Effect of polydopamine on the biomimetic mineralization of mussel-inspired calcium phosphate cement in vitro

Evaluation of enamel remineralization potential and anticariogenic efficacy of polydopamine coated biogenic amorphous calcium phosphate

OBJECTIVES

The aim of this study was to comparatively evaluate the enamel remineralization potential and antibacterial efficacy of polydopamine coated chicken eggshell derived amorphous calcium phosphate (PDA -EACP) and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP).

MATERIALS AND METHODS

EACP was synthesized from chicken eggshells, functionalized with PDA, and then characterized using high-resolution scanning electron microscopy with energy-dispersive X-ray spectroscopy (HRSEM-EDX), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). 120 enamel slabs were demineralized and randomly divided into 5 groups for the following therapeutic treatments: Group I- Control (no treatment); Group II - CPP-ACP; Group III- EACP; Group IV- PDA; Group V- PDA-EACP and subjected to a 28-day pH cycling regimen. The remineralization effects were assessed by measuring changes in Vickers Microhardness (VMH), analyzing surface morphology using SEM and performing elemental and chemical analysis through EDX and XRD. Antibacterial efficacy was evaluated using agar diffusion, direct contact, and biofilm inhibition assays using fluorescent staining method against Streptococcus mutans.

RESULTS

Post-demineralization, VMH values dropped from 340 to 350 VHN to ~ 200-214 VHN. PDA-EACP showed the highest remineralization (330.4 ± 12.2 VHN), significantly greater than EACP (295.6 ± 10.4 VHN) and CPP-ACP (265.3 ± 9.8 VHN) (p < 0.001). EDX analysis showed Ca/P ratio increased to 2.31 ± 0.34 (EACP) and 1.69 ± 0.06 (PDA-EACP). XRD confirmed superior hydroxyapatite crystallization in PDA-EACP. PDA-EACP exhibited the largest inhibition zone (15.6 ± 1.3 mm) and highest biofilm reduction (72.6% bacterial death at 1:1 dilution).

CONCLUSION

PDA-EACP enhances enamel remineralization and antibacterial activity more than CPP-ACP.

CLINICAL RELEVANCE

PDA-EACP provides a biomimetic, cost-effective, and biocompatible alternative to synthetic remineralizing agents to treat early enamel lesions. Its strong adhesion potential, mineralization and antimicrobial properties could improve clinical outcomes in managing and preventing incipient carious lesions.

A novel osteopontin biomimetic polypeptide induces collagen fiber mineralization in vitro

Collagen fibers reinforced by hydroxyapatite (HA) constitute the fundamental structures of natural bone and dentin, where non-collagenous proteins (NCPs) play a regulatory role in collagen fiber mineralization. However, the precise mechanism underlying this mineralization process remains controversial. Moreover, achieving mineralized materials with high-purity, high-mimetic, and high-efficiency, as well as elucidating the essential state of mineralized precursor, are key issues in making a breakthrough in collagen fiber mineralization. Herein, an osteopontin phosphorylated polypeptide (OPP) was designed to explore the biomimetic mineralization of collagen fibers through mineralized ion stabilization and collagen surface modification. OPP could stabilize calcium and phosphate, forming OPP-prenucleation clusters (OPP-PNCs) with small sizes and long-term stabilization. Additionally, OPP could bind to and modify collagen fibers, thereby reducing the interfacial energy. Compared to Bare-Collagen, OPP-Collagen remarkably enhanced the mineralization efficiency. Molecular dynamics simulations indicated that OPP-Collagen could sequester calcium and phosphate from OPP-PNCs to induce mineralization, while Bare-Collagen lacks this ability. This biomimetic mineralization strategy utilizing OPP-PNCs achieved both intrafibrillar and extrafibrillar mineralization of OPP-collagen fibers. The present study introduces a novel OPP-Collagen mineralization strategy that highlights the regulatory role of NCPs on the surface of natural collagen, offering valuable perspectives into the mechanisms underlying natural mineralization processes.

