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Worldwide use and disposal of plastics have reached a dramatic saturation point, polluting lands, oceans, and air across the globe. Responding to such a challenge requires, among other environmental remediation measures, the manufacture of alternative sustainable plastics. Recent studies in the area have enabled the development of degradable plastics; however, the rate and conditions required for the degradation of such materials remains under scrutiny. Here, we introduce a new class of fully plant-based, rapidly degradable lignin and zein composite blend that can be transformed into macroscopic structures using extrusion three-dimensional (3D) printing. Corn-derived zein forms the polymeric solution, while insoluble lignin granules act as a binder for enhanced printability and facile degradation. The blend showcases a shear-thinning behavior that is ideal for rapid extrusion printing into desired 3D structures, from cuvette caps to circuit boards. Biodegradation studies show that common bacteria readily found in soil and compost are able to decompose structures made with the lignin–zein composite in shorter time frames compared to a known biodegradable plastic, viz., polylactic acid. The rapid biodegradability and enhanced processability highlight the potential of lignin–zein composites to decrease our dependence on petroleum oil-based plastics.

Although delayed wound healing is an important clinical complication in diabetic patients, few targeted treatments are available, and it remains challenging to promote diabetic wound healing. Impaired neovascularization is one of the prime characteristics of the diabetic phenotype of delayed wound healing. Additionally, increased levels of reactive oxygen species (ROS) and chronic low-grade inflammation and hypoxia are associated with diabetes, which disrupts mechanisms of wound healing. We developed lignin composites with multiple wound healing-promotive functions, including pro-angiogenesis, sustained oxygenation from calcium peroxide (CaO2)-based oxygen releasing nanoparticles and ROS–scavenging with thiolated lignosulfonate that captures the elevated ROS in diabetic wounds. The sustained release of oxygen and ROS-scavenging by the lignin composites promoted endothelial cell branching and their reorganization into characteristic network formationin vitro, promoted angiogenic growth factor expression and angiogenesis in full thickness skin wounds tested in a diabetic murine model of delayed wound healing, and decreased hypoxia inducible factor-1α (HIF-1α) expression. These effects significantly increased the granulation tissue deposition and tissue repair. Our findings demonstrate that lignin composites promote diabetic wound healing without use of other drugs and show the potential of functionalized lignosulfonate for wound healing applications requiring balanced antioxidation and controlled oxygen release.

We demonstrate the impact of engineering molecular structures of poly(acrylamide) (PAAm) and poly(

The application of engineered biomaterials for wound healing has been pursued since the beginning of tissue engineering. Here, we attempt to apply functionalized lignin to confer antioxidation to the extracellular microenvironments of wounds and to deliver oxygen from the dissociation of calcium peroxide for enhanced vascularization and healing responses without eliciting inflammatory responses. Elemental analysis showed 17 times higher quantity of calcium in the oxygen releasing nanoparticles. Lignin composites including the oxygen releasing nanoparticles released around 500 ppm oxygen per day at least for 7 days. By modulating the concentration of the methacrylated gelatin, we were able to maintain the injectability of lignin composite precursors and the stiffness of lignin composites suitable for wound healing after photo-crosslinking.In situformation of lignin composites with the oxygen releasing nanoparticles enhanced the rate of tissue granulation, the formation of blood vessels and the infiltration of α-smooth muscle actin+fibroblasts into the wounds over 7 days. At 30 days after surgery, the lignin composite with oxygen generating nanoparticles remodeled the collagen architecture resembling to the reticular pattern of unwounded collagen with minimal scar formation. Thus, our study shows the potential of functionalized lignin for wound healing applications requiring balanced antioxidation and controlled release of oxygen for enhanced tissue granulation, vascularization and maturation of collagens.

In response to myocardial infarction (MI), quiescent cardiac fibroblasts differentiate into myofibroblasts mediating tissue repair. One of the most widely accepted markers of myofibroblast differentiation is the expression of Acta2 which encodes smooth muscle alpha-actin (SMαA) that is assembled into stress fibers. However, the requirement of Acta2/SMαA in the myofibroblast differentiation of cardiac fibroblasts and its role in post-MI cardiac repair remained unknown. To answer these questions, we generated a tamoxifen-inducible cardiac fibroblast-specific Acta2 knockout mouse line. Surprisingly, mice that lacked Acta2 in cardiac fibroblasts had a normal post-MI survival rate. Moreover, Acta2 deletion did not affect the function or histology of infarcted hearts. No difference was detected in the proliferation, migration, or contractility between WT and Acta2-null cardiac myofibroblasts. Acta2-null cardiac myofibroblasts had a normal total filamentous actin level and total actin level. Acta2 deletion caused a significant compensatory increase in the transcription level of non-Acta2 actin isoforms, especially Actg2 and Acta1. Moreover, in myofibroblasts, the transcription levels of cytoplasmic actin isoforms were significantly higher than those of muscle actin isoforms. In addition, we found that myocardin-related transcription factor-A is critical for myofibroblast differentiation but is not required for the compensatory effects of non-Acta2 isoforms. In conclusion, the Acta2 deletion does not prevent the myofibroblast differentiation of cardiac fibroblasts or affect the post-MI cardiac repair, and the increased expression and stress fiber formation of non-SMαA actin isoforms and the functional redundancy between actin isoforms are able to compensate for the loss of Acta2 in cardiac myofibroblasts.

