Corrosion and biological behavior of nanostructured 316L stainless steel processed by severe plastic deformation

Nanostructured metals have different mechanical, chemical, and physical behaviors in comparison with the microstructured ones. Numerous research studies demonstrated that the biological behavior of nanostructured metallic implants was improved significantly. Concerning the nanostructured metals, decreasing the corrosion rate and the releasing of hazardous ions from metallic implants, and thus increasing the biocompatibility of implants are due to improving the native oxide layer. In the present study, nanostructured 316L stainless steel (biomedical grade) was manufactured via equal channel angular pressing (ECAP) method. To do so, the 316L stainless steel (SS) was exposed to the ECAP operation for eight passes. The impact of the ECAP process on corrosion behavior of SS samples was evaluated through performing the electrochemical polarization corrosion tests in Ringer's solution. Scanning electron microscopy was employed to study the surface morphology of common SS and ECAPed SS sample after the electrochemical polarization tests. Moreover, the biological behavior of the samples was evaluated via cell culture using fibroblast cells. The corrosion test results revealed a substantial decrease of corrosion rate from 3.12 (coarse‐grained sample) to 0.42 μA cm^?2 (for nanostructured). Furthermore, the cell proliferation in the interface of nanostructured sample and cell culture medium enhanced dramatically compared with the coarse‐grained one. The much better biological behavior of nanostructured SS sample in comparison with the coarse‐grained one is mostly due to the significant decrease of corrosion rate on the surface of SS samples, and the presence of much more chrome oxide on the surface of SS sample. Copyright © 2015 John Wiley & Sons, Ltd.     

Hierarchical Functionalized Polymeric‐Ceramic Coatings on Mg‐Ca Alloys for Biodegradable Implant Applications

Magnesium‐based implants present several advantages for clinical applications, in particular due to their biocompatibility and degradability. However, degradation products can affect negatively the cell activity. In this work, a combined coating strategy to control the implant degradation and cell regulation processes is evaluated, including plasma electrolytic oxidation (PEO) that produces a 13 µm‐thick Ca, P, and Si containing ceramic coating with surface porosity, and breath figures (BF) approach that produces a porous polymeric poly(ε‐caprolactone) surface. The degradation of PCL‐PEO‐coated Mg hierarchical scaffold can be tailored to promote cell adhesion and proliferation into the porous structure. As a result, cell culture can colonize the inner PEO‐ceramic coating structure where higher amount of bioelements are present. The Mg/PEO/PCL/BF scaffolds exhibit equally good or better premyoblast cell adhesion and proliferation compared with Ti CP control. The biological behavior of this new hierarchical functionalized scaffold can improve the implantation success in bone and cardiovascular clinical applications.     

Self‐Organization of Honeycomb‐like Porous TiO2 Films by means of the Breath‐Figure Method for Surface Modification of Titanium Implants

This study describes a facile breath‐figure method for the preparation of honeycomb‐like porous TiO₂ films with an organometallic small‐molecule precursor. Multiple characterization techniques have been used to investigate the porous films and a mechanism for the formation process of porous TiO₂ films through the breath‐figure method is proposed. The pore size of the TiO₂ films could be modulated by varying the experimental parameters, such as the concentration of titanium n‐butoxide (TBT) solution, the content of cosolvent, and the air flow rate. In vitro cell‐culture experiments indicate that NIH 3T3 fibroblast cells seeded on the honeycomb‐like porous TiO₂ films show good adhesion, spreading, and proliferation behaviors, which suggests that honeycomb‐like porous TiO₂ films are an attractive biomaterial for surface modification of titanium and its alloys implants in tissue engineering to enhance their biocompatibility and bioactivity.     

