Biofunction of Polydopamine Coating in Stem Cell Culture

Adhesive thermosensitive polydopamine hydrogel containing Mn3O4 anchored halloysite clay for treatment of ulcerative colitis

Ulcerative colitis (UC), a common inflammatory bowel disease, causes ulcers of the colon and rectum. One of the important reasons for intestinal lesions caused by UC is that immune cells produce large amounts of reactive oxygen species (ROS). Herein, we developed an adhesive thermosensitive polydopamine hydrogel containing Mn3O4 nanozyme anchored halloysite nanotubes (Mn3O4@HNTs@PDA) to remove ROS produced by immune cells and treatment of UC. Halloysite nanotubes (HNTs) were used as support for the synthesis of Mn3O4 nanoparticles (∼10 nm diameter), which decreased the nanozyme size and increased the catalysis activity. Mn3O4@HNTs can simultaneously remove H2O2 and ·OH through the mutual reaction conversion between SOD-like and CAT-like enzymes. The PDA coating enables Mn3O4@HNTs to adhere well to the damaged mucosa of the inflamed colon, as an artificial mucosal barrier inhibits local oxidative stress. In the dextran sulfate sodium (DSS)-induced UC mouse model, Mn3O4@HNTs@PDA hydrogel effectively transformed the local inflammatory microenvironment and restored intestinal barrier function by scavenging ROS through enzyme-like action, promoting the expression of intestinal mucosal junction proteins. Overall, this study provided a new dosing method to remove ROS by tissue adhesive hydrogel containing nanozyme modified clay mineral, which shows promising applications in clinic gastroenteritis treatment.

Versatile platforms of mussel-inspired agarose scaffold for cell cultured meat

INTRODUCTION

Biomaterial scaffolds are critical for cell cultured meat production. polysaccharide scaffolds lack essential animal cell adhesion receptors, leading to significant challenges in cell proliferation and myogenic differentiation. Thus, enhancing cell adhesion and growth on polysaccharide scaffolds is strongly required to supply the gaps in cell-cultured meat production.

OBJECTIVES

This study aims to develop a multifunctional cell-responsive hydrogel scaffold for the in vitro production of myofibers and structured cell cultured meat through a "cell adhesion-proliferation-differentiation" strategy.

METHODS

A polydopamine coating was applied to agarose hydrogel scaffolds using a dipping technique. The capability of scaffolds for myofiber preparation was assessed by evaluating cell adhesion, proliferation, and myogenic differentiation. Utilizing isolated porcine skeletal muscle satellite cells (PSMSCs), the feasibility of structured cell cultured pork tissue supported by agarose hydrogel film scaffolds was further investigated through three-dimensional imaging and scanning electron microscopy analysis. The physicochemical properties of the structured cell cultured pork tissue were evaluated through staining and texture analysis.

RESULTS

The incorporation of a polydopamine coating facilitated a remarkable 100 % cell adhesion rate on agarose hydrogel scaffolds, which also demonstrated reusability. The agarose hydrogel scaffolds retained adequate mechanical properties, enabling the adhered cells to proliferate effectively and differentiate into myofiber. Moreover, isolated PSMSCs maintained growth potential on the agarose hydrogel scaffolds, thereby imparting the scaffolds with the ability to generate substantial quantities of multinucleated myofibers. Furthermore, we established a structured cell culture pork meat model, characterized by high-density myofibers and agarose hydrogel film scaffolds, which exhibited the texture and color typical of real pork.

CONCLUSION

The innovative agarose/polydopamine scaffold functions as a multifunctional platform for cell culture, offering novel avenues for the diversification and scalable production of cultured meat, and promising significant reductions in production costs for cell cultured meat.

Elevating Postinjection Stability in Silk Nanofibril Hydrogels to Prevent Intervertebral Disc Degeneration

Injectable hydrogels offer a minimally invasive approach to treating intervertebral disc degeneration, a prevalent condition that affects 90% of individuals and often leads to significant pain and disability. Despite being a critical yet often overlooked issue that could lead to suboptimal therapeutic outcomes, the mechanical integrity of these gels frequently diminishes postinjection due to the injection process itself. To address this challenge, our research developed a silk-nanofibril-based hydrogel enhanced through simple in situ polymerization of dopamine. The resulting hydrogel not only effectively preserved its modulus at over 1000 Pa postinjection, matching the mechanical properties of the nucleus pulposus, but also significantly enhanced its antioxidative properties to four times that of the original silk nanofibril-based hydrogel. Furthermore, both cell-based and animal studies substantiated that such a silk nanofibril-based hydrogel integrated with polydopamine exhibited significant therapeutic efficacy in the injectable treatment of intervertebral disc degeneration. Therefore, this work introduced a new perspective on the design of injectable hydrogels that could effectively address both the mechanical and biochemical challenges of degenerative disc diseases, providing a platform for subsequent therapeutic interventions.