Silver-quercetin-loaded honeycomb-like Ti-based interface combats infection-triggered excessive inflammation via specific bactericidal and macrophage reprogramming

Excessive inflammation caused by bacterial infection is the primary cause of implant failure. Antibiotic treatment often fails to prevent peri-implant infection and may induce unexpected drug resistance. Herein, a non-antibiotic strategy based on the synergy of silver ion release and macrophage reprogramming is proposed for preventing infection and bacteria-induced inflammation suppression by the organic-inorganic hybridization of silver nanoparticle (AgNP) and quercetin (Que) into a polydopamine (PDA)-based coating on the 3D framework of porous titanium (SQPdFT). Once the planktonic bacteria (e.g., Escherichia coli, Staphylococcus aureus) reach the surface of SQPdFT, released Que disrupts the bacterial membrane. Then, AgNP can penetrate the invading bacterium and kill them, which further inhibits the biofilm formation. Simultaneously, released Que can regulate macrophage polarization homeostasis via the peroxisome proliferators-activated receptors gamma (PPARγ)-mediated nuclear factor kappa-B (NF-κB) pathway, thereby terminating excessive inflammatory responses. These advantages facilitate the adhesion and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs), concomitantly suppressing osteoclast maturation, and eventually conferring superior mechanical stability to SQPdFT within the medullary cavity. In summary, owing to its excellent antibacterial effect, immune remodeling function, and pro-osteointegration ability, SQPdFT is a promising protective coating for titanium-based implants used in orthopedic replacement surgery.

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.

Enhanced mechanic properties of calcium phosphate cements via mussel-inspired adhesive as bone substitute: Highlights of their interactions

BACKGROUND

Inspired by natural bones, many organic components were added to Calcium Phosphate Cements (CPCs) to improve their mechanical strength. However, the strength of these composite CPCs is limited by the low strength of organic components itself and the weak interaction between organic components and CPCs.

OBJECTIVE

Firstly, a composite CPC containing mussel-inspired adhesive, Poly-(Dopamine Methacrylamide-co-2-methoxy Ethylacrylate) (pDM) was developed. Secondly, the interactions between pDM and CPC and their effect on mechanical properties were investigated.

METHODS

The interactions between pDM and CPC were performed by Nuclear Magnetic Resonance, Laser Raman, X-ray Photoelectron Spectroscopy, Fourier Transform-Infrared Spectroscopy and X-ray Diffraction Analysis.

RESULTS

The toughness and compressive strength of pDM-CPC scaffold were both significantly enhanced, because of the enhanced interface binding strength among CPC and pDM due to their interaction and the improved mechanical strength of pDM owing to its self-oxidation cross-linking. The toughness of pDM-CPC scaffolds increased with the increased contents of pDM, while pDM-CPC scaffold containing 35 wt.% pDM had the highest compressive strength of all, which the latter was more than five times compared to that of CPC.

CONCLUSION

The mechanically strong pDM-CPC scaffolds has potential application in bone regeneration as well as in craniofacial and orthopedic repair.

Polysaccharide-Based Composite Hydrogel with Hierarchical Microstructure for Enhanced Vascularization and Skull Regeneration

Critical-size skull defects caused by trauma, infection, and tumor resection raise great demands for efficient bone substitutes. Herein, a hybrid cross-linked hierarchical microporous hydrogel scaffold (PHCLS) was successfully assembled by a multistep procedure, which involved (i) the preparation of poly(lactic-co-glycolic)/nanohydroxyapatite (PLGA-HAP) porous microspheres, (ii) embedding the spheres in a solution of dopamine-modified hyaluronic acid and collagen I (Col I) and cross-linking via dopamine polyphenols binding to (i) Col I amino groups (via Michael addition) and (ii) PLGA-HAP (via calcium ion chelation). The introduction of PLGA-HAP not only improved the diversity of pore size and pore communication inside the matrix but also greatly enhanced the compressive strength (5.24-fold, 77.5 kPa) and degradation properties to construct a more stable mechanical structure. In particular, the PHCLS (200 mg, nHAP) promoted the proliferation, infiltration, and angiogenic differentiation of bone marrow mesenchymal stem cells in vitro, as well as significant ectopic angiogenesis and mineralization with a storage modulus enhancement of 2.5-fold after 30 days. Meanwhile, the appropriate matrix microenvironment initiated angiogenesis and early osteogenesis by accelerating endogenous stem cell recruitment in situ. Together, the PHCLS allowed substantial skull reconstruction in the rabbit cranial defect model, achieving 85.2% breaking load strength and 84.5% bone volume fractions in comparison to the natural cranium, 12 weeks after implantation. Overall, this study reveals that the hierarchical microporous hydrogel scaffold provides a promising strategy for skull defect treatment.