Three-dimensional matrices of collagen type I (Col I) are widely used in tissue engineering applications for its abundance in many tissues, bioactivity with many cell types, and excellent biocompatibility. Inspired by the structural role of lignin in a plant tissue, we found that sodium lignosulfonate (SLS) and an alkali-extracted lignin from switchgrass (SG) increased the stiffness of Col I gels. SLS and SG enhanced the stiffness of Col I gels from 52 to 670 Pa and 52 to 320 Pa, respectively, and attenuated shear-thinning properties, with the formulation of 1.8 mg/mL Col I and 5.0 mg/mL SLS or SG. In 2D cultures, the cytotoxicity of collagen-SLS to adipose-derived stromal cells was not observed and the cell viability was maintained over 7 days in 3D cultures. Collagen-SLS composites did not elicit immunogenicity when compared to SLS-only groups. Our collagen-SLS composites present a case that exploits lignins as an enhancer of mechanical properties of Col I without adverse cytotoxicity and immunogenicity for

In response to myocardial infarction (MI), quiescent cardiac fibroblasts differentiate into myofibroblasts mediating tissue repair in the infarcted area. One of the most widely accepted markers of myofibroblast differentiation is the expression of Acta2 which encodes smooth muscle alpha-actin (SMαA) that is assembled into stress fibers. However, the requirement of Acta2 / SMαA in the myofibroblast differentiation of cardiac fibroblasts and its role in post-MI cardiac repair remained largely unknown. To answer these questions, we generated a tamoxifen-inducible cardiac fibroblast-specific Acta2 knockout mouse line. Surprisingly, mice that lacked Acta2 in cardiac fibroblasts had a normal survival rate after MI. Moreover, Acta2 deletion did not affect the function or overall histology of infarcted hearts. No difference was detected in the proliferation, migration, or contractility between WT and Acta2 -null cardiac myofibroblasts. It was identified that Acta2 -null cardiac myofibroblasts had a normal total filamentous actin level and total actin level. Acta2 deletion caused a unique compensatory increase in the transcription level of Actg2 and an increase in the protein level of sarcomeric actin isoform(s). In addition, the specific muscle actin isoforms that were upregulated in Acta2 -null cardiac myofibroblasts varied between individual cells. Moreover, the formation of stress fibers by cytoplasmic actin isoforms, especially the cytoplasmic gamma-actin, was enhanced in Acta2 -null cardiac myofibroblasts despite their unchanged RNA and protein expression. In conclusion, the deletion of Acta2 does not prevent the myofibroblast differentiation of cardiac fibroblasts or affect the post-MI cardiac repair, and the increased expression and stress fiber formation of non-SMαA actin isoforms and the functional redundancy between actin isoforms are able to compensate for the loss of Acta2 in cardiac myofibroblasts.

The spatiotemporal distribution profile of polymeric nanoparticles (NPs) in the eye is important as it will determine their effectiveness as topical ocular drug delivery systems for specific eye diseases. Physical stability of the nanoparticles in an ophthalmic formulation and thermal stability of the entrapped drug are critical as well to the applicability of polymeric nanoparticles as drug delivery to the eye. To investigate these characteristics, Cy5-labeled, poly(lactic-co-glycolic acid) (PLGA) NPs (ζ-potential: -14.1±1.5 mV, size: 241.7±0.6 nm) and lutein-loaded PLGA NPs (ζ-potential: -6.7±0.3 mV, size: 210.6±3.3 nm) were synthesized, and their stability and biodistribution were assessed. Lutein-loaded NPs were stable at 4°C without significant changes in size and morphology, without significant lutein degradation, and 26% release after 5 weeks in suspension. In contrast, lutein-loaded NPs stored at 25°C and 37°C experienced significant changes in size, likely due to aggregation and surfactant dissociation; these NPs showed signs of bulk degradation based on transmission electron microscopy (TEM), and had significant lutein degradation and over 40% release after 5 weeks. Lutein loaded in NPs was more resistant to photodegradation compared to a free lutein solution when exposed to UV for 6 h, degrading 5 times slower than free lutein. To test the performance of NP therapeutics in vivo, Cy5-labled NPs were applied topically to the eyes of rats and incubated for 15 min, 30 min, or 60 min. Exterior eye tissues including the cornea, episcleral tissue, and sclera showed the highest fluorescence intensity in animals that received fluorescent nanoparticles, while the choroid was the only inner eye tissue that was significantly higher in a treatment group compared to the control group. Additionally, decreases of fluorescence in all exterior eye tissues and the choroid at 1 h compared to 30 min, indicated rapid elimination of NPs from the eye.

