Improved response of osteoprogenitor cells to titanium plasma-sprayed PEEK surfaces.

Orthopedic implants benefit from a surface that encourages direct bony ongrowth (contact osteogenesis). This process is initiated as osteoprogenitor cells attach to the implant surface and deposit a calcium-enriched, collagen-deficient interfacial layer known as the cement line, which provides an anchoring foundation for the subsequent production of collagenous bone matrix from differentiated osteoblasts. Despite the importance of the cement line, the conditions affecting its deposition are incompletely understood. The current study aimed to examine cement line formation from human osteoprogenitor cells (hFOB 1.19) on a titanium plasma-sprayed PEEK (termed Ti-PEEK) surface exhibiting hierarchical roughness, compared to two relatively flat implant materials, PEEK and Ti-6Al-4 V (Ti). The hierarchical roughness of Ti-PEEK surfaces created more surface area (40% increase at the microscale) for greater cellular proliferation and stimulated significantly increased calcium deposition, which was produced by osteoprogenitor cells in their undifferentiated state. The absence of increases in alkaline phosphatase confirmed that cells remained undifferentiated, and the lack of variation in collagen measurements supported the non-collagenous composition of the cement line. Impressively, after just 24 h, the calcium deposition measured on Ti-PEEK surfaces was 305% and 470% higher than on Ti and PEEK, respectively, providing evidence that Ti-PEEK surfaces may enhance contact osteogenesis by stimulating accelerated cement line formation from undifferentiated osteoprogenitor cells.

Effects of nanofeatures induced by severe shot peening (SSP) on mechanical, corrosion and cytocompatibility properties of magnesium alloy AZ31.

The application of biodegradable magnesium-based materials in the biomedical field is highly restricted by their low fatigue strength and high corrosion rate in biological environments. Herein, we treated the surface of a biocompatible magnesium alloy AZ31 by severe shot peening in order to evaluate the potential of surface grain refinement to enhance this alloy's functionality in a biological environment. The AZ31 samples were studied in terms of micro/nanostructural, mechanical, and chemical characteristics in addition to cytocompatibility properties. The evolution of surface grain structure and surface morphology were investigated using optical, scanning and transmission electron microscopy. Surface roughness, wettability, and chemical composition, as well as in depth-microhardness and residual stress distribution, fatigue behaviour and corrosion resistance were investigated. Cytocompatibility tests with osteoblasts (bone forming cells) were performed using sample extracts. The results revealed for the first time that severe shot peening can significantly enhance mechanical properties of AZ31 without causing adverse effects on the growth of surrounding osteoblasts. The corrosion behavior, on the other hand, was not improved; nevertheless, removing the rough surface layer with a high density of crystallographic lattice defects, without removing the entire nanocrystallized layer, provided a good potential for improving corrosion characteristics after severe shot peening and thus, this method should be studied for a wide range of orthopedic applications in which biodegradable magnesium is used. STATEMENT OF SIGNIFICANCE: A major challenge for most commonly used metals for bio-implants is their non-biodegradability that necessitates revision surgery for implant retrieval when used as fixation plates, screws, etc. Magnesium is reported among the most biocompatible metals that resorb over time without adverse tissue reactions and is indispensable for many biochemical processes in human body. However, fast and uncontrolled degradation of magnesium alloys in the physiological environment in addition to their inadequate mechanical properties especially under repeated loading have limited their application in the biomedical field. The present study providesdata on the effect of a relatively simple surface nanocrystallziation method with high potential to tailor the mechanical and chemical behavior of magnesium based material while maintaining its cytocompatibility.

Electrophoretic deposition of MgO nanoparticles imparts antibacterial properties to poly-L-lactic acid for orthopedic applications.

