolds?

Heart disease remains one of the leading causes of death in industrialized nations with myocardial infarction (MI) contributing to at least one fifth of the reported deaths. The hypoxic environment eventually leads to cellular death and scar tissue formation. The scar tissue that forms is not mechanically functional and often leads to myocardial remodeling and eventual heart failure. Tissue engineering and regenerative medicine principles provide an alternative approach to restoring myocardial function by designing constructs that will restore the mechanical function of the heart. In this review, we will describe the cellular events that take place after an MI and describe current treatments. We will also describe how biomaterials, alone or in combination with a cellular component, have been used to engineer suitable myocardium replacement constructs and how new advanced culture systems will be required to achieve clinical success.

Extracellular Matrix for Vocal Fold Lamina Propria Replacement: A Review

The vocal folds (VFs) are exposed to a number of injurious stimuli that frequently lead to aberrant structural alterations and altered biomechanical properties that clinically manifest as voice disorders. Therapies to restore both structure and function of this delicate tissue are ideal. However, such methods have not been adequately developed. Our group and others hypothesize that tissue engineering and regenerative medicine approaches, previously described for other tissue systems, hold significant promise for the VFs. In this review, we explore the concept of tissue engineering as it relates to the VFs, as well as recent studies employing both naturally and synthetically derived biomaterials, including those from laryngeal and nonlaryngeal sources, in combination with stem cells for a tissue-engineered approach to VF repair.

Response of human macrophages to wound matrices in vitro

Chronic wounds remain a major burden to the global healthcare system. Myriad wound matrices are commercially available but their mechanisms of action are poorly understood. Recent studies have shown that macrophages are highly influenced by their microenvironment, but it is not known how different biomaterials affect this interaction. Here, it was hypothesized that human macrophages respond differently to changes in biomaterial properties in vitro with respect to phenotype, including pro-inflammatory M1, anti-inflammatory M2a, known for facilitating extracellular matrix deposition and proliferation, and M2c, which has recently been associated with tissue remodeling. Using multiple donors, it was found that collagen scaffolds cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (EDC/NHS) promoted the least inflammatory phenotype in primary human macrophages compared with scaffolds cross-linked with formaldehyde or glutaraldehyde. Importantly, gene expression analysis trends were largely conserved between donors, especially TNFa (M1), CCL22 (M2a), and MRC1 (M2a). Then the response of primary and THP1 monocyte-derived macrophages to four commercially available wound matrices were compared-Integra Dermal Regeneration Template (Integra), PriMatrix Dermal Repair Scaffold (PriMatrix), AlloMend Acellular Dermal Matrix (AlloMend), and Oasis Wound Matrix (Oasis). Gene expression trends were different between primary and THP1 monocyte-derived macrophages for all six genes analyzed in this study. Finally, the behavior of primary macrophages cultured onto the wound matrices over time was analyzed. Integra and Oasis caused down-regulation of M2a markers CCL22 and TIMP3. PriMatrix caused up-regulation of TNFa (M1) and CD163 (M2c) and down-regulation of CCL22 and TIMP3 (both M2a). AlloMend caused up-regulation in CD163 (M2c). Lastly, Oasis promoted the largest increase in the combinatorial M1/M2 score, defined as the sum of M1 genes divided by the sum of M2 genes. This preliminary study suggested that biomaterials influenced the wound microenvironment to affect macrophage phenotype.

Differential gene expression in human, murine, and cell line-derived macrophages upon polarization