ObjectiveDetermine the effectiveness of evacuation systems designed to clear bioaerosols and smoke from the surgical field.Study designHigh-speed photographic evaluation of aerosol and smoke generated in simulated surgical fields.Materials and methodsSurgical site aerosol clearance was evaluated using a model of the anterior neck and prototypes for surgical site evacuator ports created using 3D printing. A commercially available electrocautery handpiece fitted with an evacuator was tested on animal tissue for smoke clearance. Both systems were connected to a commercial vacuum powered evacuation system. High speed photography was used to record videos of the aerosols and plumes. Fields were recorded with and without evacuation.ResultsEfficient aerosol clearance from an open surgical field using an evacuator port is dependent upon the port design, airflow velocity, and placement relative to the aerosol generating site. The size and surface geometry of the surgical field are also important.Surgical smoke generated with electrocautery is cleared from the field by the evacuation enclosure around the handpiece, even at high electrocautery power settings. Except for device noise, there appears to be no reason for using evacuator flow rates below the maximum setting.ConclusionsBioaerosol and smoke generated during surgery are potential sources of respiratory pathogens and pose a threat to operating room personnel. Surgical site evacuation can significantly reduce the volume of airborne particles in the field but requires careful design and deployment considerations.x

In response to myocardial infarction (MI), quiescent cardiac fibroblasts differentiate into myofibroblasts mediating tissue repair in the infarcted area. One of the most widely accepted markers of myofibroblast differentiation is the expression of Acta2 which encodes smooth muscle alpha-actin (SMαA) that is assembled into stress fibers. However, the requirement of Acta2 in the myofibroblast differentiation of cardiac fibroblasts and its role in post-MI cardiac repair were still not known. To answer these questions, we generated a tamoxifen-inducible cardiac fibroblast-specific Acta2 knockout mouse line. Surprisingly, mice that lacked Acta2 in cardiac fibroblasts had a normal survival rate after MI. Moreover, Acta2 deletion did not affect the function or overall histology of infarcted hearts. No difference was detected in the proliferation, migration, or contractility between WT cardiac fibroblasts and Acta2-null cardiac myofibroblasts. Additional analysis identified that Acta2-null cardiac myofibroblasts had a normal total filamentous actin level and total actin level. Acta2 deletion caused a unique compensatory increase in the transcription level of Actg2 and a possible increase in the protein abundance of cytoplasmic actin isoforms. In conclusion, the deletion of Acta2 does not prevent the myofibroblast differentiation of cardiac fibroblasts or affect the post-MI cardiac repair, and the increase in the expression of non-SMαA actin isoforms and the functional redundancy between actin isoforms are likely able to compensate for the loss of Acta2 in cardiac myofibroblasts.

Engineering microenvironments for accelerated myocardial repair is a challenging goal. Cell therapy has evolved over a few decades to engraft therapeutic cells to replenish lost cardiomyocytes in the left ventricle. However, compelling evidence supports that tailoring specific signals to endogenous cells rather than the direct integration of therapeutic cells could be an attractive strategy for better clinical outcomes. Of many possible routes to instruct endogenous cells, we reviewed recent cases that extracellular matrix (ECM) proteins contribute to enhanced cardiomyocyte proliferation from neonates to adults. In addition, the presence of ECM proteins exerts biophysical regulation in tissue, leading to the control of microenvironments and adaptation for enhanced cardiomyocyte proliferation. Finally, we also summarized recent clinical trials exclusively using ECM proteins, further supporting the notion that engineering ECM proteins would be a critical strategy to enhance myocardial repair without taking any risks or complications of applying therapeutic cardiac cells.

Nerve guidance conduits (NGCs) have emerged from recent advances within tissue engineering as a promising alternative to autografts for peripheral nerve repair. NGCs are tubular structures with engineered biomaterials, which guide axonal regeneration from the injured proximal nerve to the distal stump. NGC design can synergistically combine multiple properties to enhance proliferation of stem and neuronal cells, improve nerve migration, attenuate inflammation and reduce scar tissue formation. The aim of most laboratories fabricating NGCs is the development of an automated process that incorporates patient-specific features and complex tissue blueprints (e.g. neurovascular conduit) that serve as the basis for more complicated muscular and skin grafts. One of the major limitations for tissue engineering is lack of guidance for generating tissue blueprints and the absence of streamlined manufacturing processes. With the rapid expansion of machine intelligence, high dimensional image analysis, and computational scaffold design, optimized tissue templates for 3D bioprinting (3DBP) are feasible. In this review, we examine the translational challenges to peripheral nerve regeneration and where machine intelligence can innovate bottlenecks in neural tissue engineering.

Regenerating lost or damaged tissue is the primary goal of Tissue Engineering. 3D bioprinting technologies have been widely applied in many research areas of tissue regeneration and disease modeling with unprecedented spatial resolution and tissue-like complexity. However, the extraction of tissue architecture and the generation of high-resolution blueprints are challenging tasks for tissue regeneration. Traditionally, such spatial information is obtained from a collection of microscopic images and then combined together to visualize regions of interest. To fabricate such engineered tissues, rendered microscopic images are transformed to code to inform a 3D bioprinting process. If this process is augmented with data-driven approaches and streamlined with machine intelligence, identification of an optimal blueprint can become an achievable task for functional tissue regeneration. In this review, our perspective is guided by an emerging paradigm to generate a blueprint for regeneration with machine intelligence. First, we reviewed recent articles with respect to our perspective for machine intelligence-driven information retrieval and fabrication. After briefly introducing recent trends in information retrieval methods from publicly available data, our discussion is focused on recent works that use machine intelligence to discover tissue architectures from imaging and spectral data. Then, our focus is on utilizing optimization approaches to increase print fidelity and enhance biomimicry with machine learning (ML) strategies to acquire a blueprint ready for 3D bioprinting.