Microneedle-Delivered PDA@Exo for Multifaceted Osteoarthritis Treatment via PI3K-Akt-mTOR Pathway

Osteoarthritis (OA) is marked by cartilage deterioration, subchondral bone changes, and an inflammatory microenvironment. The study introduces the Microneedle-Delivered Polydopamine-Exosome (PDA@Exo MN), a therapeutic that not only preserves cartilage and promotes bone regeneration but also improves localized drug delivery through enhanced penetration capabilities. PDA@Exo MN shows strong reactive oxygen species (ROS) scavenging abilities and high biocompatibility, fostering osteogenesis and balancing anabolic and catabolic processes in cartilage. It directs macrophage polarization from M0 to the anti-inflammatory M2 phenotype. RNA sequencing of treated chondrocytes demonstrates restored cellular function and activated antioxidant responses, with modulated inflammatory pathways. The PI3K-AKT-mTOR pathway's activation, essential for PDA@Exo's effects, is confirmed via bioinformatics and Western blot. In vivo assessments robustly validate that PDA@Exo MN prevents cartilage degradation and OA progression, supported by histological assessments and micro-CT analysis, highlighting its disease-modifying impact. The excellent biocompatibility of PDA@Exo MN, verified through histological (H&E) and blood tests showing no organ damage, underscores its safety and efficacy for OA therapy, making it a novel and multifunctional nanomedical approach in orthopedics, characterized by organ-friendliness and biosecurity.

Advances in Mussel Adhesion Proteins and Mussel-Inspired Material Electrospun Nanofibers for Their Application in Wound Repair

Mussel refers to a marine organism with strong adhesive properties, and it secretes mussel adhesion protein (MAP). The most vital feature of MAP is the abundance of the 3,4-dihydroxyphenylalanine (DOPA) group and lysine, which have antimicrobial, anti-inflammatory, antioxidant, and cell adhesion-promoting properties and can accelerate wound healing. Polydopamine (PDA) is currently the most widely used mussel-inspired material characterized by good adhesion, biocompatibility, and biodegradability. It can mediate various interactions to form functional coatings on cell-material surfaces. Nanofibers based on MAP and mussel-inspired materials have been exerting a vital role in wound repair, while there is no comprehensive review presenting them. This Review introduces the structure of MAPs and their adhesion mechanisms and mussel-inspired materials. Second, it introduces the functionalized modification of MAPs and their inspired materials in electrospun nanofibers and application in wound repair. Finally, the future development direction and coping strategies of MAP and mussel-inspired materials are discussed. Moreover, this Review can offer novel strategies for the application of nanofibers in wound repair and bring about new breakthroughs and innovations in tissue engineering and regenerative medicine.

The Role of Mitochondrial Homeostasis in Mesenchymal Stem Cell Therapy-Potential Implications in the Treatment of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a hereditary disorder characterized by bones that are fragile and prone to breaking. The efficacy of existing therapies for OI is limited, and they are associated with potentially harmful side effects. OI is primarily due to a mutation of collagen type I and hence impairs bone regeneration. Mesenchymal stem cell (MSC) therapy is an attractive strategy to take advantage of the potential benefits of these multipotent stem cells to address the underlying molecular defects of OI by differentiating osteoblasts, paracrine effects, or immunomodulation. The maintenance of mitochondrial homeostasis is an essential component for improving the curative efficacy of MSCs in OI by affecting the differentiation, signaling, and immunomodulatory functions of MSCs. In this review, we highlight the MSC-based therapy pathway in OI and introduce the MSC regulation mechanism by mitochondrial homeostasis. Strategies aiming to modulate the metabolism and reduce the oxidative stress, as well as innovative strategies based on the use of compounds (resveratrol, NAD+, α-KG), antioxidants, and nanomaterials, are analyzed. These findings may enable the development of new strategies for the treatment of OI, ultimately resulting in improved patient outcomes.

Polydopamine-coated bioactive glass for immunomodulation and odontogenesis in pulpitis

Preserving vital pulp in cases of dental pulpitis is desired but remains challenging. Previous research has shown that bioactive glass (BG) possesses notable capabilities for odontogenic differentiation. However, the immunoregulatory potential of BG for inflamed pulp is still controversial, which is essential for preserving vital pulp in the context of pulpitis. This study introduces a novel approach utilizing polydopamine-coated BG (BG-PDA) which demonstrates the ability to alleviate inflammation and promote odontogenesis for vital pulp therapy. In vitro, BG-PDA has the potential to induce M2 polarization of macrophages, resulting in decreased intracellular reactive oxygen species levels, inhibition of pro-inflammatory factor, and enhancement of anti-inflammatory factor expression. Furthermore, BG-PDA can strengthen the mitochondrial function in macrophages and facilitate odontogenic differentiation of human dental pulp cells. In a rat model of pulpitis, BG-PDA exhibits the capacity to promote M2 polarization of macrophages, alleviate inflammation, and facilitate dentin bridge formation. This study highlights the notable immunomodulatory and odontogenesis-inducing properties of BG-PDA for treating dental pulpitis, as evidenced by both in vitro and in vivo experiments. These results imply that BG-PDA could serve as a promising biomaterial for vital pulp therapy.

