An investigation of the initial attachment and orientation of osteoblast-like cells on laser grooved Ti-6Al-4V surfaces

Bionic structure and biocompatibilities of long chain branched poly(L-lactic acid) oriented microcellular foaming material

In order to solve the problem of uneven microporous structure of Poly(L-lactic acid) (PLLA) bulk orientation by using biological safety multi-functional plant oil as chain extenders (CE), multi-armed flexible chains were introduced into PLLA through reactive processing to prepare long chain branched PLLA (LCB-PLLA). When the total content of the CE was 6.15 wt%, PLLA and the CE reacted most fully, while maintaining the tensile strength of PLLA and improving toughness. After introducing the LCB structure, the presence of multi-armed flexible chains increased the mobility of the molecular chains, resulting in a significantly lower degree of crystallinity. When the draw ratio up to 900 %, the crystallinity of LCB-PLLA-F-900 % was only 45.15 %, lower than that of PLLA-F-900 %. Thanks to the mobility of polymer chains can be enhanced, which reduces the degree of crystallinity while promoting the uniform growth of oriented microporous structures. Finally, an oriented micro-porous biomimetic LCB-PLLA material with an average cell diameter of 540 nm was prepared, and the results of in vitro cell culture showed that the oriented micro-porous LCB-PLLA biomimetic material was more conducive to cell proliferation.

Effect of controlled surface roughness and biomimetic coating on titanium implants adhesion to the bone: An experiment animal study

Introduction

Laser micromachining of titanium and its alloys can create micro-grooves with sizes similar to cell diameter of about 10 μm. Its coating with arginine-glycine-aspartic acid (RGD) may enhance cellular spreading and adhesion. This study aimed to evaluate the effect of laser micro-grooving and laser micro-grooving combined with RGD coating on the strength of the dental implants/bone interface using destructive mechanical pullout testing in experimental animals.

Materials and methods

In this study, the test groups consisted of 1.5-mm diameter, 5-mm long laser-grooved and laser-grooved/RGD coated titanium alloy (Ti-6Al-4 V) rods, and the control group included plain titanium alloy (Ti-6Al-4 V) rods. These rods were implanted in the mandibles of New Zealand white rabbits for 2, 4, and 6 weeks. After sacrifice, the test and control specimens were retrieved for mechanical pullout testing. The DMA 7-e was used to pull the titanium rods out of the bone, the probe position was plotted versus time graph to monitor the test progression, and the static modulus versus time graph was viewed; such graphs was then transformed into tables. The results were analyzed using the Mann-Whitney test.

Results

The laser-grooved/RGD coated rods had significantly higher pull-out strength than the laser-grooved and control rods. Additionally, the laser-grooved rods had significantly higher pull-out strength than control rods.

Conclusion

Two novel surface treatments were used: laser micro-grooving and tri peptide RGD coating, both of which had different effects on the dental implant interface. Laser grooving improved peri-implant bone healing, whereas RGD coating facilitated earlier bone-implant adhesion and better mineralization.

Tissue-Level Laser-Lok Implants Placed with a Flapless Technique: A 4-Year Clinical Study

BACKGROUND

The present study aims to analyze the use of Laser-Lok microtextured neck implants placed with a transmucosal surgical approach. The marginal bone level (MBL) and periodontal parameters were evaluated in a cohort prospective 4-year clinical study.

METHODS

A total of 41 implants were placed in 36 healthy consecutive patients (16 males, 20 females, mean age 60 ± 9 years). Tapered tissue level implants, characterized by a 2.0 mm laser-microtextured neck, were used with a flapless approach. Customized abutments and provisional resin crowns were positioned. Definitive metal-ceramic crowns were cemented approximately 4 months after insertion. Periapical radiographs were taken after 1, 3, 6, 12, 36 and 48 months from implant placement to evaluate MBL. Gingival thickness (thin/thick), plaque score (PS) and bleeding on probing (BoP) were evaluated.