Recessive dystrophic Epidermolysis Bullosa (RDEB) is caused by mutations in collagen-type VII gene critical for the dermoepidermal junction (DEJ) formation. Neither tissues of animal models nor currently available in vitro models are amenable to the quantitative assessment of mechanical adhesion between dermal and epidermal layers. Here, we created a 3D in vitro DEJ model using extracellular matrix (ECM) proteins of the DEJ anchored to a poly(ethylene glycol)-based slab (termed ECM composites) and seeded with human keratinocytes and dermal fibroblasts. Keratinocytes and fibroblasts of healthy individuals were well maintained in the ECM composite and showed the expression of collagen type VII over a 2-week period. The ECM composites with healthy keratinocytes and fibroblasts exhibited yield stress associated with the separation of the model DEJ at 0.268 ± 0.057 kPa. When we benchmarked this measure of adhesive strength with that of the model DEJ fabricated with cells of individuals with RDEB, the yield stress was significantly lower (0.153 ± 0.064 kPa) consistent with our current mechanistic understanding of RDEB. In summary, a 3D in vitro model DEJ was developed for quantification of mechanical adhesion between epidermal- and dermal-mimicking layers, which can be utilized for assessment of mechanical adhesion of the model DEJ applicable for Epidermolysis Bullosa-associated therapeutics. © 2018 The Authors. Journal Of Biomedical Materials Research Part A Published By Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3231-3238, 2018.

Rationale: Conventional 3-dimensional (3D) printing techniques cannot produce structures of the size at which individual cells interact. Objective: Here, we used multiphoton-excited 3D printing to generate a native-like extracellular matrix scaffold with submicron resolution and then seeded the scaffold with cardiomyocytes, smooth muscle cells, and endothelial cells that had been differentiated from human-induced pluripotent stem cells to generate a human-induced pluripotent stem cell–derived cardiac muscle patch (hCMP), which was subsequently evaluated in a murine model of myocardial infarction. Methods and Results: The scaffold was seeded with ≈50 000 human-induced pluripotent stem cell–derived cardiomyocytes, smooth muscle cells, and endothelial cells (in a 2:1:1 ratio) to generate the hCMP, which began generating calcium transients and beating synchronously within 1 day of seeding; the speeds of contraction and relaxation and the peak amplitudes of the calcium transients increased significantly over the next 7 days. When tested in mice with surgically induced myocardial infarction, measurements of cardiac function, infarct size, apoptosis, both vascular and arteriole density, and cell proliferation at week 4 after treatment were significantly better in animals treated with the hCMPs than in animals treated with cell-free scaffolds, and the rate of cell engraftment in hCMP-treated animals was 24.5% at week 1 and 11.2% at week 4. Conclusions: Thus, the novel multiphoton-excited 3D printing technique produces extracellular matrix–based scaffolds with exceptional resolution and fidelity, and hCMPs fabricated with these scaffolds may significantly improve recovery from ischemic myocardial injury.

Bioreactors for large-scale culture of mammalian cells are playing vital roles in biotechnology and bioengineering. Various bioreactors have been developed, but their capacity and efficiency are often limited by insufficient mass transfer rate and high shear stress. A rolled scaffold (RS) is a fully defined scaffold for high-density adherent culture of mammalian cells. The RS is a polymer film with spacers, that is rolled into a cylinder with a pre-determined gap between each turn. Cells are cultured on its inner surfaces, while media flows through the gap. The RS exhibits high surface-area-to-volume ratio over 100 cm2/mL and can transport nutrients and gases with significantly reduced shear stress via convection in a unidirectional laminar flow, rather than diffusion and random turbulent flow as in stirred-tank bioreactors. In this paper, we expanded Chinese Hamster Ovary cells with RS bioreactors and demonstrated cell culture density over 60 million cells/mL with a growth rate higher than conventional suspension culture. Besides, murine embryonic stem cells were successfully expanded without losing their pluripotency. The RS will provide an affordable, scalable, and reliable platform for large-scale culture of recombinant cells in biopharmaceutical industries and shear-sensitive stem cells for tissue engineering.

BackgroundThe use of three-dimensional printing has been rapidly expanding over the last several decades. Virtual surgical three-dimensional simulation and planning has been shown to increase efficiency and accuracy in various clinical scenarios.ObjectivesTo report the feasibility of three-dimensional printing in paediatric laryngotracheal stenosis and discuss potential applications of three-dimensional printed models in airway surgery.MethodRetrospective case series in a tertiary care aerodigestive centre.ResultsThree-dimensional printing was undertaken in two cases of paediatric laryngotracheal stenosis. One patient with grade 4 subglottic stenosis with posterior glottic involvement underwent an extended partial cricotracheal reconstruction. Another patient with grade 4 tracheal stenosis underwent tracheal resection and end-to-end anastomosis. Models of both tracheas were printed using PolyJet technology from a Stratasys Connex2 printer.ConclusionIt is feasible to demonstrate stenosis in three-dimensional printed models, allowing for patient-specific pre-operative surgical simulation. The models serve as an educational tool for patients’ understanding of the surgery, and for teaching residents and fellows.