Anti-Stress and Anti-ROS Effects of MnOx-Functionalized Thermosensitive Nanohydrogel Protect BMSCs for Intervertebral Disc Degeneration Repair

Stem cell transplantation is proven to be a promising strategy for intervertebral disc degeneration (IDD) repair. However, replicative senescence of bone marrow-derived mesenchymal stem cells (BMSCs), shear damage during direct injection, mechanical stress, and the reactive oxygen species (ROS)-rich microenvironment in degenerative intervertebral discs (IVDs) cause significant cellular damage and limit the therapeutic efficacy. Here, an injectable manganese oxide (MnOx)-functionalized thermosensitive nanohydrogel is proposed for BMSC transplantation for IDD therapy. The MnOx-functionalized thermosensitive nanohydrogel not only successfully protects BMSCs from shear force and mechanical stress before and after injection, but also repairs the harsh high-ROS environment in degenerative IVDs, thus effectively increasing the viability of BMSCs and resident nucleus pulposus cells (NPCs). The MnOx-functionalized thermosensitive nanohydrogel provides mechanical protection for stem cells and helps to remove endogenous ROS, providing a promising stem cell delivery platform for the treatment of IDD.

Gold nanoparticle adsorption alters the cell stiffness and cell wall bio-chemical landscape of Candida albicans fungal cells

HYPOTHESIS

Nanomaterials have been extensively investigated for a wide range of biomedical applications, including as antimicrobial agents, drug delivery vehicles, and diagnostic devices. The commonality between these biomedical applications is the necessity for the nanoparticle to interact with or pass through the cellular wall and membrane. Cell-nanomaterial interactions/uptake can occur in various ways, including adhering to the cell wall, forming aggregates on the surface, becoming absorbed within the cell wall itself, or transversing into the cell cytoplasm. These interactions are common to mammalian cells, bacteria, and yeast cells. This variety of interactions can cause changes to the integrity of the cell wall and the cell overall, but the precise mechanisms underpinning such interactions remain poorly understood. Here, we investigate the interaction between commonly investigated gold nanoparticles (AuNPs) and the cell wall/membrane of a model fungal cell to explore the general effects of interaction and uptake.

EXPERIMENTS

The interactions between 100 nm citrate-capped AuNPs and the cell wall of Candida albicans fungal cells were studied using a range of advanced microscopy techniques, including atomic force microscopy, confocal laser scanning microscopy, scanning electron microscopy, transmission electron microscopy, and synchrotron-FTIR micro-spectroscopy.

FINDINGS

In most cases, particles adhered on the cell surface, although instances of particles being up-taken into the cell cytoplasm and localised within the cell wall and membrane were also observed. There was a measurable increase in the stiffness of the fungal cell after AuNPs were introduced. Analysis of the synchrotron-FTIR data showed significant changes in spectral features associated with phospholipids and proteins after exposure to AuNPs.

Pulmonary decellularized extracellular matrix (dECM) modified polyethylene terephthalate three-dimensional cell carriers regulate the proliferation and paracrine activity of mesenchymal stem cells

Introduction: Mesenchymal stem cells (MSCs) possess a high degree of self-renewal capacity and in vitro multi-lineage differentiation potential. Decellularized materials have garnered considerable attention due to their elevated biocompatibility, reduced immunogenicity, excellent biodegradability, and the ability to partially mimic the in vivo microenvironment conducive to cell growth. To address the issue of mesenchymal stem cells losing their stem cell characteristics during two-dimensional (2D) cultivation, this study established three-dimensional cell carriers modified with lung decellularized extracellular matrix and assessed its impact on the life activities of mesenchymal stem cells. Methods: This study employed PET as a substrate material, grafting with polydopamine (PDA), and constructing a decellularized extracellular matrix (dECM) coating on its surface, thus creating the PET/PDA/dECM three-dimensional (3D) composite carrier. Subsequently, material characterization of the cellular carriers was conducted, followed by co-culturing with human umbilical cord mesenchymal stem cells in vitro, aiming to investigate the material's impact on the proliferation and paracrine activity of mesenchymal stem cells. Results and Discussion: Material characterization demonstrated successful grafting of PDA and dECM materials, and it had complete hydrophilicity, high porosity, and excellent mechanical properties. The material was rich in various ECM proteins (collagen I, collagen IV , laminin, fibronectin, elastin), indicating good biocompatibility. In long-term in vitro cultivation (14 days) experiments, the PET/PDA/dECM three-dimensional composite carrier significantly enhanced adhesion and proliferation of human umbilical cord-derived mesenchymal stem cells (HUCMSCs), with a proliferation rate 1.9 times higher than that of cells cultured on tissue culture polystyrene (TCPS) at day 14. Furthermore, it effectively maintained the stem cell characteristics, expressing specific antigens for HUCMSCs. Through qPCR, Western blot, and ELISA experiments, the composite carrier markedly promoted the expression and secretion of key cell factors in HUCMSCs. These results demonstrate that the PET/PDA/dECM composite carrier holds great potential for scaling up MSCs' long-term in vitro cultivation and the production of paracrine factors.