On the Future Design of Bio‐Inspired Polyetheretherketone Dental Implants

Polyetheretherketone (PEEK) is a promising implant material because of its excellent mechanical characteristics. Although this polymer is a standard material in spinal applications, PEEK is not in use in the manufacturing of dental implants, where titanium is still the most‐used material. This may be caused by its relative bio‐inertness. By the use of various surface modification techniques, efforts have been made to enhance its osseointegrative characteristics to enable the polymer to be used in dentistry. In this feature paper, the state‐of‐the‐art for dental implants is given and different surface modification techniques of PEEK are discussed. The focus will lie on a covalently attached surface layer mimicking natural bone. The usage of such covalently anchored biomimetic composite materials combines many advantageous properties: A biocompatible organic matrix and a mineral component provide the cells with a surrounding close to natural bone. Bone‐related cells may not recognize the implant as a foreign body and therefore, may heal and integrate faster and more firmly. Because neither metal‐based nor ceramics are ideal material candidates for a dental implant, the combination of PEEK and a covalently anchored mineralized biopolymer layer may be the start of the desired evolution in dental surgery.     

Dual Ag/ZnO‐Decorated Micro‐/Nanoporous Sulfonated Polyetheretherketone with Superior Antibacterial Capability and Biocompatibility via Layer‐by‐Layer Self‐Assembly Strategy

Polyetheretherketone is attractive for dental and orthopedic applications due to its mechanical attributes close to that of human bone; however, the lack of antibacterial capability and bioactivity of polyetheretherketone has substantially impeded its clinical applications. Here, a dual therapy implant coating is developed on the 3D micro‐/nanoporous sulfonated polyetheretherketone via layer‐by‐layer self‐assembly of Ag ions and Zn ions. Material characterization studies have indicated that nanoparticles consisting of elemental Ag and ZnO are uniformly incorporated on the porous sulfonated polyetheretherketone surface. The antibacterial assays demonstrate that Ag‐decorated sulfonated polyetheretherketone and Ag/ZnO‐codecorated sulfonated polyetheretherketone effectively inhibit the reproduction of Gram‐negative and Gram‐positive bacteria. Owing to the coordination of micro‐/nanoscale topological cues and Zn induction, the Ag/ZnO‐codecorated sulfonated polyetheretherketone substrates are found to enhance biocompatibility (cell viability, spreading, and proliferation), and hasten osteodifferentiation and ‐maturation (alkaline phosphate activity (ALP) production, and osteogenesis‐related genetic expression), compared with the Ag‐decorated sulfonated polyetheretherketone and the ZnO‐decorated sulfonated polyetheretherketone counterparts. The dual therapy Ag/ZnO‐codecorated sulfonated polyetheretherketone has an appealing bacteriostatic performance and osteogenic differentiation potential, showing great potential for dental and orthopedic implants.     

A “Cell‐Friendly” Window for the Interaction of Cells with Hyaluronic Acid/Poly‐l‐Lysine Multilayers

Polyelectrolyte multilayers assembled from hyaluronic acid (HA) and poly‐l ‐lysine (PLL) are most widely studied showing excellent reservoir characteristics to host molecules of diverse nature; however, thick (HA/PLL)_n films are often found cell repellent. By a systematic study of the adhesion and proliferation of various cells as a function of bilayer number “n” a correlation with the mechanical and chemical properties of films is developed. The following cell lines have been studied: mouse 3T3 and L929 fibroblasts, human foreskin primary fibroblasts VH‐Fib, human embryonic kidney HEK‐293, human bone cell line U‐2‐OS, Chinese hamster ovary CHO‐K and mouse embryonic stem cells. All cells adhere and spread well in a narrow “cell‐friendly” window identify in the range of n = 12–15. At n < 12, the film is inhomogeneous and at n > 15, the film is cell repellent for all cell lines. Cellular adhesion correlates with the mechanical properties of the films showing that softer films at higher “n” number exhibiting a significant decrease of the Young's modulus below 100 kPa are weakly adherent to cells. This trend cannot be reversed even by coating a strong cell‐adhesive protein fibronectin onto the film. This indicates that mechanical cues plays a major role for cell behavior, also in respect to biochemical ones.     