The mechanisms by which macrophages control the inflammatory response, wound healing, biomaterial-interactions, and tissue regeneration appear to be related to their activation/differentiation states. Studies of macrophage behavior in vitro can be useful for elucidating their mechanisms of action, but it is not clear to what extent the source of macrophages affects their apparent behavior, potentially affecting interpretation of results. Although comparative studies of macrophage behavior with respect to cell source have been conducted, there has been no direct comparison of the three most commonly used cell sources: murine bone marrow, human monocytes from peripheral blood (PB), and the human leukemic monocytic cell line THP-1, across multiple macrophage phenotypes. In this study, we used multivariate discriminant analysis to compare the in vitro expression of genes commonly chosen to assess macrophage phenotype across all three sources of macrophages, as well as those derived from induced pluripotent stem cells (iPSCs), that were polarized towards four distinct phenotypes using the same differentiation protocols: M(LPS,IFN) (aka M1), M(IL4,IL13) (aka M2a), M(IL10) (aka M2c), and M(-) (aka M0) used as control. Several differences in gene expression trends were found among the sources of macrophages, especially between murine bone marrow-derived and human blood-derived M(LPS,IFN) and M(IL4,IL13) macrophages with respect to commonly used phenotype markers like CCR7 and genes associated with angiogenesis and tissue regeneration like FGF2 and MMP9. We found that the genes with the most similar patterns of expression among all sources were CXCL-10 and CXCL-11 for M(LPS,IFN) and CCL17 and CCL22 for M(IL4,IL13). Human PB-derived macrophages and human iPSC-derived macrophages showed similar gene expression patterns among the groups and genes studied here, suggesting that iPSC-derived monocytes have the potential to be used as a reliable cell source of human macrophages for in vitro studies. These findings could help select appropriate markers when testing macrophage behavior in vitro and highlight those markers that may confuse interpretation of results from experiments employing macrophages from different sources.

Controlled release of cytokines using silk-biomaterials for macrophage polarization

Polarization of macrophages into an inflammatory (M1) or anti-inflammatory (M2) phenotype is important for clearing pathogens and wound repair, however chronic activation of either type of macrophage has been implicated in several diseases. Methods to locally control the polarization of macrophages is of great interest for biomedical implants and tissue engineering. To that end, silk protein was used to form biopolymer films that release either IFN-γ or IL-4 to control the polarization of macrophages. Modulation of the solubility of the silk films through regulation of β-sheet (crystalline) content enabled a short-term release (4-8 h) of either cytokine, with smaller amounts released out to 24 h. Altering the solubility of the films was accomplished by varying the time that the films were exposed to water vapor. The released IFN-γ or IL-4 induced polarization of THP-1 derived macrophages into the M1 or M2 phenotypes, respectively. The silk biomaterials were able to release enough IFN-γ or IL-4 to repolarize the macrophage from M1 to M2 and vice versa, demonstrating the well-established plasticity of macrophages. High β-sheet content films that are not soluble and do not release the trapped cytokines were also able to polarize macrophages that adhered to the surface through degradation of the silk protein. Chemically conjugating IFN-γ to silk films through disulfide bonds allowed for longer-term release to 10 days. The release of covalently attached IFN-γ from the films was also able to polarize M1 macrophages in vitro. Thus, the strategy described here offers new approaches to utilizing biomaterials for directing the polarization of macrophages.

Derivation and characterization of porcine vocal fold extracellular matrix scaffold

OBJECTIVES/HYPOTHESIS

To optimize decellularization of porcine vocal folds (VF) and quantify human bone marrow-derived mesenchymal stem cell (BM-MSC) interactions with this matrix to provide a foundation for regenerative approaches to VF repair.

STUDY DESIGN AND METHODS

Vocal folds were dissected from porcine larynges and three decellularization protocols were compared, each consisting of washes and mechanical agitations with different combinations of reagents. DNA content was analyzed via Quant-iT Picogreen assay and hematoxylin and eosin staining. Bone marrow-derived MSCs were then seeded onto the decellularized VF matrices. Morphology, metabolic activity, DNA content, and gene expression were assessed using LIVE/DEAD Cell Viability, alamarBlue Cell Viability Assay, Quant-iT Picogreen assay, and quantitative polymerase chain reaction, respectively.

