Research: Other uses

Medical and Nano-fibre Applications Research

1. Medical Applications

1.1 Analytical Control Of Wollastonite For Biomedical Applications By Use Of Atomic Absorption Spectrometry And Inductively Coupled Plasma Atomic Emission Spectrometry

Abstract: Preliminary in vitro experiments revealed that wollastonite (CaSiO3) is a potentially highly bioactive material that forms a hyroxyapatite (HA) surface layer on exposure to simulated body fluid with an ion concentration, pH and temperature virtually identical with those of human blood plasma. The formation of the HA layer is an essential requirement for an artificial material to be used as bioactive bone substitute. This finding opens up a wide field for biomedical applications of wollastonite. Biomaterials used as implants in the human body require strict control of trace elements and of the toxic species specified in American Society for Testing and Materials F-1185-88 (As, Cd, Hg and Pb) in ceramic hydroxyapatite for surgical implantation. In this work, two types of pseudowollastonite, the high temperature form of wollastonite, were analysed by using cold vapour atomic absorption spectrometry and hydride generation atomic absorption spectrometry, in order to determine the elements stated in the above-mentioned norm, and inductively coupled plasma atomic emission spectrometry to establish the SiO2/CaO ratio of the two materials and analyse for all other impurities introduced by the raw materials and by the processes of synthesis, sintering and grinding. Barium and Mg were especially prominent in raw materials, and Zr, Y, Mg, W, Co and Ni come mainly from the processing.
Conclusion: The results obtained allow the following conclusions to be drawn:
  • (a) The electrofused pseudowollastonite contains more impurities than its sintered counterpart (0.73% vs. 0.24%).
  • (b) The presence of Zr, Y, W, Co, Ni, Cr and Mg can largely be ascribed to the prolonged grinding required to ensure adequate grain fineness in the material. On the other hand, Zr, Y and Mg come from the attrition mills, where the grinding bodies were zirconia balls partly stabilized with yttria and magnesia respectively. Also, W came from the WC mortar, which include Co, Ni and Cr in their alloys.
  • (c) The proposed ICP-AES methodology allows one to analyse for Pb and Cd at the concentration levels established by ASTM F-1185-88 (5 ppm for Cd and 30 ppm for Pb). This is not the case with Hg and As, the maximum allowed levels for which (5 and 3 ppm, respectively, are not afforded by this technique and require the use of CVAAS and HGAAS, respectively.
  • (d) Due to the fact that there were no electrofused or sintered pseudowollastonite standard samples, we had recourse to an attack process previously used in other silicate-based materials, 22 which does not produce any loss of volatile elements. This and the absence of spectral interferences in the selected lines in ICP-AES guarantee reliable results in the analysis of the impurities.
  • (e) The precision obtained in the ICP-AES determination of SiO2 and CaO is comparable to that afforded by gravimetric procedures. The excellent result obtained in this respect can be ascribed to: (i) the flux (Li2B4O7) and graphite crucible used to disaggregate samples, which ensured through solubilization of silica; and (ii) the use of a Y internal standard.
  • (f) The microstructures observed and the presence of very small amounts of highly distorted cristobalite in the psW-M sample are consistent with the SiO2/CaO ratios obtained and the procedures used to produce the materials studied (electrofusion and sintering). In addition, the higher impurity content in the psW-M sample is consistent with its higher content in vitreous phase.
  • (g) Based on the results, both materials can be used for bone implants. In this respect, even that with the higher impurity content exhibited no adverse reaction to SBF, rather, the reactivity of both materials was similar.

1.2 Porous Apatite-Wollastonite Glass-Ceramic As An Intramedullary Plug

Abstract: We evaluated the efficacy and biocompatibility of porous apatite-wollastonite glass ceramic (AW-GC) as an intramedullary plug in total hip replacement (THR) for up to two years in 22 adult beagle dogs. Cylindrical porous AW-GC rods (70% porosity, mean pore size 200 _m) were prepared. Four dogs were killed at 1, 3, 6 and 12 months each and six at 24 months after implantation. Radiological evaluation confirmed the efficacy of porous AW-CG as an intramedullary plug. Histological evaluation showed osteoconduction at one month and resorption of the porous AW-GC, which was replaced by newly-formed bone, at 24 months. Our findings indicate that porous AW-GC can be used clinically as an intramedullary plug in THR.
Discussion: There are various techniques for plugging the femoral canal, each with advantages and disadvantages. The use of PMMA plugs prolongs the operating time and requires handling of a large amount of cement and instruments.4 Insertion of a cancellous bone plug taken from the excised femoral head requires experience and specialised instruments.8,9 Polyethylene plugs are easier to use, but do not always achieve adequate and consistent occlusion of the femoral canal.4,11
Although cylindrical porous AW-GC may be insufficient to occlude the elliptical shape of the femoral canal, the insertion of several spherical-shaped AW-GC plugs and their compaction are thought to achieve complete plugging of the femoral canal without any migration or leakage. Raut, Siney and Wroblewski25 reported excellent clinical results in one-stage revision of a discharging infected THR using antibiotic-soaked PMMA bone cement and Kawanabe et al26 described the efficacy of antibiotic-soaked AWGC blocks as a new drug delivery system for osteomyelitis in vitro and in vivo.  Neo et al27 reported that particles of AW-GC of 100 to 220 _m implanted into rat tibiae were not resorbed completely, even after 96 weeks. The resorbed or replaced width of the surface of AW-GC was less than 50 _m per year. In our study, the thickness of the wall of porous AWGC was 10 to 30 _m, and the AW-GC was subtotally resorbed within two years. It is often difficult to remove the plug through the medullary canal at revision operations. Giardino et al12 found that intramedullary plugs made of poly D, L-lactic acid (PDLLA) completely disappeared in the femoral medullary cavity of rabbits 26 weeks after implantation. Although the rate of resorption of porous AW-GC is lower than that of bioresorbable materials including PDLLA, it is resorbed within two years. We conclude that porous AW-GC is effective as an intramedullary plug and has good biocompatibility and resorption within two years.