In Vitro and In Vivo Evaluation of a Bio-Inspired Adhesive for Bone Fixation

Compared to metallic hardware, an effective bone adhesive can revolutionize the treatment of clinically challenging situations such as comminuted, articular, and pediatric fractures. The present study aims to develop such a bio-inspired bone adhesive, based upon a modified mineral-organic adhesive with tetracalcium phosphate (TTCP) and phosphoserine (OPS) by incorporating nanoparticles of polydopamine (nPDA). The optimal formulation, which was screened using in vitro instrumental tensile adhesion tests, was found to be 50%_molTTCP/50%_molOPS-2%_wtnPDA with a liquid-to-powder ratio of 0.21 mL/g. This adhesive has a substantially stronger adhesive strength (1.0-1.6 MPa) to bovine cortical bone than the adhesive without nPDA (0.5-0.6 MPa). To simulate a clinical scenario of autograft fixation under low mechanical load, we presented the first in vivo model: a rat fibula glued to the tibia, on which the TTCP/OPS-nPDA adhesive (n = 7) was shown to be effective in stabilizing the graft without displacement (a clinical success rate of 86% and 71% at 5 and 12 weeks, respectively) compared to a sham control (0%). Significant coverage of newly formed bone was particularly observed on the surface of the adhesive, thanks to the osteoinductive property of nPDA. To conclude, the TTCP/OPS-nPDA adhesive fulfilled many clinical requirements for the bone fixation, and potentially could be functionalized via nPDA to offer more biological activities, e.g., anti-infection after antibiotic loading.

Multifunctional and multimodality theranostic nanomedicine for enhanced phototherapy

Photodynamic therapy (PDT) has attracted much attention in recent years for its favorable therapeutic efficacy in cancer therapy. However, PDT alone is insufficient to improve the therapeutic efficiency mainly due to the limited penetration depth of light, the insufficient O₂ supply in the hypoxic microenvironment, and the high level of reducing substances in cancer cells. To overcome these limitations, a multifunctional MnO₂ nanoparticle was constructed with honeycomb MnO₂ which was loaded with the photosensitizer Ce6 and modified with polydopamine on its surface (HMnO₂/C&P) to achieve efficient PDT/mild photothermal treatment (PTT) combination therapy. HMnO₂/C&P had high drug loading contents (11.2% Ce6) and can be responsive to the tumor microenvironment (TME), supply O₂ to alleviate the hypoxic microenvironment, and clear GSH to reduce the consumption of ROS, thus enhancing the PDT effect. The introduction of PDA can improve the stability of HMnO₂/C&P, and further give the ability of PTT to act as nanomedicine. The results of in vitro and in vivo experiments show that HMnO₂/C&P based PDT/mild PTT combination therapy has an excellent inhibitory effect on tumor growth. Meanwhile, HMnO₂/C&P can act as a fluorescence imaging reagent and a TME triggerable magnetic resonance imaging (MRI) contrast agent, thus having excellent multimodal self-tracking abilities. Collectively, this study provides a new perspective on the design of multifunctional theranostic nanomedicine to maximize the efficacy of cancer phototherapy.

Photo-Responded Antibacterial Therapy of Reinfection in Percutaneous Implants by Nanostructured Bio-Heterojunction

Percutaneous implants may experience infection for several times during their servicing periods. They need antibacterial activity and durability to reduce recurrent infection and cytocompatibility to reconstruct biosealing. A novel photoresponse bio-heterojunction (PCT) is developed herein. It consists of TiO₂ nanotubes loaded with CuS nanoparticles and wrapped with polydopamine (PDA) layer. In PCT, a built-in electric field directing from TiO₂ to CuS and then to PDA is formed, and with near-infrared (NIR) irradiation, it drives photoexcited electrons to transfer in opposite direction, resulting in the separation of electron-hole pairs and formation of reactive oxygen species (ROS). Simultaneously, PCT shows photothermal effect due to nonradiative relaxation of photoexcited electrons and thermal vibration of lattices. The synergic effect of photogenerated ROS and hyperthermia increases bacterial membrane permeability and leakage of cellular components, endowing PCT with outstanding antibacterial performance. More importantly, PCT has good antibacterial durability and cytocompatibility due to the inhibited leaching of CuS by PDA layer. In reinfected models, with NIR irradiation, PCT sterilizes bacteria, reduces inflammatory response and enhances re-integration of soft tissue efficiently. This work provides an outstanding bio-heterojunction for percutaneous implants in treating reinfection by NIR irradiation and rebuilding biosealing.

Effect of mussel-inspired polydopamine on the reinforced properties of 3D printed β-tricalcium phosphate/polycaprolactone scaffolds for bone regeneration

Bioceramic/polymer scaffolds have been considered as potential grafts used for facilitating bone healing. Unfortunately, the poor interfacial interaction between polymer matrices and bioceramic fillers limited their use in practical medicine. Thus, a facile strategy for reinforcing the three-dimensional printed β-tricalcium phosphate/polycaprolactone scaffolds through employing polydopamine modified-ceramics as fillers. The effects of the dopamine precursor on the compressive strength, degradability, cell proliferation, osteogenic differentiation, and in vivo osteogenicity were measured. The results indicated that the concentration of dopamine could remarkably affect the thickness and density of the polydopamine layer on fillers, further varying the compressive strength (1.23-fold to 1.64-fold), degradability, and osteogenicity of the scaffolds. More importantly, the presence of polydopamine in the three-dimensional printed composite scaffolds not only facilitated the proliferation, alkaline phosphatase activity and mineralization of mesenchymal stem cells, but also stimulated the formation of neo-bone tissue in femur defects. Taking together, the proposed scaffolds might serve as a candidate for bone regeneration.

