Publications by authors named "Jonathan Campbell Knowles"

19 Publications

  • Page 1 of 1

A Study on Myogenesis by Regulation of Reactive Oxygen Species and Cytotoxic Activity by Selenium Nanoparticles.

Antioxidants (Basel) 2021 Oct 29;10(11). Epub 2021 Oct 29.

Institute of Tissue Regeneration Engineering (ITREN), Dankook University, 119 Dandae-ro, Cheonan 31116, Chungcheongnam-do, Korea.

Reactive oxygen species (ROS) are continuously produced by skeletal muscle during contractile activity and even at rest. However, the ROS generated from excessive exercise or traumatic damage may produce more ROS than can be neutralized by an antioxidant capacity, which can be harmful to muscle function. In particular, selenium is a known antioxidant that regulates physiological functions such as cell differentiation and anti-inflammatory function. In this study, we developed nano-sized antioxidative biomaterials using selenium to investigate the protective and differentiation effects against C2C12 myoblasts in an HO-induced oxidative stress environment. The selenium nanoparticles (SeNPs) were produced with a size of 35.6 ± 4.3 nm and showed antioxidant effects according to the 3,3',5,5'-tetramethylbenzidine assay. Then, SeNPs were treated to C2C12 cells with or without HO. Our results showed that SeNPs reduced C2C12 apoptosis and intracellular ROS levels. Additionally, SeNPs effectively up-regulated in the presence of HO, , , , and myosin heavy chain, which are well known to increase during myoblast differentiation as assayed by qRT-PCR, immunocytochemistry-staining, western blotting. These results demonstrate that SeNPs can accelerate differentiation with its protective effects from the ROS environment and can be applied to the treatment of skeletal muscle in a cellular redox environment.
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http://dx.doi.org/10.3390/antiox10111727DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8615179PMC
October 2021

Selenium Nanoparticles as Candidates for Antibacterial Substitutes and Supplements against Multidrug-Resistant Bacteria.

Biomolecules 2021 07 14;11(7). Epub 2021 Jul 14.

Institute of Tissue Regeneration Engineering (ITREN), Dankook University, Cheonan 31116, Korea.

In recent years, multidrug-resistant (MDR) bacteria have increased rapidly, representing a major threat to human health. This problem has created an urgent need to identify alternatives for the treatment of MDR bacteria. The aim of this study was to identify the antibacterial activity of selenium nanoparticles (SeNPs) and selenium nanowires (SeNWs) against MDR bacteria and assess the potential synergistic effects when combined with a conventional antibiotic (linezolid). SeNPs and SeNWs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential, and UV-visible analysis. The antibacterial effects of SeNPs and SeNWs were confirmed by the macro-dilution minimum inhibitory concentration (MIC) test. SeNPs showed MIC values against methicillin-sensitive (MSSA), methicillin-resistant (MRSA), vancomycin-resistant (VRSA), and vancomycin-resistant enterococci (VRE) at concentrations of 20, 80, 320, and >320 μg/mL, respectively. On the other hand, SeNWs showed a MIC value of >320 μg/mL against all tested bacteria. Therefore, MSSA, MRSA, and VRSA were selected for the bacteria to be tested, and SeNPs were selected as the antimicrobial agent for the following experiments. In the time-kill assay, SeNPs at a concentration of 4X MIC (80 and 320 μg/mL) showed bactericidal effects against MSSA and MRSA, respectively. At a concentration of 2X MIC (40 and 160 μg/mL), SeNPs showed bacteriostatic effects against MSSA and bactericidal effects against MRSA, respectively. In the synergy test, SeNPs showed a synergistic effect with linezolid (LZD) through protein degradation against MSSA and MRSA. In conclusion, these results suggest that SeNPs can be candidates for antibacterial substitutes and supplements against MDR bacteria for topical use, such as dressings. However, for use in clinical situations, additional experiments such as toxicity and synergistic mechanism tests of SeNPs are needed.
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http://dx.doi.org/10.3390/biom11071028DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8301847PMC
July 2021

Biological Potential of Polyethylene Glycol (PEG)-Functionalized Graphene Quantum Dots in In Vitro Neural Stem/Progenitor Cells.