RESULTS

After 48 months, all implants were safe from complications. No complications, peri-implantitis, early implant failures or mucositis occurred. The survival rate was 100%. Mean MBL during the follow-up was -0.15 ± 0.18 at T1, -0.29 ± 0.29 at T3, -0.45 ± 0.37 at T6, -0.53 ± 0.45 at T12, -1.06 ± 1.13 at T 36 and -1.10 ± 0.89 at T 48. Implants placed 2-3 months after tooth extraction revealed lower MBL variation when compared to those placed immediately (in fresh extraction sockets) or in completely healed ridges (delayed group). Narrower diameter implants (3.8 mm) showed significantly higher MBL variation when compared to 4.6 diameter implants. Multilevel analysis at T48 revealed that among all the evaluated variables, implant diameter was the factor mostly associated with MBL modifications (p = 0.027).

CONCLUSION

This 4-year clinical study supports the use of Laser-Lok implants placed at tissue level with a flapless approach. A limited bone loss during the 48-month follow-up was observed. Periodontal parameters were stable with no sign of inflammation or soft tissue alteration. The use of Laser-Lok implants with transmucosal surgery represents a suitable technique with a minimally invasive approach.

Aptamer/Hydroxyapatite-Functionalized Titanium Substrate Promotes Implant Osseointegration via Recruiting Mesenchymal Stem Cells

Endowing bone regeneration materials with both stem cell recruitment and osteoinduction properties is a key factor in promoting osseointegration of titanium (Ti) implants. In this study, Apt19s-grafted oxidized hyaluronic acid (OHA) was deposited onto a protein-mediated biomineralization hydroxyapatite (HAp) coating of Ti. HAp was achieved by the treatment of lysozyme and tris(2-carboxyethyl) phosphonate mixture and then soaked in calcium ion (Ca²⁺) solution to obtain functional Ti substrate (Ti/HAp/OHA-Apt). In vitro studies confirmed that Ti/HAp/OHA-Apt could effectively maintain the sustained release of Apt19s from Ti for 7 days. The released Apt19s significantly enhanced the migration of bone marrow mesenchymal stem cells (MSCs), which was reflected by the experiment of transwell assay, wound healing, and zymogram detection. Compared with pure Ti, Ti/HAp/OHA-Apt was able to adjust the adsorption of functional proteins at the Ti-based interface to expose their active sites, which significantly increased the expression of adhesion-associated proteins (vinculin and tensin) in MSCs to promote their adhesion on Ti-based interface. In vitro cell experiments of alkaline phosphatase activity staining, mineralization detection, and expression of osteogenesis-related genes showed that Ti/HAp/OHA-Apt significantly enhanced the osteogenic differentiation ability of MSCs, which may be highly related to the porous structure of hydroxyapatite on Ti interface. In vivo test of Micro-CT, H&E staining, and histochemical staining further confirmed that Ti/HAp/OHA-Apt was able to promote MSC recruitment at the peri-implant interface to form new bone. This work provides a new approach to develop functional Ti-based materials for bone defect repair.

3D printed zirconia dental implants with integrated directional surface pores combine mechanical strength with favorable osteoblast response

Dental implants need to combine mechanical strength with promoted osseointegration. Currently used subtractive manufacturing techniques require a multi-step process to obtain a rough surface topography that stimulates osseointegration. Advantageously, additive manufacturing (AM) enables direct implant shaping with unique geometries and surface topographies. In this study, zirconia implants with integrated lamellar surface topography were additively manufactured by nano-particle ink-jetting. The ISO-14801 fracture load of as-sintered implants (516±39 N) resisted fatigue in 5-55°C water thermo-cycling (631±134 N). Remarkably, simultaneous mechanical fatigue and hydrothermal aging at 90°C significantly increased the implant strength to 909±280 N due to compressive stress generated at the seamless transition of the 30-40 µm thick, rough and porous surface layer to the dense implant core. This unique surface structure induced an elongated osteoblast morphology with uniform cell orientation and allowed for osteoblast proliferation, long-term attachment and matrix mineralization. In conclusion, the developed AM zirconia implants not only provided high long-term mechanical resistance thanks to the dense core along with compressive stress induced at the transition zone, but also generated a favorable osteoblast response owing to the integrated directional surface pores. STATEMENT OF SIGNIFICANCE: : Zirconia ceramics are becoming the material of choice for metal-free dental implants, however significant efforts are required to obtain a rough/porous surface for enhanced osseointegration, along with the risk of surface delamination and/or microstructure variation. In this study, we addressed the challenge by additively manufacturing implants that seamlessly combine dense core with a porous surface layer. For the first time, a unique surface with a directional lamellar pore morphology was additively obtained. This AM implant also provided strength as strong as conventionally manufactured zirconia implants before and after long-term fatigue. Favorable osteoblast response was proved by in-vitro cell investigation. This work demonstrated the opportunity to AM fabricate novel ceramic implants that can simultaneously meet the mechanical and biological functionality requirements.