Surface polydopamine modification of bone defect repair materials: Characteristics and applications

Bone defects are a common challenge for clinical orthopedic surgeons. The existing bone defect repair materials are difficult to achieve satisfactory osseointegration between the material and the bone. Therefore, it is increasingly important to find effective methods to improve the integration of the materials with the bone and thus facilitate bone defect repair. Researchers have found that polydopamine (PDA) has a structure and properties similar to the adhesive proteins secreted by mussels in nature, with good biocompatibility, bioactivity, hydrophilicity, bio-adhesion and thermal stability. PDA is therefore expected to be used as a surface modification material for bone repair materials to improve the bonding of bone repair materials to the bone surface. This paper reviews research related to PDA-modified bone repair materials and looks at their future applications.

CD271 antibody-functionalized microspheres capable of selective recruitment of reparative endogenous stem cells for in situ bone regeneration

In the strategy of in situ bone regeneration, it used to be difficult to specifically recruit bone marrow mesenchymal stem cells (BM-MSCs) by a single marker. Recently, CD271 has been considered to be one of the most specific markers to isolate BM-MSCs; however, the effectiveness of CD271 antibodies in recruiting BM-MSCs has not been explored yet. In this study, we developed novel CD271 antibody-functionalized chitosan (CS) microspheres with the aid of polydopamine (PDA) coating to recruit endogenous BM-MSCs for in situ bone regeneration. The CS microspheres were sequentially modified with PDA and CD271 antibody through dopamine self-polymerization and bioconjugation, respectively. In vitro studies showed that the CD271 antibody-functionalized microspheres selectively captured significantly more BM-MSCs from a fluorescently labeled heterotypic cell population than non-functionalized controls. In addition, the PDA coating was critical for supporting stable adhesion and proliferation of the captured BM-MSCs. Effective early recruitment of CD271⁺ stem cells by the functionalized microspheres at bone defect site of SD rat was observed by the CD271/DAPI immunofluorescence staining, which led to significantly enhanced new bone formation in rat femoral condyle defect over long term. Together, findings from this study have demonstrated, for the first time, that the CD271 antibody-functionalized CS microspheres are promising for in situ bone regeneration.

Effects of polydopamine coatings on nucleation modes of surface mineralization from simulated body fluid

Polydopamine (PDA) has been recently used as a versatile priming layer for further functionalization of a biomaterial surface, particularly in biomimetic mineralization of biomaterials. Yet most of the existing literature is on inorganic substrates and the underlying effects of the PDA layer coatings on the nucleation and mineralization process and the mineral-substrate interface have not been clearly identified. Here we aimed to investigate the effects of the PDA layer on the nucleation and growth and interfacial morphology of calcium phosphate mineral layer (CaP) from 10× simulated body fluid (10× SBF) on polymeric substrates. It is found that the nucleation of CaP on PDA-coated surface favors a mixed “islanding” and planar growth mode (Stranski–Krastanov) while the “islanding” mode (Volmer–Weber) was observed on the surface without PDA. This different early nucleation stage of mineralization was found to correlate with a more “bonded” interface between the mineral layer and the PDA-coated substrates, a slight increase in the interfacial strength and a different delamination mode. This study therefore provided new insights on how polydopamine priming layer influenced the mineralization process and the interface between the mineral layer and the substrate.

Strategies for Using Polydopamine to Induce Biomineralization of Hydroxyapatite on Implant Materials for Bone Tissue Engineering

In the field of tissue engineering, there are several issues to consider when designing biomaterials for implants, including cellular interaction, good biocompatibility, and biochemical activity. Biomimetic mineralization has gained considerable attention as an emerging approach for the synthesis of biocompatible materials with complex shapes, categorized organization, controlled shape, and size in aqueous environments. Understanding biomineralization strategies could enhance opportunities for novel biomimetic mineralization approaches. In this regard, mussel-inspired biomaterials have recently attracted many researchers due to appealing features, such as strong adhesive properties on moist surfaces, improved cell adhesion, and immobilization of bioactive molecules via catechol chemistry. This molecular designed approach has been a key point in combining new functionalities into accessible biomaterials for biomedical applications. Polydopamine (PDA) has emerged as a promising material for biomaterial functionalization, considering its simple molecular structure, independence of target materials, cell interactions for adhesion, and robust reactivity for resulting functionalization. In this review, we highlight the strategies for using PDA to induce the biomineralization of hydroxyapatite (HA) on the surface of various implant materials with good mechanical strength and corrosion resistance. We also discuss the interactions between the PDA-HA coating, and several cell types that are intricate in many biomedical applications, involving bone defect repair, bone regeneration, cell attachment, and antibacterial activity.