Micronano Titanium Accelerates Mesenchymal Stem Cells Aging through the Activation of Senescence-Associated Secretory Phenotype

Stem cell senescence is one of the most representative events of organism aging and is responsible for many physiological abnormalities and disorders. In the scenario of orthopedic disease treatment, stem cell aging may affect the implantation outcome and even lead to operation failure. To explore whether stem cell aging will affect the osteointegration effect of titanium implant, a widely used micronano titanium (MNT) was fabricated. We first verified the expected osteointegration effect of the MNT, which could be attributed to the improvement of stem cell adhesion and osteogenic differentiation. Then, we obtained aged-derived bone marrow mesenchymal stem cells (BMSCs) and studied their biological behaviors on MNT both in vitro and in vivo. We found that compared with normal rats, MNT did not significantly improve the osteointegration in aged rats. Compared with normal rats, fewer endogenous stem cells were observed at the implant-host interface, and the expression of p21 (senescence marker) was also higher. We further confirmed that MNT promoted the nuclear localization of NF-κB in senescent stem cells through the activation of p38 MAPK, thereby inducing the occurrence of the senescence-associated secretory phenotype (SASP) and ultimately leading to the depletion of the stem-cell pool at the implant-host interface. However, the activation of p38 MAPK can still promote the osteogenic differentiation of nonsenescent BMSCs. These results showed an interesting paradoxical balance between osteogenesis and senescence on MNT surfaces and also provided insights for the design of orthopedic implants for aging patients.

Influence of a Composite Polylysine-Polydopamine-Quaternary Ammonium Salt Coating on Titanium on Its Ostogenic and Antibacterial Performance

Thin oxide layers form easily on the surfaces of titanium (Ti) components, with thicknesses of <100 nm. These layers have excellent corrosion resistance and good biocompatibility. Ti is susceptible to bacterial development on its surface when used as an implant material, which reduces the biocompatibility between the implant and the bone tissue, resulting in reduced osseointegration. In the present study, Ti specimens were surface-negatively ionized using a hot alkali activation method, after which polylysine and polydopamine layers were deposited on them using a layer-by-layer self-assembly method, then a quaternary ammonium salt (QAS) (EPTAC, DEQAS, MPA-N⁺) was grafted onto the surface of the coating. In all, 17 such composite coatings were prepared. Against Escherichia coli and Staphylococcus aureus, the bacteriostatic rates of the coated specimens were 97.6 ± 2.0% and 98.4 ± 1.0%, respectively. Thus, this composite coating has the potential to increase the osseointegration and antibacterial performance of implantable Ti devices.

Mannosylated polydopamine nanoparticles alleviate radiation- induced pulmonary fibrosis by targeting M2 macrophages and inhibiting the TGF-β1/Smad3 signaling pathway

Radiation-induced pulmonary fibrosis (RIPF), one type of pulmonary interstitial diseases, is frequently observed following radiation therapy for chest cancer or accidental radiation exposure. Current treatments against RIPF frequently fail to target lung effectively and the inhalation therapy is hard to penetrate airway mucus. Therefore, this study synthesized mannosylated polydopamine nanoparticles (MPDA NPs) through one-pot method to treat RIPF. Mannose was devised to target M2 macrophages in the lung through CD 206 receptor. MPDA NPs showed higher efficiency of penetrating mucus, cellular uptake and ROS-scavenging than original polydopamine nanoparticles (PDA NPs) in vitro. In RIPF mice, aerosol administration of MPDA NPs significantly alleviated the inflammatory, collagen deposition and fibrosis. The western blot analysis demonstrated that MPDA NPs inhibited TGF-β1/Smad3 signaling pathway against pulmonary fibrosis. Taken together this study provide a novel M2 macrophages-targeting nanodrugs through aerosol delivery for the prevention and targeted treatment for RIPF.

A liquid metal-polydopamine composite for cell culture and electro-stimulation

Gallium (Ga) is a low melting point metal in the liquid state in the biological environment which presents a unique combination of fluidity, softness, and metallic electrical and thermal properties. In this work, liquid Ga is proposed as a biocompatible electrode material for cell culture by electro-stimulation since the cytotoxicity of Ga is generally considered low and some Ga compounds have been reported to exhibit anti-bacterial and anti-inflammatory activities. Complementarily, polydopamine (PDA) was coated on liquid Ga to increase the attachment capability of cells on the liquid Ga electrode and provide enhanced biocompatibility. The liquid Ga layer could be readily painted at room temperature on a solid inert substrate, followed by the formation of a nanoscale PDA coating layer resulting in a conformable and biocompatible composite electrode. The PDA layer was shown to coordinate with Ga³⁺, which is sourced from liquid Ga, providing electrical conductivity in the cell culture medium. The PDA-Ga³⁺ composite acted as a conductive substrate for advanced electro-stimulation for cell culture methods of representative animal fibroblasts. The cell proliferation was observed to increase by ∼143% as compared to a standard glass coverslip at a low potential of 0.1 V of direct coupling stimulation. This novel PDA-Ga³⁺ composite has potential applications in cell culture and regenerative medicine.

