Effect of surface chemistry on the integrin induced pathway in regulating vascular endothelial cells migration

Molecularly Imprinted Macroporous Hydrogel Promotes Bone Regeneration via Osteogenic Induction and Osteoclastic Inhibition

Macroporous hydrogels offer physical supportive spaces and bio-instructive environment for the seeded cells, where cell-scaffold interactions directly influence cell fates and subsequently affect tissue regeneration post-implantation. Effectively modifying bioactive motifs at the inner pore surface provides appropriate niches for cell-scaffold interactions. A molecular imprinting method and sacrificial templates are introduced to prepare inner pore surface modification in the macroporous hydrogels. In detail, acrylated bisphosphonates (Ac-BPs) chelating to templates (CaCO3 particles) are anchored on the inner pore surface of the methacrylated gelatin (GelMA)-methacrylated hyaluronic acid (HAMA)-poly (ethylene glycol) diacrylate (PEGDA) macroporous hydrogel (GHP) to form a functional hydrogel scaffold (GHP-int-BP). GHP-int-BP, but not GHP, effectively crafts artificial cell niches to substantially alter cell fates, including osteogenic induction and osteoclastic inhibition, and promote in situ bone regeneration. These findings highlight that molecular imprinting on the inner pore surface in the hydrogel efficiently creates orthogonally additive bio-instructive scaffolds for bone regeneration.

Dynamic RGD ligands derived from highly mobile cyclodextrins regulate spreading and proliferation of endothelial cells to promote vasculogenesis

A thiolated RGD was incorporated into the threaded allyl-β-cyclodextrins (Allyl-β-CDs) of the polyrotaxane (PR) through a thiol-ene click reaction, resulting in the formation of dynamic RGD ligands on the PR surface (dRGD-PR). When maintaining consistent RGD density and other physical properties, endothelial cells (ECs) cultured on dRGD-PR exhibited significantly increased cell proliferation and a larger cell spreading area compared to those on the non-dynamic RGD (nRGD-PCL). Furthermore, ECs on dRGD-PR demonstrated elevated expression levels of FAK, p-FAK, and p-AKT, along with a larger population of cells in the G2/M stage during cell cycle analysis, in contrast to cells on nRGD-PCL. These findings suggest that the movement of the RGD ligands may exert additional beneficial effects in promoting EC spreading and proliferation, beyond their essential adhesion and proliferation-promoting capabilities, possibly mediated by the RGD-integrin-FAK-AKT pathway. Moreover, in vitro vasculogenesis tests were conducted using two methods, revealing that ECs cultured on dRGD-PR exhibited much better vasculogenesis than nRGD-PCL in vitro. In vivo testing further demonstrated an increased presence of CD31-positive tissues on dRGD-PR. In conclusion, the enhanced EC spreading and proliferation resulting from the dynamic RGD ligands may contribute to improved in vitro vasculogenesis and in vivo vascularization.

Material matters: Degradation products affect regenerating Schwann cells

Devices to treat peripheral nerve injury (PNI) must balance many considerations to effectively guide regenerating nerves across a gap and achieve functional recovery. To enhance efficacy, design features like luminal fillers have been explored extensively. Material choice for PNI devices is also critical, as the determining factor of device mechanics, and degradation rate and has increasingly been found to directly impact biological response. This study investigated the ways in which synthetic polymer materials impact the differentiation state and myelination potential of Schwann cells, peripheral nerve glia. Microporous substrates of polycaprolactone (PCL), poly(lactide-co-glycolide) (PLGA) 85:15, or PLGA 50:50 were chosen, as materials already used in nerve repair devices, representing a wide range of mechanics and degradation profiles. Schwann cells co-cultured with dorsal root ganglion (DRG) neurons on the substrates expressed more mature myelination proteins (MPZ) on PLGA substrates compared to PCL. Changes to myelination and differentiation state of glia were reflected in adhesion proteins expressed by glia, including β-dystroglycan and integrin α6, both laminin binding proteins. Importantly, degradation products of the polymers affected glial expression independently of direct attachment. Fast degrading PLGA 50:50 substrates released measurable amounts of degradation products (lactic acid) within the culture period, which may push Schwann cells towards glycolytic metabolism, decreasing expression of early transcription factors like sox10. This study shows the importance of understanding not only material effects on attachment, but also on cellular metabolism which drives myelination responses.