Polydopamine regulated hydroxyapatite microspheres grown in the three-dimensional honeycomb-like mollusk shell-derived organic template for osteogenesis

Layered osteochondral composite scaffolds are considered as a promising strategy for the treatment of osteochondral defects. However, the insufficient osseous support and integration of the subchondral bone layer frequently result in the failure of osteochondral repair. Therefore, it is essentially important to explore new subchondral bone constructs tailored to support bone integration and healing. In this study, a novel three-dimensional porous biomimetic construct (HA/pDA-OTMS) was successfully developed by polydopamine (pDA) regulating hydroxyapatite (HA) microspheres grown in the honeycomb-like mollusk shell-derived organic template (OTMS). The biomimetic OTMS had good mechanical properties, high toughness, biodegradability and excellent biocompatibility. Moreover, the long-range ordered cavity structure of OTMS allowed the smallest material to create the largest and most stable geometric space, endowing it high HA loading capacity. The modification of pDA on OTMS surface effectively promoted the mineral nucleation of HA in the micro-nano cavities of OTMS. The compression mechanical tests showed that the combination of inorganic HA and organic pDA-OTMS greatly improved the mechanical properties of the construct. Additionally, the HA/pDA-OTMS composite provided adequate 3-D support for osteoblast cell attachment, proliferation and differentiation, as well as significantly up-regulated the expression of osteogenesis-related genes. These results demonstrated that as-prepared HA/pDA-OTMS constructs with combined mechanical strength and excellent osteogenic activity show great application prospects in subchondral bone regeneration.

The Significance and Utilisation of Biomimetic and Bioinspired Strategies in the Field of Biomedical Material Engineering: The Case of Calcium Phosphat-Protein Template Constructs

This review provides a summary of recent research on biomimetic and bioinspired strategies applied in the field of biomedical material engineering and focusing particularly on calcium phosphate-protein template constructs inspired by biomineralisation. A description of and discussion on the biomineralisation process is followed by a general summary of the application of the biomimetic and bioinspired strategies in the fields of biomedical material engineering and regenerative medicine. Particular attention is devoted to the description of individual peptides and proteins that serve as templates for the biomimetic mineralisation of calcium phosphate. Moreover, the review also presents a description of smart devices including delivery systems and constructs with specific functions. The paper concludes with a summary of and discussion on potential future developments in this field.

Bioinspired by both mussel foot protein and bone sialoprotein: universal adhesive coatings for the promotion of mineralization and osteogenic differentiation

Natural protein bioinspired coatings are developed to promote the mineralization and osteogenic differentiation of MC3T3-E1 cells for implant material use.

Fabrication and Evaluation of 3D Printed Poly(l-lactide) Scaffold Functionalized with Quercetin-Polydopamine for Bone Tissue Engineering

Quercetin (Qu), a bioflavonoid, has been reported to positively affect bone metabolism. For the first time, Qu with different concentrations was utilized to functionalize 3D-printed poly(l-lactide) (PLLA) scaffold with the aid of a polydopamine (PDA) layer through a convenient and effective way in this study. Results revealed that the coexistence of PDA and Qu can capacitate the 3D-printed PLLA scaffold to possess rougher surface, as well as better hydrophilicity and compressive properties. The resulting PDA- and Qu-modified PLLA scaffolds (Qu/PD-PLLA) can sustainably release Qu to some extent, which is more beneficial to the proliferation and attachment of MC3T3-E1 cells, upregulating ALP activity and calcium nodules as well as promoting the expression of related osteogenic genes and proteins. More significantly, such a positive impact of the Qu on the cell affinity and osteogenic activity played in a dose-dependent manner. This study revealed the potential of the 3D-printed Qu/PD-PLLA scaffolds with a certain amount of Qu as bone-repair materials.

Melatonin decorated 3D-printed beta-tricalcium phosphate scaffolds promoting bone regeneration in a rat calvarial defect model

3D-printed β-TCP scaffolds decorated with melatonin via dopamine mussel-inspired chemistry enhance the osteogenesis and in vivo bone regeneration.