Micro‐Nanostructures of Cellulose‐Collagen for Critical Sized Bone Defect Healing

Bone tissue engineering strategies utilize biodegradable polymeric matrices alone or in combination with cells and factors to provide mechanical support to bone, while promoting cell proliferation, differentiation, and tissue ingrowth. The performance of mechanically competent, micro‐nanostructured polymeric matrices, in combination with bone marrow stromal cells (BMSCs), is evaluated in a critical sized bone defect. Cellulose acetate (CA) is used to fabricate a porous microstructured matrix. Type I collagen is then allowed to self‐assemble on these microstructures to create a natural polymer‐based, micro‐nanostructured matrix (CAc). Poly (lactic‐co‐glycolic acid) matrices with identical microstructures serve as controls. Significantly higher number of implanted host cells are distributed in the natural polymer based micro‐nanostructures with greater bone density and more uniform cell distribution. Additionally, a twofold increase in collagen content is observed with natural polymer based scaffolds. This study establishes the benefits of natural polymer derived micro‐nanostructures in combination with donor derived BMSCs to repair and regenerate critical sized bone defects. Natural polymer based materials with mechanically competent micro‐nanostructures may serve as an alternative material platform for bone regeneration.     

Fabrication and In vitro Bioactivity of Robust Hydroxyapatite Coating on Porous Titanium Implant

Compared witli the traditional dental implant, TixOs■ manufactured by direct laser metal forming(DLMF) technology exhibits improved capability for bone osteointegration due to its porous surface structure, and has achieved remarkable clinical effect. However, like the traditional titanium and other alloyed implants, the porous titanium implant TixOsR also has relatively weak bioactivity. To address this issue, a proper surface modification method may be needed. Hydroxyapatite(HA) has been widely used in implant surface coating for its similar chemical composition to bone tissue and its osteoconductive properties. Thus, combining TixOs■ implants with hydroxyapatite can be an efficient way to enhance their bioactivity. We herewith reported a competent pulsed laser deposition(PLD) method of coating nano-sized HA thin film onto the porous TixOs■ implant. The HA coatings were characterized by means of scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDS), X-ray photoelectron spectroscopy(XPS) and focused ion beam(FIB) method, and nanocrystal sized thin HA films were identified on the surface of TixOs■ implants. The low cytotoxicity and improved cell proliferation ability of HA coated implants were further tested and verified using MC 3T3 E1 cells with the consideration of the controlling group. Our results show that a stable and bioactive HA tliin film is able to form on the surtace of the porous titanium implant by PLD method.This may benefit the fiirther clinical application of TixOs■ implants.     

Mass‐producible Nano‐featured Polystyrene Surfaces for Regulating the Differentiation of Human Adipose‐derived Stem Cells

In this study, we report an efficient and cost‐effective method of fabricating polystyrene (PS) nano‐featured substrates containing nanopore (NPo) and nanopillar (NPi) arrays based on hot embossing using nickel nano‐stamps. We investigate the behavior of adipose‐derived stem cells (ASCs), including adhesion, morphology, proliferation and differentiation, on the replicated PS surfaces. Compared to a flat substrate, NPo‐ and NPi‐featured substrates do not alter the morphology of stem cells. However, both NPo‐ and NPi‐featured substrates induce different integrin expression and lower formation of focal adhesion complexes. In addition, ASCs on the NPo‐featured substrate exhibit greater adipogenic differentiation, while the NPi‐featured substrate induces higher osteogenic differentiation.