Study on the effect of surface characteristics of short-pulse laser patterned titanium alloy on cell proliferation and osteogenic differentiation

Concise, low-cost preparation of titanium alloy implants with high cell proliferation and osteogenic differentiation is urgently needed. Nanosecond laser ablation of titanium alloy has the advantages of short processing time, less pollution, and non-contact. In this research, we adopt a nanosecond UV laser to process the closed groove and cross groove titanium alloys with length to width ratio of 1:1, 2.5:1, 4:1, and 6:1. The surface morphology, surface roughness, phase, element distribution, surface chemistry, and wettability were characterized. The effect of the patterned surface's properties on the adhesion, proliferation, and osteogenic differentiation of stem cells was studied. The results show the laser-ablated lattice structure's surface energy can increase rapidly in the natural environment. The cell adhesion of stem cells on a lattice structure with low roughness and high surface energy is optimal. The element concentration at the ablated edges is higher than at the bottom under Marangoni and surface tension. Stem cells preferentially adhere to the ablated edges with high roughness, element concentration, and hardness. Cell differentiation is chiefly affected by patterning structure. On the surface of the boss structure with a length to width ratio of 2.5:1, the proportion of cell length to diameter is about 2.5, and the cell area is greater. The osteogenic differentiation of cells is the highest on the surface.

Multi-Scale Surface Treatments of Titanium Implants for Rapid Osseointegration: A Review

The propose of this review was to summarize the advances in multi-scale surface technology of titanium implants to accelerate the osseointegration process. The several multi-scaled methods used for improving wettability, roughness, and bioactivity of implant surfaces are reviewed. In addition, macro-scale methods (e.g., 3D printing (3DP) and laser surface texturing (LST)), micro-scale (e.g., grit-blasting, acid-etching, and Sand-blasted, Large-grit, and Acid-etching (SLA)) and nano-scale methods (e.g., plasma-spraying and anodization) are also discussed, and these surfaces are known to have favorable properties in clinical applications. Functionalized coatings with organic and non-organic loadings suggest good prospects for the future of modern biotechnology. Nevertheless, because of high cost and low clinical validation, these partial coatings have not been commercially available so far. A large number of in vitro and in vivo investigations are necessary in order to obtain in-depth exploration about the efficiency of functional implant surfaces. The prospective titanium implants should possess the optimum chemistry, bionic characteristics, and standardized modern topographies to achieve rapid osseointegration.

Friction stability and cellular behaviors on laser textured Ti-6Al-4V alloy implants with bioinspired micro-overlapping structures

The grain structure and surface morphology of bio-implants act as a pivotal part in altering cell behavior. Titanium alloy bone screws, as common implants, are prone to screws loosening and complications threat in the physiological environment due to their inferior anti-wear and surface inertia. Manufacturing bone screws with high wear resistance and ideal biocompatibility has always been a challenge. In this study, a series of overlapping morphologies inspired by the hierarchical structure of fish scales and micro bulges of shrimp were structured on Ti-6Al-4V implant by laser texturing. The results indicate that the textured patterns could improve cell attachment, proliferation, and osteogenic differentiation. The short-term response of human bone marrow-derived mesenchymal stem cells (hBMSCs) on the textured surface are more sensitive to the microstructure than the surface roughness, wettability, grain size and surface chemical elements of the textured surfaces. More importantly, the friction-increasing and friction-reducing type overlapping structures exhibit excellent friction stability at different stages of modified simulated body fluid (m-SBF) soaking. The overlapping structure (Micro-smooth stacked ring: MSSR) is more beneficial to promote the formation of apatite. Deposited spherical-like apatite particles can act as a "lubricant" on the MSSR surface during the friction process to alleviate the adhesion wear of the surface. Meanwhile, apatite particles participate in the formation of friction film, which plays an effective role in reducing friction and antiwear in corrosion solution (m-SBF) for a long time. These features show that the combination of soaking treatment in m-SBF solution with laser-textured MSSR structure is expected to be an efficient and environmentally friendly strategy to prolong the service life of bone screws and reducing the complications of mildly osteoporotic implants.