Enhancement in sustained release of antimicrobial peptide and BMP-2 from degradable three dimensional-printed PLGA scaffold for bone regeneration

One of the goals of bone tissue engineering is to create scaffolds with well-defined, inter-connected pores, excellent biocompatibility and osteoinductive ability. Three-dimensional (3D)-printed polymer scaffold coated with bioactive peptide are an effective approach to fabricating ideal bone tissue engineering scaffolds for bone defect repair. However, the current strategy of adding bioactive peptides generally cause degradation to the polymer materials or damage the bioactivity of the biomolecules. Thus, in this study, we used a biomimetic process via poly(dopamine) coating to prepare functional 3D PLGA porous scaffolds with immobilized BMP-2 and ponericin G1 that efficiently regulate the osteogenic differentiation of preosteoblasts (MC3T3-E1) and simultaneously inhibit of pathogenic microbes, thereby enhancing biological activity. In this study, we analysed a 3D PLGA porous scaffold by scanning electron microscopy, water contact angle measurements, and materials testing. Subsequently, we examined the adsorption, release and in vitro antimicrobial activity of the 3D PLGA. Surface characterization showed that poly(dopamine) surface modification could more efficiently mediate the immobilization of BMP-2 and ponericin G1 onto the scaffold surfaces than physical adsorption, and that ponericin G1-immobilized 3D PLGA scaffolds were able to maintain long-term antibacterial activity. We evaluated the influence on cell adhesion, proliferation and differentiation by culturing MC3T3-E1 cells on different modified 3D PLGA scaffolds in vitro. The biological results indicate that MC3T3-E1 cell attachment and proliferation on BMP-2/ponericin G1-immobilized 3D PLGA scaffolds were much higher than those on other groups. Calcium deposition, and gene expression results showed that the osteogenic differentiation of cells was effectively improved by loading the 3D PLGA scaffold with BMP-2 and ponericin G1. In summary, our findings indicated that the polydopamine-assisted surface modification method can be a useful tool for grafting biomolecules onto biodegradable implants, and the dual release of BMP-2 and ponericin G1 can enhance the osteointegration of bone implants and simultaneously inhibit of pathogenic microbes. Therefore, we conclude that the BMP-2/ponericin G1-loaded PLGA 3D scaffolds are versatile and biocompatible scaffolds for bone tissue engineering.

One of the goals of bone tissue engineering is to create scaffolds with well-defined, inter-connected pores, excellent biocompatibility and osteoinductive ability.

Surface Modification of Calcium Silicate via Mussel-Inspired Polydopamine and Effective Adsorption of Extracellular Matrix to Promote Osteogenesis Differentiation for Bone Tissue Engineering

Calcium silicate-based cement has garnered huge interest in recent years, due to its versatility and potential in mass fabrication of a variety of bioceramics. For this study, the main objective was to fabricate functionalized calcium silicate (CS) powder integrated with a simple bio-inspired surface modification using polydopamine (PDA), to regulate cellular behaviors such as cellular adhesion, and subsequently cell differentiation and proliferation. For this study, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques were used to analyze the chemical compositions and observe the surface characteristics of our PDA coated CS cements. Such modifications were found to enhance Wharton Jelly's mesenchymal stem cells (WJMSC) in various ways. Firstly, PDA-coated CS cements were found to significantly enhance cell adhesion with higher expressions of cell adhesion markers, such as focal adhesion kinase and integrins. This was further supported by morphology analysis of the cells. This enhanced cell adhesion, in turn, led to significantly higher secretion of extracellular matrix (ECM) proteins, such as collagen I and fibronectin, which directly promoted cell attachments and proliferation. In our osteogenesis assays, it was found that secretion and expression of osteogenesis related genes and proteins were significantly higher and were dependent on the PDA content. Therefore, these results demonstrated that such simple bio-inspired modification techniques of synthetic degradable CS cements can be applied as a future modification, to modify and convert inert surfaces of synthetic bone grafts to enhance and modulate the cell behaviors of WJMSCs. This in turn can be used as a potential alternative for further bioengineering research.

Polydopamine Surface Chemistry: A Decade of Discovery

Polydopamine is one of the simplest and most versatile approaches to functionalizing material surfaces, having been inspired by the adhesive nature of catechols and amines in mussel adhesive proteins. Since its first report in 2007, a decade of studies on polydopamine molecular structure, deposition conditions, and physicochemical properties have ensued. During this time, potential uses of polydopamine coatings have expanded in many unforeseen directions, seemingly only limited by the creativity of researchers seeking simple solutions to manipulating surface chemistry. In this review, we describe the current state of the art in polydopamine coating methods, describe efforts underway to uncover and tailor the complex structure and chemical properties of polydopamine, and identify emerging trends and needs in polydopamine research, including the use of dopamine analogs, nitrogen-free polyphenolic precursors, and improvement of coating mechanical properties.