Bacterial infection of implanted biomaterials is a serious problem that increases health care costs and negatively affects a considerable fraction of orthopedic procedures. In this field, magnesium oxide nanoparticles (MgO NPs) have emerged as a promising material to combat bacterial infection while maintaining or improving bone cell functions. Here, MgO NPs were electrophoretically deposited onto poly-L-lactic acid (PLLA) sheets to achieve a coating of highly exposed MgO NPs that directly influenced cell-substrate interactions at short time scales. Samples were characterized for their surface chemistry, crystal structure, roughness, wettability, degradation characteristics, and their ability to support the growth of human fibroblasts and osteoblasts, as well as their resistance to colonization by Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa. In general, increasing the applied voltage during deposition increased the surface coverage of the coating and significantly decreased the colonization of all three bacterial strains (up to a 90% reduction). Furthermore, S. aureus cells that did attach onto substrates prepared at high voltages exhibited trademark signs of membrane damage and cell death. Importantly, MTS cell viability assays indicated that osteoblast adhesion increased with increasing deposition voltage, while fibroblast adhesion exhibited the opposite trend. Thus, although requiring more studies, this research provides the first evidence that MgO NP coatings prepared at relatively high voltages (120-150 V) may have the ability to resist bacterial colonization, promote bone cell attachment, and curb fibrous capsule formation. Therefore, it is recommended that this technology be further investigated and developed for numerous orthopedic applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3136-3147, 2017.

Shape-dependent antibacterial effects of non-cytotoxic gold nanoparticles.

Gold nanoparticles (AuNPs) of various shapes (including spheres, stars and flowers), with similar dimensions, were synthesized and evaluated for their antibacterial effects toward Staphylococcus aureus, a bacterium responsible for numerous life-threatening infections worldwide. Optical growth curve measurements and Gompertz modeling showed significant AuNP shape- and concentration-dependent decreases in bacterial growth with increases in bacterial growth lag time. To evaluate prospective use in in vivo systems, the cytotoxicity of the same AuNPs was evaluated toward human dermal fibroblasts in vitro by 3-(4,5 dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) viability assays and confocal microscopy. No indication of any mammalian cell toxicity or morphological effects was found. Additionally, it was observed that the AuNPs were readily internalized in fibroblasts after 4 days of incubation. Most importantly, the results of the present study showed that gold nanoflowers in particular possessed the most promising non-cytotoxic mammalian cell behavior with the greatest shape-dependent antibacterial activity-promising properties for their future investigation in a wide range of anti-infection applications.

Selenium nanoparticles incorporated into titania nanotubes inhibit bacterial growth and macrophage proliferation.

Since implants often fail due to infection and uncontrolled inflammatory responses, we designed an in vitro study to investigate the antibacterial and anti-inflammatory properties of titanium dioxide nanotubes (TNTs) incorporated with selenium nanoparticles (SeNPs). Selenium incorporation was achieved by the reaction of sodium selenite (Na2SeO3) with glutathione (GSH) under a vacuum in the presence of TNTs. Two types of bacteria and macrophages were cultured on the samples to determine their respective antibacterial and anti-inflammatory properties. The results showed that the TNT samples incorporating SeNPs (TNT-Se) inhibited the growth of Escherichia coli and Staphylococcus aureus compared to unmodified TNTs, albeit the SeNP concentration still needs to be optimized for maximal effect. At their maximum effect, the TNT-Se samples reduced the density of E. coli by 94.6% and of S. aureus by 89.6% compared to titanium controls. To investigate the underlying mechanism of this effect, the expression of six E. coli genes were tracked using qRT-PCR. Results indicated that SeNPs weakened E. coli membranes (ompA and ompF were down-regulated), decreased the function of adhesion-mediating proteins (csgA and csgG were progressively down-regulated with increasing SeNP content), and induced the production of damaging reactive oxygen species (ahpF was up-regulated). Moreover, TNT-Se samples inhibited the proliferation of macrophages, indicating that they can be used to control the inflammatory response and even prevent chronic inflammation, a condition that often leads to implant failure. In conclusion, we demonstrated that SeNP-TNTs display antibacterial and anti-inflammatory properties that are promising for improving the performance of titanium-based implants for numerous orthopedic and dental applications.