Nanomaterials (Basel) 2021 May 29;11(6). Epub 2021 May 29.

Institute of Tissue Regeneration Engineering (ITREN), Dankook University, 119 Dandae-ro, Cheonan 31116, Korea.

Stem cell therapy is one of the novel and prospective fields. The ability of stem cells to differentiate into different lineages makes them attractive candidates for several therapies. It is essential to understand the cell fate, distribution, and function of transplanted cells in the local microenvironment before their applications. Therefore, it is necessary to develop an accurate and reliable labeling method of stem cells for imaging techniques to track their translocation after transplantation. The graphitic quantum dots (GQDs) are selected among various stem cell labeling and tracking strategies which have high photoluminescence ability, photostability, relatively low cytotoxicity, tunable surface functional groups, and delivering capacity. Since GQDs interact easily with the cell and interfere with cell behavior through surface functional groups, an appropriate surface modification needs to be considered to get close to the ideal labeling nanoprobes. In this study, polyethylene glycol (PEG) is used to improve biocompatibility while simultaneously maintaining the photoluminescent potentials of GQDs. The biochemically inert PEG successfully covered the surface of GQDs. The PEG-GQDs composites show adequate bioimaging capabilities when internalized into neural stem/progenitor cells (NSPCs). Furthermore, the bio-inertness of the PEG-GQDs is confirmed. Herein, we introduce the PEG-GQDs as a valuable tool for stem cell labeling and tracking for biomedical therapies in the field of neural regeneration.
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http://dx.doi.org/10.3390/nano11061446DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8226482PMC
May 2021

The Effect of Selenium Nanoparticles on the Osteogenic Differentiation of MC3T3-E1 Cells.

Nanomaterials (Basel) 2021 Feb 23;11(2). Epub 2021 Feb 23.

Institute of Tissue Regeneration Engineering (ITREN), Dankook University, 119 Dandae-ro, Cheonan, Chungcheongnam-do 31116, Korea.

Reactive oxygen species (ROS) regulate various functions of cells, including cell death, viability, and differentiation, and nanoparticles influence ROS depending on their size and shape. Selenium is known to regulate various physiological functions, such as cell differentiations and anti-inflammatory functions, and plays an important role in the regulation of ROS as an antioxidant. This study aims to investigate the effect of selenium nanoparticles (SeNPs) on the differentiation of osteogenic MC3T3-E1 cells. After fabrication of SeNPs with a size of 25.3 ± 2.6 nm, and confirmation of its oxidase-like activity, SeNPs were added to MC3T3-E1 cells with or without HO: 5~20 μg/mL SeNPs recovered cells damaged by 200 μM HO via the intracellular ROS downregulating role of SeNPs, revealed by the ROS staining assay. The increase in osteogenic maturation with SeNPs was gradually investigated by expression of osteogenic genes at 3 and 7 days, Alkaline phosphatase activity staining at 14 days, and Alizarin red S staining at 28 days. Therefore, the role of SeNPs in regulating ROS and their therapeutic effects on the differentiation of MC3T3-E1 cells were determined, leading to possible applications for bone treatment.
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http://dx.doi.org/10.3390/nano11020557DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7926403PMC
February 2021

Grapefruit Seed Extract as a Natural Derived Antibacterial Substance against Multidrug-Resistant Bacteria.

Antibiotics (Basel) 2021 Jan 18;10(1). Epub 2021 Jan 18.

Institute of Tissue Regeneration Engineering (ITREN), Dankook University, Cheonan, Chungcheongnam-do 31116, Korea.

