锂铝硅系光敏微晶玻璃的研究进展和应用

自Li₂O-Al₂O₃-SiO₂系光敏微晶玻璃诞生以来,人们便期望将其优秀的异向刻蚀能力应用于微型结构件的制造中。目前,对锂铝硅系光敏微晶玻璃材料的研究主要集中在成核机理、析晶过程和组分、性质间的关系等方面。光敏微晶玻璃的光敏性和结晶性能密不可分,光敏性决定了晶核的形成,而生成的偏硅酸锂晶体则决定了其异向刻蚀能力。因而对成核机理和析晶过程的研究至关重要,亦有利于了解玻璃的本质。而随着科学技术的发展进步,光敏微晶玻璃的某些性能已不能很好地满足应用要求,如介电损耗和化学稳定性,因此提高光敏微晶玻璃的性能变得必要。随着研究的日益深入,光敏微晶玻璃在实际应用中也暴露出一些问题,如刻蚀精度、壁角倾斜度、内壁光滑度、介电损耗高等,这些问题制约着该材料的发展,亟待解决。 本文阐述了锂铝硅系光敏微晶玻璃的光敏化诱导析晶原理,详细介绍了Li₂O-Al₂O₃-SiO₂系光敏微晶玻璃的研究进展以及在三维集成电路、微流控芯片和微通道板等方面的应用,分析了现阶段存在的问题,并指出了今后光敏微晶玻璃的研究方向。     

Preparation of mica/apatite glass-ceramics biomaterials

Glass-ceramics have become more and more important biomaterials. In this work mica glass/apatite composites with various compositions were prepared by casting and subsequent heat treatments. The effects of composition, phase constitution and crystallinity on mechanical properties, including elastic modulus and transverse rupture strength (TRS), were investigated by using X-ray diffraction analyses (XRD), scanning electron microscopy (SEM) and mechanical tests. Results show that addition of apatite composition in mica glass accelerates the crystallization process and induces the formation of fluoroapatite phase, and the nucleation of apatite crystals occurs before that of mica crystals. The fuoroapatite in this work is needle-like, which is almost the same to that in human bone. The transverse rupture strength increases with the content of fluoroapatite and the crystallinity increasing, except that at a low apatite content the mechanical properties are lower than those of mica glass under the same processing conditions. The transverse rupture strength and elastic modulus obtained in this work fall in the range of those of human bone. SBF immersion test demonstrates good bioactivity of this biomaterial.     

Needle-like apatite-leucite glass-ceramic as a base material for the veneering of metal restorations in dentistry

A needle-like apatite-leucite glass-ceramic was prepared in the SiO₂-Al₂O₃-Na₂O-K₂O-P₂O₅-F system. Nucleation and crystallization processes were studied in bulk and powdered samples. The crystallization of leucite follows the mechanism of surface crystallization. After the precipitation of NaCaPO₄ crystals and another unknown crystal phase, the formation of needle-like apatite is based on a volume nucleation and crystallization process. The mechanism of the formation of needle-like apatite differs to those of apatite precipitation in glass-ceramics. The morphology of needle-like apatite is comparable to that of apatite in natural teeth.The properties of the glass-ceramic, especially the good chemical durability, the optical properties, as well as mechanical and thermal properties allow glass-ceramic to be used as a main component in a bio-material for the veneering of metal restorations in dentistry.     

MgO-Al2O3-SiO2系堇青石微晶玻璃的制备及性能研究

采用高温熔融法制备了MgO-Al2O3-SiO2系堇青石微晶玻璃,采用DTA、XRD等对试样的热处理工艺和力学性能进行了分析,详细讨论了晶化温度、晶化时间、核化温度及核化时间对该系微晶玻璃力学性能及显微结构的影响。结果表明,对于实验研究的MgO-Al2O3-SiO2系玻璃,于600℃核化处理4h,于1100℃晶化处理2h,可以得到具有较好性能的堇青石基微晶玻璃,其抗弯强度可达182MPa。     

Impartation of apatite‐forming ability to chitosan nanofibres by using apatite nuclei

Chitosan nanofibre–apatite nuclei composites obtained by mixing apatite nuclei which possess high apatite‐forming ability with chitosan nanofibre have been expected to be novel bone restorative materials with suitable properties such as light weight, low coefficient of thermal expansion, high mechanical strength, biocompatibility and bioactivity. In this study, the authors prepared three types of apatite nuclei by changing the reaction time aimed to optimise their crystallinity and fabricated their composites with chitosan nanofibre. In order to evaluate the bioactivity in vitro, the authors tested apatite‐forming ability in simulated body fluid. As a result, the materials showed enough apatite‐forming ability in a short time by mixing chitosan nanofibre and apatite nuclei with extremely low crystallinity and their high reactivity in simulated body fluid.Inspec keywords: calcium compounds, nanofibres, bioceramics, bone, polymer fibres, nanocomposites, filled polymers, nanomedicine, nanofabricationOther keywords: apatite‐forming ability, chitosan nanofibre‐apatite nuclei composites, bone restorative materials, reaction time, crystallinity, in vitro bioactivity, simulated body fluid, Ca₁₀ (PO₄)₆ (OH)₂      

