Defined Surface Immobilization of Glycosaminoglycan Molecules for Probing and Modulation of Cell–Material Interactions

Recent Advances in Dopamine-Based Membrane Surface Modification and Its Membrane Distillation Applications

Surface modification of membranes is essential for improving flux and resistance to contamination for membranes. This is of great significance for membrane distillation, which relies on the vapor pressure difference across the membrane as the driving force. In recent years, biomimetic mussel-inspired substances have become the research hotspots. Among them, dopamine serves as surface modifiers that would achieve highly desirable and effective membrane applications owing to their unique physicochemical properties, such as universal adhesion, enhanced hydrophilicity, tunable reducibility, and excellent thermal conductivity. The incorporation of a hydrophilic layer, along with the utilization of photothermal properties and post-functionalization capabilities in modified membranes, effectively addresses challenges such as low flux, contamination susceptibility, and temperature polarization during membrane distillation. However, to the best of our knowledge, there is still a lack of comprehensive and in-depth discussions. Therefore, this paper systematically compiles the modification method of dopamine on the membrane surface and summarizes its application and mechanism in membrane distillation for the first time. It is believed that this paper would provide a reference for dopamine-assisted membrane separation during production, and further promote its practical application.

Nanoclay-Modified Hyaluronic Acid Microspheres for Bone Induction by Sustained rhBMP-2 Delivery

Microspheres (MSs) are ideal candidates as biological scaffolds loading with growth factors or cells for bone tissue engineering to repair irregular alveolar bone defects by minimally invasive injection. However, the high initial burst release of growth factor and low cell attachment limit the application of microspheres. The modification of microspheres often needs expensive experiments facility or complex chemical reactions, which is difficult to achieve and may bring other problems. In this study, a sol-grade nanoclay, laponite XLS is used to modify the surface of MSs to enhance its affinity to either positively or negatively charged proteins and cells without changing the interior structure of the MSs. Recombinant human bone morphogenetic protein-2 (rhBMP-2) is used as a representation of growth factor to check the osteoinduction ability of laponite XLS-modified MSs. By modification, the protein sustained release, cell loading, and osteoinduction ability of MSs are improved. Modified by 1% laponite XLS, the MSs can not only promote osteogenic differentiation of MC3T3-E1 cells by themselves, but also enhance the effect of the rhBMP-2 below the effective dose. Collectively, the study provides an easy and viable method to modify the biological behavior of microspheres for bone tissue regeneration.

Horseradish peroxidase-catalyzed formation of polydopamine for ultra-sensitive magnetic relaxation sensing of aflatoxin B1

Aflatoxin B₁ as one of the most toxic mycotoxins poses a major health risk to humans and animals. Highly sensitive detection methods of aflatoxin B₁ are urgently required because of its low abundance in biological samples. In this work, we developed a magnetic relaxation sensing strategy using enzyme-catalyzed formation of polydopamine for signal amplification. Horseradish peroxidase can catalyze the reaction to generate polydopamine that assembles magnetic nanoparticles for magnetic relaxation sensing with a high signal-to-noise ratio. Combined with the specific antigen-antibody interaction, this magnetic sensor enables fast and ultra-sensitive detection of aflatoxin B₁ by using transverse relaxation time (T₂) as a readout. Under optimized conditions, the linear range of this magnetic sensor for detecting aflatoxin B₁ is from 10 pg/mL to 10 ng/mL, and the limit of detection is 0.35 pg/mL. This sensor has been challenged for the quantitative analysis of aflatoxin B₁ in animal feed samples that is promising for real-world applications.

Artificial M2 macrophages for disease-modifying osteoarthritis therapeutics

Osteoarthritis (OA) is one of the most common joint diseases worldwide and the focus is shifting to disease prevention and the pharmaceutical and surgical treatment of early OA. However, at present few have proven ability to block or delay the progression of OA. Nevertheless, M2 macrophages present an anti-inflammatory function and promote cartilage repair, thereby alleviating OA in mice. However, it is a significant challenge to regulate the helpful secretion of M2 macrophages on demand toward disease-modifying osteoarthritis therapeutics. Here, artificial M2 macrophage (AM2M) with yolk-shell structure was proposed and fabricated to enhance the therapeutic efficacy of M2 macrophages in the treatment of OA. AM2M was composed of macrophage membrane as "shell" and inflammation-responsive nanogel as "yolk". The nanogel was prepared via physical interaction of gelatin and chondroitin sulfate (ChS) through ionic bond and hydrogen bond, achieving burst release to down-regulate inflammation during acute flares and sustainable release to repair cartilage during low inflammatory activity. Furthermore, AM2M exhibited the targeting and long-term residence in the inflamed area and blocked the immune stimulation of macrophages by ChS. Therefore, our fabrication provided a new insight that artificial M2 macrophages are expected to break a vicious and self-perpetuating cycle of OA.