     

Multifunctional Coating Improves Cell Adhesion on Titanium by using Cooperatively Acting Peptides

Promotion of cell adhesion on biomaterials is crucial for the long‐term success of a titanium implant. Herein a novel concept is highlighted combining very stable and affine titanium surface adhesive properties with specific cell binding moieties in one molecule. A peptide containing l ‐3,4‐dihydroxyphenylalanine was synthesized and affinity to titanium was investigated. Modification with a cyclic RGD peptide and a heparin binding peptide (HBP) was realized by an efficient on‐resin combination of Diels–Alder reaction with inverse electron demand and Cu^I catalyzed azide–alkyne cycloaddition. The peptide was fluorescently labeled by thiol Michael addition. Conjugating the cyclic RGD and HBP in one peptide gave improved spreading, proliferation, viability, and the formation of well‐developed actin cytoskeleton and focal contacts of osteoblast‐like cells.     

造孔剂对电泳沉积制备多孔HA涂层及其生物活性的影响

采用水热法制得的羟基磷灰石(HA)纳米粉体,分别与造孔剂葡萄糖(Glu)、壳聚糖(CS)、炭粉(C)3种微粒(＜38.5 μm)配置成质量比1∶1的悬浮液,电泳沉积 烧结制备钛基多孔HA涂层,并对制得的3种多孔HA涂层在模拟体液浸泡前后的表面形貌、化学组成及物相变化进行表征。 结果表明,经700 ℃烧结处理后制得的3种多孔HA涂层在1.5倍人体模拟体液中浸泡5 d后,多孔HA涂层表面均被层状生长的碳磷灰石颗粒完全覆盖,颗粒直径在5~25 μm,说明这些多孔HA涂层均具有良好的生物活性。 其中以CS为造孔剂制得的多孔HA涂层结合强度最高,达19.5 MPa,有望开发成为新型的人骨植入生物陶瓷材料。     

Hemocompatible and Bioactive Heparin‐Loaded PCL‐α‐TCP Fibrous Membranes for Bone Tissue Engineering

The combination of bioactive components such as calcium phosphates and fibrous structures are encouraging niche‐mimetic keys for restoring bone defects. However, the importance of hemocompatibility of the membranes is widely ignored. Heparin‐loaded nanocomposite poly(ε‐caprolactone) (PCL)‐α‐tricalcium phosphate (α‐TCP) fibrous membranes are developed to provide bioactive and hemocompatible constructs for bone tissue engineering. Nanocomposite membranes are optimized based on bioactivity, mechanical properties, and cell interaction. Consequently, various concentrations of heparin molecules are loaded within nanocomposite fibrous membranes. In vitro heparin release profiles reveal a sustained release of heparin over the period of 14 days without an initial burst. Moreover, heparin encapsulation enhances mesenchymal stem cell (MSC) attachment and proliferation, depending on the heparin content. It is concluded that the incorporation of heparin within TCP–PCL fibrous membranes provides the most effective cellular interactions through synergistic physical and chemical cues.     

STOCK: Structure mapper and online coarse‐graining kit for molecular simulations

We present a web toolkit STructure mapper and Online Coarse‐graining Kit for setting up coarse‐grained molecular simulations. The kit consists of two tools: structure mapping and Boltzmann inversion tools. The aim of the first tool is to define a molecular mapping from high, for example, all‐atom, to low, that is, coarse‐grained, resolution. Using a graphical user interface it generates input files, which are compatible with standard coarse‐graining packages, for example, Versatile Object‐oriented Toolkit for Coarse‐graining Applications and DL_CGMAP. Our second tool generates effective potentials for coarse‐grained simulations preserving the structural properties, for example, radial distribution functions, of the underlying higher resolution model. The required distribution functions can be provided by any simulation package. Simulations are performed on a local machine and only the distributions are uploaded to the server. The applicability of the toolkit is validated by mapping atomistic pentane and polyalanine molecules to a coarse‐grained representation. Effective potentials are derived for systems of TIP3P (transferable intermolecular potential 3 point) water molecules and salt solution. The presented coarse‐graining web toolkit is available at http://stock.cmm.ki.si . © 2014 Wiley Periodicals, Inc.     