Rejuvenation of Mesenchymal Stem Cells to Ameliorate Skeletal Aging

Advanced age is a shared risk factor for many chronic and debilitating skeletal diseases including osteoporosis and periodontitis. Mesenchymal stem cells develop various aging phenotypes including the onset of senescence, intrinsic loss of regenerative potential and exacerbation of inflammatory microenvironment via secretory factors. This review elaborates on the emerging concepts on the molecular and epigenetic mechanisms of MSC senescence, such as the accumulation of oxidative stress, DNA damage and mitochondrial dysfunction. Senescent MSCs aggravate local inflammation, disrupt bone remodeling and bone-fat balance, thereby contributing to the progression of age-related bone diseases. Various rejuvenation strategies to target senescent MSCs could present a promising paradigm to restore skeletal aging.

PDMS Micropatterns Coated with PDA and RGD Induce a Regulatory Macrophage-like Phenotype

Regulatory macrophages (Mreg) are a special cell type that present a potential therapeutic strategy for various inflammatory diseases. In vitro, Mreg generation mainly takes 7-10 days of treatment with chemicals, including cytokines. In the present study, we established a new approach for Mreg generation using a three-dimensional (3D) micropatterned polydimethylsiloxane (PDMS) surface coated with a natural biopolymer adhesive polydopamine (PDA) and the common cell adhesion peptide motif arginylglycylaspartic acid (RGD). The 3D PDMS surfaces were fabricated by photolithography and soft lithography techniques and were subsequently coated with an RGD+PDA mixture to form a surface that facilitates cell adhesion. Human monocytes (THP-1 cells) were cultured on different types of 2D or 3D micropatterns for four days, and the cell morphology, elongation, and Mreg marker expression were assessed using microscopic and flow cytometric analyses. The cells grown on the PDA+RGD-coated 3D micropatterns (20-µm width/20-µm space) exhibited the most elongated morphology and strongest expression levels of Mreg markers, such as CD163, CD206, CD209, CD274, MER-TK, TREM2, and DHRS9. The present study demonstrated that PDA+RGD-coated 3D PDMS micropatterns successfully induced Mreg-like cells from THP-1 cells within four days without the use of cytokines, suggesting a time- and cost-effective method to generate Mreg-like cells in vitro.

An antioxidant and antibacterial polydopamine-modified thermo-sensitive hydrogel dressing for Staphylococcus aureus-infected wound healing

Bacteria-infected wound healing is a complex and chronic process that poses a great threat to human health. A thermo-sensitive hydrogel that undergoes a sol-gel transition at body temperature is an attractive wound dressing for healing acceleration and infection prevention. In this paper, we present a thermo-sensitive and reactive oxygen species (ROS)-scavenging hydrogel based on polydopamine modified poly(ε-caprolactone-co-glycolide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-glycolide) (PDA/P2) triblock copolymer. The PDA/P2 solution at a concentration of 30 wt% could form a gel at 34-38 °C. The ROS-scavenging ability of PDA/P2 was demonstrated by DPPH and ABTS assays and intracellular ROS downregulation in RAW264.7 cells. Furthermore, silver nanoparticles were encapsulated in the hydrogel (PDA/P2-4@Ag gel) to provide antibacterial activity against E. coli and S. aureus. An in vivo S. aureus-infected rat model demonstrated that the PDA/P2-4@Ag hydrogel dressing could promote wound healing via inhibiting bacterial growth, alleviating the inflammatory response, and inducing angiogenesis and collagen deposition. This study provides a new strategy to prepare temperature-sensitive hydrogel-based multifunctional wound dressings.

Polydopamine-modified decellularized intestinal scaffolds loaded with adipose-derived stem cells promote intestinal regeneration

Regeneration of gastrointestinal tissues remains a great challenge due to their unique microenvironment. Functional composite decellularized scaffolds have shown great potential in gastrointestinal repair and inducing gastrointestinal tissue-specific proliferation. In this study, polydopamine (PDA)-mediated surface modification of decellularized intestinal scaffolds (DIS), combined with adipose tissue-derived stem cells (ADSC), was used to promote intestinal wound healing while avoiding intestinal resection. The results showed that DIS had good biocompatibility and could maintain the growth and proliferation of ADSC. Moreover, PDA-coated DIS not only had anti-infection ability but could also further promote the secretory activity for the paracrine effects of ADSC. ADSC cultured on PDA-DIS produced significantly higher levels of anti-inflammatory and proangiogenic cytokines than those cultured on plastic plates or DIS. In vivo, ADSC-PDA-DIS significantly promoted intestinal wound closure in rat intestinal defect models. Moreover, ADSC-PDA-DIS was able to induce more neovascularization at 4 weeks postoperatively and promoted macrophage recruitment to accelerate wound healing. Taken together, the results showed that PDA-modified DIS could significantly improve the efficacy of stem cell therapy, and ADSC-PDA-DIS could improve the wound healing process with anti-infection effects, enhancing neovascularization and immunoregulation, which may be of great clinical significance for gastrointestinal regeneration.