Multidrug-resistant (MDR) bacteria are increasing due to the abuse and misuse of antibiotics, and nosocomial infections by MDR bacteria are also increasing. The aim of this study was to identify new substances that can target MDR bacteria among 12 plant extracts that are known to have antibacterial effects. The experiments were performed by the disk diffusion test and microdilution minimum inhibitory concentration (MIC) test, as described by the Clinical and Laboratory Standards Institute (CLSI). By screening against methicillin-sensitive (MSSA), grapefruit seed extract (GSE) was selected from 12 plant extracts for subsequent experiments. GSE showed antibacterial effects against methicillin-resistant (MRSA) and vancomycin-resistant (VRSA) in the disk diffusion test. Even at the lowest concentration, GSE showed antibacterial activity in the microdilution MIC test. As a result, we can conclude that GSE is a naturally derived antibacterial substance that exhibits a favorable antibacterial effect even at a very low concentration, so it is a good candidate for a natural substance that can be used to prevent or reduce nosocomial infections as coating for materials used in medical contexts or by mixing a small amount with other materials.
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http://dx.doi.org/10.3390/antibiotics10010085DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7830962PMC
January 2021

Physical Properties and Biofunctionalities of Bioactive Root Canal Sealers In Vitro.

Nanomaterials (Basel) 2020 Sep 4;10(9). Epub 2020 Sep 4.

Institute of Tissue Regeneration Engineering (ITREN), Dankook University, 119 Dandae-ro, Cheonan 31116, Korea.

Calcium silicate-based bioactive glass has received significant attention for use in various biomedical applications due to its excellent bioactivity and biocompatibility. However, the bioactivity of calcium silicate nanoparticle-incorporated bioactive dental sealer is not much explored. Herein, three commercially available bioactive root canal sealers (Endoseal MTA (EDS), Well-Root ST (WST), and Nishika Canal Sealer BG (NBG)) were compared with a resin-based control sealer (AH Plus (AHP)) in terms of physical, chemical, and biological properties. EDS and NBG showed 200 to 400 nm and 100 to 200 nm nanoparticle incorporation in the SEM image, respectively, and WST and NBG showed mineral deposition in Hank's balanced salt solution after 28 days. The flowability and film thickness of all products met the ISO 3107 standard. Water contact angle, linear dimensional changes, and calcium and silicate ion release were significantly different among groups. All bioactive root canal sealers released calcium ions, while NBG released ~10 times more silicon ions than the other bioactive root canal sealers. Under the cytocompatible extraction range, NBG showed prominent cytocompatibility, osteogenecity, and angiogenecity compared to other sealers in vitro. These results indicate that calcium silicate nanoparticle incorporation in dental sealers could be a potential strategy for dental periapical tissue regeneration.
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http://dx.doi.org/10.3390/nano10091750DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7559325PMC
September 2020

Digital Image Correlation and Strain Gauges to Map and Compare Strain in Teeth with Different Quantity and Quality of Remaining Tooth Structure.

Int J Prosthodont 2019 Jan/Feb;32(1):82-90

Purpose: To evaluate strain in teeth with differing quality and quantity of tooth surface loss by utilizing surface displacement field measured using digital image correlation (DIC) and strain gauges (SG).

Materials And Methods: A total of 80 mesio-occlusodistal preparations were carried out in human maxillary premolars. Ten sound premolars served as a control group, and treated samples were divided into two groups of 40 each according to the composition of the prepared walls (composed of either enamel and dentin [E + De] or dentin only [De]). Each group was then divided into four subgroups of 10 each according to the selected cusp height-to-width ratio (A = 2:1 mm; B = 3:1 mm; C = 3:1.5 mm; D = 4.5:1.5 mm). The samples were uni-axially loaded to 130 N, and strain was recorded using DIC and SG.

Results: With SG testing, control samples recorded the lowest strain values and were significantly different from all test groups. However, DIC failed to detect strain in control samples, as it was too low. With DIC, group D showed the lowest strain readings among all the dimension groups and was significantly different from groups A and B, but the composition of the remaining tooth structure did not show any significant effects. With SG testing, remaining wall dimension and composition both had significant effects: Group A scored the highest strain at all compositions, and E + De had better resistance to load stresses than De only.

Conclusion: For both testing methodologies, height (≥ 3 mm) and width (1 to 1.5 mm) of the remaining tooth structure had an effect on strain. Tooth compositions of E + De resisted strain better than De counterparts at all dimensions.
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http://dx.doi.org/10.11607/ijp.6044DOI Listing
October 2019

Phase-Tunable Calcium Phosphate Biomaterials Synthesis and Application in Protein Delivery.

ACS Biomater Sci Eng 2015 Oct 1;1(10):947-954. Epub 2015 Sep 1.