Surface modification of chitosan film via polydopamine coating to promote biomineralization in bone tissue engineering

Chitosan-based material has been widely used as bone substitute due to its good biocompatibility and biodegradability. However, the hydrophobic surface of chitosan film constrains the osteogenesis mineralization in the process of bone regeneration. For this reason, we develop a novel polydopamine-modified chitosan film suitable for bone tissue engineering applications by a simple and feasible route in this study. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirm the process of surface modification. For comparison, surface wettability, the capacity of mineralization in vitro, and biocompatibility of the chitosan film and the polydopamine-modified chitosan film were assessed. Research results indicate that the polydopamine-modified chitosan film has good hydrophilicity. It is very evident that the polydopamine treatment significantly influences the biomineralization capacity of the chitosan-based substrates, which enhance the growth rate of apatite on the modified chitosan film. Besides, MC3T3-E1 osteoblast experiments demonstrate that the cells can adhere and grow well on the polydopamine-modified chitosan film. It is anticipated that this polydopamine-modified chitosan film, which can be prepared in large quantities simply, should have potential applications in bone tissue engineering.

Biomineralization: From Material Tactics to Biological Strategy

Biomineralization is an important tactic by which biological organisms produce hierarchically structured minerals with marvellous functions. Biomineralization studies typically focus on the mediation function of organic matrices on inorganic minerals, which helps scientists to design and synthesize bioinspired functional materials. However, the presence of inorganic minerals may also alter the native behaviours of organic matrices and even biological organisms. This progress report discusses the latest achievements relating to biomineralization mechanisms, the manufacturing of biomimetic materials and relevant applications in biological and biomedical fields. In particular, biomineralized vaccines and algae with improved thermostability and photosynthesis, respectively, demonstrate that biomineralization is a strategy for organism evolution via the rational design of organism-material complexes. The successful modification of biological systems using materials is based on the regulatory effect of inorganic materials on organic organisms, which is another aspect of biomineralization control. Unlike previous studies, this study integrates materials and biological science to achieve a more comprehensive view of the mechanisms and applications of biomineralization.

Synergistic Inhibition of Enamel Demineralization by Peptide 8DSS and Fluoride

The biomimetic peptide 8DSS has shown beneficial effects in promoting remineralization of demineralized enamel in vitro. Here we examined the ability of 8DSS alone and in combination with fluoride to inhibit enamel demineralization during pH-cycling mimicking intraoral conditions. Enamel blocks were subjected to 9 days of pH-cycling in the presence of 1,000 ppm NaF (positive control), distilled-deionized water (DDW; negative control), 25 μM 8DSS alone, 25 μM 8DSS with 500 ppm NaF (8DSS-FL) or 25 μM 8DSS with 1,000 ppm NaF (8DSS-FH) twice daily for 1 min each time. The blocks were analyzed in terms of surface microhardness (SMH), fluoride uptake and mineral content. The 8DSS-treated blocks showed significantly lower mineral loss, shallower lesions and higher SMH than the DDW-treated blocks. No significant differences were observed between the blocks treated with 8DSS alone or fluoride alone. The blocks treated with 8DSS alone or DDW showed similar amounts of fluoride uptake, which was the lowest of all the treatment groups. The blocks treated with 8DSS-FL or 8DSS-FH did not differ significantly, and both groups showed significantly greater SMH and fluoride uptake as well as significantly lower mineral loss and shallower lesions than the NaF-treated blocks. Mineral content was significantly higher in the 8DSS-treated blocks than in the DDW-treated blocks from the surface layer (10 µm) to the lesion depth (110 µm), and it was significantly higher in the blocks treated with 8DSS-FL or 8DSS-FH than in the NaF-treated blocks from 10 to 90 µm. These findings illustrate the potential of 8DSS for inhibiting enamel demineralization and for enhancing the anticaries effect of NaF.

Reinforcement of a new calcium phosphate cement with dopamine-mediated strontium-doped calcium polyphosphate-modified polycaprolactone fibers

To improve the performance of calcium phosphate cement, dopamine/PCL fibers and strontium-doped calcium polyphosphate/D/PCL fibers were respectively incorporated into Sr-containing calcium phosphate cement to develop a novel bone cement.

