Silk fibroin, gelatin, and human placenta extracellular matrix-based composite hydrogels for 3D bioprinting and soft tissue engineering

BACKGROUND

There is a great clinical need and it remains a challenge to develop artificial soft tissue constructs that can mimic the biomechanical properties and bioactivity of natural tissue. This is partly due to the lack of suitable biomaterials. Hydrogels made from human placenta offer high bioactivity and represent a potential solution to create animal-free 3D bioprinting systems that are both sustainable and acceptable, as placenta is widely considered medical waste. A combination with silk and gelatin polymers can bridge the biomechanical limitations of human placenta chorion extracellular matrix hydrogels (hpcECM) while maintaining their excellent bioactivity.

METHOD

In this study, silk fibroin (SF) and tyramine-substituted gelatin (G-TA) were enzymatically crosslinked with human placental extracellular matrix (hpcECM) to produce silk-gelatin-ECM composite hydrogels (SGE) with tunable mechanical properties, preserved elasticity, and bioactive functions. The SGE composite hydrogels were characterized in terms of gelation kinetics, protein folding, and bioactivity. The cyto- and biocompatibility of the SGE composite was determined by in vitro cell culture and subcutaneous implantation in a rat model, respectively. The most cell-supportive SGE formulation was then used for 3-dimensional (3D) bioprinting that induced chemical crosslinking during extrusion.

CONCLUSION

Addition of G-TA improved the mechanical properties of the SGE composite hydrogels and inhibited crystallization and subsequent stiffening of SF for up to one month. SGE hydrogels exhibit improved and tunable biomechanical properties and high bioactivity for encapsulated cells. In addition, its use as a bioink for 3D bioprinting with free reversible embedding of suspended hydrogels (FRESH) has been validated, opening the possibility to fabricate highly complex scaffolds for artificial soft tissue constructs with natural biomechanics in future.

Chorion-derived extracellular matrix hydrogel and fibronectin surface coatings show similar beneficial effects on endothelialization of expanded polytetrafluorethylene vascular grafts

The endothelium plays an important regulatory role for cardiovascular homeostasis. Rapid endothelialization of small diameter vascular grafts (SDVGs) is crucial to ensure long-term patency. Here, we assessed a human placental chorionic extracellular matrix hydrogel (hpcECM-gel) as coating material and compared it to human fibronectin in-vitro. hpcECM-gels were produced from placental chorion by decellularization and enzymatic digestion. Human umbilical vein endothelial cells (HUVECs) were seeded to non-, fibronectin- or hpcECM-gel-coated expanded polytetrafluorethylene (ePTFE) SDVGs. Coating efficiency as well as endothelial cell proliferation, migration and adhesion studies on grafts were performed. hpcECM-gel depicted high collagen and glycosaminoglycan content and neglectable DNA amounts. Laminin and fibronectin were both retained in the hpcECM-gel after the decellularization process. HUVEC as well as endothelial progenitor cell attachment were both significantly enhanced on hpcECM-gel coated grafts. HUVECs seeded to hpcECM-gel depicted significantly higher platelet endothelial cell adhesion molecule-1 (PECAM-1) expression in the perinuclear region. Cell retention to flow was enhanced on fibronectin and hpcECM-gel coated grafts. Since hpcECM-gel induced a significantly higher endothelial cell adhesion to ePTFE than fibronectin, it represents a possible alternative for SDVG modification to improve endothelialization.

S-nitroso human serum albumin as a nitric oxide donor in drug-eluting vascular grafts: Biofunctionality and preclinical evaluation