Extracellular matrix (ECM) proteins are structural elements of tissue and also potent signaling molecules. Previously, our laboratory showed that ECM of 2D coatings can trigger differentiation of bone marrow-derived mesenchymal stem cells (MSCs) into mesodermal lineages in an ECM-specific manner over 14 days, in some cases comparable to chemical induction. To test whether a similar effect was possible in a 3D, tissue-like environment, we designed a synthetic-natural biomaterial composite. The composite can present whole-molecule ECM proteins to cells, even those that do not spontaneously form hydrogels ex vivo, in 3D. To this end, we entrapped collagen type I, laminin-111, or fibronectin in ECM composites with MSCs and directly compared markers of mesodermal differentiation including cardiomyogenic (ACTC1), osteogenic (SPP1), adipogenic (PPARG), and chondrogenic (SOX9) in 2D versus 3D. We found the 3D condition largely mimicked the 2D condition such that the addition of type I collagen was the most potent inducer of differentiation to all lineages tested. One notable difference between 2D and 3D was pronounced adipogenic differentiation in 3D especially in the presence of exogenous collagen type I. In particular, PPARG gene expression was significantly increased ∼16-fold relative to chemical induction, in 3D and not in 2D. Unexpectedly, 3D engagement of ECM proteins also altered immunomodulatory function of MSCs in that expression of IL-6 gene was elevated relative to basal levels in 2D. In fact, levels of IL-6 gene expression in 3D composites containing exogenously supplied collagen type I or fibronectin were statistically similar to levels attained in 2D with tumor necrosis factor-α (TNF-α) stimulation and these levels were sustained over a 2-week period. Thus, this novel biomaterial platform allowed us to compare the biochemical impact of whole-molecule ECM proteins in 2D versus 3D indicating enhanced adipogenic differentiation and IL-6 expression of MSC in the 3D context. Exploiting the biochemical impact of ECM proteins on MSC differentiation and immunomodulation could augment the therapeutic utility of MSCs.

Printing of polymeric composites into desired patterns and shapes has revolutionized small-scale manufacturing processes. However, high-resolution printing of adaptive materials that change shape in response to external stimuli remains a significant technical challenge. The article presents a new approach of printing thermoresponsive poly(N-isopropylacrylamide) into macroscopic structures that dynamically reconfigure in response to heating and cooling cycles. The printing process is performed using an external laser source, which enables thermal cross-linking of the polymer ink consisting of monomer, cross-linker, initiator, and inorganic nanoparticles. It is shown that the addition of silica nanoparticles enhances the mechanical properties of poly(N-isopropylacrylamide) while maintaining its thermoresponsiveness at micrometer-scale resolution, which otherwise is not feasible by extrusion-based three-dimensional printing techniques. It is demonstrated that spatial reconfiguration of the printed monolayers upon increasing temperature is governed by the local geometry, which enables mimicking the reconfiguration of plant leaves in a natural environment. The study lays a foundation for developing a new fabrication platform to print thermoresponsive structures that may find applications in biomedical implants, sensors, and other multi-responsive materials.

Methods to generate murine cardiomyocytes from pluripotent stem cells (PSCs) in vitro are resource and time intensive. All current protocols require exogenously provided soluble factors and almost all utilize embryoid body formation to modulate pathways associated with mesoderm specification and cardiomyocyte differentiation. Here, we developed a simple protocol without EBs and without exogenous soluble factors that enabled cardiomyocyte differentiation of a murine induced PSC line based on controlled nutrient deprivation in 2D monolayer cultures. We showed that this protocol reproducibly imposed metabolic stress and consequently modulated active β-catenin levels to yield functional cardiomyocytes. The yield of cardiomyocytes and calcium handling kinetics were comparable to existing approaches. However, this approach did not produce consistent results between murine PSC lines suggesting signaling pathways linking nutrient deprivation to β-catenin activation are not universally conserved and may be a remnant of the parent population from which the induced PSCs were derived.

Solid organ fabrication is an ultimate goal of Regenerative Medicine. Since the introduction of Tissue Engineering in 1993, functional biomaterials, stem cells, tunable microenvironments, and high-resolution imaging technologies have significantly advanced efforts to regenerate in vitro culture or tissue platforms. Relatively simple flat or tubular organs are already in (pre)clinical trials and a few commercial products are in market. The road to more complex, high demand, solid organs including heart, kidney and lung will require substantive technical advancement. Here, we consider two emerging technologies for solid organ fabrication. One is decellularization of cadaveric organs followed by repopulation with terminally differentiated or progenitor cells. The other is 3D bioprinting to deposit cell-laden bio-inks to attain complex tissue architecture. We reviewed the development and evolution of the two technologies and evaluated relative strengths needed to produce solid organs, with special emphasis on the heart and other tissues of the cardiovascular system.

Fusion of donor mesenchymal stem cells with parenchymal cells of the recipient can occur in the brain, liver, intestine and heart following transplantation. The therapeutic benefit or detriment of resultant hybrids is unknown. Here we sought a global view of phenotypic diversification of mesenchymal stem cell-cardiomyocyte hybrids and associated time course. Using single-cell RNA-seq, we found hybrids consistently increase ribosome components and decrease genes associated with the cell cycle suggesting an increase in protein production and decrease in proliferation to accommodate the fused state. But in the case of most other gene groups, hybrids were individually distinct. In fact, though hybrids can express a transcriptome similar to individual fusion partners, approximately one-third acquired distinct expression profiles in a single day. Some hybrids underwent reprogramming, expressing pluripotency and cardiac precursor genes latent in parental cells and associated with developmental and morphogenic gene groups. Other hybrids expressed genes associated with ontologic cancer sets and two hybrids of separate experimental replicates clustered with breast cancer cells, expressing critical oncogenes and lacking tumor suppressor genes. Rapid transcriptional diversification of this type garners consideration in the context of cellular transplantation to damaged tissues, those with viral infection or other microenvironmental conditions that might promote fusion.