Multifunctional hydroxyapatite and hopeite coatings on SS254 by laser rapid manufacturing for improved osseointegration and antibacterial character: A comparative study

Orthopaedic metallic implant's long-term success strongly depends upon the two main factors: osseointegration and antibacterial character. Bioceramic (hydroxyapatite and hopeite) coatings have been proven effective for getting strong osseointegration and antibacterial character. However, deterioration of bioceramic coatings during the implantation period can adversely affect its overall biological performance. To conquer this issue, this research work recommends an innovative process route of laser rapid manufacturing for depositing bioceramic (hydroxyapatite and hopeite) coatings with metallurgical bonding. Microstructure, phase composition, antibacterial efficacy and bioactivity were evaluated using scanning electron microscopy, X-ray diffraction, fluorescence-activated cell sorting technique and simulated body fluid immersion test. The promising results obtained from these characterizations and testing establish the new process route laser rapid manufacturing as an effective alternative to deposit multifunctional bioceramic (hydroxyapatite and hopeite) coatings on metallic prosthetic-orthopaedic implants.

Enhanced Osseointegration of Titanium Alloy Implants with Laser Microgrooved Surfaces and Graphene Oxide Coating

Rapid and effective osseointegration, as a critical factor in affecting the success rate of titanium (Ti) implants in orthopedic applications, is significantly affected by their surface microstructure and chemical composition. In this work, surface microgrooved Ti-6Al-4V alloys with graphene oxide coating (Ti-G-GO) were fabricated by a combination of laser processing and chemical assembly techniques. The osteogenic capability in vitro and new bone formation in vivo of the implants were systematically investigated, and biomechanical pull-out tests of the screws were also performed. First, in vitro studies indicated that the optimal microgroove width of the titanium alloy surface was 45 μm (Ti-G), and the optimum GO concentration was 1 mg/mL. Furthermore, the effects of the surface microstructure and GO coating on the in vitro bioactivity were investigated through culturing bone marrow mesenchymal stem cells (BMSCs) on the surface of titanium alloy plates. The results showed that the BMSCs cultured on the Ti-G-GO group exhibited the best adhesion, proliferation, and differentiation, compared with that on the Ti-G and Ti groups. Micro-computed tomography evaluation, histological analysis, and pull-out testing demonstrated that both Ti-G and Ti-G-GO implants had the higher osseointegration than the untreated Ti implant. Moreover, the osteogenic capability of the Ti-G-GO group appeared to be superior to that of the Ti-G group, which could be attributed to the improvement of surface wettability and apatite formation by the GO coatings. These results suggest that the combination of the microgroove structure and GO coatings exhibits considerable potential for enhancing the surface bioactivation of materials, and the combination modification is expected to be used on engineered titanium alloy surfaces to enhance osseointegration for orthopedic applications.

Minireview: Laser-Induced Formation of Microbubbles-Biomedical Implications

Recent work is summarized that shows how microbubbles may have potential utility in biomedical situations as (i) highly localized generators of intense white light in an aqueous environment, (ii) disruptors of matter in aqueous solution, (iii) essential precursors in laser-writing structures on substrates on which biological cells can be spatially aligned, and (iv) mediators in the fabrication of hierarchical nanostructures that enhance signals in biological Raman spectroscopy. Indeed, microbubbles generated upon laser irradiation of surfaces have many more ramifications than originally thought, with implications in the laser modification of surfaces producing either hydrophilicity or hydrophobicity. Many more possibilities remain to be explored and exploited.

Surface Texture-Based Surface Treatments on Ti6Al4V Titanium Alloys for Tribological and Biological Applications: A Mini Review

Surface texture (ST) has been confirmed as an effective and economical surface treatment technique that can be applied to a great range of materials and presents growing interests in various engineering fields. Ti6Al4V which is the most frequently and successfully used titanium alloy has long been restricted in tribological-related operations due to the shortcomings of low surface hardness, high friction coefficient, and poor abrasive wear resistance. Ti6Al4V has benefited from surface texture-based surface treatments over the last decade. This review begins with a brief introduction, analysis approaches, and processing methods of surface texture. The specific applications of the surface texture-based surface treatments for improving surface performance of Ti6Al4V are thoroughly reviewed from the point of view of tribology and biology.

