Activity of alkaline phosphatase adsorbed and grafted on “polydopamine” films

Non-covalent small molecule partnership for redox-active films: Beyond polydopamine technology

HYPOTHESIS

The possibility to use hexamethylenediamine (HMDA) to impart film forming ability to natural polymers including eumelanins and plant polyphenols endowed with biological activity and functional properties has been recently explored with the aim to broaden the potential of polydopamine (PDA)-based films overcoming their inherent limitations. 5,6-dihydroxyindole-2-carboxylic acid, its methyl ester (MeDHICA) and eumelanins thereof were shown to exhibit potent reducing activity.

EXPERIMENTS

MeDHICA and HMDA were reacted in aqueous buffer, pH 9.0 in the presence of different substrates to assess the film forming ability. The effect of different reaction parameters (pH, diamine chain length) on film formation was investigated. Voltammetric and AFM /SEM methods were applied for analysis of the film redox activity and morphology. HPLC, MALDI-MS and ¹HNMR were used for chemical characterization. The film reducing activity was evaluated in comparison with PDA by chemical assays and using UV stressed human immortalized keratinocytes (HaCat) cells model.

FINDINGS

Regular and homogeneous yellowish films were obtained with moderately hydrophobic properties. Film deposition was optimal at pH 9, and specifically induced by HMDA. The film consisted of HMDA and monomeric MeDHICA accompanied by dimers/small oligomers, but no detectable MeDHICA/HMDA covalent conjugation products. Spontaneous assembly of self-organized networks held together mainly by electrostatic interactions of MeDHICA in the anion form and HMDA as the dication is proposed as film deposition mechanism. The film displayed potent reducing properties and exerted significant protective effects from oxidative stress on HaCaT.

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.

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.

Coating Ti6Al4V implants with nanocrystalline diamond functionalized with BMP-7 promotes extracellular matrix mineralization in vitro and faster osseointegration in vivo

The present study investigates the effect of an oxidized nanocrystalline diamond (O-NCD) coating functionalized with bone morphogenetic protein 7 (BMP-7) on human osteoblast maturation and extracellular matrix mineralization in vitro and on new bone formation in vivo. The chemical structure and the morphology of the NCD coating and the adhesion, thickness and morphology of the superimposed BMP-7 layer have also been assessed. The material analysis proved synthesis of a conformal diamond coating with a fine nanostructured morphology on the Ti6Al4V samples. The homogeneous nanostructured layer of BMP-7 on the NCD coating created by a physisorption method was confirmed by AFM. The osteogenic maturation of hFOB 1.19 cells in vitro was only slightly enhanced by the O-NCD coating alone without any increase in the mineralization of the matrix. Functionalization of the coating with BMP-7 resulted in more pronounced cell osteogenic maturation and increased extracellular matrix mineralization. Similar results were obtained in vivo from micro-CT and histological analyses of rabbit distal femurs with screws implanted for 4 or 12 weeks. While the O-NCD-coated implants alone promoted greater thickness of newly-formed bone in direct contact with the implant surface than the bare material, a further increase was induced by BMP-7. It can be therefore concluded that O-NCD coating functionalized with BMP-7 is a promising surface modification of metallic bone implants in order to improve their osseointegration.

Recent advances in dopamine-based materials constructed via one-pot co-assembly strategy

Dopamine-based materials have attracted widespread interest due to the outstanding physicochemical and biological properties. Since the first report on polydopamine (PDA) films, great efforts have been devoted to develop new fabrication strategies for obtaining novel nanostructures and desirable properties. Among them, one-pot co-assembly strategy offers a unique pathway for integrating multiple properties and functions into dopamine-based platform in a single simultaneous co-deposition step. This review focuses on the state of the art development of one-pot multicomponent self-assembly of dopamine-based materials and summarizes various single-step co-deposition approaches, including PDA-assisted adaptive encapsulation, co-assembly of dopamine with other molecules through non-covalent interactions or covalent interactions. Moreover, emerging applications of dopamine-based materials in the fields ranging from sensing, cancer therapy, catalysis, oil/water separation to antifouling are outlined. In addition, some critical remaining challenges and opportunities are discussed to pave the way towards the rational design and applications of dopamine-based materials.

A simple method to construct a low-cost immunosensor based on a dithiol-functionalized polydopamine platform

A simple and low-cost electrochemical CEA immunosensor was investigated via the self-polymerization of dopamine and a dithiol compound spacer for the covalent immobilization of antibodies. The designed CEA immunosensor exhibited a linear response and a low detection limit.