Aims: Stem cell transplantation holds promise as a therapeutic approach for the repair of damaged myocardial tissue. One challenge of this approach is efficient delivery and long-term retention of the stem cells. Although several synthetic and natural biomaterials have been developed for this purpose, the ideal formulation has yet to be identified. Materials & methods: Here we investigate the utility of a nondenatured, noncrosslinked, commercially available natural biomaterial (TissueMend® [TEI Biosciences, Boston, MA, USA]) for delivery of human mesenchymal stem cells (MSCs) to the murine heart. Results: We found that MSCs attached, proliferated and migrated within and out of the TissueMend matrix in vitro. Human MSCs delivered to damaged murine myocardium via the matrix (2.3 × 104 ± 0.8 × 104 CD73+ cells/matrix) were maintained in vivo for 3 weeks and underwent at least three population doublings during that period (21.9 × 104 ± 14.4 × 104 CD73+ cells/matrix). In addition, collagen within the TissueMend matrix could be remodeled by MSCs in vivo, resulting in a significant decrease in the coefficient of alignment of fibers (0.12 ± 0.12) compared with the matrix alone (0.28 ± 0.07), and the MSCs were capable of migrating out of the matrix and into the host tissue. Conclusion: Thus, TissueMend matrix offers a commercially available, biocompatible and malleable vehicle for the delivery and retention of stem cells to the heart.

The development of vaccines and other immunotherapies has been complicated by heterogeneous antigen display and the use of incompletely defined immune adjuvants with complex mechanisms of action. We have observed strong antibody responses in mice without the coadministration of any additional adjuvant by noncovalently assembling a T and B cell epitope peptide into nanofibers using a short C-terminal peptide extension. Self-assembling peptides have been explored recently as scaffolds for tissue engineering and regenerative medicine, but our results indicate that these materials may also be useful as chemically defined adjuvants. In physiological conditions, these peptides self-assembled into long, unbranched fibrils that displayed the epitope on their surfaces. IgG1, IgG2a, and IgG3 were raised against epitope-bearing fibrils in levels similar to the epitope peptide delivered in complete Freund’s adjuvant (CFA), and IgM production was even greater for the self-assembled epitope. This response was dependent on self-assembly, and the self-assembling sequence was not immunogenic by itself, even when delivered in CFA. Undetectable levels of interferon-gamma, IL-2, and IL-4 in cultures of peptide-challenged splenocytes from immunized mice suggested that the antibody responses did not involve significant T cell help.

Self-assembling peptides and peptide derivatives bearing cell-binding ligands are increasingly being investigated as defined cell culture matrices and as scaffolds for regenerative medicine. In order to systematically refine such scaffolds to elicit specific desired cell behaviors, ligand display should ideally be achieved without inadvertently altering other physicochemical properties such as viscoelasticity. Moreover, for in vivo applications, self-assembled biomaterials must exhibit low immunogenicity. In the present study, multi-peptide co-assembling hydrogels based on the beta-sheet fibrillizing peptide Q11 (QQKFQFQFEQQ) were designed such that they presented RGDS or IKVAV ligands on their fibril surfaces. In co-assemblies of the ligand-bearing peptides with Q11, ligand incorporation levels capable of influencing the attachment, spreading, morphology, and growth of human umbilical vein endothelial cells (HUVECs) did not significantly alter the materials’ fibrillization, beta-turn secondary structure, or stiffness. RGDS-Q11 specifically increased HUVEC attachment, spreading, and growth when co-assembled into Q11 gels, whereas IKVAV-Q11 exerted a more subtle influence on attachment and morphology. Additionally, Q11 and RGDS-Q11 were minimally immunogenic in mice, making Q11-based biomaterials attractive candidates for further investigation as defined, modular extracellular matrices for applications in vitro and in vivo.

The extracellular matrix (ECM) impacts stem cell differentiation, but identifying formulations supportive of differentiation is challenging in 3D models. Prior efforts involving combinatorial ECM arrays seemed intuitively advantageous. We propose an alternative that suggests reducing sample size and technological burden can be beneficial and accessible when coupled to design of experiments approaches. We predict optimized ECM formulations could augment differentiation of cardiomyocytes derived in vitro. We employed native chemical ligation to polymerize 3D poly (ethylene glycol) hydrogels under mild conditions while entrapping various combinations of ECM and murine induced pluripotent stem cells. Systematic optimization for cardiomyocyte differentiation yielded a predicted solution of 61%, 24% and 15% of collagen type I, laminin-111 and fibronectin, respectively. This solution was confirmed by increased numbers of cardiac troponin T, α-myosin heavy chain and α-sarcomeric actinin-expressing cells relative to suboptimum solutions. Cardiomyocytes of composites exhibited connexin43 expression, appropriate contractile kinetics and intracellular calcium handling. Further, adding a modulator of adhesion, thrombospondin-1, abrogated cardiomyocyte differentiation. Thus, the integrated biomaterial platform statistically identified an ECM formulation best supportive of cardiomyocyte differentiation. In future, this formulation could be coupled with biochemical stimulation to improve functional maturation of cardiomyocytes derived in vitro or transplanted in vivo.