RESULTS

The most successful decellularization protocol removed 95% DNA content within 1 day, compared to several days required for previously described protocols. Histology confirmed the retention of extracellular matrix (ECM) and its components, including glycosaminoglycans, collagen, and fibrin, while void of nuclear/cellular content. Decellularized scaffolds were then seeded with BM-MSCs. Similar DNA quantities were observed after 24 hours of seeding within the VF-ECM scaffold when compared to cells on tissue culture plastic (TCP). LIVE/DEAD staining of the seeded VF-ECM confirmed excellent cell viability, and the metabolic activity of BM-MSCs increased significantly on VF-ECM compared to TCP. Endoglin gene expression decreased, suggestive of differentiation.

CONCLUSION

Porcine VFs can be efficiently decellularized within 5 hours using a combination of sodium deoxycholate and peracetic acid. Decellularized VF-ECM supported attachment and growth of human BM-MSCs, with evidence of differentiation.

LEVEL OF EVIDENCE

N/A.

BMP protein-mediated crosstalk between inflammatory cells and human pluripotent stem cell-derived cardiomyocytes

Following cardiac injury, the ischaemic heart tissue is characterized by the invasion of pro-inflammatory (M1) and pro-healing (M2) macrophages. Any engineered cardiac tissue will inevitably interact with the inflammatory environment found at the site of myocardial infarction at the time of implantation. However, the interactions between the inflammatory and the cardiac repair cells remain poorly understood. Here we recapitulated in vitro some of the important cellular events found at the site of myocardial injury, such as macrophage recruitment and their effect on cardiac differentiation and maturation, by taking into account the involvement of paracrine-mediated signalling. By using a 3D inverted invasion assay, we found that cardiomyocyte (CM) conditioned medium can trigger the recruitment of pro-inflammatory (M1) macrophages, through a mechanism that involves, in part, CM-derived BMP4. Pro-inflammatory (M1) macrophages were also found to affect CM proliferation and differentiation potential, in part due to BMP molecules secreted by macrophages. These effects involved the activation of the canonical outside-in signalling pathways, such as SMAD1,5,8, which are known to be activated during myocardial injury in vivo. In the present study we propose a new role for CM- and macrophage-derived BMP proteins during the recruitment of macrophage subtypes and the maturation of repair cells, representing an important step towards creating a functional cardiac patch with superior therapeutic properties. Copyright © 2015 John Wiley & Sons, Ltd.

Toward beta cell replacement for diabetes

The discovery of insulin more than 90 years ago introduced a life-saving treatment for patients with type 1 diabetes, and since then, significant progress has been made in clinical care for all forms of diabetes. However, no method of insulin delivery matches the ability of the human pancreas to reliably and automatically maintain glucose levels within a tight range. Transplantation of human islets or of an intact pancreas can in principle cure diabetes, but this approach is generally reserved for cases with simultaneous transplantation of a kidney, where immunosuppression is already a requirement. Recent advances in cell reprogramming and beta cell differentiation now allow the generation of personalized stem cells, providing an unlimited source of beta cells for research and for developing autologous cell therapies. In this review, we will discuss the utility of stem cell-derived beta cells to investigate the mechanisms of beta cell failure in diabetes, and the challenges to develop beta cell replacement therapies. These challenges include appropriate quality controls of the cells being used, the ability to generate beta cell grafts of stable cellular composition, and in the case of type 1 diabetes, protecting implanted cells from autoimmune destruction without compromising other aspects of the immune system or the functionality of the graft. Such novel treatments will need to match or exceed the relative safety and efficacy of available care for diabetes.

Macrophages modulate engineered human tissues for enhanced vascularization and healing

Tissue engineering is increasingly based on recapitulating human physiology, through integration of biological principles into engineering designs. In spite of all progress in engineering functional human tissues, we are just beginning to develop effective methods for establishing blood perfusion and controlling the inflammatory factors following implantation into the host. Functional vasculature largely determines tissue survival and function in vivo. The inflammatory response is a major regulator of vascularization and overall functionality of engineered tissues, through the activity of different types of macrophages and the cytokines they secrete. We discuss here the cell-scaffold-bioreactor systems for harnessing the inflammatory response for enhanced tissue vascularization and healing. To this end, inert scaffolds that have been considered for many decades a "gold standard" in regenerative medicine are beginning to be replaced by a new generation of "smart" tissue engineering systems designed to actively mediate tissue survival and function.