Biopolymer coating for particle surface engineering and their biomedical applications

Surface engineering of particles based on a polymeric coating is of great interest in materials design and applications. Due to the disadvantages of non-biodegradability and undesirable biocompatibility, the application of petroleum-based synthetic polymers coating in the biomedical field has been greatly limited. In addition, there is lack of a universal surface modification method to functionalize particles of different compositions, sizes, shapes, and structures. Thus, it is imperative to develop a versatile biopolymeric coating with good biocompatibility and tunable biodegradability for the preparation of functional particle materials regardless of their surface chemical and physical structures. Recently, the natural polysaccharide polymers (e.g. chitosan and cellulose), polyphenol-based biopolymers (e.g. polydopamine and tannic acid), and proteins (e.g. amyloid-like aggregates) have been utilized in surface modification of particles, and applications of these modified particles in the field of biomedicine have been also intensively exploited. In this review, the preparation of the above three coatings on particles surface are summarized, and the applications of these materials in drug loading/release, biomineralization, cell immobilization/protection, enzyme immobilization/protection, and antibacterial/antiviral are exemplified. Finally, the challenges and the future research directions on biopolymer coating for particles surface engineering are prospected.

Long-acting PFI-2 small molecule release and multilayer scaffold design achieve extensive new formation of complex periodontal tissues with unprecedented fidelity

The faithful engineering of complex human tissues such as the bone/soft tissue/mineralized tissue interface in periodontal tissues requires innovative molecular cues in conjunction with tailored scaffolds. To address the loss of periodontal bone and connective tissues following periodontal disease, we have generated a polydopamine and collagen coated electrospun PLGA-PCL (PP) scaffold enriched with the small molecule mediator PFI-2 (PP-PFI-pDA-COL-PFI). In vitro 3D studies using PDL progenitors revealed that the PP-PFI-pDA-COL-PFI scaffold substantially enhanced Alizarin Red staining, increased Ca/P ratios 4-fold, and stimulated cell proliferation more than 12-fold compared to PP-controls, suggestive of its potential for mineralized tissue engineering. When applied in our experimental periodontitis model, the PP-PFI-pDA-COL-PFI scaffold resulted in a substantial 34% reduction in alveolar bone defect height, a 25% root-length gain in periodontal attachment, and the formation of highly ordered regenerated acellular cementum twice as thick as in controls. Explaining the mechanism of PFI-2 mineralized tissue regeneration in periodontal tissues, PFI-2 inhibited SETD7-mediated β-Catenin protein methylation and increased β-Catenin nuclear localization. Together, dual-level PFI-2 incorporation into a degradable, dopamine/collagen coated PLGA/PCL scaffold backbone resulted in the regeneration of the tripartite periodontal complex with unprecedented fidelity, including periodontal attachment and new formation of mineralized tissues in inflamed periodontal environments.

The effects of process parameters on polydopamine coatings employed in tissue engineering applications

The biomaterials’ success within the tissue engineering field is hinged on the capability to regulate tissue and cell responses, comprising cellular adhesion, as well as repair and immune processes’ induction. In an attempt to enhance and fulfill these biomaterials’ functions, scholars have been inspired by nature; in this regard, surface modification via coating the biomaterials with polydopamine is one of the most successful inspirations endowing the biomaterials with surface adhesive properties. By employing this approach, favorable results have been achieved in various tissue engineering-related experiments, a significant one of which is the more rapid cellular growth observed on the polydopamine-coated substrates compared to the untreated ones; nonetheless, some considerations regarding polydopamine-coated surfaces should be taken into account to control the ultimate outcomes. In this mini-review, the importance of coatings in the tissue engineering field, the different types of surfaces requiring coatings, the significance of polydopamine coatings, critical factors affecting the result of the coating procedure, and recent investigations concerning applications of polydopamine-coated biomaterials in tissue engineering are thoroughly discussed.

Polydopamine-Mediated Protein Adsorption Alters the Epigenetic Status and Differentiation of Primary Human Adipose-Derived Stem Cells (hASCs)

Polydopamine (PDA) is a biocompatible cell-adhesive polymer with versatile applications in biomedical devices. Previous studies have shown that PDA coating could improve cell adhesion and differentiation of human mesenchymal stem cells (hMSCs). However, there is still a knowledge gap in the effect of PDA-mediated protein adsorption on the epigenetic status of MSCs. This work used gelatin-coated cell culture surfaces with and without PDA underlayer (Gel and PDA-Gel) to culture and differentiate primary human adipose-derived stem cells (hASCs). The properties of these two substrates were significantly different, which, in combination with a variation in extracellular matrix (ECM) protein bioactivity, regulated cell adhesion and migration. hASCs reduced focal adhesions by downregulating the expression of integrins such as αV, α1, α2, and β1 on the PDA-Gel compared to the Gel substrate. Interestingly, the ratio of H3K27me3 to H3K27me3+H3K4me3 was decreased, but this only occurred for upregulation of AGG and BMP4 genes during chondrogenic differentiation. This result implies that the PDA-Gel surface positively affects the chondrogenic, but not adipogenic and osteogenic, differentiation. In conclusion, for the first time, this study demonstrates the sequential effects of PDA coating on the biophysical property of adsorbed protein and then focal adhesions and differentiation of hMSCs through epigenetic regulation. This study sheds light on PDA-mediated mechanotransduction.

