Magneto-Driven Gradients of Diamagnetic Objects for Engineering Complex Tissues

Engineering complex tissues represents an extraordinary challenge and, to date, there have been few strategies developed that can easily recapitulate native‐like cell and biofactor gradients in 3D materials. This is true despite the fact that mimicry of these gradients may be essential for the functionality of engineered graft tissues. Here, a non‐traditional magnetics‐based approach is developed to predictably position naturally diamagnetic objects in 3D hydrogels. Rather than magnetizing the objects within the hydrogel, the magnetic susceptibility of the surrounding hydrogel precursor solution is enhanced. In this way, a range of diamagnetic objects (e.g., polystyrene beads, drug delivery microcapsules, and living cells) are patterned in response to a brief exposure to a magnetic field. Upon photo‐crosslinking the hydrogel precursor, object positioning is maintained, and the magnetic contrast agent diffuses out of the hydrogel, supporting long‐term construct viability. This approach is applied to engineer cartilage constructs with a depth‐dependent cellularity mirroring that of native tissue. These are thought to be the first results showing that magnetically unaltered cells can be magneto‐patterned in hydrogels and cultured to generate heterogeneous tissues. This work provides a foundation for the formation of opposing magnetic‐susceptibility‐based gradients within a single continuous material

Impact of guidance documents on translational large animal studies of cartilage repair

Promising therapies for cartilage repair are translated through large animal models toward human application. To guide this work, regulatory agencies publish recommendations (“guidance documents”) to direct pivotal large animal studies. These are meant to aid in study design, outline metrics for judging efficacy, and facilitate comparisons between studies. To determine the penetrance of these documents in the field, we synthesized the recommendations of the American Society for Testing and Materials, U.S. Food and Drug Administration, and European Medicines Agency into a scoring system and performed a systematic review of the past 20 years of preclinical cartilage repair studies. Our hypothesis was that the guidance documents would have a significant impact on how large animal cartilage repair studies were performed. A total of 114 publications meeting our inclusion criteria were reviewed for adherence to 24 categories extracted from the guidance documents, including 11 related to study design and description and 13 related to study outcomes. Overall, a weak positive trend was observed over time (P=0.004, R2=0.07, slope=0.63%/year), with overall adherence (the sum of study descriptors and outcomes) ranging from 32±16% to 58±14% in any individual year. There was no impact of the publication of the guidance documents on adherence (P =0.264 to 0.50). Given that improved adherence would expedite translation, we discuss the reasons for poor adherence and outline approaches to increase and promote their more widespread adoption

Macro- to Microscale Strain Transfer in Fibrous Tissues is Heterogeneous and Tissue-Specific

AbstractMechanical deformation applied at the joint or tissue level is transmitted through the macroscale extracellular matrix to the microscale local matrix, where it is transduced to cells within these tissues and modulates tissue growth, maintenance, and repair. The objective of this study was to investigate how applied tissue strain is transferred through the local matrix to the cell and nucleus in meniscus, tendon, and the annulus fibrosus, as well as in stem cell-seeded scaffolds engineered to reproduce the organized microstructure of these native tissues. To carry out this study, we developed a custom confocal microscope-mounted tensile testing device and simultaneously monitored strain across multiple length scales. Results showed that mean strain was heterogeneous and significantly attenuated, but coordinated, at the local matrix level in native tissues (35–70% strain attenuation). Conversely, freshly seeded scaffolds exhibited very direct and uniform strain transfer from the tissue to the local matrix level (15–25% strain attenuation). In addition, strain transfer from local matrix to cells and nuclei was dependent on fiber orientation and tissue type. Histological analysis suggested that different domains exist within these fibrous tissues, with most of the tissue being fibrous, characterized by an aligned collagen structure and elongated cells, and other regions being proteoglycan (PG)-rich, characterized by a dense accumulation of PGs and rounder cells. In meniscus, the observed heterogeneity in strain transfer correlated strongly with cellular morphology, where rounder cells located in PG-rich microdomains were shielded from deformation, while elongated cells in fibrous microdomains deformed readily. Collectively, these findings suggest that different tissues utilize distinct strain-attenuating mechanisms according to their unique structure and cellular phenotype, and these differences likely alter the local biologic response of such tissues and constructs in response to mechanical perturbation

Engineering meniscus structure and function via multi-layered mesenchymal stem cell-seeded nanofibrous scaffolds