In situ ornamenting poly(ε-caprolactone) electrospun fibers with different fiber diameters using chondrocyte-derived extracellular matrix for chondrogenesis of mesenchymal stem cells

Biomimetic instructive tissue engineering scaffolds are critical for achieving successful tissue regeneration. In the present study, we developed a novel scaffold via ornamenting poly(ε-caprolactone) (PCL) electrospun fibers with a chondrocyte-derived extracellular matrix (ECM)-coating, which was applied for chondrogenesis of mesenchymal stem cells (MSCs). PCL fibrous films with different fiber diameters (1282±121 nm, 549±61 nm and 285±38 nm) were first prepared via electrospinning. Rabbit articular chondrocytes (rACs) were cultured on PCL fibrous scaffolds, followed by a decellularization treatment to generate decellularized ECM (dECM)-coated PCL scaffolds (dECM/PCL). Rabbit bone marrow-derived MSCs (rMSCs) were then seeded onto these scaffolds and adhesion, proliferation and chondrogenic differentiation were evaluated. dECM/PCL scaffolds displayed distinct surface microstructural features with varying fiber diameters and fibrous mesh-like ECM with more developed collagen fibers was observed on nanofibers. On dECM/PCL scaffolds, rMSCs tended to spread more at 24 h post-seeding and proliferated better within 7 d compared to those on uncoated PCL scaffolds. Based on analysis of gene expression, rMSCs underwent the best chondrogenic differentiation on dECM/PCL scaffolds of 549-nm fibers. Collectively, such dECM/PCL composite scaffolds are very promising for cartilage tissue regeneration.

Establishment of a 1, 4, 7, 10-tetraazacyclododecane-1,4,7,10-tetraacetic acid mono-N-hydroxysuccinimide ester (DOTA-NHS-ester) based lectin microarray for efficiently detecting serum glycans in gastric cancers

Development of cancers is involved in changes of a variety of glycans. Lectin microarray is one of the most powerful methodologies for investigation of glycan alterations in biological samples with its advantages of high through-put, selectivity and specificity of the technique. However, utilization of lectin microarrays available commercially keeps of great challenges. In this study, we took use of the molecular self-assembled monolayer technique to modify a gold surface with the reagent 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid mono-N-hydroxysuccinimide ester (DOTA-NHS-ester) in combination with 16-amino-1-hexadecanethiol hydrochloride. Cross-linking effect of DOTA-NHS-ester is brought about via activating three -OH ends to three terminals of succinylimidines, making selective binding of the terminal amino groups in proteins possible. We immobilized ten commercial lectins on the platform and measured changes of serum lectin-matched glycans in patients with gastric cancer. The results demonstrated that this biochip modification platform conferred impressive chemical surface stabilization, sensitivity and geometric images. We observed that all the serum glycans tested in the patients were significantly higher than those in the controls (P < 0.05). The biochip would provide a versatile platform for investigation of potential glycan biomarkers in making tumor diagnosis decision and analyzing escape of tumors from immunity.

Versatile Polydopamine Platforms: Synthesis and Promising Applications for Surface Modification and Advanced Nanomedicine

As a mussel-inspired material, polydopamine (PDA), possesses many properties, such as a simple preparation process, good biocompatibility, strong adhesive property, easy functionalization, outstanding photothermal conversion efficiency, and strong quenching effect. PDA has attracted increasingly considerable attention because it provides a simple and versatile approach to functionalize material surfaces for obtaining a variety of multifunctional nanomaterials. In this review, recent significant research developments of PDA including its synthesis and polymerization mechanism, physicochemical properties, different nano/microstructures, and diverse applications are summarized and discussed. For the sections of its applications in surface modification and biomedicine, we mainly highlight the achievements in the past few years (2016-2019). The remaining challenges and future perspectives of PDA-based nanoplatforms are discussed rationally at the end. This timely and overall review should be desirable for a wide range of scientists and facilitate further development of surface coating methods and the production of PDA-based materials.

A versatile salt-based method to immobilize glycosaminoglycans and create growth factor gradients

Glycosaminoglycans (GAGs) are known to play pivotal roles in physiological processes and pathological conditions. To study interactions of GAGs with proteins, immobilization of GAGs is often required. Current methodologies for immobilization involve modification of GAGs and/or surfaces, which can be time-consuming and may involve specialized equipment. Here, we use an efficient and low-cost method to immobilize GAGs without any (chemical) modification using highly concentrated salt solutions. A number of salts from the Hofmeister series were probed for their capacity to immobilize heparin and chondroitin-6-sulfate on microtiter plates applying single chain antibodies against GAGs for detection (ELISA). From all salts tested, the cosmotropic salt ammonium sulfate was most efficient, especially at high concentrations (80–100% (v/v) saturation). Immobilized GAGs were bioavailable as judged by their binding of FGF2 and VEGF, and by their susceptibility towards GAG lyases (heparinase I, II and III, chondroitinase ABC). Using 80% (v/v) saturated ammonium sulfate, block and continuous gradients of heparin were established and a gradient of FGF2 was created using a heparin block gradient as a template. In conclusion, high concentrations of ammonium sulfate are effective for immobilization of GAGs and for the establishment of gradients of both GAGs and GAG-binding molecules, which enables the study to the biological roles of GAGs.