Natural cardiac extracellular matrix hydrogels for cultivation of human stem cell-derived cardiomyocytes

Biomaterial scaffolds made of natural and synthetic materials are designed to serve as a structural and informational template for cell attachment and tissue formation. The use of native extracellular matrix (ECM) is of special interest for the culture of cardiac stem and progenitor cells due to the presence of intrinsic regulatory factors regulating cardiac function. We describe here how to obtain native ECM hydrogels from porcine hearts for the culture of human embryonic, induced pluripotent, and somatic stem cells for cardiac tissue engineering and regenerative medicine applications.

The regulation of growth and metabolism of kidney stem cells with regional specificity using extracellular matrix derived from kidney

Native extracellular matrix (ECM) that is secreted and maintained by resident cells is of great interest for cell culture and cell delivery. We hypothesized that specialized bioengineered niches for stem cells can be established using ECM-derived scaffolding materials. Kidney was selected as a model system because of the high regional diversification of renal tissue matrix. By preparing the ECM from three specialized regions of the kidney (cortex, medulla, and papilla; whole kidney, heart, and bladder as controls) in three forms: (i) intact sheets of decellularized ECM, (ii) ECM hydrogels, and (iii) solubilized ECM, we investigated how the structure and composition of ECM affect the function of kidney stem cells (with mesenchymal stem cells, MSCs, as controls). All three forms of the ECM regulated KSC function, with differential structural and compositional effects. KSCs cultured on papilla ECM consistently displayed lower proliferation, higher metabolic activity, and differences in cell morphology, alignment, and structure formation as compared to KSCs on cortex and medulla ECM, effects not observed in corresponding MSC cultures. These data suggest that tissue- and region-specific ECM can provide an effective substrate for in vitro studies of therapeutic stem cells.

Decellularization of human and porcine lung tissues for pulmonary tissue engineering

BACKGROUND

The only definitive treatment for end-stage organ failure is orthotopic transplantation. Lung extracellular matrix (LECM) holds great potential as a scaffold for lung tissue engineering because it retains the complex architecture, biomechanics, and topologic specificity of the lung. Decellularization of human lungs rejected from transplantation could provide "ideal" biologic scaffolds for lung tissue engineering, but the availability of such lungs remains limited. The present study was designed to determine whether porcine lung could serve as a suitable substitute for human lung to study tissue engineering therapies.

METHODS

Human and porcine lungs were procured, sliced into sheets, and decellularized by three different methods. Compositional, ultrastructural, and biomechanical changes to the LECM were characterized. The suitability of LECM for cellular repopulation was evaluated by assessing the viability, growth, and metabolic activity of human lung fibroblasts, human small airway epithelial cells, and human adipose-derived mesenchymal stem cells over a period of 7 days.

RESULTS

Decellularization with 3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) showed the best maintenance of both human and porcine LECM, with similar retention of LECM proteins except for elastin. Human and porcine LECM supported the cultivation of pulmonary cells in a similar way, except that the human LECM was stiffer and resulted in higher metabolic activity of the cells than porcine LECM.

CONCLUSIONS

Porcine lungs can be decellularized with CHAPS to produce LECM scaffolds with properties resembling those of human lungs, for pulmonary tissue engineering. We propose that porcine LECM can be an excellent screening platform for the envisioned human tissue engineering applications of decellularized lungs.