Department of Chemical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom.

Calcium phosphates (CaP) are important biomaterials used in tissue engineering and drug delivery, due to their biocompatibility, low toxicity, and osteoconductivity. However, controlling the phase of CaP, especially tricalcium phosphate (TCP), is very challenging under mild conditions, particularly when using one preparation protocol for all CaP phases. It is also crucial to produce these biomaterials economically and reproducibly. Herein, three of the most commonly employed CaP, including beta-tricalcium phosphate (β-TCP), dicalcium phosphate anhydrous (DCPA), and hydroxyapatite (HA) were, for the first time, successfully synthesized by altering the reaction solvent, using calcium acetate monohydrate as a precursor and a rapid microwave-assisted synthetic method. A variety of CaP particle morphologies were obtained, including elliptical and plate-shaped with different porosities. Compared with conventional heating, CaP biomaterials synthesized using microwave heating showed greater reproducibility, higher yields, and shorter reaction time. By varying the reaction solvents, morphologies and phases of CaP were controlled, leading to an enhanced protein bovine serum albumin (BSA) loading, with a higher BSA absorption observed according to the trend DCPA> β-TCP > HA. Furthermore, the phase, specific surface area, and pore size were shown to play decisive roles in protein desorption with a higher release amount observed according to the trend DCPA > β-TCP > HA. Finally, it is found that larger pores are also beneficial to BSA adsorption.
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http://dx.doi.org/10.1021/acsbiomaterials.5b00179DOI Listing
October 2015

Biological performance of titania containing phosphate-based glasses for bone tissue engineering applications.

Mater Sci Eng C Mater Biol Appl 2014 Feb 11;35:307-13. Epub 2013 Nov 11.

Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, United Kingdom; Department of Nanobiomedical Science & BK21 Plus NBM Global Reserch Center for Regenerative Medicine, Dankook University, Cheonan 330-714, Republic of Korea. Electronic address:

The interplay between glass chemistry, structure, degradation kinetics, and biological activity provides flexibility for the development of scaffolds with highly specific cellular response. The aim of this study was therefore to investigate the role of titania inclusion into the phosphate-based glass on its ability to stimulate osteoblast-like human osteosarcoma (HOS) cells to adhere, proliferate and differentiate. In depth morphological and biochemical characterisation was performed on HOS cells cultured on the surface of glass discs. Cell proliferation was also studied in the presence of the glass extract. Cell differentiation, through osteoblast phenotype genes, alkaline phosphatase (ALP) activity and osteocalcin production, was carried out using normal or osteogenic media. Both Thermanox® and titania free glass were used as controls. The data demonstrated that titania inclusion provides desired cytocompatible surface that supported initial cell attachment, sustained viability, and increased cell proliferation similar or significantly higher than Thermanox®. The modified glasses regulated osteoblastic cell differentiation as detected by osteoblast phenotype gene transcription and upregulated ALP and osteocalcin expression. Using osteogenic media had no significant effect on ALP activity and osteocalcin expression. Therefore, titania modified phosphate glasses may have future use as bone tissue engineering scaffolds.
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http://dx.doi.org/10.1016/j.msec.2013.10.029DOI Listing
February 2014

Effect of cavity design on tooth surface strain.

J Prosthet Dent 2013 Nov 29;110(5):369-75. Epub 2013 Sep 29.

Senior Lecturer, Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute and School of Dentistry, University of Southern Santa Catarina (UNISUL), Tubarão, Brazil. Electronic address:

Statement Of Problem: The loss of tooth structure can increase cuspal flexure, thereby reducing the fracture resistance of the tooth, or open the tooth-restoration interface, leading to microleakage.

Purpose: The purpose of this study was to evaluate tooth strain in teeth with different cavity preparations after loading and unloading.

Material And Methods: Ten intact human maxillary premolars were selected and embedded in epoxy resin molds. Constantan strain gauges were used and tested as an intact tooth (group I), occlusal cavity (group O), mesio-occlusal cavity (group MO), and finally mesio-occluso-distal cavity (group MOD). All teeth were subjected to gradual nondestructive occlusal loading and unloading (50 N, 70 N, 90 N, 110 N, 130 N, 50 N, 0 N) in a servohydraulic testing machine. All data were analyzed statistically by performing a repeated measures ANOVA with load and cavity as factors to compare the relevant mean strains, and a Bonferroni post hoc test was performed for multiple comparisons (α=.05).