Functional attachment of primary neurons and glia on radiopaque implantable biomaterials for nerve repair

Repairing peripheral nerve injuries remains a challenge, even with use of auxiliary implantable biomaterial conduits. After implantation the location or function of polymeric devices cannot be assessed via clinical imaging modalities. Adding nanoparticle contrast agents into polymers can introduce radiopacity enabling imaging using computed tomography. Radiopacity must be balanced with changes in material properties impacting device function. In this study radiopaque composites were made from polycaprolactone and poly(lactide-co-glycolide) 50:50 and 85:15 with 0-40 wt% tantalum oxide (TaOx) nanoparticles. To achieve radiopacity, ≥5 wt% TaOx was required, with ≥20 wt% TaOx reducing mechanical properties and causing nanoscale surface roughness. Composite films facilitated nerve regeneration in an in vitro co-culture of adult glia and neurons, measured by markers for myelination. The ability of radiopaque films to support regeneration was driven by the properties of the polymer, with 5-20 wt% TaOx balancing imaging functionality with biological response and proving that in situ monitoring is feasible.

Metabolic Glycoengineering: A Promising Strategy to Remodel Microenvironments for Regenerative Therapy

Cell-based regenerative therapy utilizes the differentiation potential of stem cells to rejuvenate tissues. But the dynamic fate of stem cells is calling for precise control to optimize their therapeutic efficiency. Stem cell fate is regulated by specific conditions called "microenvironments." Among the various factors in the microenvironment, the cell-surface glycan acts as a mediator of cell-matrix and cell-cell interactions and manipulates the behavior of cells. Herein, metabolic glycoengineering (MGE) is an easy but powerful technology for remodeling the structure of glycan. By presenting unnatural glycans on the surface, MGE provides us an opportunity to reshape the microenvironment and evoke desired cellular responses. In this review, we firstly focused on the determining role of glycans on cellular activity; then, we introduced how MGE influences glycosylation and subsequently affects cell fate; at last, we outlined the application of MGE in regenerative therapy, especially in the musculoskeletal system, and the future direction of MGE is discussed.

Radiopaque Implantable Biomaterials for Nerve Repair

Repairing peripheral nerve injuries remains a clinical challenge. To enhance nerve regeneration and functional recovery, the use of auxiliary implantable biomaterial conduits has become widespread. After implantation, there is currently no way to assess the location or function of polymeric biomedical devices, as they cannot be easily differentiated from surrounding tissue using clinical imaging modalities. Adding nanoparticle contrast agents into polymer matrices can introduce radiopacity and enable imaging using computed tomography (CT), but radiopacity must be balanced with changes in material properties that impact device function and biological response. In this study radiopacity was introduced to porous films of polycaprolactone (PCL) and poly(lactide-co-glycolide) (PLGA) 50:50 and 85:15 with 0-40wt% biocompatible tantalum oxide (TaO x ) nanoparticles. To achieve radiopacity, at least 5wt% TaO x was required, with ≥ 20wt% TaO x leading to reduced mechanical properties and increased nano-scale surface roughness of films. As polymers used for peripheral nerve injury devices, films facilitated nerve regeneration in an in vitro co-culture model of glia (Schwann cells) and dorsal root ganglion neurons (DRG), measured by expression markers for myelination. The ability of radiopaque films to support nerve regeneration was determined by the properties of the polymer matrix, with a range of 5-20wt% TaO x balancing both imaging functionality with biological response and proving that in situ monitoring of nerve repair devices is feasible.