1.3 Wollastonite Nanofiber–Doped Self-Setting Calcium Phosphate Bioactive Cement For Bone Tissue Regeneration

Abstract: The purpose of this study was to synthesize a self-setting bioactive cement by incorporation of wollastonite nanofibers (WNFs) into calcium phosphate cement (CPC). The composition, morphology, setting time, compressive strength, hydrophilicity, and degradation of WNF-doped CPC (wnf-CPC) were investigated. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and inductively coupled plasma atomic emission spectroscopy were utilized. Additionally, methyl-thiazolyl-tetrazolium bromide assay, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, and histological evaluation were used to study the cell and tissue responses to wnf-CPC, both in vitro and in vivo. The results confirmed that the addition of WNFs into CPC had no obvious effect on the setting time or the compressive strength of wnf-CPC, provided the WNF amount was not more than 10 wt%. However, the hydrophilicity and degradability of wnf-CPC were significantly improved by the addition of WNFs – this was because of the change of microstructure caused by the WNFs. The preferred dissolution of WNFs caused the formation of microporosity in wnf-CPC when soaked in tris hydrochloride solution. The microporosity enlarged the surface area of the wnf-CPC and so promoted degradation of the wnf-CPC when in contact with liquid. In addition, MG-63 cell attachment and proliferation on the wnf-CPC were superior to that on the CPC, indicating that incorporation of WNFs into CPC improved the biological properties for wnf-CPC. Following the implantation of wnf-CPC into bone defects of rabbits, histological evaluation showed that wnf-CPC enhanced the efficiency of new bone formation in comparison with CPC, indicating excellent biocompatibility and osteogenesis of wnf-CPC. In conclusion, wnf-CPC exhibited promising prospects in bone regeneration.
Conclusion: A bioactive cement, wnf-CPC, was fabricated and characterized by incorporation of WNFs into CPC. The results revealed that the addition of WNFs into CPC had no obvious effect on the setting time and compressive strength of the wnf-CPC, provided the WNF amount was not more than 10 wt%. Furthermore, incorporation of WNFs into CPC could significantly improve the hydrophilicity and degradability. The wnf-CPC had special surface properties that could promote the attachment and proliferation of MG-63 cells. In addition, the dissolution associated with WNFs and Ca phosphate produces an environment rich in Ca and Si, which may be responsible for stimulating cell growth and prolif¬eration. Histological evaluation confirmed that wnf-CPC exhibited improved efficiency of bone regeneration. The results suggest that the improved biological properties of cell and tissue responses to wnf-CPC could contribute to special surface properties of the wnf-CPC, and to the release of Ca and Si ions into cell culture medium. In conclusion, wnf-CPC exhibited promising prospects in bone regeneration

2. Nanofibre Applications

2.1 Effects of Wollastonite Nanofibers on Biological Durability of Poplar Wood (Populus nigra) against Trametes versicolor

The effect of impregnation with wollastonite nanofibers, a nontoxic mineral material, on the biological durability of poplar wood (Populus nigra) against a white-rot fungus (Trametes versicolor) was studied. Wollastonite nano-suspension with a concentration of 6.3% was used; the size range of the nano-wollastonite (NW) was 30 to 110 nm. Results showed that decay exposed for 16 weeks in accordance with the standard DIN-52176 specifications resulted in a 47.5% mass loss in control specimens, while in the NW-impregnated specimens, only 3.6% mass loss occurred. Mechanical tests on separate sets of specimens impregnated with NW without exposure to the decay organism showed no significant difference in the mechanical properties. Thus, it can be concluded that impregnating poplar wood with NW as a preservative significantly increases the biological durability of poplar wood against deterioration by Trametes versicolor. Furthermore, it does not have negative effects on the mechanical properties in the impregnated poplar specimens.