Results: The repeated measures ANOVA did not provide any evidence of an interaction between load and cavity but indicated a significant difference in the mean strains both between the loads (P<.001) and between the cavity groups (P<.001).

Conclusions: MOD cavities presented statistically significantly higher values of strain than MO, O, or intact teeth, and a significant increase in the values of mean strain for all cavities was observed, even with intact teeth, when nondestructive occlusal loading was increased.
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http://dx.doi.org/10.1016/j.prosdent.2013.08.004DOI Listing
November 2013

Titanium and strontium-doped phosphate glasses as vehicles for strontium ion delivery to cells.

J Biomater Appl 2011 May 10;25(8):877-93. Epub 2010 Mar 10.

University College London, Eastman Dental Institute, London, UK.

This study investigated the use of a Ti-containing quaternary phosphate glass system P(2)O(5)-Na(2)O-CaO-TiO(2) as a vehicle for strontium ion delivery to cells. Four glass compositions were manufactured: 0.5P(2)O(5)-0.15Na(2)O-0.05TiO(2)-(0.3 - x)CaO-xSrO (x = 0, 0.01, 0.03, and 0.05). Structural characterization revealed that sodium calcium phosphate is the dominant phase in all the glasses. Degradation studies demonstrated highly linear glass degradation, with Sr-containing glasses degrading at higher rates than the Sr-free glass. Biocompatibility studies using MG63 cells showed that the Sr-containing glasses possess excellent cell attachment and growth, particularly over short periods (~4 days).
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http://dx.doi.org/10.1177/0885328210362125DOI Listing
May 2011

Ion release characteristics, precipitate formation and sealing ability of a phosphate glass-polycaprolactone-based composite for use as a root canal obturation material.

Dent Mater 2009 Mar 18;25(3):400-10. Epub 2008 Dec 18.

UCL Eastman Dental Institute, Unit of Endodontology, Division of Restorative Dental Science, London, UK.

Objectives: The filling material used to obturate root canal systems during the common dental procedure, root canal treatment, has popularly involved gutta-percha (GP) in one of its many forms for almost a 100 years. An optimal root filling material should provide a predictable seal, inhibit or kill residual bacteria, prevent re-contamination and facilitate periapical healing. Although the goal of obturation is stated as the creation of a "seal", its precise role still remains elusive and the seal offered suspect. The primary goal of the study was to develop a novel polycaprolactone/phosphate glass composite deliverable as a root filling and capable of releasing ionic species to enable a predictable seal in an aqueous environment.

Materials And Methods: Different compositions of polycaprolactone-iron phosphate glass (Fe(2)O(3) 1, 3 and 5mol%) composites were produced and delivered into an ex vivo root canal model. Standardized root canals were prepared in extracted human teeth. The teeth were examined for root filling adaptation and precipitate formation (SEM), ion release (Na(+), Ca(2+), PO(4)(3-), P(2)O(7)(4-), P(3)O(9)(3-), and P(5)O(10)(5-)), and sealing ability. The experiments were controlled with teeth obturated with contemporary GP and a conventional zinc-oxide/eugenol sealer.

Results: Adaptation of the experimental material was statistically significantly better than the GP control groups. Precipitate formation was noted in some specimens but all released various ionic species in an inverse proportion to the iron oxide concentration. The experimental material exhibited significantly (P<0.001) less leakage after 7 days immersion in saline compared with those not immersed, or the control GP group.

Significance: PCL-phosphate glass composites showed good potential as a root filling material capable of producing a seal in an aqueous environment without a sealer.
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http://dx.doi.org/10.1016/j.dental.2008.10.010DOI Listing
March 2009

Control of surface free energy in titanium doped phosphate based glasses by co-doping with zinc.

J Biomed Mater Res B Appl Biomater 2009 May;89(2):392-407

Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, London WC1X 8LD, United Kingdom.