Modulation of integrin receptor by polyphenols: Downstream Nrf2-Keap1/ARE and associated cross-talk mediators in cardiovascular diseases

As a group of heterodimeric and transmembrane glycoproteins, integrin receptors are widely expressed in various cell types overall the body. During cardiovascular dysfunction, integrin receptors apply inhibitory effects on the antioxidative pathways, including nuclear factor erythroid 2-related factor 2 (Nrf2)-Kelch like ECH Associated Protein 1 (Keap1)/antioxidant response element (ARE) and interconnected mediators. As such, dysregulation in integrin signaling pathways influences several aspects of cardiovascular diseases (CVDs) such as heart failure, arrhythmia, angina, hypertension, hyperlipidemia, platelet aggregation and coagulation. So, modulation of integrin pathway could trigger the downstream antioxidant pathways toward cardioprotection. Regarding the involvement of multiple aforementioned mediators in the pathogenesis of CVDs, as well as the side effects of conventional drugs, seeking for novel alternative drugs is of great importance. Accordingly, the plant kingdom could pave the road in the treatment of CVDs. Of natural entities, polyphenols are multi-target and accessible phytochemicals with promising potency and low levels of toxicity. The present study aims at providing the cardioprotective roles of integrin receptors and downstream antioxidant pathways in heart failure, arrhythmia, angina, hypertension, hyperlipidemia, platelet aggregation and coagulation. The potential role of polyphenols has been also revealed in targeting the aforementioned dysregulated signaling mediators in those CVDs.

Surface processing for iron-based degradable alloys: A preliminary study on the importance of acid pickling

The formation of a heterogeneous oxidized layer, also called scale, on metallic surfaces is widely recognized as a rapid manufacturing event for metals and their alloys. Partial or total removal of the scale represents a mandatory integrated step for the industrial fabrication processes of medical devices. For biodegradable metals, acid pickling has already been reported as a preliminary surface preparation given further processes, such as electropolishing. Unfortunately, biodegradable medical prototypes presented discrepancies concerning acid pickling studies based on samples with less complex geometry (e.g., non-uniform scale removal and rougher surface). Indeed, this translational knowledge lacks a detailed investigation on this process, deep characterization of treated surfaces properties, as well as a comprehensive discussion of the involved mechanisms. In this study, the effects of different acidic media (HCl, HNO3, H3PO4, CH3COOH, H2SO4 and HF), maintained at different temperatures (21 and 60 °C) for various exposition time (15-240 s), on the chemical composition and surface properties of a Fe-13Mn-1.2C biodegradable alloy were investigated. Changes in mass loss, morphology and wettability evidenced the combined effect of temperature and time for all conditions. Pickling in HCl and HF solutions favor mass loss (0.03-0.1 g/cm2) and effectively remove the initial scale.

Mechanistic Insight in Surface Nanotopography Driven Cellular Migration

Cellular migration plays a vital role in many physiological processes. To elucidate the role of surface nanotopography on the downstream signaling pathways underlying cell migration, model surfaces having well-defined hill-like surface nanotopography and uniform surface chemistry were designed and implemented using plasma polymerization and covalent attachment of nanoparticles of predetermined size. A scratch wound assay, immunostaining, and gene expression of focal adhesion (FA) proteins were performed to determine the influence of surface nanotopography on cell migration. The results of this study demonstrate that the gap closure between cell monolayers is faster on surfaces having greater nanoscale topography. The phenomenon is predominantly driven by cell migration and was independent from cell proliferation. Qualitative and quantitative assessment of proteins involved in the signaling pathways underlying cell migration showed significant modulation by surface nanotopography. Specifically, focal adhesion sites decreased with the increase in surface nanotopography scale while the expression of FA proteins increased. This implies that nanotopography mediated modulation of cell migration is directly governed by the recruitment of receptor and adapter proteins responsible for cell-surface interaction. The results of this study indicate that biomaterial devices and constructs having rationally designed surface nanotopography and chemistry could be utilized to regulate wound healing and tissue regeneration.