Limiting the precise study of the biochemical impact of whole molecule extracellular matrix (ECM) proteins on stem cell differentiation is the lack of 3D in vitro models that can accommodate many different types of ECM. Here we sought to generate such a system while maintaining consistent mechanical properties and supporting stem cell survival. To this end, we used native chemical ligation to cross-link poly(ethylene glycol) macromonomers under mild conditions while entrapping ECM proteins (termed ECM composites) and stem cells. Sufficiently low concentrations of ECM were used to maintain constant storage moduli and pore size. Viability of stem cells in composites was maintained over multiple weeks. ECM of composites encompassed stem cells and directed the formation of distinct structures dependent on ECM type. Thus, we introduce a powerful approach to study the biochemical impact of multiple ECM proteins (either alone or in combination) on stem cell behavior.

The extracellular matrix (ECM) of the embryonic heart guides assembly and maturation of cardiac cell types and, thus, may serve as a useful template, or blueprint, for fabrication of scaffolds for cardiac tissue engineering. Surprisingly, characterization of the ECM with cardiac development is scattered and fails to comprehensively reflect the spatiotemporal dynamics making it difficult to apply to tissue engineering efforts. The objective of this work was to define a blueprint of the spatiotemporal organization, localization, and relative amount of the four essential ECM proteins, collagen types I and IV (COLI, COLIV), elastin (ELN), and fibronectin (FN) in the left ventricle of the murine heart at embryonic stages E12.5, E14.5, and E16.5 and 2 days postnatal (P2). Second harmonic generation (SHG) imaging identified fibrillar collagens at E14.5, with an increasing density over time. Subsequently, immunohistochemistry (IHC) was used to compare the spatial distribution, organization, and relative amounts of each ECM protein. COLIV was found throughout the developing heart, progressing in amount and organization from E12.5 to P2. The amount of COLI was greatest at E12.5 particularly within the epicardium. For all stages, FN was present in the epicardium, with highest levels at E12.5 and present in the myocardium and the endocardium at relatively constant levels at all time points. ELN remained relatively constant in appearance and amount throughout the developmental stages except for a transient increase at E16.5. Expression of ECM mRNA was determined using quantitative polymerase chain reaction and allowed for comparison of amounts of ECM molecules at each time point. Generally, COLI and COLIII mRNA expression levels were comparatively high, while COLIV, laminin, and FN were expressed at intermediate levels throughout the time period studied. Interestingly, levels of ELN mRNA were relatively low at early time points (E12.5), but increased significantly by P2. Thus, we identified changes in the spatial and temporal localization of the primary ECM of the developing ventricle. This characterization can serve as a blueprint for fabrication techniques, which we illustrate by using multiphoton excitation photochemistry to create a synthetic scaffold based on COLIV organization at P2. Similarly, fabricated scaffolds generated using ECM components, could be utilized for ventricular repair.

Once damaged, cardiac tissue does not readily repair and is therefore a primary target of regenerative therapies. One regenerative approach is the development of scaffolds that functionally mimic the cardiac extracellular matrix (ECM) to deliver stem cells or cardiac precursor populations to the heart. Technological advances in micro/nanotechnology, stem cell biology, biomaterials and tissue decellularization have propelled this promising approach forward. Surprisingly, technological advances in optical imaging methods have not been fully utilized in the field of cardiac regeneration. Here, we describe and provide examples to demonstrate how advanced imaging techniques could revolutionize how ECM-mimicking cardiac tissues are informed and evaluated.

Extracellular matrices (ECMs) are complex materials, containing at least dozens of different macromolecules that are assembled together, thus complicating their optimization towards applications in 3D cell culture or tissue engineering. The natural complexity of ECMs has limited cell-matrix investigations predominantly to experiments where only one matrix component is adjusted at a time, making it difficult to uncover interactions between different matrix components or to efficiently determine optimal matrix compositions for specific desired biological responses. Here we have developed modular synthetic ECMs based on peptide self-assembly whose incorporation of multiple different peptide ligands can be adjusted. The peptides can co-assemble in a wide range of combinations to form hydrogels of uniform morphology and consistent mechanical properties, but with precisely varied mixtures of peptide ligands. The modularity of this system in turn enabled multi-factorial experimental designs for investigating interactions between these ligands and for determining a multi-peptide matrix formulation that maximized endothelial cell growth. In cultures of HUVECs, we observed a previously unknown antagonistic interaction between the laminin-derived peptide YIGSR and RGDS-mediated cell attachment and growth. We also identified an optimized combination of self-assembled peptides bearing the ligands RGDS and IKVAV that led to endothelial cell growth equivalent to that on native full-length fibronectin. Both of these findings would have been challenging to uncover using more traditional one-factor-at-a-time analyses.

Extracellular matrices (ECMs) are challenging design targets for materials synthesis because they serve multiple biological roles, and they are composed of multiple molecular constituents. In addition, their composition and activities are dynamic and variable between tissues, and they are difficult to study mechanistically in physiological contexts. Nevertheless, the design of synthetic ECMs is a central consideration in applications such as regenerative medicine and 3D cell culture. In order to produce synthetic matrices having both multi-component construction and high levels of compositional definition, strategies based on molecular self-assembly are receiving increasing interest. These approaches are described in this tutorial review and compared with the structures and processes in native ECMs that serve as their inspiration.