Human mesenchymal stem cell behavior on femtosecond laser-textured Ti-6Al-4V surfaces

AIM

The aim of the present work was to investigate ultrafast laser surface texturing as a surface treatment of Ti-6Al-4V alloy dental and orthopedic implants to improve osteoblastic commitment of human mesenchymal stem cells (hMSCs).

MATERIALS & METHODS

Surface texturing was carried out by direct writing with an Yb:KYW chirped-pulse regenerative amplification laser system with a central wavelength of 1030 nm and a pulse duration of 500 fs. The surface topography and chemical composition were investigated by scanning electron microscopy and x-ray photoelectron spectroscopy, respectively. Three types of surface textures with potential interest to improve implant osseointegration can be produced by this method: laser-induced periodic surface structures (LIPSSs); nanopillars (NPs); and microcolumns covered with LIPSSs, forming a bimodal roughness distribution. The potential of the laser treatment in improving hMSC differentiation was assessed by in vitro study of hMSCs spreading, adhesion, elongation and differentiation using epifluorescence microscopy at different times after cell seeding, after specific stainings and immunostainings.

RESULTS

Cell area and focal adhesion area were lower on the laser-textured surfaces than on a polished reference surface. Obviously, the laser-textured surfaces have an impact on cell shape. Osteoblastic commitment was observed independently of the surface topography after 2 weeks of cell seeding. When the cells were cultured (after 4 weeks of seeding) in osteogenic medium, LIPSS- and NP- textured surfaces enhanced matrix mineralization and bone-like nodule formation as compared with polished and microcolumn-textured surfaces.

CONCLUSION

The present work shows that surface nanotextures consisting of LIPSSs and NPs can, potentially, improve hMSC differentiation into an osteoblastic lineage.

An accelerated buoyancy adhesion assay combined with 3-D morphometric analysis for assessing osteoblast adhesion on microgrooved substrata

An accelerated negative buoyancy method has been developed to assess cell adhesion strength. This method has been used in conjunction with 3-D morphometric analysis to understand the effects of surface topology on cell response. Aligned micro-grooved surface topographies (with a range of groove depths) were produced on stainless steel 316L substrates by laser ablation. An investigation was carried out on the effect of the micro-grooved surface topography on cell adhesion strength, cell and nucleus volumes, cell phenotypic expression and attachment patterns. Increased hydrophobicity and anisotropic wettability was observed on surfaces with deeper grooves. A reduction was noted in cell volume, projected areas and adhesion sites for deeper grooves, linked to lower cell proliferation and differentiation rates and also to reduced adhesion strength. The results suggest that the centrifugation assay combined with three-dimensional cell morphometric analysis has considerable potential for obtaining improved understanding of the cell/substrate interface.

Manipulating mammalian cell by phase transformed titanium surface fabricated through ultra-short pulsed laser synthesis

Developing cell sensitive indicators on interacting substrates that allows specific cell manipulation by a combination of physical, chemical or mechanical cues is a challenge for current biomaterials. Hence, various fabrication approaches have been created on a variety of substrates to mimic or create cell specific cues. However, to achieve cell specific cues a multistep process or a post-chemical treatment is often necessitated. So, a simple approach without any chemical or biological treatment would go a long way in developing bio-functionalized substrates to effectively modulate cell adhesion and interaction. The present investigation is aimed to study the manipulative activity induced by phase transformed titanium surface. An ultra-short laser is used to fabricate the phase transformed titanium surface where a polymorphic titanium oxide phases with titanium monoxide (TiO), tri-titanium oxide (Ti3O) and titanium dioxide (TiO2) have been synthesized on commercially pure titanium. Control over oxide phase transformed area was demonstrated via a combination of laser scanning time (laser pulse interaction time) and laser pulse widths (laser pulse to pulse separation time). The interaction of phase transformed titanium surface with NIH3T3 fibroblasts and MC3T3-E1 osteoblast cells developed a new bio-functionalized platforms on titanium based biomaterials to modulate cell migration and adhesion. The synthesized phase transformed titanium surface on the whole appeared to induce directional cues for cell migration with unique preferential cell adhesion unseen by other fabrication approaches. The precise bio-functionalization controllability exhibited during fabrication offers perceptible edge for developing a variety of smart bio-medical devices, implants and cardiovascular stents where the need in supressing specific cell adhesion and proliferation is of great demand.