Silk Film Stiffness Modulates Corneal Epithelial Cell Mechanosignaling

Silk fibroin films are excellent candidate biomaterials for corneal tissue engineering due to their optical transparency, biocompatibility, and mechanical strength. Their tunable chemical and mechanical properties open the possibility of engineering cellular microenvironments that can both mimic native corneal tissue and provide stimuli to actively promote wound regeneration. While silk film mechanical properties, such as surface topography, have demonstrated the ability to control corneal epithelial cell wound regenerating behavior, few studies have explored the stiffness tunability of these films and its cellular effects. Cells are known actively sense the stiffness of their surroundings and processes such as cell adhesion, migration, proliferation, and expression of stem markers can be strongly influenced by matrix stiffness. This study develops technical solutions that allow for both the fabrication of films with stiffnesses similar to corneal tissue and also for their characterization in an aqueous, native-like environment at a scale relevant to cellular forces. Physiological evidence demonstrates that corneal epithelial cells are mechanosensitive to films of different stiffnesses and show that cell spreading, cytoskeletal tension, and molecular mechanotransducer localization are associated with film stiffness. These results indicate that silk film stiffness can be used to regulate cell behavior for the purposes of ocular surface repair.

Response of Endothelial Cells to Gelatin-Based Hydrogels

The establishment of confluent endothelial cell (EC) monolayers on implanted materials has been identified as a concept to avoid thrombus formation but is a continuous challenge in cardiovascular device engineering. Here, material properties of gelatin-based hydrogels obtained by reacting gelatin with varying amounts of lysine diisocyanate ethyl ester were correlated with the functional state of hydrogel contacting venous EC (HUVEC) and HUVEC's ability to form a monolayer on these hydrogels. The density of adherent HUVEC on the softest hydrogel at 37 °C (G' = 1.02 kPa, E = 1.1 ± 0.3 kPa) was significantly lower (125 mm^-1) than on the stiffer hydrogels (920 mm^-1; G' = 2.515 and 5.02 kPa, E = 4.8 ± 0.8 and 10.3 ± 1.2 kPa). This was accompanied by increased matrix metalloprotease activity (9 pmol·min^-2 compared to 0.6 pmol·min^-2) and stress fiber formation, while cell-to-cell contacts were comparable. Likewise, release of eicosanoids (e.g., prostacyclin release of 1.7 vs 0.2 pg·mL^-1·cell^-1) and the pro-inflammatory cytokine MCP-1 (8 vs <1.5 pg·mL^-1·cell^-1) was higher on the softer than on the stiffer hydrogels. The expressions of pro-inflammatory markers COX-2, COX-1, and RAGE were slightly increased on all hydrogels on day 2 (up to 200% of the control), indicating a weak inflammation; however, the levels dropped to below the control from day 6. The study revealed that hydrogels with higher moduli approached the status of a functionally confluent HUVEC monolayer. The results indicate the promising potential especially of the discussed gelatin-based hydrogels with higher G' as biomaterials for implants foreseen for the venous system.

Biological responses to physicochemical properties of biomaterial surface

Biomedical scientists use chemistry-driven processes found in nature as an inspiration to design biomaterials as promising diagnostic tools, therapeutic solutions, or tissue substitutes. While substantial consideration is devoted to the design and validation of biomaterials, the nature of their interactions with the surrounding biological microenvironment is commonly neglected. This gap of knowledge could be owing to our poor understanding of biochemical signaling pathways, lack of reliable techniques for designing biomaterials with optimal physicochemical properties, and/or poor stability of biomaterial properties after implantation. The success of host responses to biomaterials, known as biocompatibility, depends on chemical principles as the root of both cell signaling pathways in the body and how the biomaterial surface is designed. Most of the current review papers have discussed chemical engineering and biological principles of designing biomaterials as separate topics, which has resulted in neglecting the main role of chemistry in this field. In this review, we discuss biocompatibility in the context of chemistry, what it is and how to assess it, while describing contributions from both biochemical cues and biomaterials as well as the means of harmonizing them. We address both biochemical signal-transduction pathways and engineering principles of designing a biomaterial with an emphasis on its surface physicochemistry. As we aim to show the role of chemistry in the crosstalk between the surface physicochemical properties and body responses, we concisely highlight the main biochemical signal-transduction pathways involved in the biocompatibility complex. Finally, we discuss the progress and challenges associated with the current strategies used for improving the chemical and physical interactions between cells and biomaterial surface.