Currently available synthetic small diameter vascular grafts reveal low patency rates due to thrombosis and intimal hyperplasia. Biofunctionalized grafts releasing nitric oxide (NO) in situ may overcome these limitations. In this study, a drug-eluting vascular graft was designed by blending polycaprolactone (PCL) with S-nitroso-human-serum-albumin (S-NO-HSA), a nitric oxide donor with prolonged half-life. PCL-S-NO-HSA grafts and patches were fabricated via electrospinning. The fabrication process was optimized. Patches were characterized in vitro for their morphology, drug release, biomechanics, inflammatory effects, cell proliferation, and expression of adhesion molecules. The selected optimized formulation (8%PCL-S-NO-HSA) had superior mechanical/morphological properties with high protein content revealing extended NO release (for 28 days). 8%PCL-S-NO-HSA patches significantly promoted endothelial cell proliferation while limiting smooth muscle cell proliferation. Expression of adhesion molecules (ICAM-1, VCAM-1) and pro-inflammatory macrophage/cytokine markers (CD80, IL-1α, TNF-α) was significantly reduced. 8%PCL-S-NO-HSA patches had superior immunomodulatory properties by up-regulating anti-inflammatory cytokines (IL-10) and M2 macrophage marker (CD163) at final time points. Grafts were further evaluated in a small rodent model as aortic implants up to 12 weeks. Grafts were assessed by magnetic resonance imaging angiography (MRI) in vivo and after retrieval by histology. All grafts remained 100 % patent with no signs of thrombosis or calcification. 8%PCL-S-NO-HSA vascular grafts supported rapid endothelialization, whereas smooth muscle cell proliferation was hampered in earlier phases. This study indicates that 8%PCL-S-NO-HSA grafts effectively support long-term in situ release of bioactive NO. The beneficial effects observed can be promising features for long-term success of small diameter vascular grafts. STATEMENT OF SIGNIFICANCE: Despite extensive research in the field of small diameter vascular graft replacement, there is still no appropriate substitute to autografts yet. Various limitations are associated with currently available synthetic vascular grafts such as thrombogenicity and intimal hyperplasia. Therefore, developing new generations of such conduits has become a major focus of research. One of the most significant signaling molecules that are involved in homeostasis of the vascular system is nitric oxide. The new designed nitric-oxide eluting vascular grafts described in this study induce rapid surface endothelialization and late migration of SMCs into the graft wall. These beneficial effects have potential to improve current limitations of small diameter vascular grafts.

Assessment of a long-term in vitro model to characterize the mechanical behavior and macrophage-mediated degradation of a novel, degradable, electrospun poly-urethane vascular graft

An assessment tool to evaluate the degradation of biodegradable materials in a more physiological environment is still needed. Macrophages are critical players in host response, remodeling and degradation. In this study, a cell culture model using monocyte-derived primary macrophages was established to study the degradation, macro-/micro-mechanical behavior and inflammatory behavior of a new designed, biodegradable thermoplastic polyurethane (TPU) scaffold, over an extended period of time in vitro. For in vivo study, the scaffolds were implanted subcutaneously in a rat model for up to 36 weeks. TPU scaffolds were fabricated via the electrospinning method. This technique provided a fibrous scaffold with an average fiber diameter of 1.39 ± 0.76 μm and an average pore size of 7.5 ± 1.1 μm. The results showed that TPU scaffolds supported the attachment and migration of macrophages throughout the three-dimensional matrix. Scaffold degradation could be detected in localized areas, emphasizing the role of adherent macrophages in scaffold degradation. Weight loss, molecular weight and biomechanical strength reduction were evident in the presence of the primary macrophage cells. TPU favored the switch from initial pro-inflammatory response of macrophages to an anti-inflammatory response over time both in vitro and in vivo. Expression of MMP-2 and MMP-9 (the key enzymes in tissue remodeling based on ECM modifications) was also evident in vitro and in vivo. This study showed that the primary monocyte-derived cell culture model represents a promising tool to characterize the degradation, mechanical behavior as well as biocompatibility of the scaffolds during an extended period of observation.

Long Term Evaluation of Nanofibrous, Bioabsorbable Polycarbonate Urethane Grafts for Small Diameter Vessel Replacement in Rodents

OBJECTIVE

Biodegradable materials for in situ vascular tissue engineering could meet the increasing clinical demand for sufficient synthetic small diameter vascular substitutes in aortocoronary bypass and peripheral vascular surgery. The aim of this study was to design a new degradable thermoplastic polycarbonate urethane (dPCU) with improved biocompatibility and optimal biomechanical properties. Electrospun conduits made from dPCU were evaluated in short and long term follow up and compared with expanded polytetrafluoroethylene (ePTFE) controls.