Effect of low-level mechanical vibration on osteogenesis and osseointegration of porous titanium implants in the repair of long bone defects

Emerging evidence substantiates the potential of porous titanium alloy (pTi) as an ideal bone-graft substitute because of its excellent biocompatibility and structural properties. However, it remains a major clinical concern for promoting high-efficiency and high-quality osseointegration of pTi, which is beneficial for securing long-term implant stability. Accumulating evidence demonstrates the capacity of low-amplitude whole-body vibration (WBV) in preventing osteopenia, whereas the effects and mechanisms of WBV on osteogenesis and osseointegration of pTi remain unclear. Our present study shows that WBV enhanced cellular attachment and proliferation, and induced well-organized cytoskeleton of primary osteoblasts in pTi. WBV upregulated osteogenesis-associated gene and protein expression in primary osteoblasts, including OCN, Runx2, Wnt3a, Lrp6 and β-catenin. In vivo findings demonstrate that 6-week and 12-week WBV stimulated osseointegration, bone ingrowth and bone formation rate of pTi in rabbit femoral bone defects via μCT, histological and histomorphometric analyses. WBV induced higher ALP, OCN, Runx2, BMP2, Wnt3a, Lrp6 and β-catenin, and lower Sost and RANKL/OPG gene expression in rabbit femora. Our findings demonstrate that WBV promotes osteogenesis and osseointegration of pTi via its anabolic effect and potential anti-catabolic activity, and imply the promising potential of WBV for enhancing the repair efficiency and quality of pTi in osseous defects.

Effect of Ceramic Scaffold Architectural Parameters on Biological Response

Numerous studies have focused on the optimization of ceramic architectures to fulfill a variety of scaffold functional requirements and improve biological response. Conventional fabrication techniques, however, do not allow for the production of geometrically controlled, reproducible structures and often fail to allow the independent variation of individual geometric parameters. Current developments in additive manufacturing technologies suggest that 3D printing will allow a more controlled and systematic exploration of scaffold architectures. This more direct translation of design into structure requires a pipeline for design-driven optimization. A theoretical framework for systematic design and evaluation of architectural parameters on biological response is presented. Four levels of architecture are considered, namely (1) surface topography, (2) pore size and geometry, (3) porous networks, and (4) macroscopic pore arrangement, including the potential for spatially varied architectures. Studies exploring the effect of various parameters within these levels are reviewed. This framework will hopefully allow uncovering of new relationships between architecture and biological response in a more systematic way as well as inform future refinement of fabrication techniques to fulfill architectural necessities with a consideration of biological implications.

Integrin-mediated osteoblastic adhesion on a porous manganese-incorporated TiO2 coating prepared by plasma electrolytic oxidation

This study was conducted to evaluate the bioactivity of manganese-incorporated TiO₂ (Mn-TiO₂) coating prepared on titanium (Ti) plate by plasma electrolytic oxidation (PEO) technique in Ca-, P- and Mn-containing electrolytes. The surface topography, phase and element compositions of the coatings were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometry (EDS), respectively. The adhesion of osteoblast-like MG63 cells onto Ti, TiO₂ and Mn-TiO₂ surfaces was evaluated, and the signal transduction pathway involved was confirmed by the sequential expression of the genes for integrins β₁, β₃, α₁ and α₃, focal adhesion kinase (FAK), and the extracellular regulated kinases (ERKs), including ERK1 and ERK2. The results obtained indicated that Mn was successfully incorporated into the porous nanostructured TiO₂ coating, and did not alter the surface topography or the phase composition of the coating. The adhesion of the MG63 cells onto the Mn-incorporated TiO₂ coating was significantly enhanced compared with that on the Mn-free TiO₂ coating and the pure Ti plates. In addition, the enhanced cell adhesion on the Mn-TiO₂ coatings may have been mediated by the binding of the integrin subunits, β₁ and α₁, and the subsequent signal transduction pathway, involving FAK and ERK2. The study indicated that the novel Mn-TiO₂ coating has potential for orthopedic implant applications, and that further investigations are required.