Fabrication of a Cell-Friendly Poly(dimethylsiloxane) Culture Surface via Polydopamine Coating

In this study, we fabricated a poly(dimethylsiloxane) (PDMS) surface coated with polydopamine (PDA) to enhance cell adhesion. PDA is well known for improving surface adhesion on various surfaces due to the abundant reactions enabled by the phenyl, amine, and catechol groups contained within it. To confirm the successful surface coating with PDA, the water contact angle and X-ray photoelectron spectroscopy were analyzed. Human umbilical vein endothelial cells (HUVECs) and human-bone-marrow-derived mesenchymal stem cells (MSCs) were cultured on the PDA-coated PDMS surface to evaluate potential improvements in cell adhesion and proliferation. HUVECs were also cultured inside a cylindrical PDMS microchannel, which was constructed to mimic a human blood vessel, and their growth and performance were compared to those of cells grown inside a rectangular microchannel. This study provides a helpful perspective for building a platform that mimics in vivo environments in a more realistic manner.

Polydopamine at biological interfaces

In the last years coating of surfaces in the presence of dopamine or other catecholamines in oxidative conditions to yield "polydopamine" films has become a popular, easy and versatile coating methodology. Polydopamine(s) offer(s) also a rich chemistry allowing to post-functionalize the obtained coatings with metal nanoparticles with polymers and proteins. However, the interactions either of covalent or non-covalent nature between polydopamine and biomolecules has only been explored more recently. They allow polydopamine to become a material, in the form of nanoparticles, membranes and other assemblies, in its own right not just as a coating. It is the aim of this review to describe the most recent advances in the design of composites between polydopamine and related eumelanin like materials with biomolecules like proteins, nucleotides, oligosaccharides and lipid assemblies. Furthermore, the interactions between polydopamine and living cells will be also reported.

Immuno-activated mesenchymal stem cell living electrospun nanofibers for promoting diabetic wound repair

Diabetic wound is the leading cause of non-traumatic amputations in which oxidative stress and chronic inflammation are main factors affecting wound healing. Although mesenchymal stem cells (MSCs) as living materials can promote skin regeneration, they are still vulnerable to oxidative stress which limits their clinical applications. Herein, we have prepared (polylactic-co-glycolic acid) (PLGA) nanofibers electrospun with LPS/IFN-γ activated macrophage cell membrane. After defining physicochemical properties of the nanofibers modified by LPS/IFN-γ activated mouse RAW264.7 cell derived membrane (RCM-fibers), we demonstrated that the RCM-fibers improved BMMSC proliferation and keratinocyte migration upon oxidative stress in vitro. Moreover, bone marrow derived MSCs (BMMSCs)-loaded RCM-fibers (RCM-fiber-BMMSCs) accelerated wound closure accompanied by rapid re-epithelialization, collagen remodeling, antioxidant stress and angiogenesis in experimental diabetic wound healing in vivo. Transcriptome analysis revealed the upregulation of genes related to wound healing in BMMSCs when co-cultured with the RCM-fibers. Enhanced healing capacity of RCM-fiber-BMMSCs living material was partially mediated through CD200-CD200R interaction. Similarly, LPS/IFN-γ activated THP-1 cell membrane coated nanofibers (TCM-fibers) exhibited similar improvement of human BMMSCs (hBMMSCs) on diabetic wound healing in vivo. Our results thus demonstrate that LPS/IFN-γ activated macrophage cell membrane-modified nanofibers can in situ immunostimulate the biofunctions of BMMSCs, making this novel living material promising in wound repair of human diabetes.

Polydopamine Decorated Microneedles with Fe-MSC-Derived Nanovesicles Encapsulation for Wound Healing

Wound dressing with the capacities of antioxidation, antiinflammation, and efficient angiogenesis induction is expected for effectively promoting wound healing. Herein, a novel core-shell hyaluronic acid (HA) microneedle (MN) patch with ferrum-mesenchymal stem cell-derived artificial nanovesicles (Fe-MSC-NVs) and polydopamine nanoparticles (PDA NPs) encapsulated in the needle tips is presented for wound healing. Fe-MSC-NVs containing multifunctional therapeutic cytokines are encapsulated in the inner HA core of the MN tips for accelerating angiogenesis. The PDA NPs are encapsulated in the outer methacrylated hyaluronic acid (HAMA) shell of the MN tips to overcome the adverse impacts from reactive oxygen species (ROS)-derived oxidative stress. With the gradual degradation of HAMA patch tips in the skin, the PDA NPs are sustainably released at the lesion to suppress the ROS-induced inflammation reaction, while the Fe-MSC-NVs significantly increase the migration, proliferation, and tube formation of human umbilical vein endothelial cells (HUVEC). More attractively, the combination of PDA NPs and Fe-MSC-NVs further promotes M2 macrophage polarization, thereby suppressing wound inflammation. Through in vivo experiment, the Fe-MSC-NVs/PDA MN patch shows an excellent effect for diabetic wound healing. These features of antioxidation, antiinflammation, and pro-angiogenesis indicate the proposed composite core-shell MN patch is valuable for clinical wound healing applications.