Apatite-forming ability of polyglutamic acid hydrogels in a body-simulating environment

Artificial joints can replace damaged joints provided the surrounding bone is sufficiently dense. However, elderly patients generally have reduced osteoporosis-associated bone density. Therefore, restitution of bone density is essential to ensure implantation. Injectable and resorbable bioactive fillers with bone-bonding ability (osteoconductivity) are promising, as osteoporosis can be reversed with minimal invasion. Osteoconduction occurs through the surface formation of biologically active hydroxyapatite via reactions with body fluids. Heterogeneous nucleation of the hydroxyapatite is catalysed by specific surface functional groups. In addition, release of Ca²⁺ ions into the surrounding fluids enhances apatite nucleation by increasing its degree of supersaturation. We tested injectable bioactive filler made from cross-linked polyglutamic acid (PGA). This has many carboxyl groups that facilitate apatite nucleation. An insoluble hydrogel can be formed by cross-linkage. We exposed PGA gels to a simulated body fluid for 7 days. Trace amounts of calcium phosphate were formed, but were not identified as bone-like apatite by X-ray diffraction. However, formation of a bone-like apatite layer was detected using pre-treatment with CaCl₂ solutions (>0.01 mol dm⁻³) dose dependently. Thus, this chemically cross-linked PGA gel could induce the heterogeneous nucleation of hydroxyapatite in a body environment, and this was enhanced by pre-treatment with CaCl₂.     

Compositional dependence of formation of an apatite layer on glass-ceramics in simulated physiological solution

In simulated physiological solution, an apatite layer is formed on the surface of apatite-containing glass-ceramics having the ability to bond to living bone. In this study, the influence of composition in the system CaO-P₂O₅-SiO₂-MgO, Al₂O₃ on apatite layer formation is investigated. On CaO-P₂O₅-SiO₂ glass-ceramics, an apatite layer was formed rapidly in simulated physiological solution. However, a solution containing an excess of Mg²⁺ prevented apatite layer formation. On glass-ceramics containing MgO, the amount of apatite formed on the surface decreased. An apatite layer was not formed on glass-ceramics containing Al₂O₃. The prevention of apatite layer formation on glass-ceramics containing MgO is attributed to an increase of Mg²⁺ concentration in the solution. It is thought that glass-ceramics containing Al₂O₃ form are Al₂O₃-rich layer, and that this layer prevents the formation of an apatite layer.     

Improvement in crystallinity of apatite coating on titanium with the insertion of CaF2 buffer layer

In the apatite coatings on Ti the heat treatment process is necessary to crystallize the apatite structure for improved chemical stability and biological properties. However, the heat treatment normally degrades the mechanical strength of the coating layer associated with thermally induced stress. In this study, we aimed to improve the crystallization of apatite coating by using calcium fluoride (CaF₂) as a buffer layer. The insertion of a thin layer of CaF₂ (0.2–1 μm) between apatite and Ti significantly improved the crystallization behavior of apatite. Moreover, this crystallization was more enhanced as the thickness of CaF₂ was increased. When a 1 μm-thick CaF₂ was inserted, the crystallization of apatite initiated at a temperature as low as 320 °C, being a dramatic improvement in the crystallization when considering the crystallization initiation temperature of a bare apatite coating on Ti was ∼450 °C. As a result of this crystallization enhancement, the dissolution behavior of CaF₂-inserted apatite coatings was more stable than that of the bare apatite coating, showing much reduced initial-burst effect. Preliminary cellular assay showed the CaF₂-inserted apatite coating provided a substrate for cells to spread and grow favorably, as being similar to the bare apatite coating. This novel way of apatite coating on Ti using CaF₂ buffer layer may be useful in the coating systems particularly requiring low temperature processing and increased crystallinity with high chemical stability.     