Macrophages modulate the viability and growth of human mesenchymal stem cells

Following myocardial infarction, tissue repair is mediated by the recruitment of monocytes and their subsequent differentiation into macrophages. Recent findings have revealed the dynamic changes in the presence of polarized macrophages with pro-inflammatory (M1) and anti-inflammatory (M2) properties during the early (acute) and late (chronic) stages of cardiac ischemia. Mesenchymal stem cells (MSCs) delivered into the injured myocardium as reparative cells are subjected to the effects of polarized macrophages and the inflammatory milieu. The present study investigated how cytokines and polarized macrophages associated with pro-inflammatory (M1) and anti-inflammatory (M2) responses affect the survival of MSCs. Human MSCs were studied using an in vitro platform with individual and combined M1 and M2 cytokines: IL-1β, IL-6, TNF-α, and IFN-γ (for M1), and IL-10, TGF-β1, TGF-β3, and VEGF (for M2). In addition, polarization molecules (M1: LPS and IFN-γ; M2: IL-4 and IL-13) and common chemokines (SDF-1 and MCP-1) found during inflammation were also studied. Indirect and direct co-cultures were conducted using M1 and M2 polarized human THP-1 monocytes. M2 macrophages and their associated cytokines supported the growth of hMSCs, while M1 macrophages and their associated cytokines inhibited the growth of hMSCs in vitro under certain conditions. These data imply that an anti-inflammatory (M2) environment is more accommodating to the therapeutic hMSCs than a pro-inflammatory (M1) environment at specific concentrations.

Optimizing dynamic interactions between a cardiac patch and inflammatory host cells

Damaged heart muscle has only a minimal ability for regeneration following myocardial infarction in which cardiomyocytes are lost to ischemia. The most clinically promising approach to regeneration of cardiac muscle currently under investigation is that of injecting cardiogenic repair cells or implanting a preformed tissue-engineered patch. While major advances are being made in the derivation of functional human cardiomyocytes and the development of tissue-engineering modalities for cardiac repair, the host environment into which the repair cells are placed is largely overlooked. Within seconds of myocardial ischemia, hypoxia sets in in the myocardium and the inflammatory response starts, characterized by rapid deployment of circulating cells and the release of paracrine and autocrine signals. Therefore, the inflammatory conditions under which these interactions take place, the design of the scaffold material used, and the maturity of the implanted cells will determine the outcomes of any stem cell-based therapy. We discuss here the interactions between implanted and inflammatory cells of the host, which are critical for the design of effective heart repair therapies.

Preparation of cardiac extracellular matrix from an intact porcine heart

Whole organ engineering would benefit from a three-dimensional scaffold produced from intact organ-specific extracellular matrix (ECM). The microenvironment and architecture provided by such a scaffold would likely support site-appropriate cell differentiation and spatial organization. The methods to produce such scaffolds from intact organs require customized decellularization protocols. In the present study, intact adult porcine hearts were successfully decellularized in less than 10 h using pulsatile retrograde aortic perfusion. Serial perfusion of an enzymatic, nonionic detergent, ionic detergent, and acid solution with hypotonic and hypertonic rinses was used to systematically remove cellular content. The resultant cardiac ECM retained collagen, elastin, and glycosaminoglycans, and mechanical integrity. Cardiac ECM supported the formation of organized chicken cardiomyocyte sarcomere structure in vitro. The intact decellularized porcine heart provides a tissue engineering template that may be beneficial for future preclinical studies and eventual clinical applications.

Geometry and force control of cell function

Tissue engineering is becoming increasingly ambitious in its efforts to create functional human tissues, and to provide stem cell scientists with culture systems of high biological fidelity. Novel engineering designs are being guided by biological principles, in an attempt to recapitulate more faithfully the complexities of native cellular milieu. Three-dimensional (3D) scaffolds are being designed to mimic native-like cell environments and thereby elicit native-like cell responses. Also, the traditional focus on molecular regulatory factors is shifting towards the combined application of molecular and physical factors. Finally, methods are becoming available for the coordinated presentation of molecular and physical factors in the form of controllable spatial and temporal gradients. Taken together, these recent developments enable the interrogation of cellular behavior within dynamic culture settings designed to mimic some aspects of native tissue development, disease, or regeneration. We discuss here these advanced cell culture environments, with emphasis on the derivation of design principles from the development (the biomimetic paradigm) and the geometry-force control of cell function (the biophysical regulation paradigm).