1st Symposium on Polydopamine and NanoTech Poland 2018: Conference Report

The NanoTech Poland is an annual international conference with a strong scientific agenda focused on nanotechnology in energy, environment, and biomedicine. The Nanotech Poland 2018 was held at the NanoBioMedical Centre and Department of Physics at Adam Mickiewicz University in Poznań from June 6th to June 9th. The aim of NanoTech Poland 2018 was to bring together the scientific community's principal investigators, scientists, researchers, analysts, clinicians, policy makers, industry experts, and well-established and budding entrepreneurs to discuss the present and future perspectives in nanotechnology and nanoscience research and development. This year, the 1st Symposium on Polydopamine was held on June 6th. This forum was dedicated to the application of polydopamine and related catechol materials in a variety of research fields, both at the nano- and macroscale. The symposium gathered leading scientists from this important research field from top universities and institutions that have been involved in the research revolved around polydopamine. With over 200 national and international participants, NanoTech Poland 2018 and the 1st Symposium on Polydopamine provided a forum to present and discuss the latest scientific news from the field of nanotechnology with a strong interdisciplinary aspect and bioinspired materials.

Enzymatically Active Polydopamine @ Alkaline Phosphatase Nanoparticles Produced by NaIO4 Oxidation of Dopamine

Polydopamine (PDA) deposition, obtained from the oxidation of dopamine and other catecholamines, is a universal way to coat all known materials with a conformal coating which can subsequently be functionalized at will. The structural analogies between polydopamine and eumelanin, the black-brown pigment of the skin, were incited to produce stable polydopamine nanoparticles in solution, instead of amorphous precipitates obtained from the oxidation of dopamine. Herein, we demonstrate that size-controlled and colloidally stable PDA-based nanoparticles can be obtained in acidic conditions, where spontaneous auto-oxidation of dopamine is suppressed, using sodium periodate as the oxidant and a protein, like alkaline phosphatase (ALP), as a templating agent. The size of the PDA@ALP nanoparticles depends on the dopamine/enzyme ratio and the obtained particles display enzymatic activity of alkaline phosphatase, with an activity extending up to two weeks after particle synthesis. The PDA@ALP nanoparticles can be engineered in polyelectrolyte multilayered films to potentially design model biosensors.

AgNPs-decorated 3D printed PEEK implant for infection control and bone repair

Polyetheretherketone (PEEK) is an ideal substitute material for bone tissue engineering, which can avoid the stress shielding phenomenon due to its similar mechanical properties to natural human bone. Complex bone defect and postoperative infection are still two enormous challenges in orthopedic clinics. It's well-known that additive manufacturing possesses the merits of high-precision and rapid prototyping, thus it easily meets the needs of mold processing. In the present study, we developed a novel Ag-decorated 3D printed PEEK via catecholamine chemistry. SEM image showed that silver nanoparticles (AgNPs) were evenly anchored on the surface. The following antibacterial tests, including bacterial inhibition ring, bacterial dynamics curves and antibiofilm test, indicated that the Ag-decorated 3D PEEK scaffolds displayed significant antibacterial effect towards Gram-negative and Gram-positive bacteria. Then MG-63 cells were seeded on samples for cell proliferation and ALP activity tests. The results demonstrated the scaffold modified with AgNPs could support cell proliferation, and enhanced higher alkaline phosphatase activity compared with pure PEEK scaffold. Expectedly, this dual functional 3D material holds great potential application in clinical bone tissue repair.

Composite Materials and Films Based on Melanins, Polydopamine, and Other Catecholamine-Based Materials

Polydopamine (PDA) is related to eumelanins in its composition and structure. These pigments allow the design, inspired by natural materials, of composite nanoparticles and films for applications in the field of energy conversion and the design of biomaterials. This short review summarizes the main advances in the design of PDA-based composites with inorganic and organic materials.

Additively Manufactured Macroporous Titanium with Silver-Releasing Micro-/Nanoporous Surface for Multipurpose Infection Control and Bone Repair - A Proof of Concept