Chemical reaction of bioactive glass and glass-ceramics with a simulated body fluid

Glass-ceramic A-W containing crystalline apatite and wollastonite in an MgO-CaO-SiO₂ glassy matrix bonds to living bone through an apatite layer which is formed on its surface in the body. The parent glass G of glass-ceramic A-W and glass-ceramic A, which has the same composition as glass-ceramic A-W but contains only the apatite, also bond to living bone through the surface apatite layer, whereas glass-ceramic A-W(Al), which contains the apatite and wollastonite in an MgO-CaO-SiO₂-Al₂O₃ glassy matrix, neither forms the surface apatite layer nor bonds to living bone. In the present study, in order to reveal the mechanism of formation of the surface apatite layer, changes in ion concentrations of a simulated body fluid with immersion of these four kinds of glass and glass-ceramics were investigated. Bioactive glass G and glass-ceramics A and A-W all showed appreciable increases in Ca and Si concentrations, accompanied by an appreciable decrease in P concentration, whereas non-bioactive glass-ceramic A-W(Al) hardly showed any element concentration change. It was speculated from these results that dissolution of the Ca(II) and Si(IV) ions from bioactive glass and glass-ceramics plays an important role in forming the apatite layer on their surfaces in the body.     

Effect of P2O5, B2O3 and PbO on the sinterability of β.quartz solid solution and gahnite glass-ceramics

The effect of P₂O₅, B₂O₃ and PbO additives on the sintering and crystallization behaviour of .quartz solid solution and gahnite glass-ceramics were investigated. According to our results, only the addition of PbO to glasses produces sinterable glass-ceramics containing .quartz solid solution gahnite as the sole crystalline phases, respectively. The nucleation mechanism of the glasses were determined by the Ozawa equation and their activation energy for crystallization were determined by the modified form of the Kissinger, Matusita and Marotta equations. The results indicate that the better sinterability of the lead bearing .q._ss glass-ceramic than the lead free one could be explained by changes of bulk to surface nucleation and increase of its activation energy for crystallization. At the other hand, it could not be observed any differences between the nucleation mechanism and the activation energy for crystallization of the lead bearing and lead free gahnite glass-ceramics. Then the differences in sinterability of the two glass-ceramics could not be explained by comparison of theirs activation energy for crystallization.     

晶化温度对白云鄂博东尾矿微晶玻璃析晶及性能的影响

利用白云鄂博东尾矿和粉煤灰为主要原料,添加少量石英砂、氧化钙等化学原料,制得了高性能的CaO-MgO-Al2 O3-SiO2(CMAS)系尾矿微晶玻璃,研究了微晶玻璃制备过程中的核化及晶化处理条件对其微观结构及性能的影响。首先通过 DTA、XRD、SEM 及 HRTEM 等测试手段对微晶玻璃的析晶过程进行了表征。结果表明,适当的核化处理温度可使微晶玻璃中产生磁铁矿晶核,这些晶核可作为异质表面促进主晶相辉石相的析出。性能测试结果表明微晶玻璃的密度、抗折强度及耐酸度与微晶玻璃晶化温度有关,晶化温度为850℃的微晶玻璃试样结晶程度最高、综合性能最优。更高的晶化温度导致微晶玻璃中空隙及缺陷的产生,反而降低了其物化特性。     

晶化温度对白泥粉煤灰玻璃陶瓷抗折强度的影响

本文以制碱白泥和粉煤灰为主要原料,添加适量添加剂,制备了白泥粉煤灰玻璃陶瓷。通过差热分析（DTA）确定了核化、晶化温度;研究了不同热处理温度对白泥粉煤灰玻璃陶瓷抗折强度的影响,并采用X射线衍射仪（XRD）和扫描电子显微镜（SEM）分析了结晶物相和微观结构。研究结果表明,热处理温度对白泥粉煤灰玻璃陶瓷的抗折强度有较大影响,最佳的热处理温度为900℃。     

Polymeric crystallization and condensation of calcium polyphosphate glass

Calcium polyphosphate (Ca(PO₃)₂)_n (CPP) is under investigation as a resorbable bone biomaterial. Sintering CPP glass particles in humid air produces a porous, interconnected, degradable, crystalline construct that is suitable for connective tissue engineering applications. Porous CPP constructs sintered at 585 °C dissolved in water more rapidly than those sintered at 950 °C. FTIR, ³¹P NMR, powder XRD, and density data for CPP glass and fully crystalline fibers were compared with data for the as-sintered and partially dissolved constructs sintered at 585 or 950 °C. The results suggest that condensation continues during sintering, and CPP glass crystallizes in a process analogous to the crystallization of linear organic polymers. During sintering, water vapor caused hydrolytic degradation of the surface polyphosphate chains, forming a surface layer with different dissolution properties than the particle interior. Thus, sintering CPP glass results in a heterogeneous crystalline product that impacts the dissolution rate of CPP as a degradable biomaterial.     