Osteogenesis of human adipose-derived stem cells on poly(dopamine)-coated electrospun poly(lactic acid) fiber mats

Electrospinning is a versatile technique to generate large quantities of micro- or nano-fibers from a wide variety of shapes and sizes of polymer. The aim of this study is to develop functionalized electrospun nano-fibers and use a mussel-inspired surface coating to regulate adhesion, proliferation and differentiation of human adipose-derived stem cells (hADSCs). We prepared poly(lactic acid) (PLA) fibers coated with polydopamine (PDA). The morphology, chemical composition, and surface properties of PDA/PLA were characterized by SEM and XPS. PDA/PLA modulated hADSCs' responses in several ways. Firstly, adhesion and proliferation of hADSCs cultured on PDA/PLA were significantly enhanced relative to those on PLA. Increased focal adhesion kinase (FAK) and collagen I levels and enhanced cell attachment and cell cycle progression were observed upon an increase in PDA content. In addition, the ALP activity and osteocalcin of hADSCs cultured on PDA/PLA were significantly higher than seen in those cultured on a pure PLA mat. Moreover, hADSCs cultured on PDA/PLA showed up-regulation of the ang-1 and vWF proteins associated with angiogenesis differentiation. Our results demonstrate that the bio-inspired coating synthetic degradable PLA polymer can be used as a simple technique to render the surfaces of synthetic biodegradable fibers, thus enabling them to direct the specific responses of hADSCs.

Poly(Dopamine)-Assisted Immobilization of Xu Duan on 3D Printed Poly(Lactic Acid) Scaffolds to Up-Regulate Osteogenic and Angiogenic Markers of Bone Marrow Stem Cells

Three-dimensional printing is a versatile technique to generate large quantities of a wide variety of shapes and sizes of polymer. The aim of this study is to develop functionalized 3D printed poly(lactic acid) (PLA) scaffolds and use a mussel-inspired surface coating and Xu Duan (XD) immobilization to regulate cell adhesion, proliferation and differentiation of human bone-marrow mesenchymal stem cells (hBMSCs). We prepared PLA scaffolds and coated with polydopamine (PDA). The chemical composition and surface properties of PLA/PDA/XD were characterized by XPS. PLA/PDA/XD controlled hBMSCs' responses in several ways. Firstly, adhesion and proliferation of hBMSCs cultured on PLA/PDA/XD were significantly enhanced relative to those on PLA. In addition, the focal adhesion kinase (FAK) expression of cells was increased and promoted cell attachment depended on the XD content. In osteogenesis assay, the osteogenesis markers of hBMSCs cultured on PLA/PDA/XD were significantly higher than seen in those cultured on a pure PLA/PDA scaffolds. Moreover, hBMSCs cultured on PLA/PDA/XD showed up-regulation of the ang-1 and vWF proteins associated with angiogenic differentiation. Our results demonstrate that the bio-inspired coating synthetic PLA polymer can be used as a simple technique to render the surfaces of synthetic scaffolds active, thus enabling them to direct the specific responses of hBMSCs.

Poly(dopamine) coating of 3D printed poly(lactic acid) scaffolds for bone tissue engineering

3D printing is a versatile technique to generate large quantities of a wide variety of shapes and sizes of polymer. The aim of this study is to develop functionalized 3D printed poly(lactic acid) (PLA) scaffolds and use a mussel-inspired surface coating to regulate cell adhesion, proliferation and differentiation of human adipose-derived stem cells (hADSCs). We prepared PLA 3D scaffolds coated with polydopamine (PDA). The chemical composition and surface properties of PDA/PLA were characterized by XPS. PDA/PLA modulated hADSCs' responses in several ways. Firstly, adhesion and proliferation, and cell cycle of hADSCs cultured on PDA/PLA were significantly enhanced relative to those on PLA. In addition, the collagen I secreted from cells was increased and promoted cell attachment and cell cycle progression were depended on the PDA content. In osteogenesis assay, the ALP activity and osteocalcin of hADSCs cultured on PDA/PLA were significantly higher than seen in those cultured on pure PLA scaffolds. Moreover, hADSCs cultured on PDA/PLA showed up-regulation of the ang-1 and vWF proteins associated with angiogenic differentiation. Our results demonstrate that the bio-inspired coating synthetic PLA polymer can be used as a simple technique to render the surfaces of synthetic scaffolds active, thus enabling them to direct the specific responses of hADSCs.

Polydopamine-induced nanocomposite Ag/CaP coatings on the surface of titania nanotubes for antibacterial and osteointegration functions

A mussel-inspired novel nano silver/calcium phosphate (CaP) composite coating was prepared on anodized Ti, with its surface maintaining preferable biological performance and possessing long-term antibacterial ability.