Hydrogel hybrid porcine pericardium for the fabrication of a pre-mounted TAVI valve with improved biocompatibility

Transcatheter aortic valve implantation (TAVI) has been developed years ago for patients who cannot undergo a surgical aortic valve replacement (SAVR). Although TAVI possesses the advantages of lower trauma and simpler manipulation compared to SAVR, the need for storage in glutaraldehyde (GLU) and a tedious intraoperative assembly process have caused great inconvenience for its further application. A pre-mounted TAVI valve assembled by mounting a dry valve frame to a delivery system is expected to address these problems. However, the currently used GLU treated leaflet cannot unfold normally after being crimped for a long-term and loses its function when the BHV is assembled to the catheter. Besides, its cytotoxicity and immune response after implantation are still problems to be solved. In the present study, a hydrogel hybrid porcine pericardium (HHPP) approach was developed to endow the BHVs with a favorable unfolding property and good biocompatibility. Three monomers with different charge characteristics (sodium acrylate, 2-methacryloyloxyethyl phosphorylcholine, and acryloyloxyethyltrimethyl ammonium chloride) were complexed with GLU treated PP (GLU-PP) to form three kinds of HHPPs (SAAH-PP, MPCH-PP, and DACH-PP). The results of the crimping simulation experiment showed that all HHPPs could quickly recover in PBS after being folded for 10 days, while the traditional BHVs (GLU-PP) could not recover under the same conditions. Bovine serum albumin adsorption and platelet adhesion test showed that SAAH-PP and MPCH-PP had good anti-adhesion abilities. A cell culture study indicated that all the three HHPPs promoted HUVEC growth and proliferation. In vivo biocompatibility studies showed that the immune response induced by MPCH-PP was reduced compared to that by GLU-PP. These studies demonstrated that the strategy of MPC hydrogel hybridization may be an effective approach to prepare a pre-mounted TAVI valve with improved biocompatibility.

Facile preparation of a controlled-release tubular scaffold for blood vessel implantation

Salvianic acid-loaded mesoporous silica nanoparticles into gelatin/polyurethane bilayered small-diameter tubular scaffold were prepared by thermally induced phase separation (TIPS) and electrospinning. Mesoporous silica nanoparticles (MSNs) were selected as carriers to load salvianic acid (SAL). The SAL-loaded MSNs (SAL@MSNs) with an optimized SAL loading efficiency of 10% was initially dispersed in gelatin solution and under a vacuum freeze-drying process as an inner layer of vascular scaffolds. Then, poly(ester-urethane)urea (C-PEEUU) nanofibers were electrospun outside the SAL@MSNs/Gelatin vascular scaffold to strengthen the spongy matrix. The loaded SAL within the MSNs/Gelatin/C-PEEUU bilayered small-diameter tubular scaffold showed a sustained release profile and good mechanical properties. In addition, the drug-loaded composite scaffold showed no unfavorable effects on the adhesion and proliferation of endothelial cells. Moreover, no intimal hyperplasia and acute thrombosis was observed in the short-term implantation in rabbit's carotid artery. We believe the SAL@MSNs/Gelatin/C-PEEUU bilayered vascular scaffolds have promise for vascular tissue engineering applications.