Despite advances in tissue engineering for the knee meniscus, it remains a challenge to match the complex macroscopic and microscopic structural features of native tissue, including the circumferentially and radially aligned collagen bundles essential for mechanical function. To mimic this structural hierarchy, this study developed multi-lamellar mesenchymal stem cell (MSC)-seeded nanofibrous constructs. Bovine MSCs were seeded onto nanofibrous scaffolds comprised of poly(ε-caprolactone) with fibers aligned in a single direction (0° or 90° to the scaffold long axis) or circumferentially aligned (C). Multi-layer groups (0°/0°/0°, 90°/90°/90°, 0°/90°/0°, 90°/0°/90°, and C/C/C) were created and cultured for a total of 6 weeks under conditions favoring fibrocartilaginous tissue formation. Tensile testing showed that 0° and C single layer constructs had stiffness values several fold higher than 90° constructs. For multi-layer groups, the stiffness of 0°/0°/0° constructs was higher than all other groups, while 90°/90°/90° constructs had the lowest values. Data for collagen content showed a general positive interactive effect for multi-layers relative to single layer constructs, while a positive interaction for stiffness was found only for the C/C/C group. Collagen content and cell infiltration occurred independent of scaffold alignment, and newly formed collagenous matrix followed the scaffold fiber direction. Structural hierarchies within multi-lamellar constructs dictated biomechanical properties, and only the C/C/C constructs with non-orthogonal alignment within layers featured positive mechanical reinforcement as a consequence of the layered construction. These multi-layer constructs may serve as functional substitutes for the meniscus as well as test beds to understand the complex mechanical principles that enable meniscus function

Female and male Leach\u27s Storm Petrels (Hydrobates leucorhous) pursue different foraging strategies during the incubation period

Reproduction in procellariiform birds is characterized by a single egg clutch, slow development, a long breeding season and obligate biparental care. Female Leach\u27s Storm Petrels Hydrobates leucorhous, nearly monomorphic members of this order, produce eggs that are between 20 and 25% of adult bodyweight. We tested whether female foraging behaviour differs from male foraging behaviour during the ~ 44-day incubation period across seven breeding colonies in the Northwest Atlantic. Over six breeding seasons, we used a combination of Global Positioning System and Global Location Sensor devices to measure characteristics of individual foraging trips during the incubation period. Females travelled significantly greater distances and went farther from the breeding colony than did males on individual foraging trips. For both sexes, the longer the foraging trip, the greater the distance. Independent of trip duration, females travelled farther, and spent a greater proportion of their foraging trips prospecting widely, as defined by behavioural categories derived from a hidden Markov Model. For both sexes, trip duration decreased with date. Sex differences in these foraging metrics were apparently not a consequence of morphological differences or spatial segregation. Our data are consistent with the idea that female foraging strategies differed from male foraging strategies during incubation in ways that would be expected if females were still compensating for egg formation

Effects of Mesenchymal Stem Cell and Growth Factor Delivery on Cartilage Repair in a Mini-Pig Model

We have recently shown that mesenchymal stem cells (MSCs) embedded in a hyaluronic acid (HA) hydrogel and exposed to chondrogenic factors (transforming growth factor–β3 [TGF-β3]) produce a cartilage-like tissue in vitro. The current objective was to determine if these same factors could be combined immediately prior to implantation to induce a superior healing response in vivo relative to the hydrogel alone

Evaluation of surgical fixation methods for the implantation of melt electrowriting-reinforced hyaluronic acid hydrogel composites in porcine cartilage defects

The surgical repair of articular cartilage remains an ongoing challenge in orthopedics. Tissue engineering is a promising approach to treat cartilage defects; however, scaffolds must (i) possess the requisite material properties to support neocartilage formation, (ii) exhibit sufficient mechanical integrity for handling during implantation, and (iii) be reliably fixed within cartilage defects during surgery. In this study, we demonstrate the reinforcement of soft norbornene-modified hyaluronic acid (NorHA) hydrogels via the melt electrowriting (MEW) of polycaprolactone to fabricate composite scaffolds that support encapsulated porcine mesenchymal stromal cell (pMSC, three donors) chondrogenesis and cartilage formation and exhibit mechanical properties suitable for handling during implantation. Thereafter, acellular MEW-NorHA composites or MEW-NorHA composites with encapsulated pMSCs and precultured for 28 days were implanted in full-thickness cartilage defects in porcine knees using either bioresorbable pins or fibrin glue to assess surgical fixation methods. Fixation of composites with either biodegradable pins or fibrin glue ensured implant retention in most cases (80%); however, defects treated with pinned composites exhibited more subchondral bone remodeling and inferior cartilage repair, as evidenced by micro-computed tomography (micro-CT) and safranin O/fast green staining, respectively, when compared to defects treated with glued composites. Interestingly, no differences in repair tissue were observed between acellular and cellularized implants. Additional work is required to assess the full potential of these scaffolds for cartilage repair. However, these results suggest that future approaches for cartilage repair with MEW-reinforced hydrogels should be carefully evaluated with regard to their fixation approach for construct retention and surrounding cartilage tissue damage