Potential‐Responsive Surfaces for Manipulation of Cell Adhesion,Release, and Differentiation

In living systems, interfacial molecular interactions control many biological processes. New stimuli‐responsive strategies are desired to provide versatile model systems that can regulate cell behavior in vitro. Described here are potential‐responsive surfaces that control cell adhesion and release as well as stem cell differentiation. Cell adhesion can be modulated dynamically by applying negative and positive potentials to surfaces functionalized with tailored monolayers. This process alters cell morphology and ultimately controls behavior and the fate of the cells. Cells can be detached from the electrode surface as intact clusters with different geometries using electrochemical potentials. Importantly, morphological changes during adhesion guide stem cell differentiation. The higher accessibility of the peptide under a positive applied potential causes phenotypic changes in the cells that are hallmarks of osteogenesis, whereas lower accessibility of the peptide promoted by negative potentials leads to adipogenesis.     

Bioactivity and mechanical properties of nickel‐incorporated hydrogenated carbon nanocomposite thin films

In this paper, the influence of nickel incorporation on the mechanical properties and the in vitro bioactivity of hydrogenated carbon thin films were investigated in detail. Amorphous hydrogenated carbon (a‐C:H) and nickel‐incorporated hydrogenated carbon (Ni/a‐C:H) thin films were deposited onto the Si substrates by using reactive biased target ion beam deposition technique. The films' chemical composition, surface roughness, microstructure and mechanical properties were investigated by using XPS, AFM, TEM, nanoindentation and nanoscratch test, respectively. XPS results have shown that the film surface is mainly composed of nickel, nickel oxide and nickel hydroxide, whereas at the core is nickel carbide (Ni₃C) only. The presence of Ni₃C has increased the sp² carbon content and as a result, the mechanical hardness of the film was decreased. However, Ni/a‐C:H films shows very low friction coefficient with higher scratch‐resistance behavior than that of pure a‐C:H film. In addition, in vitro bioactivity study has confirmed that it is possible to grow dense bone‐like apatite layer on Ni/a‐C:H films. Thus, the results have indicated the suitability of the films for bone‐related implant coating applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Coarse‐grained A‐graft‐B model of poly(lactic acid) for molecular dynamics simulations

A mesoscopic model of poly(lactic acid) is developed where the polymer is represented as an A‐graft‐B chain with monomer units consisting of two covalently connected beads. A coarse‐graining algorithm is proposed to convert an atomistic model of PLA into a coarse‐grained one. The developed model is based on atomistic simulations of oligolactides to take into account terminal groups correctly. It was used for coarse‐grained simulations of polylactide. Gyration radii and end to end distances of polymer chains as well as the density of the polymer melt are shown to be in a good agreement with those obtained from atomistic simulations. The thermal expansion coefficients of the OLA melts calculated using the coarse‐grained model are in reasonable agreement with those obtained from all‐atom molecular dynamics. The model provides a 17‐fold speedup compared with atomistic calculations. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 604–612     

Synthetic,Chemically Defined Polymer‐Coated Microcarriers for the Expansion of Human Mesenchymal Stem Cells

Mesenchymal stem cells (MSC), also called marrow stromal cells, are adult cells that have attracted interest for their potential uses in therapeutic applications. There is a pressing need for scalable culture systems due to the large number of cells needed for clinical treatments. Here, a tailorable thin polymer coating—poly(poly(ethylene glycol) methyl ether methacrylate‐ran‐vinyl dimethyl azlactone‐ran‐glycidyl methacrylate) [P(PEGMEMA‐r‐VDM‐r‐GMA); PVG]—to the surface of commercially available polystyrene and glass microcarriers to create chemically defined surfaces for large‐scale cell expansion is applied. These chemically defined microcarriers create a reproducible surface that does not rely on the adsorption of xenogenic serum proteins to mediate cell adhesion. Specifically, this coating method anchors PVG copolymer through ring opening nucleophilic attack by amine residues on poly‐l ‐lysine that is pre‐adsorbed to the surface of microcarriers. Importantly, this anchoring reaction preserves the monomer VDM reactivity for subsequent functionalization with an integrin‐specific Arg‐Gly‐Asp peptide to enable cell adhesion and expansion via a one‐step reaction in aqueous media. MSCs cultured on PVG‐coated microcarriers achieve sixfold expansion—similar to the expansion achieved on PS microcarriers—and retain their ability to differentiate after harvesting.     