Surface Patterning and Innate Physicochemical Attributes of Silk Films Concomitantly Govern Vascular Cell Dynamics

Functional impairment of vascular cells is associated with cardiovascular pathologies. Recent literature clearly presents evidence relating cell microenvironment and their function. It is crucial to understand the cell-material interaction while designing a functional tissue engineered vascular graft. Natural silk biopolymer has shown potential for various tissue-engineering applications. In the present work, we aimed to explore the combinatorial effect of variable innate physicochemical properties and topographies of silk films on functional behavior of vascular cells. Silk proteins from different varieties (mulberry Bombyx mori, BM; and non-mulberry Antheraea assama, AA) possess unique inherent amino acid composition that leads to variable surface properties (roughness, wettability, chemistry, and mechanical stiffness). In addition, we engineered the silk film surfaces and printed a microgrooved pattern to induce unidirectional cell orientation mimicking their native form. Patterned silk films induced unidirectional alignment of porcine vascular cells. Regardless of alignment, endothelial cells (ECs) proliferated favorably on AA films; however, it suppressed production of nitric oxide (NO), an endogenous vasodilator. Unidirectional alignment of smooth muscle cells (SMCs) encouraged contractile phenotype as indicated by minimal cell proliferation, increment of quiescent (G0) phase cells, and upregulation of contractile genes. Moderately hydrophilic flat BM films induced cell aggregation and augmented the expression of contractile genes (for SMCs) and endothelial nitric oxide synthase, eNOS (for ECs). Functional studies further confirmed SMCs' alignment improving collagen production, remodeling ability (matrix metalloproteinase, MMP-2 and MMP-9 production) and physical contraction. Altogether, this study confirms vascular cells' functional behavior is crucially regulated by synergistic effect of their alignment and cell-substrate interfacial properties.

Smart mechanosensing machineries enable migration of vascular smooth muscle cells in atherosclerosis-relevant 3D matrices

At the early stage of atherosclerosis, neointima is formed due to the migration of vascular smooth muscle cells (VSMCs) from the media to the intima. VSMCs are surrounded by highly adhesive 3D matrices. They take specific strategies to cross various 3D matrices in the media, including heterogeneous collagen and mechanically strong basement membrane. Migration of VSMCs is potentially caused by biomechanical mechanism. Most in vitro studies focus on cell migration on 2D substrates in response to biochemical factors. How the cells move through 3D matrices under the action of mechanosensing machineries remains unexplored. In this review, we propose that several interesting tension-dependent machineries act as "tractor"-posterior myosin II accumulation, and "wrecker"-anterior podosome maintaining, to power VSMCs ahead. VSMCs embedded in 3D matrices may accumulate a minor myosin II isoform, myosin IIB, at the cell rear. Anisotropic myosin IIB distribution creates cell rear, polarizes cell body, pushes the nucleus and reshapes the cell body, and cooperates with a uniformly distributed myosin IIA to propel the cell forward. On the other hand, matrix digestion by podosome further promote the migration when the matrix becomes denser. Actomyosin tension activates Src to induce podosome in soft 3D matrices and retain the podosome integrity to steadily digest the matrix.

Parallel Control over Surface Charge and Wettability Using Polyelectrolyte Architecture: Effect on Protein Adsorption and Cell Adhesion

Surface charge and wettability, the two prominent physical factors governing protein adsorption and cell adhesion, have been extensively investigated in the literature. However, a comparison between these driving forces in terms of their independent and cooperative effects in affecting adhesion is rarely explored on a systematic and quantitative level. Herein, we formulate a protocol that features two-dimensional control over both surface charge and wettability with limited cross-parameter influence. This strategy is implemented by controlling both the polyion charge density in the layer-by-layer (LbL) assembly process and the polyion side-chain chemical structures. The 2D property matrix spans surface isoelectric points ranging from 5 to 9 and water contact angles from 35 to 70°, with other interferential factors (e.g., roughness) eliminated. The interplay between these two surface variables influences protein (bovine serum albumin, lysozyme) adsorption and 3T3 fibroblast cell adhesion. For proteins, we observe the presence of thresholds for surface wettability and electrostatic driving forces necessary to affect adhesion. Beyond these thresholds, the individual effects of electrostatic forces and wettability are observed. For fibroblast, both surface charge and wettability have an effect on its adhesion. The combined effects of positive charge and hydrophilicity lead to the highest cell adhesion, whereas negative charge and hydrophobicity lead to the lowest cell adhesion. Our design strategy can potentially form the basis for studying the distinct behaviors of electrostatic force or wettability driven interfacial phenomena and serve as a reference in future studies assessing protein adsorption and cell adhesion to surfaces with known charge and wettability within the property range studied here.