To significantly improve the biocompatibility of titanium doped phosphate based glasses, codoping with zinc has been attempted. This study investigated the effect of doping a quaternary 15Na(2)O:30CaO:5TiO(2):50P(2)O(5) glass with zinc oxide (1, 3, and 5 mol %) on bulk, structural, surface, and biological properties; the results were compared with glasses free from ZnO and/or TiO(2). ZnO as adjunct to TiO(2) was effective in changing density, interchain bond forces, degradation behavior, and ions released from the degrading glasses. Incorporation of both TiO(2) and ZnO in T5Z1, T5Z3, and T5Z5 glasses reduced the level of Zn(2+) release by two to three orders of magnitude compared with glasses containing ZnO only (Z5). (31)P NMR results for T5Z1, T5Z3, and T5Z5 glasses showed the presence of Q(3) species suggesting that the TiO(2) is acting as a network former, and the phosphate network becomes slightly more connected with increasing ZnO incorporation. Regardless of their relative lower hydrophilicity and surface reactivity compared with the control glass free from TiO(2) and ZnO (T0Z0), these glasses have significantly higher surface reactivity compared with Thermanox. This has been also reflected in the maintenance of >98% viable Osteoblasts, proliferation rate, and expression level of osteoblastic marker genes in a comparable manner to Thermanox and T5 glasses, particularly T5Z1 and T5Z3 glasses. However, T0Z0 and Z5 glasses showed significantly reduced viability compared to Thermanox. Therefore, it can be concluded that ZnO doped titanium phosphate glasses, T5Z1 and T5Z3 in particular, can be promising substrates for bone tissue engineering applications.
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http://dx.doi.org/10.1002/jbm.b.31227DOI Listing
May 2009

Effect of surface treatment on the bioactivity of nickel-titanium.

Acta Biomater 2008 Nov 9;4(6):1969-84. Epub 2008 Jun 9.

Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.

In this paper, the bioactive properties of Ni-Ti alloy after different surface treatments were evaluated in different media (Hanks' balanced salt solution, Dulbecco's modified Eagle's medium and osteogenic). Evaluation was performed on the basis of X-ray photoelectron spectroscopy and atomic force microscopy studies after immersing samples for up to 24h in the relevant media. This allowed assessment of the kinetics of Ca(2+) and P(5+) precipitation and early interaction of the media with surfaces. In addition, the surface free energy was measured and the influence of heat treatment on phase transformation temperatures and rate of nickel and titanium ion release was investigated. The most favourable bioactive properties were observed for simply ground Ni-Ti samples when evaluated in HBSS, which showed similar properties to reference positive samples (BioactiveTi). On the other hand, samples heat-treated at 600 degrees C showed very low levels of precipitation of Ca and P. Most interestingly, evaluation in the media containing organic components (protein, vitamins, antibiotics and drugs) revealed that bioactivity for all the samples was at the same level (except for the reference negative) irrespective of the surface preparation method. It demonstrated that organic components interact with the surface rapidly, forming a thin protein layer, and this altered the surface properties of the samples, making them bioactive. No significant difference in kinetics of the Ca(2+) and P(5+) precipitation were observed. Nevertheless, further ion release and chemical composition evaluation revealed that alkali treatment and spark oxidation cannot be considered as a useful for biomedical application due to very high levels of Ni in the top layer (alkali-treated) and high rate of Ni release (spark-oxidized and alkali-treated).
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http://dx.doi.org/10.1016/j.actbio.2008.05.010DOI Listing
November 2008

Chemical, corrosion and topographical analysis of stainless steel implants after different implantation periods.

J Biomater Appl 2008 Jul 8;23(1):51-71. Epub 2008 May 8.

Division of Biomaterials and Tissue Engineering UCL Eastman Dental Institute, University College London 256 Gray's Inn Road, London WC1X 8LD, UK.