Self-assembly has been increasingly utilized in recent years to create peptide-based biomaterials for 3D cell culture, tissue engineering, and regenerative medicine, but the molecular determinants of these materials' immunogenicity have remained largely unexplored. In this study, a set of molecules that self-assembled through coiled coil oligomerization was designed and synthesized, and immune responses against them were investigated in mice. Experimental groups spanned a range of oligomerization behaviors and included a peptide from the coiled coil region of mouse fibrin that did not form supramolecular structures, an engineered version of this peptide that formed coiled coil bundles, and a peptide-PEG-peptide triblock bioconjugate that formed coiled coil multimers and supramolecular aggregates. In mice, the native peptide and engineered peptide did not produce any detectable antibody response, and none of the materials elicited detectable peptide-specific T cell responses, as evidenced by the absence of IL-2 and interferon-gamma in cultures of peptide-challenged splenocytes or draining lymph node cells. However, specific antibody responses were elevated in mice injected with the multimerizing peptide-PEG-peptide. Minimal changes in secondary structure were observed between the engineered peptide and the triblock peptide-PEG-peptide, making it possible that the triblock's multimerization was responsible for this antibody response.

Peptides, peptidomimetics, and peptide derivatives that self-assemble into fibrillar gels have received increasing interest as synthetic extracellular matrices for applications in 3D cell culture and regenerative medicine. Recently, several of these fibrillizing molecules have been functionalized with bioactive components and chemical features such as cell-binding ligands, degradable sequences, drug eluting compounds, and cross-linkable groups, thereby producing gels that can reliably display multiple factors simultaneously. This capacity for incorporating precise levels of many different biological and chemical factors is advantageous given the natural complexity of cell-matrix interactions that many current biomaterial strategies seek to mimic. In this review, recent efforts in the area of fibril-forming peptide materials are described, and advantages of biomaterials containing multiple modular elements are outlined. In addition, a few hurdles and open questions surrounding fibrillar peptide gels are discussed, including issues of the materials' structural heterogeneity, challenges in fully characterizing the diversity of their self-assembled structures, and incomplete knowledge of how the materials are processed in vivo.

This chapter describes peptide design strategies for the construction of nanostructured materials. It begins with a brief tutorial of amino acid structure and function and then describes higher-order assemblies of peptides and peptidomimetics. Primarily β-sheet fibril-forming peptides and α-helical coiled coil systems are discussed, as these systems have received particular attention in recent years for building nanostructured materials. Useful properties that arise from peptide construction are addressed, including stimulus-responsiveness, modularity, and multifunctionality, and a number of technological applications are described, including Tissue Engineering, antimicrobials, drug delivery, and nanoscale electronics. The chapter is meant to be an introduction for researchers or students in nanotechnology who may wish to extend their approaches into the biomolecular realm, and it also provides a compendium of recent advances for experts in the field of nanoscale peptide materials.

Hydrogels produced from self-assembling peptides and peptide derivatives are being investigated as synthetic extracellular matrices for defined cell culture substrates and scaffolds for regenerative medicine. In many cases, however, they are less stiff than the tissues and extracellular matrices they are intended to mimic, and they are prone to cohesive failure. We employed native chemical ligation to produce peptide bonds between the termini of fibrillized β-sheet peptides to increase gel stiffness in a chemically specific manner while maintaining the morphology of the self-assembled fibrils. Polymerization, fibril structure, and mechanical properties were measured by SDS–PAGE, mass spectrometry, TEM, circular dichroism, and oscillating rheometry; and cellular responses to matrix stiffening were investigated in cultures of human umbilical vein endothelial cells (HUVECs). Ligation led to a fivefold increase in storage modulus and a significant enhancement of HUVEC proliferation and expression of CD31 on the surface of the gels. The approach was also orthogonal to the inclusion of unprotected RGD-functionalized self-assembling peptides, which further increased proliferation. This strategy broadens the utility of self-assembled peptide materials for applications that require enhancement or modulation of matrix mechanical properties by providing a chemoselective means for doing so without significantly disrupting the gels' fibrillar structure.

The plasticity and immunomodulatory capacity of mesenchymal stem cells (MSCs) have spurred clinical use in recent years. However, clinical outcomes vary and many ascribe inconsistency to the tissue source of MSCs. Yet unconsidered is the extent of heterogeneity of individual MSCs from a given tissue source with respect to differentiation potential and immune regulatory function. Here we use single-cell RNA-seq to assess the transcriptional diversity of murine mesenchymal stem cells derived from bone marrow. We found genes associated with MSC multipotency were expressed at a high level and with consistency between individual cells. However, genes associated with osteogenic, chondrogenic, adipogenic, neurogenic and vascular smooth muscle differentiation were expressed at widely varying levels between individual cells. Further, certain genes associated with immunomodulation were also inconsistent between individual cells. Differences could not be ascribed to cycles of proliferation, culture bias or other cellular process, which might alter transcript expression in a regular or cyclic pattern. These results support and extend the concept of lineage priming of MSCs and emphasize caution for in vivo or clinical use of MSCs, even when immunomodulation is the goal, since multiple mesodermal (and even perhaps ectodermal) outcomes are a possibility. Purification might enable shifting of the probability of a certain outcome, but is unlikely to remove multilineage potential altogether.