Molecular dynamics simulations of adsorption and desorption of bone morphogenetic protein-2 on textured hydroxyapatite surfaces

Interactions between bone morphogenetic protein-2 (BMP-2) and biomaterial surfaces are of great significance in the fields of regenerative medicine and bone tissue engineering. In this work, the adsorption and desorption behaviors of BMP-2 on a series of nano-textured hydroxyapatite (HAP) surfaces were systematically investigated by combined molecular dynamic (MD) simulations and steered molecular dynamic (SMD) simulations. The textured HAP surfaces exhibited nanostructured topographies and played a critical role in the mediation of dynamic behaviors of BMP-2. Compared to the HAP-flat model, the HAP-1:1 group (means ridge vs groove = 1:1) showed the excellent ability to capture BMP-2, less conformation change of BMP-2 molecule, and high cysteine-knot stability during the adsorption and desorption processes. These findings suggest that nano-textured HAP surfaces are more capable of loading BMP-2 molecules, and most importantly, they can help maintain a higher biological activity of BMP-2 cargos. In the present study, for the first time, we have deeply clarified the adsorption and desorption dynamics of BMP-2 on various nano-textured HAP surfaces at the atomic level, which can provide significant guidelines for the future design of BMP-2-based tissue engineering implants/scaffolds. STATEMENT OF SIGNIFICANCE: By using combined molecular dynamic (MD) simulations and steered molecular dynamic (SMD) simulations, the adsorption and desorption dynamics of bone morphogenetic protein-2 (BMP-2) dimer on a series of nano-textured hydroxyapatite (HAP) surfaces at the atomic level were presented in details for the first time. We have proved that the HAP-1:1 model (means ridge vs groove = 1:1) possessed excellent ability to capture BMP-2, less conformation change, and high cysteine-knot stability. As a result, the nano-textured topography of HAP-1:1 could maintain a relatively high biological activity of BMP-2 cargos. This work could provide theoretical guidelines for the design of BMP-2-based implants/scaffolds for bone tissue engineering.

Localization and promotion of recombinant human bone morphogenetic protein-2 bioactivity on extracellular matrix mimetic chondroitin sulfate-functionalized calcium phosphate cement scaffolds

Localization of recombinant human bone morphogenetic protein-2 (rhBMP-2) with continuous and effective osteogenic stimulation is still a great challenge in the field of bone regeneration. To achieve this aim, rhBMP-2 was tethered on chondroitin sulfate (CS)-functionalized calcium phosphate cement (CPC) scaffolds through specific noncovalent interactions. CS, one of the core glycosaminoglycans, was covalently conjugated onto CPC scaffolds with the assistance of polydopamine (PDA) and further immobilized rhBMP-2 in a biomimetic form. The CPC-PDA-CS scaffolds not only controlled the release kinetics and presentation state of rhBMP-2 but also effectively increased the expression levels of bone morphogenetic protein receptors (BMPRs) and enhanced the recognitions of the remaining rhBMP-2 to BMPRs. Strikingly, the rhBMP-2-loaded CPC-PDA-CS significantly promoted the cellular surface translocation of BMPRs (especially BMPR-IA). In vivo studies demonstrated that, compared with the rhBMP-2 upon CPC and CPC-PDA, the rhBMP-2 upon CPC-PDA-CS exhibited sustained release and induced high quality and more ectopic bone formation. Collectively, these results suggest that rhBMP-2 can be localized within CS-functionalized CPC scaffolds and exert continuous, long-term, and effective osteogenic stimulation. Thus, this work could provide new avenues in mimicking bone extracellular matrix microenvironment and localizing growth factor activity for enhanced bone regeneration.

STATEMENT OF SIGNIFICANCE

A bioinspired chondroitin sulfate (CS)-functionalized calcium phosphate cement (CPC) platform was developed to tether recombinant human bone morphogenetic protein-2 (rhBMP-2), which could exhibit continuous, long-term, and effective osteogenic stimulation in bone tissue engineering. Compared with rhBMP-2-loaded CPC, the rhBMP-2-loaded CPC-polydopamine-CS scaffolds induced higher expression of bone morphogenetic protein receptors (BMPRs), greater cellular surface translocation of bone morphogenetic protein receptor-IA, higher binding affinity of BMPRs/rhBMP-2, and thus higher activation of the drosophila gene mothers against decapentaplegic protein-1/5/8 (Smad1/5/8) and extracellular-regulated protein kinases-1/2 (ERK1/2) signaling. This work can provide new guidelines for the design of BMP-2-based bioactive materials for bone regeneration.