Probing the Adhesion of Hepatocellular Carcinoma HepG2 and SK‐Hep‐1 Cells

Carcinoma cell differentiation stage is an important indicator of cell behavior. For example, cell mobility is much higher for poorly‐differentiated hepatocellular carcinoma SK‐Hep‐1 cells than for well‐differentiated HepG2 cells. In this study, we have cultured HepG2 and SK‐Hep‐1 cells on chemically patterned polydimethylsiloxane (PDMS) substrates to observe differences in the adhesion properties and cell structure that occur due to the patterns. Both cell lines showed a preference for the hydrophobic regions on the patterned PDMS surface with SK‐Hep‐1 cells achieving a higher density than HepG2 for the same cell‐count solutions. Further, SK‐Hep‐1 cells adopted the square or hexagonal shape of the surface patterns while HepG2 cells maintained their more rounded shape. AFM force measurement arrays were also performed on the cell surfaces to measure and map adhesion values between the tip and cell surface membrane. These results demonstrate that, in addition to cell shape and size, adhesion expression in hepatocellular carcinoma cells is differentiation stage dependent. Further, the ability of the SK‐Hep‐1 cells to adopt the shape of the substrate pattern indicates they are more structurally labile, which may contribute to their higher mobility.     

Spatially controlled cell adhesion via micropatterned surface modification of poly(dimethylsiloxane)

Spatial control of cell growth on surfaces can be achieved by the selective deposition of molecules that influence cell adhesion. The fabrication of such substrates often relies upon photolithography and requires complex surface chemistry to anchor adhesive and inhibitory molecules. The production of simple, cost-effective substrates for cell patterning would benefit numerous areas of bioanalytical research including tissue engineering and biosensor development. Poly(dimethylsiloxane) (PDMS) is routinely used as a biomedical implant material and as a substrate for microfluidic device fabrication; however, the low surface energy and hydrophobic nature of PDMS inhibits its bioactivity. We present a method for the surface modification of PDMS to promote localized cell adhesion and proliferation. Thin metal films are deposited onto PDMS through a physical mask in the presence of a gaseous plasma. This treatment generates topographical and chemical modifications of the polymer surface. Removal of the deposited metal exposes roughened PDMS regions enriched with hydrophilic oxygen-containing species. The morphology and chemical composition of the patterned substrates were assessed by optical and atomic force microscopies as well as X-ray photoelectron spectroscopy. We observed a direct correlation between the surface modification of PDMS and the micropatterned adhesion of fibroblast cells. This simple protocol generates inexpensive, single-component substrates capable of directing cell attachment and growth.     

Micro‐arc oxidation and electrophoretic deposition of nano‐grain merwinite (Ca3MgSi2O8) surface coating on magnesium alloy as biodegradable metallic implant

Magnesium alloys are promising biomaterials as biodegradable implant for orthopedic applications. However, their low corrosion resistance and poor bioactivity have prohibited their implant applications. In order to enhance these two properties, a nano‐grain merwinite coating was prepared on magnesium alloy. Its corrosion and the bioactivity behavior were characterized with electrochemical and immersion tests. The results showed that the nano‐grain merwinite coating can improve both the corrosion resistance and the bioactivity of the magnesium alloy making it an appropriate material for biodegradable bone implants. Copyright © 2014 John Wiley & Sons, Ltd.