METHODS

Both conduits were investigated prior to implantation to assess their biocompatibility and inflammatory potential via real time polymerase chain reaction using a macrophage culture. dPCU grafts (n = 28) and ePTFE controls (n = 28) were then implanted into the infrarenal abdominal aorta of Sprague-Dawley rats. After seven days, one, six, and 12 months, grafts were analysed by histology and immunohistochemistry (IHC) and assessed biomechanically.

RESULTS

Anti-inflammatory signalling was upregulated in dPCU conduits and increased significantly over time in vitro. dPCU and ePTFE grafts offered excellent long and short term patency rates (92.9% in both groups at 12 months) in the rat model without dilatation or aneurysm formation. In comparison to ePTFE, dPCU grafts showed transmural ingrowth of vascular specific cells resulting in a structured neovessel formation around the graft. The graft material was slowly reduced, while the compliance of the neovessel increased over time.

CONCLUSION

The newly designed dPCU grafts have the potential to be safely applied for in situ vascular tissue engineering applications. The degradable substitutes showed good in vivo performance and revealed desirable characteristics such as biomechanical stability, non-thrombogenicity, and minimal inflammatory response after long term implantation.

Bi-directional cell-pericellular matrix interactions direct stem cell fate

Modifiable hydrogels have revealed tremendous insight into how physical characteristics of cells' 3D environment drive stem cell lineage specification. However, in native tissues, cells do not passively receive signals from their niche. Instead they actively probe and modify their pericellular space to suit their needs, yet the dynamics of cells' reciprocal interactions with their pericellular environment when encapsulated within hydrogels remains relatively unexplored. Here, we show that human bone marrow stromal cells (hMSC) encapsulated within hyaluronic acid-based hydrogels modify their surroundings by synthesizing, secreting and arranging proteins pericellularly or by degrading the hydrogel. hMSC's interactions with this local environment have a role in regulating hMSC fate, with a secreted proteinaceous pericellular matrix associated with adipogenesis, and degradation with osteogenesis. Our observations suggest that hMSC participate in a bi-directional interplay between the properties of their 3D milieu and their own secreted pericellular matrix, and that this combination of interactions drives fate.

Acellular vascular matrix grafts from human placenta chorion: Impact of ECM preservation on graft characteristics, protein composition and in vivo performance

Small diameter vascular grafts from human placenta, decellularized with either Triton X-100 (Triton) or SDS and crosslinked with heparin were constructed and characterized. Graft biochemical properties, residual DNA, and protein composition were evaluated to compare the effect of the two detergents on graft matrix composition and structural alterations. Biocompatibility was tested in vitro by culturing the grafts with primary human macrophages and in vivo by subcutaneous implantation of graft conduits (n = 7 per group) into the flanks of nude rats. Subsequently, graft performance was evaluated using an aortic implantation model in Sprague Dawley rats (one month, n = 14). In situ graft imaging was performed using MRI angiography. Retrieved specimens were analyzed by electromyography, scanning electron microscopy, histology and immunohistochemistry to evaluate cell migration and the degree of functional tissue remodeling. Both decellularization methods resulted in grafts of excellent biocompatibility in vitro and in vivo, with low immunogenic potential. Proteomic data revealed removal of cytoplasmic proteins with relative enrichment of ECM proteins in decelluarized specimens of both groups. Noteworthy, LC-Mass Spectrometry analysis revealed that 16 proteins were exclusively preserved in Triton decellularized specimens in comparison to SDS-treated specimens. Aortic grafts showed high patency rates, no signs of thrombus formation, aneurysms or rupture. Conduits of both groups revealed tissue-specific cell migration indicative of functional remodeling. This study strongly suggests that decellularized allogenic grafts from the human placenta have the potential to be used as vascular replacement materials. Both detergents produced grafts with low residual immunogenicity and appropriate mechanical properties. Observed differences in graft characteristics due to preservation method had no impact on successful in vivo performance in the rodent model.