Enzyme responsive GAG-based natural-synthetic hybrid hydrogel for tunable growth factor delivery and stem cell differentiation

We describe an enzymatically formed chondroitin sulfate (CS) and poly(ethylene glycol) (PEG) based hybrid hydrogel system, which by tuning the architecture and composition of modular building blocks, allows the application-specific tailoring of growth factor delivery and cellular responses. CS, a negatively charged sulfate-rich glycosaminoglycan of the extracellular matrix (ECM), known for its growth factor binding and stem cell regulatory functions, is used as a starting material for the engineering of this biomimetic materials platform. The functionalization of CS with transglutaminase factor XIII specific substrate sequences is utilized to allow cross-linking of CS with previously described fibrin-mimetic TG-PEG hydrogel precursors. We show that the hydrogel network properties can be tuned by varying the degree of functionalization of CS as well as the ratio and concentrations of PEG and CS precursors. Taking advantage of TG-PEG hydrogel, compatible tagged bio-functional building blocks, including RGD peptides or matrix metalloproteinase sensitive domains, can be incorporated on demand allowing the three-dimensional culture and expansion of human bone marrow mesenchymal stem cells (BM-MSCs). The binding of bone morphogenetic protein-2 (BMP-2) in a CS concentration dependent manner and the BMP-2 release mediated osteogenic differentiation of BM-MSCs indicate the potential of CS-PEG hybrid hydrogels to promote regeneration of bone tissue. Their modular design allows facile incorporation of additional signaling elements, rendering CS-PEG hydrogels a highly flexible platform with potential for multiple biomedical applications.

The paracrine effects of adipose-derived stem cells on neovascularization and biocompatibility of a macroencapsulation device

The foreign-body response to biomaterials compromises the performance of many biomedical devices by severe fibrosis and limited neovascularization. Mesenchymal stem cells are known to secrete cytokines for treating inflammatory conditions. In this study, we aim to investigate whether the paracrine products of adipose-derived mesenchymal stem cells (ADSCs) can affect the microenvironment of biomaterials and improve tissue responses to biomaterial implants. A model system was built by loading ADSC spheroids into a macroencapsulation device composed of polytetrafluoroethylene (PTFE) filtration membranes. Soluble ADSC factors that diffused out of the device in vitro promoted the angiogenetic activity of endothelial cells and affected the secretion pattern of macrophages. In vivo study was carried out by subcutaneously embedding blank or ADSC-laden devices in rats. Following a 4 week implantation, the ADSC-laden devices were better vascularized and induced significantly less fibrotic tissue formation in comparison to the non-cellular controls. This study may facilitate our understanding of foreign-body responses and suggest new ways to improve the tissue reaction of biomedical devices for cell-based therapy.

Chondroitin-6-sulfate attenuates inflammatory responses in murine macrophages via suppression of NF-κB nuclear translocation

Inflammation is a host protective response to noxious stimuli, and excessive production of pro-inflammatory mediators by macrophages (mφ) can lead to numerous pathological conditions. In this study, immunomodulatory effects of immobilized and soluble glycosaminoglycans (GAGs) on mouse-bone-marrow-derived mφ were compared by measuring nitric oxide (NO). We demonstrate here that all GAGs studied except for heparin were able to modulate interferon-γ/lipopolysaccharide (IFN-γ/LPS)-induced NO release by mφ to varying extents after 24h of incubation. In particular, the modulatory activities of soluble chondroitin-6-sulfate (C6S), hyaluronic acid and heparan sulfate altered markedly after covalent immobilization. Of these, soluble C6S exhibited the strongest NO inhibitory activity, and the inhibition was dose- and time-dependent. Moreover, C6S significantly reduced pro-inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-α production by IFN-γ/LPS- or LPS-activated mφ. Specifically, the C6S-mediated suppression of mφ pro-inflammatory phenotype was accompanied by an increase in the IL-10 level, suggesting a possible switch towards anti-inflammatory/wound healing M2 state. In addition, the highest magnitude of inhibitory effects was obtained when cells were pre-treated with C6S prior to IFN-γ/LPS or LPS challenge, suggesting an additional role for C6S in protection against microbial infection. Further investigations reveal that the anti-inflammatory effects of C6S on activated mφ may be ascribed at least in part to suppression of NF-κB nuclear translocation.