Water absorption of poly(methyl methacrylate) measured by vertical interference microscopy

PMMA (poly(methyl methacrylate)) is widely used to prepare orthopedic cements. They are in direct contact with cells and body fluids. PMMA, despite its hydrophobic nature, can absorb ~2% w/w water. We have evaluated by vertical interference microscopy if water absorption can produce a significant swelling in different types of PMMA blocks: pure, with a plasticizer, with a cross-linker, and in two types of commercial bone cements. Graphite rods which do not swell in water were used as internal standard. Hardness, indentation modulus, plastic, and elastic works were determined by nanoindentation under a 25mN fixed force. Vertical interference microscopy was used to image the polymer in the dry state and hydrated states (after 24 h in distilled water). On the surface of the polished polymers (before and after hydration), we measured roughness by the fractal dimension, the swelling in the vertical and the lateral directions. For each polymer block, four images were obtained and values were averaged. Comparison and standardization of the images in the dry and hydrated states were done with Matlab software. The average value measured on the graphite rod between the two images (dried and hydrated) was used for standardization of the images which were visualized in 3D. After grinding, a small retraction was noticeable between the surface of the rod and the polymers. A retraction ring was also visible around the graphite rod. After hydration, only the pure PMMA and bone cements had a significant swelling in the vertical direction. The presence of polymer beads in the cements limited the swelling in the lateral direction. Swelling parameters correlated with the nanoindentation data. PMMA can swell by absorbing a small amount of water and this induces a swelling that varies with the polymer composition and particle inclusions.

Parallel optical trap assisted nanopatterning on rough surfaces

There exist many optical lithography techniques for generating nanostructures on hard, flat surfaces over large areas. However, few techniques are able to create such patterns on soft materials or surfaces with pre-existing structure. To address this need, we demonstrate the use of parallel optical trap assisted nanopatterning (OTAN) to provide an efficient and robust direct-write method of producing nanoscale features without the need for focal plane adjustment. Parallel patterning on model surfaces of polyimide with vertical steps greater than 1.5 µm shows a feature size uncertainty better than 4% across the step and lateral positional accuracy of 25 nm. A Brownian motion model is used to describe the positional accuracy enabling one to predict how variation in system parameters will affect the nanopatterning results. These combined results suggest that OTAN is a viable technique for massively parallel direct-write nanolithography on non-traditional surfaces.

Preparation and characterization of biomimetically and electrochemically deposited hydroxyapatite coatings on micro-arc oxidized Ti-13Nb-13Zr

Surface properties and corrosion resistance analyses of Ti-13Nb-13Zr coated by an oxide film (obtained by micro-arc oxidation at 300 V) or an oxide/hydroxyapatite (HA) film are reported. HA films were biomimetically or electrochemically deposited on the alloy/oxide surface, and their properties compared. Both the biomimetic and the electrochemical method yielded rough and globular apatite surfaces (10-20 μm globules for the former and 1-2 μm for the latter). As inferred from XRD data, the electrochemical method yielded more biologic-like HA films, while the biomimetic method yielded films containing a mixture of calcium phosphate phases. Coated Ti-13Nb-13Zr samples were immersed in an aerated PBS solution and continuously analyzed during 49 days. Considering that, after immersion, the biomimetically deposited films presented smaller variations in thickness and morphology and higher electric resistance (determined by electrochemical impedance spectroscopy), they clearly provide significantly better protection to the Ti-13Nb-13Zr alloy when in PBS solution.

Surface characteristics and in vitro biocompatibility of titanium anodized in a phosphoric acid solution at different voltages

The surface of commercially pure titanium was modified by anodization treatment in a phosphoric acid solution at different voltages: 100 V, 200 V and 300 V. The surface characteristics of anodic TiO2 layers and their influence on the cell response were investigated. Micrographs by scanning electron microscopy revealed that the dense and uniform oxide layer obtained at 100 V exhibits a nanostructured surface which is similar to the surface of natural tooth cementum. In contrast, porous oxide layers without nanometer features were produced at higher voltages. Thin film x-ray diffraction analysis confirmed the existence of anatase in the oxide layer obtained at 300 V, but not in oxide layers obtained at 100 V and 200 V. The in vitro biocompatibility study of oxide layers demonstrated greater cell adhesion and proliferation of the oxide layer obtained at 100 V compared to the other two kinds of oxide layers.