Prevention of collagen hydrogel contraction using polydopamine-coating and alginate outer shell increases cell contractile force

Collagen is the most abundant protein in the extracellular matrix of mammals and has a great effect on various cell behaviors including adhesion, differentiation, and migration. However, it is difficult to utilize collagen gel as a physical scaffold in vitro because of its severe contraction. Decrease in the overall hydrogel volume induces changes in cell distribution, and mass transfer within the gel. Uncontrolled mechanical and physiological factors in the fibrous matrix result in uncontrolled cell behaviors in the surrounding cells. In this study, two strategies were used to minimize the contraction of collagen gel. A disk-shaped frame made of polydopamine-coated polydimethylsiloxane (PDMS) prevented horizontal contraction at the edge of the hydrogel. The sequentially cross-linked collagen gel with alginate outer shell (CA-shell) structure inhibited the vertical gel contraction. The combined method synergistically prevented the hydrogel from shrinkage in long-term 3D cell culture. We observed the shift in balance of differentiation from adipogenesis to osteogenesis in mesenchymal stem cells under the environment where gel contraction was prevented, and confirmed that this phenomenon is closely associated with the mechanotransduction based on Yes-associated protein (YAP) localization. Development of this contraction inhibition platform made it possible to investigate the influence of regulation of cellular microenvironments. The physical properties of the hydrogel fabricated in this study were similar to that of pure collagen gel but completely changed the cell behavior within the gel by inhibition of gel contraction. The platform can be used to broaden our understanding of the fundamental mechanism underlying cell-matrix interactions and reproduce extracellular matrix in vivo.

Near-infrared light control of GelMA/PMMA/PDA hydrogel with mild photothermal therapy for skull regeneration

The development of bone tissue engineering indicates some new paths for bone defect repair. Mild photothermal therapy (PTT) is flourishing as an exciting potential method for bone regeneration. Polydopamine nanoparticles exhibit good absorption at infrared wavelengths and can be used as a viable option for the application of mild PTT to bone defects. Herein, a gelatin-methacryloyl/poly(methyl methacrylate)/polydopamine (GelMA/PMMA/PDA) hydrogel was formulated and assessed in terms of mechanical and biological features. We observed that the addition of methacryloyl groups into gelatin and the introduction of PMMA improved the mechanical properties of the hydrogel and ensure the biosecurity. The GelMA/PMMA/PDA hydrogel demonstrated favorable photothermal ability, biocompatibility, and osteogenic effect. In the rat skull defect model, the GelMA/PMMA/PDA hydrogel with mild PTT possesses better bone repair compared with hydrogel-only and control groups. Thus, this mild photothermal hydrogel platform has a beneficial osteogenic ability and provides a novel approach to treat bone defects.

Dopamine-assisted co-deposition of hydroxyapatite-functionalised nanoparticles of polydopamine on implant surfaces to promote osteogenesis in environments with high ROS levels

Environments with high reactive oxygen species (ROS) levels, which are common in patients with diseases such as diabetes, periodontitis, and osteoporosis, impair the osseointegration of implants. To address this issue, by using a one-pot dopamine-assisted co-deposition method, we constructed a three-dimensional coating of hydroxyapatite-functionalised nanoparticles of polydopamine (HA/nPDAs) on implant surfaces, where polydopamine is designed to protect cells via scavenging excessive ROS and HA facilitates osteogenesis. First, nanoparticles of polydopamine (nPDAs) were prepared by self-polymerization and assembly of dopamine under alkaline conditions, and HA/nPDAs were obtained by incubating nPDAs in simulated body fluid (SBF) due to metal chelation and ionic interactions triggered by the catechol moieties of PDA. Thereafter, HA/nPDAs with thickness of ~4 μm were constructed on titanium surfaces by immersing titanium discs in a weak alkaline solution of HA/nPDAs and dopamine through interface interactions driven by catechol chemistry. The properties of coatings (e.g., thickness, composition, hydrophilia and morphology) can be controlled by preparation conditions such as mineralization time and reactant concentration. The coatings display efficient ROS-scavenging ability, promote cell proliferation, and upregulate the activity of alkaline phosphatase and the expression of osteogenesis-related genes in environments with high or normal ROS levels, demonstrating the great promise of such coatings for osseointegration promotion, especially in the state of high ROS in diseases. This study provides a facile, efficient, mild, and universal strategy in engineering functional surfaces on any substrates for diversified applications by simple variation of co-deposited components, through taking advantages of versatile catechol chemistry and nanoparticles with stereo structure and great specific surface area.