Adding MgO nanoparticles to hydroxyapatite-PLLA nanocomposites for improved bone tissue engineering applications.

Magnesium plays an important role in the body, mediating cell-extracellular matrix interactions and bone apatite structure and density. This study investigated, for the first time, the effects of adding magnesium oxide (MgO) nanoparticles to poly (l-lactic acid) (PLLA) and to hydroxyapatite (HA) nanoparticle-PLLA composites for orthopedic tissue engineering applications. Results showed that MgO nanoparticles significantly enhanced osteoblast adhesion and proliferation on HA-PLLA nanocomposites while maintaining mechanical properties (Young's modulus ∼1,000 MPa) suitable for cancellous bone applications. Additionally, osteoblasts (or bone-forming cells) cultured in the supernatant of degrading nanocomposites showed improved proliferation in the presence of magnesium, indicating that the increased alkalinity of solutions containing MgO nanocomposites had no toxic effects towards cells. These results together indicated the promise of further studying MgO nanoparticles as additive materials to polymers to enhance the integration of implanted biomaterials with bone.

The influence of nanostructured features on bacterial adhesion and bone cell functions on severely shot peened 316L stainless steel.

Substrate grain structure and topography play major roles in mediating cell and bacteria activities. Severe plastic deformation techniques, known as efficient metal-forming and grain refining processes, provide the treated material with novel mechanical properties and can be adopted to modify nanoscale surface characteristics, possibly affecting interactions with the biological environment. This in vitro study evaluates the capability of severe shot peening, based on severe plastic deformation, to modulate the interactions of nanocrystallized metallic biomaterials with cells and bacteria. The treated 316L stainless steel surfaces were first investigated in terms of surface topography, grain size, hardness, wettability and residual stresses. The effects of the induced surface modifications were then separately studied in terms of cell morphology, adhesion and proliferation of primary human osteoblasts (bone forming cells) as well as the adhesion of multiple bacteria strains, specifically Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, and ampicillin-resistant Escherichia coli. The results indicated a significant enhancement in surface work hardening and compressive residual stresses, maintenance of osteoblast adhesion and proliferation as well as a remarkable decrease in the adhesion and growth of gram-positive bacteria (S. aureus and S. epidermidis) compared to non-treated and conventionally shot peened samples. Impressively, the decrease in bacteria adhesion and growth was achieved without the use of antibiotics, for which bacteria can develop a resistance towards anyway. By slightly grinding the surface of severe shot peened samples to remove differences in nanoscale surface roughness, the effects of varying substrate grain size were separated from those of varying surface roughness. The expression of vinculin focal adhesions from osteoblasts was found to be singularly and inversely related to grain size, whereas the attachment of gram-positive bacteria (S. aureus and S. epidermidis) decreased with increasing nanoscale surface roughness, and was not affected by grain refinement. Ultimately, this study demonstrated the advantages of the proposed shot peening treatment to produce multifunctional 316L stainless steel materials for improved implant functions without necessitating the use of drugs.

Promoting the public's oral health: the Department of Health and Human Services, U.S. Public Health Service, and the U.S. Public Health Service Commissioned Corps.

The story of the Department of Health and Human Services (DHHS), its United States Public Health Service (US PHS), and the US PHS Commissioned Corps is comprised of people and programs aimed at protecting and promoting the nation's health, including oral health. The federal precursors of these organizations focused on clinical services for federal beneficiaries, and with time grew to include federal support for community and state programs for underserved and institutionalized populations; biomedical and behavioral research conduct: drug, device, and food regulatory activities; and, most recently, an enhanced response to biodefense and emergency readiness, among other activities. An essential component of the workforce addressing these activities is the US PHS Commissioned Corps, directed by the Surgeon General of the US PHS. This corps is a mobile, uniformed health service assigned to programs throughout the DHHS, as well as to other departments and agencies as needed. Dentistry has been a critical part of these programs and of the corps since their inception.