Oxygen diffusivity of biologic and synthetic scaffold materials for tissue engineering

Scaffolds for tissue engineering and regenerative medicine applications are commonly manufactured from synthetic materials, intact or isolated components of extracellular matrix (ECM), or a combination of such materials. After surgical implantation, the metabolic requirements of cells that populate the scaffold depend upon adequate gas and nutrient exchange with the surrounding microenvironment. The present study measured the oxygen transfer through three biologic scaffold materials composed of ECM including small intestinal submucosa (SIS), urinary bladder submucosa (UBS), and urinary bladder matrix (UBM), and one synthetic biomaterial, Dacron. The oxygen diffusivity was calculated from Fick's first law of diffusion. Each material permitted measurable oxygen diffusion. The diffusivity of SIS was found to be dependent on the direction of oxygen transfer; the oxygen transfer in the abluminal-to-luminal direction was significantly greater than the luminal-to-abluminal direction. The oxygen diffusivity of UBM and UBS were similar despite the presence of an intact basement membrane on the luminal surface of UBM. Dacron showed oxygen diffusivity values seven times greater than the ECM biomaterials. The current study showed that each material has unique oxygen diffusivity values, and these values may be dependent on the scaffold's ultrastructure.

Degradation products of extracellular matrix affect cell migration and proliferation

Biologic scaffolds composed of extracellular matrix (ECM) are utilized in numerous regenerative medicine applications to facilitate the constructive remodeling of tissues and organs. The mechanisms by which the host remodeling response occurs are not fully understood, but recent studies suggest that both constituent growth factors and biologically active degradation products derived from ECM play important roles. The objective of the present study was to determine if degradation of ECM scaffold materials in vitro by methods that are biochemically and physiologically relevant can yield products that possess chemotactic and/or mitogenic activities for fully differentiated mammalian endothelial cells and undifferentiated multipotential progenitor cells. ECM harvested from porcine urinary bladder was degraded enzymatically with pepsin/hydrochloric acid or papain. The ECM degradation products were tested for chemoattractant properties utilizing either 48-well chemotaxis filter migration microchambers or fluorescence-based filter migration assays, and were tested for mitogenic properties in cell proliferation assays. Results showed that ECM degradation products possessed chemotactic and mitogenic activities for multipotential progenitor cells and that the same degradation products inhibited both chemotaxis and proliferation of differentiated endothelial cells. These findings support the concept that degradation products of ECM bioscaffolds are important modulators of the recruitment and proliferation of appropriate cell types during the process of ECM scaffold remodeling.

Hydrated versus lyophilized forms of porcine extracellular matrix derived from the urinary bladder

Biologic scaffolds composed of naturally occurring extracellular matrix (ECM) are currently in clinical use for the repair and reconstruction of damaged or missing tissues. The material and structural properties of the ECM scaffold are important determinants of the potential clinical applications and these properties may be affected by manufacturing steps, processing steps, and storage conditions. The present study compared the structural properties of hydrated and lyophilized forms of a biologic scaffold derived from the porcine urinary bladder (urinary bladder matrix or UBM). The structural properties evaluated include: maximum load and elongation, maximum tangential stiffness, energy absorbed, suture retention strength, ball-burst strength, and the hydrostatic permeability index. Other properties that were investigated include changes in the water content, structural morphology, and thickness and the ability to support in vitro growth of NIH 3T3 cells. Lyophilization caused no changes in the structural properties evaluated with the exception of a decrease in maximum elongation. NIH 3T3 cells showed invasion of the scaffold when seeded on the abluminal side of both hydrated and lyophilized UBM, and there were more cells present on lyophilized UBM when compared to hydrated UBM devices after the 7-days culture period. Irreversible changes were observed in the microstructure and ultrastructure of lyophilized UBM devices. We conclude that lyophilization affects the overall in vitro cell growth of NIH 3T3 cells and the ultrastructural morphology of UBM devices, but does not result in significant changes in structural properties.