Restoring large-scale bone defects, where osteogenesis is slow while infections lurk, with biomaterials represents a formidable challenge in orthopedic clinics. Here, we propose a scaffold-based multipurpose anti-infection and bone repairing strategy to meet such restorative needs. To do this, personalized multifunctional titanium meshes were produced through an advanced additive manufacturing process and dual "TiO₂-poly(dopamine)/Ag (nano)" post modifications, yielding macroporous constructs with micro-/nanoporous walls and nanosilver bullets immobilized/embedded therein. Ultrahigh loading capacity and durable release of Ag⁺ were accomplished. The scaffolds were active against planktonic/adherent bacteria (Gram-negative and positive) for up to 12 weeks. Additionally, they not only defended themselves from biofilm colonization but also helped destroy existing biofilms, especially in combination with antibiotics. Further, the osteoblasts/bacteria coculture study displayed that the engineered surfaces aided MG-63 cells to combat bacterial invasion. Meanwhile, the scaffolds elicited generally acceptable biocompatibility (cell adhesion, proliferation, and viability) and hastened osteoblast differentiation and maturation (alkaline phosphatase production, matrix secretion, and calcification), by synergy of micro-/nanoscale topological cues and bioactive catecholamine chemistry. Although done ex vivo, these studies reveal that our three-in-one strategy (infection prophylaxis, infection fighting, and bone repair) has great potential to simultaneously prevent/combat infections and bridge defected bone. This work provides new thoughts to the use of enabling technologies to design biomaterials that resolve unmet clinical needs.

Sonochemically-Produced Metal-Containing Polydopamine Nanoparticles and Their Antibacterial and Antibiofilm Activity

A facile one-pot sonochemical synthesis of Cu-, Ag-, and hybrid Cu/Ag-based polydopamine nanoparticles (Cu-, Ag-, and Cu/Ag-PDA-NPs) and the mechanisms by which they exert antibacterial and antibiofilm activities are reported. We showed that the nanoparticles are spherical with a core-shell structure. Whereas Cu is chelated to the shell of Cu-PDA-NPs in oxidation states of +1/+2, the core of Ag-PDA-NPs is filled with elemental Ag°. Sonochemical irradiation of dopamine in the presence of both Cu(2+) and Ag(+) generates hybrid Cu/Ag-PDA-NPs, whose shells are composed of Cu-chelated PDA with Ag° in the core. The redox potential of the metals was found to be the main determinant of the location and oxidation state of the metals. Leaching studies under physiological conditions reveal a relatively fast release of Cu ions from the shell, whereas Ag leaches very slowly from the core. The metal-containing PDA-NPs are highly microbicidal and exhibit potent antibiofilm activity. The combination of both metals in Cu/Ag-PDA-NPs is especially effective against bacteria and robust biofilms, owing to the dual bactericidal mechanisms of the metals. Most importantly, both Ag- and Cu/Ag-PDA-NPs proved to be significantly more antibacterial than commercial Ag-NPs while exhibiting lower toxicity toward NIH 3T3 mouse embryonic fibroblasts. Mechanistically, the metal-containing PDA-NPs generate stable PDA-semiquinone and reactive oxygen species under physiological conditions, which contribute at least partly to the antimicrobial activity. We also demonstrated that simple treatment of surfaces with Ag-PDA-NPs converts them to antibacterial, the activity of which was preserved even after prolonged storage under ambient conditions.

Antibacterial and antibiofilm surfaces through polydopamine-assisted immobilization of lysostaphin as an antibacterial enzyme

Antibiotic resistance and the colonization of bacteria on surfaces, often as biofilms, prolong hospitalization periods, increase mortality, and are thus major concerns for health care providers. There is an urgent need for antimicrobial and antibiofilm surface treatments that are permanent, can eradicate both biofilms and planktonic pathogens over long periods of time, and do not select for resistant strains. In this study, we have demonstrated a simple, robust, and biocompatible method that utilizes the adhesive property of polydopamine (PDA) to covalently attach the antimicrobial enzyme lysostaphin (Lst) to a variety of surfaces to generate antibacterial and antibiofilm interfaces. The immobilization of the recombinant Lst onto PDA-coated surfaces was carried out under physiological conditions, most probably through the C-terminal His6-tag fragment of the enzyme, minimizing the losses of bioagent activity. The modified surfaces were extensively characterized by X-ray photoelectron spectroscopy and peak force quantitative nanomechanical mapping (PeakForce QNM) AFM-based method, and the presence of Lst on the surfaces was further confirmed immunochemically using anti-Lst antibody. We also found that, in contrast to the physically adsorbed Lst, the covalently attached Lst does not leach from the surfaces and maintains its endopeptidase activity to degrade the staphylococcal cell wall, avoiding most intracellular bacterial resistance mechanisms. Moreover, the Lst-coated surfaces kill hospital strains of Staphylococcus aureus in less than 15 min and prevent biofilm formation. This immobilization method should be applicable also to other proteins and enzymes that are recombinantly expressed to include the His6-tag fragment.