In-vitro/In-vivo comparison of leuprolide acetate release from an in-situ forming plga system

A poly (lactide-co-glycolide) (PLGA) implant was used to control the release profile of leuprolide acetate (LA) drug. The system is an in-situ polymeric precipitation system. And the formulation consisted of PLGA polymer, LA drug and N-methyl-2-pyrrolidon solvent with no additives. First, the formulation was injected into PBS solution for in-vitro studies and then it was administered to the animal models (female rats) for in-vivo release studies. The release profiles of leuprolide acetate were measured by UV spectrophotometry for a period of 28 days. The initial burst release of LA was 14% in in-vitro whereas it was 7% in in-vivo. In-vitro and in-vivo release profiles of LA had similar trends after 72 hours. However, the rate of LA release was slower in-vivo. This might be attributed to the limited diffusion process of solvent and the drug molecules. This could be due to presence of an additional pressure caused by the surrounding tissue and also the presence of small amount of water between cells in the subcutaneous site. Cross-section and surface of the implants were studied via scanning electron microscopy. Morphology of both in-vitro and in-vivo implants confirmed the release behaviours. No toxicity effects were reported in the histopathological assay. Furthermore, the pharmacological analysis showed more inactive ovaries due to release of LA.

Predicting athletic success motivation using mental skin and emotional intelligence and its components in male athletes

AIM

The aim of this study was to predict athletic success motivation by mental skills, emotional intelligence and its components.

METHODS

The research sample consisted of 153 male athletes who were selected through random multistage sampling. The subjects completed the Mental Skills Questionnaire, Bar-On Emotional Intelligence questionnaire and the perception of sport success questionnaire. Data were analyzed using Pearson correlation coefficient and multiple regressions.

RESULT

Regression analysis shows that between the two variables of mental skill and emotional intelligence, mental skill is the best predictor for athletic success motivation and has a better ability to predict the success rate of the participants. Regression analysis results showed that among all the components of emotional intelligence, self-respect had a significantly higher ability to predict athletic success motivation.

CONCLUSION

The use of psychological skills and emotional intelligence as an mediating and regulating factor and organizer cause leads to improved performance and can not only can to help athletes in making suitable and effective decisions for reaching a desired goal.

Size mapping of electric field-assisted production of polycaprolactone particles

In this investigation, biodegradable polycaprolactone polymeric particles (300-4500 nm in diameter) were prepared by jetting a solution in an electric field. An extensive study has been carried out to determine how the size and size distribution of the particles generated can be controlled by systematically varying the polymer concentration in solution (and thereby its viscosity and electrical conductivity), and also the selected flow rate (2-50 microl min(-1)) and applied voltage (0-15 kV) during particle generation. Change in these parameters affects the mode of jetting, and within the stable cone-jet mode window, an increase in the applied voltage (approx. 15 kV) resulted in a reduction in particle size and this was more pronounced at high flow rates (such as; 30, 40 and 50 microl min(-1)) in the same region. The carrier particles were more polydisperse at the peripheral regions of the stable cone-jet mode, as defined in the applied voltage-flow rate parametric map. The effect of loading a drug on the particle size, size distribution and encapsulation efficiency was also studied. Release from drug-loaded particles was investigated using UV spectrophotometry over 45 days. This work demonstrates a powerful method of generating drug-loaded polymeric particles, with the ability to control size and polydispersivity, which has great potential in several categories of biotechnology requiring carrier particles, such as drug delivery and gene therapy.

One-step electrohydrodynamic production of drug-loaded micro- and nanoparticles

The objective of this work was to produce drug-loaded nanometre- and micrometre-scale particles using a single-step process that provides control over particle size and size distribution. Co-axial electrohydrodynamic processing was used, at ambient temperature and pressure, with poly(lactic-co-glycolic acid) as the polymeric coating material and oestradiol as the encapsulated drug. The particle diameter was varied from less than 120 nm to a few micrometres, by simple methodical adjustments in the processing parameters (polymer concentration and applied voltage). In vitro studies were performed to determine the drug release profile from the particles during unassisted and ultrasound-stimulated degradation in simulated body fluid. An encapsulation efficiency of approximately 70% was achieved and release of the drug was sustained for a period of over 20 days. Exposing the particles to ultrasound (22.5 kHz) increased the rate of release by approximately 8 per cent. This processing method offers several advantages over conventional emulsification techniques for the preparation of drug-loaded particles. Most significantly, process efficiency and the drug's functionality are preserved, as complex multistep processing involving harsh solvents, other additives and elevated temperatures or pressures are avoided. Production rates of 10(12) particles min(-1) can be achieved with a single pair of co-axial needles and the process is amenable to being scaled up by using multiple sets.