Collagen fiber alignment and biaxial mechanical behavior of porcine urinary bladder derived extracellular matrix

The collagen fiber alignment and biomechanical behavior of naturally occurring extracellular matrix (ECM) scaffolds are important considerations for the design of medical devices from these materials. Both should be considered in order to produce a device to meet tissue specific mechanical requirements (e.g., tendon vs. urinary bladder), and could ultimately affect the remodeling response in vivo. The present study evaluated the collagen fiber alignment and biaxial mechanical behavior of ECM scaffold material harvested from porcine urinary bladder tunica mucosa and basement membrane (together referred to as urinary bladder matrix (UBM)) and ECM harvested from urinary bladder submucosa (UBS). Since the preparation of UBM allows for control of the direction of delamination, the effect of the delamination method on the mechanical behavior of UBM was determined by delaminating the submucosa and other abluminal layers by scraping along the longitudinal axis of the bladder (apex to neck) (UBML) or along the circumferential direction (UBMC). The processing of UBS does not allow for similar directional control. UBML and UBS had similar collagen fiber distributions, with a preferred collagen fiber alignment along the longitudinal direction. UBMC showed a more homogenous collagen fiber orientation. All samples showed a stiffer mechanical behavior in the longitudinal direction. Despite similar collagen fiber distributions, UBML and UBS showed quite different mechanical behavior for the applied loading patterns with UBS showing a much more pronounced toe region. The mechanical behavior for UBMC in both directions was similar to the mechanical behavior of UBML. There are distinct differences in the mechanical behavior of different layers of ECM from the porcine urinary bladder, and the processing methods can substantially alter the mechanical behavior observed.

Hybrid nanofibrous scaffolds from electrospinning of a synthetic biodegradable elastomer and urinary bladder matrix

Synthetic materials can be electrospun into submicron or nanofibrous scaffolds to mimic extracellular matrix (ECM) scale and architecture with reproducible composition and adaptable mechanical properties. However, these materials lack the bioactivity present in natural ECM. ECM-derived scaffolds contain bioactive molecules that exert in vivo mimicking effects as applied for soft tissue engineering, yet do not possess the same flexibility in mechanical property control as some synthetics. The objective of the present study was to combine the controllable properties of a synthetic, biodegradable elastomer with the inherent bioactivity of an ECM derived scaffold. A hybrid electrospun scaffold composed of a biodegradable poly(ester-urethane)urea (PEUU) and a porcine ECM scaffold (urinary bladder matrix, UBM) was fabricated and characterized for its bioactive and physical properties both in vitro and in vivo. Increasing amounts of PEUU led to linear increases in both tensile strength and breaking strain while UBM incorporation led to increased in vitro smooth muscle cell adhesion and proliferation and in vitro mass loss. Subcutaneous implantation of the hybrid scaffolds resulted in increased scaffold degradation and a large cellular infiltrate when compared with electrospun PEUU alone. Electrospun UBM/PEUU combined the attractive bioactivity and mechanical features of its individual components to result in scaffolds with considerable potential for soft tissue engineering applications.

Uniaxial and biaxial properties of terminally sterilized porcine urinary bladder matrix scaffolds

Scaffolds composed of extracellular matrix have been successfully used to support the reconstruction of a variety of tissues in preclinical studies and in clinical applications. As an off-the-shelf product, extracellular matrix (ECM) scaffolds must be subjected to terminal sterilization before use. The choice of sterilization method may alter the integrity of the ECM's composition and structure such that the mechanical and material properties are adversely affected. The present study evaluated selected structural properties of an ECM scaffold derived from the urinary bladder termed urinary bladder matrix after being sterilized by three different methods: ethylene oxide (ETO) (750 mg/h for 16 h), gamma irradiation (2.0 Mrads), or electron beam irradiation (e-beam) (2.2 Mrads). The structural properties that were evaluated include maximum force, maximum elongation, maximum tangential stiffness, energy dissipation, and ball-burst strength. All sterilization methods affected at least two of the measured properties. ETO was shown to have the least detrimental effect upon the measured properties. Gamma and e-beam irradiation were shown to decrease the uniaxial and biaxial strength, maximum tangential stiffness, and the energy dissipation of the ECM scaffolds. The present study showed that the choice of terminal sterilization method affects the structural properties of scaffolds composed of extracellular matrix.