On-chip enzymatic assay for chloramphenicol acetyltransferase using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Herein, we report a chloramphenicol (CAP) acetyltransferase (CAT) activity assay based on self-assembled monolayers on gold as an alternative to conventional CAT reporter gene assay systems, which sometimes require toxic materials and complicated steps that limit their use. A CAP derivative presented on a monolayer was converted to the acetylated CAP by CAT in the presence of acetyl-CoA. The conversion was directly monitored by observing the molecular weight changes in CAP using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. CAT activity was determined under various reaction conditions by changing reaction times, CAT and acetyl-CoA concentrations. As a practical application, we identified gene expression in bacteria that were transformed with pCAT plasmid DNA. Our strategy can provide a simple and rapid assay that eliminates some commonly used but potentially detrimental steps in enzymatic assays, such as radioactive labeling and complicated separation and purification of analytes prior to detection.

Revascularization of decellularized lung scaffolds: principles and progress

There is a clear unmet clinical need for novel biotechnology-based therapeutic approaches to lung repair and/or replacement, such as tissue engineering of whole bioengineered lungs. Recent studies have demonstrated the feasibility of decellularizing the whole organ by removal of all its cellular components, thus leaving behind the extracellular matrix as a complex three-dimensional (3D) biomimetic scaffold. Implantation of decellularized lung scaffolds (DLS), which were recellularized with patient-specific lung (progenitor) cells, is deemed the ultimate alternative to lung transplantation. Preclinical studies demonstrated that, upon implantation in rodent models, bioengineered lungs that were recellularized with airway and vascular cells were capable of gas exchange for up to 14 days. However, the long-term applicability of this concept is thwarted in part by the failure of current approaches to reconstruct a physiologically functional, quiescent endothelium lining the entire vascular tree of reseeded lung scaffolds, as inferred from the occurrence of hemorrhage into the airway compartment and thrombosis in the vasculature in vivo. In this review, we explore the idea that successful whole lung bioengineering will critically depend on 1) preserving and/or reestablishing the integrity of the subendothelial basement membrane, especially of the ultrathin respiratory membrane separating airways and capillaries, during and following decellularization and 2) restoring vascular physiological functionality including the barrier function and quiescence of the endothelial lining following reseeding of the vascular compartment. We posit that physiological reconstitution of the pulmonary vascular tree in its entirety will significantly promote the clinical translation of the next generation of bioengineered whole lungs.

Mesoporous bioactive glass surface modified poly(lactic-co-glycolic acid) electrospun fibrous scaffold for bone regeneration

A mesoporous bioactive glass (MBG) surface modified with poly(lactic-co-glycolic acid) (PLGA) electrospun fibrous scaffold for bone regeneration was prepared by dip-coating a PLGA electrospun fibrous scaffold into MBG precursor solution. Different surface structures and properties were acquired by different coating times. Surface morphology, chemical composition, microstructure, pore size distribution, and hydrophilicity of the PLGA-MBG scaffold were characterized. Results of scanning electron microscopy indicated that MBG surface coating made the scaffold rougher with the increase of MBG content. Scaffolds after MBG modification possessed mesoporous architecture on the surface. The measurements of the water contact angles suggested that the incorporation of MBG into the PLGA scaffold improved the surface hydrophilicity. An energy dispersive spectrometer evidenced that calcium-deficient carbonated hydroxyapatite formed on the PLGA-MBG scaffolds after a 7-day immersion in simulated body fluid. In vitro studies showed that the incorporation of MBG favored cell proliferation and osteogenic differentiation of human mesenchymal stem cells on the PLGA scaffolds. Moreover, the MBG surface-modified PLGA (PLGA-MBG) scaffolds were shown to be capable of providing the improved adsorption/release behaviors of bone morphogenetic protein-2 (BMP-2). It is very significant that PLGA-MBG scaffolds could be effective for BMP-2 delivery and bone regeneration.