The aim of this work is to examine the corrosion properties, chemical composition, and material-implant interaction after different periods of implantation of plates used to correct funnel chest. The implants are made of 316L stainless steel. Examinations are carried out on three implants: new (nonimplanted) and two implanted for 29 and 35 months. The corrosion study reveals that in the potential range that could occur in the physiological condition the new bar has the lowest current density and the highest corrosion potential. This indicates that the new plate has the highest corrosion resistance and the corrosion resistance could be reduced during implantation by the instruments used during the operation. XPS analysis reveals changes in the surface chemistry. The longer the implantation time the more carbon and oxygen are observed and only trace of elements such as Cr, Mo are detected indicating that surface is covered by an organic layer. On some parts of the implants whitish tissue is observed: the thickness of which increased with the time of implantation. This tissue was identified as an organic layer; mainly attached to the surface on the areas close to where the implant was bent to attain anatomical fit and thus where the implant has higher surface roughness. The study indicates that the chest plates are impaired by the implantation procedure and contact with biological environment. The organic layer on the surface shows that the implant did not stay passive but some reactions at the tissue-implant interface occurred. These reactions should be seen as positive, as it indicates that the implants were accepted by the tissues. Nevertheless, if the implants react, they may continue to release chromium, nickel, and other harmful ions long term as indicated by lower corrosion resistance of the implants following implantation.
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http://dx.doi.org/10.1177/0885328207083728DOI Listing
July 2008

Effect of increasing titanium dioxide content on bulk and surface properties of phosphate-based glasses.

Acta Biomater 2008 May 7;4(3):523-34. Epub 2007 Dec 7.

Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.

There is an ingoing need for more effective and less costly bone substitute materials. In a previous study, addition of titanium dioxide (TiO2) up to 5 mol.% was shown to be effective in controlling glass degradation, and this was reflected in enhanced gene expression and bone-forming capacity of phosphate-based glasses. In the current study, incorporation of the maximum possible amount of TiO2 has been attempted in order to further improve the biological response of these glasses. This report describes the physical, surface properties and short-term response of an osteoblast cell line (MG63) on phosphate glasses doped with the maximum possible TiO2 content. The results showed that a maximum of 15 mol.% TiO2 can be incorporated into the ternary formulations while maintaining their amorphous nature; such incorporation was associated with a significant increase in density and glass transition temperature. On crystallization, X-ray diffraction analysis showed the presence of TiP2O7 and NaCa(PO3)3 as the main phases for all TiO2-containing glasses, while beta-(CaP2O6) was only detected for 10 and 15 mol.% TiO2 glasses. The degradation rate, however, was significantly reduced by an order of magnitude with incorporation of 10 and 15 mol.% TiO2, and this was reflected in the released ions. This change in the bulk properties, produced with TiO2 incorporation, was also associated with a significant change in the hydrophilicity and surface reactivity of these glasses. Even though the addition of TiO2 reduced the hydrophilicity and the surface free energy of these glasses compared to TiO2 free composition, TiO2-containing glasses still have a significantly reactive surface layer compared to Thermanox. Generally glasses with 5-15 mol.% TiO2 supported MG63 cell growth and maintained high cell viability for up to 7 days culture, which is comparable to Thermanox. Based on the results obtained from this study, TiO2-containing phosphate glasses are promising substrates for bone tissue engineering applications.
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http://dx.doi.org/10.1016/j.actbio.2007.11.007DOI Listing
May 2008

Nanomechanical evaluation of nickel-titanium surface properties after alkali and electrochemical treatments.

J R Soc Interface 2008 Sep;5(26):1009-22

Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.

In this paper, the suitability of alkali treatment followed by heat treatment at 600 degrees C, and spark oxidation for nickel-titanium, intended for medical applications such as pins, wires and clamps, was evaluated on the basis of nanomechanical and wear testing. In addition, the chemical composition and topography of the surface layer, wetting ability, corrosion resistance and influence of the heat treatment on structure of the alloy were also investigated. The results showed that the highest hardness was observed for alkali-treated samples, and this could be correlated with the structure of the sample that contained martensite and a higher phase transformation temperature. This treatment caused a very large increase of nickel in the top layer and decreased resistance in pitting corrosion. These results disqualified the treatment to be considered as useful for medical applications. On the other hand, the hardness of the oxidized samples was at the same level as that obtained for ground reference samples. Moreover, the oxide layer was enriched with phosphorus, and it was predominantly composed of TiO2 and phosphorus oxides. This 3.1 microm thick layer had good adhesion to the substrate as indicated by scratch testing and wear resistant in nanowear testing. However, the oxidation did not significantly increase the corrosion resistance of the alloy compared with reference samples.
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http://dx.doi.org/10.1098/rsif.2007.1313DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2607424PMC
September 2008

Processing, characterisation, and biocompatibility of zinc modified metaphosphate based glasses for biomedical applications.