Anti-HIV-1 activity of anionic polymers: a comparative study of candidate microbicides

BACKGROUND: Cellulose acetate phthalate (CAP) in soluble form blocks coreceptor binding sites on the virus envelope glycoprotein gp120 and elicits gp41 six-helix bundle formation, processes involved in virus inactivation. CAP is not soluble at pH < 5.5, normal for microbicide target sites. Therefore, the interaction between insoluble micronized CAP and HIV-1 was studied. Carbomer 974P/BufferGel; carrageenan; cellulose sulfate; dextran/dextrin sulfate, poly(napthalene sulfonate) and poly(styrene-4-sulfonate) are also being considered as anti-HIV-1 microbicides, and their antiviral properties were compared with those of CAP. METHODS: Enzyme linked immunosorbent assays (ELISA) were used to (1) study HIV-1 IIIB and BaL binding to micronized CAP; (2) detect virus disintegration; and (3) measure gp41 six-helix bundle formation. Cells containing integrated HIV-1 LTR linked to the β-gal gene and expressing CD4 and coreceptors CXCR4 or CCR5 were used to measure virus infectivity. RESULTS: 1) HIV-1 IIIB and BaL, respectively, effectively bound to micronized CAP. 2) The interaction between HIV-1 and micronized CAP led to: (a) gp41 six-helix bundle formation; (b) virus disintegration and shedding of envelope glycoproteins; and (c) rapid loss of infectivity. Polymers other than CAP, except Carbomer 974P, elicited gp41 six-helix bundle formation in HIV-1 IIIB but only poly(napthalene sulfonate), in addition to CAP, had this effect on HIV-1 BaL. These polymers differed with respect to their virucidal activities, the differences being more pronounced for HIV-1 BaL. CONCLUSIONS: Micronized CAP is the only candidate topical microbicide with the capacity to remove rapidly by adsorption from physiological fluids HIV-1 of both the X4 and R5 biotypes and is likely to prevent virus contact with target cells. The interaction between micronized CAP and HIV-1 leads to rapid virus inactivation. Among other anionic polymers, cellulose sulfate, BufferGel and aryl sulfonates appear most effective in this respect

Mechanically Induced Chromatin Condensation Requires Cellular Contractility in Mesenchymal Stem Cells

This work was supported by the National Institutes of Health (R01 AR056624, R01 EB02425, T32 AR007132, and P30 AR050950). Additional support was provided by a Montague Research Award from the Perelman School of Medicine and a University of Pennsylvania University Research Foundation Award

Strongly exchange-coupled triplet pairs in an organic semiconductor

From biological complexes to devices based on organic semiconductors, spin interactions play a key role in the function of molecular systems. For instance, triplet-pair reactions impact operation of organic light-emitting diodes as well as photovoltaic devices. Conventional models for triplet pairs assume they interact only weakly. Here, using electron spin resonance, we observe long-lived, strongly-interacting triplet pairs in an organic semiconductor, generated via singlet fission. Using coherent spin-manipulation of these two-triplet states, we identify exchange-coupled (spin-2) quintet complexes co-existing with weakly coupled (spin-1) triplets. We measure strongly coupled pairs with a lifetime approaching 3 µs and a spin coherence time approaching 1 µs, at 10 K. Our results pave the way for the utilization of high-spin systems in organic semiconductors.Gates-Cambridge Trust, Winton Programme for the Physics of Sustainability, Freie Universität Berlin within the Excellence Initiative of the German Research Foundation, Engineering and Physical Sciences Research Council (Grant ID: EP/G060738/1)This is the author accepted manuscript. The final version is available from Nature Publishing Group at http://dx.doi.org/10.1038/nphys3908