Effect of storage upon material properties of lyophilized porcine extracellular matrix derived from the urinary bladder

Xenogeneic extracellular matrices (ECMs) have been developed as off-the-shelf biologic scaffolds that have been effectively used in preclinical and clinical applications for tissue reconstruction. Such materials must be suitable for terminal sterilization and capable of storage for extended periods of time without significant changes in material properties and bioactivity. Material properties of interest for ECM scaffolds include hydrostatic permeability index (PI), uniaxial maximum load and elongation, maximum tangential stiffness (MTS), suture retention strength (SRS), and ball-burst strength (BBS). The present study evaluated these material properties for lyophilized forms of an ECM scaffold derived from the porcine urinary bladder, termed urinary bladder matrix (UBM), that was terminally sterilized by e-beam irradiation at 22 kGy and stored at room temperature (RT; 20-24 degrees C) or refrigerated temperature (REFT; 4-8 degrees C) for up to 12 months. UBM devices showed no change in SRS, BBS, and hydrostatic PI after the evaluation period. Lyophilized devices stored at RT showed an increase in maximum load and MTS while devices stored at REFT showed an increase in maximum elongation after 1 year of storage (p < 0.05). These results indicate that structural changes in the UBM device may slowly occur as a function of prolonged storage and storage temperature.

Esophageal reconstruction with ECM and muscle tissue in a dog model

An in vivo study was conducted to determine if an extracellular matrix (ECM) scaffold co-localized with autologous muscle tissue could achieve constructive remodeling of esophageal tissue without stricture. ECM derived from the porcine urinary bladder was processed, decellularized, configured into a tube shape, and terminally sterilized for use as a bioscaffold for esophageal reconstruction in a dog model. Twenty-two dogs were divided into four groups, three groups of five and one group of seven. Groups 1 and 2 were repaired with either ECM alone or muscle tissue alone, respectively. Groups 3 and 4 were repaired with ECM plus either a partial (30%) covering with muscle tissue or a complete (100%) covering with muscle tissue, respectively. Animals in groups 1 and 2 were sacrificed within approximately 3 weeks because of the formation of intractable esophageal stricture. Four of five dogs in group 3 and six of seven dogs in group 4 were survived for 26 days to 230 days and showed constructive remodeling of esophageal tissue with the formation of well organized esophageal tissue layers, minimal stricture, esophageal motility, and a normal clinical outcome. Mechanical testing of a subset of the remodeled esophageal tissue from animals in groups 3 and 4 showed progressive remodeling from a relatively stiff, non-compliant ECM tube structure toward a tissue with near normal biomechanical properties. We conclude that ECM bioscaffolds plus autologous muscle tissue, but not ECM scaffolds or muscle tissue alone, can facilitate the in situ reconstitution of structurally and functionally acceptable esophageal tissue.

Analytically derived material properties of multilaminated extracellular matrix devices using the ball-burst test

Xenogeneic extracellular matrices (ECMs) have been shown to be effective as naturally occurring scaffolds for soft-tissue repair. As acellular tissue substitutes at the time of surgical implantation, ECMs are subjected to the mechanical forces and micro-environmental conditions representative of the anatomical location in which they are placed. Ideally such natural scaffolds would possess mechanical properties that allow for normal tissue function in and around the implant site. The ball-burst test was used to simulate biaxial forces and to determine the strength of the ECM scaffold under a relevant physiological loading condition. The ball-burst test, in itself, does not quantify intrinsic mechanical properties and therefore a methodology was developed to determine the maximum stress resultant tangent modulus (MSRTM) or the maximum stress tangent modulus (MSTM), stress to failure (sigma(f)), failure stress resultant (N(f)), ball-burst pressure (P), and maximum elongation (lambda(max)) from the raw ball-burst data obtained at a constant-rate of transverse. The analytical methodology was compared to finite element simulations and showed good correlation with the analytical solution presented. The proposed approximations were used to compute biaxial failure properties for a variety of multilaminate ECM devices with varying number of layers, disinfection and sterilization, and organ origin.