J Mater Sci Mater Med 2008 Apr 1;19(4):1669-79. Epub 2007 Dec 1.

Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.

Bulk and structural properties of zinc oxide (0 up to 20 mol%) containing phosphate glasses, developed for biomedical applications, were investigated throughout this study using differential thermal analysis (DTA), differential scanning calorimetry, X-ray powder diffraction and 31P and 23Na MAS NMR. Surface wettability and MG63 viability were also considered for surface characterisation of these glasses. The results indicated that incorporation of zinc oxide as a dopant into phosphate glasses produced a significant increase in density; however, the thermal properties presented in glass transition, and melting temperatures were reduced. NaZn(PO3)3 was detected in the X-Ray Powder Diffraction Analysis (XRD) trace of zinc containing glasses, and the proportion of this phase increased with increasing zinc oxide content. NaCa(PO3)3 as a second main phase and CaP2O6 in minor amounts were also detected. The 31P and 23Na MAS NMR results suggested that the relative abundances of the Q1 and Q2 phosphorus sites, and the local sodium environment were unaffected as CaO was replaced by ZnO in this system. The replacement of CaO with ZnO did seem to have the effect of increasing the local disorder of the Q2 metaphosphate chains, but less so for the Q1 chain-terminating sites which were already relatively disordered due to the proximity of modifying cations. Glasses with zinc oxide less than 5 mol% showed higher surface wettability, while those with 5 up to 20 mol% showed comparable wettability as zinc oxide free glasses. Regardless of the high hydrophilicity and surface reactivity of these zinc oxide containing glasses, they had lower biocompatibility, in particular 10-20 mol% ZnO, compared to both zinc free glasses and Thermanox. This may be associated with the release of significant amount of Zn2+ enough to be toxic to MG63.
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http://dx.doi.org/10.1007/s10856-007-3313-1DOI Listing
April 2008

In vitro bioactivity and gene expression by cells cultured on titanium dioxide doped phosphate-based glasses.

Biomaterials 2007 Jul 18;28(19):2967-77. Epub 2007 Mar 18.

Division of Biomaterials and Tissue Engineering, Eastman Dental Institute, University College London, 256 Gray's Inn Road, London WC1X 8LD, UK.

In our previous study, glasses with 50 P(2)O(5)-(20-15) Na(2)O-30 CaO-(0-5 mol%) TiO(2) have been prepared by the conventional melt-quenching process. MG63 cell proliferation, gene expression, in vivo biocompatibility, and bioactivity of these glasses is the concern of this study. The results showed that addition of TiO(2) in small amounts up to 5 mol% enhanced the biocompatibility of these glasses. The cell metabolic activity was conspicuous, on 3 and 5 mol% TiO(2) compositions in particular, with no significant difference from Thermanox control over a period of 21 days. The findings from the gene expression study showed that, at day 1 and on 5 mol% TiO(2) glass, core binding protein factor alpha 1 (Cbfa1) and alkaline phosphatase (ALP) showed significantly lower transcription level; however, collagen type I alpha subunit I (COLIAI) and Osteonectin (Sparc) showed no significant differences compared to the control. At day 7, all these genes transcription levels were not significantly different form the control, but at day 14, they were significantly higher than the control. Moreover, there were no significant differences detected in these genes on both 3 and 5 mol% TiO(2) glasses up to 7 days. At day 14; however, 5 mol% TiO(2) glasses showed significantly higher level than 3 mol% TiO(2) composition. This was also correlated by the presence of new bone tissue at the bone-particles interface for 5 mol% TiO(2) composition after 5 weeks of implantation in rat calvarium. Regardless of this favourable cell response and gene up-regulation, these glasses showed no evidence of apatite layer formation after 14 days incubation in SBF.
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http://dx.doi.org/10.1016/j.biomaterials.2007.03.018DOI Listing
July 2007
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