In vitro studies of novel CaO–SiO2–MgO system composite bioceramics

In this study, a series of CaO–SiO₂–MgO composites with different β-CaSiO₃ (CS)/Mg₂SiO₄ (M₂S) composite ratios were prepared to produce new bioactive and biodegradable biomaterials for potential bone repair. The mechanical properties of CS–M₂S composites increased steadily with the increase of M₂S ratios in composites. Dissolution tests in Tris–HCl buffer solution showed obvious differences with different CS initial composite ratio in composites. The dissolution rate increased with the increase of CS composite ratio, which suggested that the solubility of composites could be tailored by adjusting the initial CS/M₂S composite ratio. Formation of bone-like apatite on a range of CS–M₂S composites with CS weight percentage ranging from 0 to 100 has been investigated in simulated body fluid (SBF). The presence of bone-like apatite layer on the composite surface after soaking in SBF was demonstrated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM). The results showed that the apatite formation ability of the CS–M₂S composite with 70% CS was detected after 10 days immersion. In vitro cell experiments showed that the 50 and 70% CS composites supported greater osteoblast-like cell proliferation as compared with pure M₂S (p < 0.05). The results of this study suggested that the CS–M₂S composites with 50 and 70% initial CS composite amount might be more suitable for preparation of bone repair materials.     

Microstructure characteristics for anorthite composite glass with nucleating agents of TiO2 under non-isothermal crystallization

The anorthite-based composite glass doped with TiO₂ and B₂O₃ was prepared by quenching of molten droplets. Phase development and crystals microstructure of glass were investigated under non-isothermal conditions. A glass transition temperature of 770°C and an exothermal peak around 870°C in the DTA trace was associated with anorthite crystallization (CaAl₂Si₂O₈). For glass specimens under nucleation and crystallization heat-treatment, the final predominant phase was identified as anorthite. Anorthite crystals show preferential nucleation at specific sites with rutile TiO₂ crystals precipitated from the glassy matrix and anorthite crystallization is governed by heterogeneous volume nucleation. The introduced TiO₂ plays the role of nucleating agents to reduce the crystallization temperature lower than 900°C for anorthite-based glass-ceramics. Chemical compositions could be related to the crystal microstructures on different characteristic regions. It was observed that the sintering aid of B₂O₃ neither reacted with nor dissolved in the anorthite or rutile TiO₂ crystals, and remained a glassy phase in the matrix. Occurrence of acicular precipitations was attributed to the orientation growth of TiO₂ crystals. Anorthite crystals were observed to grow with the forms of feathery-spherical particles, having a tendency to coalescence into a huge domain.     

Development of fluorapatite cement for dental enamel defects repair

In order to restore the badly carious lesion of human dental enamel, a crystalline paste of fluoride substituted apatite cement was synthesized by using the mixture of tetracalcium phosphate (TTCP), dicalcium phosphate anhydrous (DCPA) and ammonium fluoride. The apatite cement paste could be directly filled into the enamel defects (cavities) to repair damaged dental enamel. The results indicated that the hardened cement was fluorapatite [Ca₁₀(PO₄)₆F₂, FA] with calcium to phosphorus atom molar ratio (Ca/P) of 1.67 and Ca/F ratio of 5. The solubility of FA cement in Tris–HCl solution (pH = 5) was slightly lower than the natural enamel, indicating the FA cement was much insensitive to the weakly acidic solutions. The FA cement was tightly combined with the enamel surface, and there was no obvious difference of the hardness between the FA cement and natural enamel. The extracts of FA cement caused no cytotoxicity on L929 cells, which satisfied the relevant criterion on dental biomaterials, revealing good cytocompatibility. In addition, the results showed that the FA cement had good mechanical strength, hydrophilicity, and anti-bacterial adhesion properties. The study suggested that using FA cement was simple and promising approach to effectively and conveniently restore enamel defects.     

Investigations on the in vitro bioactivity of swift heavy oxygen ion irradiated hydroxyapatite

Poly(propylene fumarate) (PPF) is an ultraviolet-curable and biodegradable polymer with potential applications for bone regeneration. In this study, we designed and fabricated three-dimensional (3D) porous scaffolds based on a PPF polymer network using micro-stereolithography (MSTL). The 3D scaffold was well fabricated with a highly interconnected porous structure and porosity of 65%. These results provide a new scaffold fabrication method for tissue engineering. Surface modification is a commonly used and effective method for improving the surface characteristics of biomaterials without altering their bulk properties that avoids the expense and long time associated with the development of new biomaterials. Therefore, we examined surface modification of 3D scaffolds by applying accelerated biomimetic apatite and arginine-glycine-aspartic acid (RGD) peptide coating to promote cell behavior. The apatite coating uniformly covered the scaffold surface after immersion for 24 h in 5-fold simulated body fluid (5SBF) and then the RGD peptide was applied. Finally, the coated 3D scaffolds were seeded with MC3T3-E1 pre-osteoblasts and their biologic properties were evaluated using an MTS assay and histologic staining. We found that 3D PPF/diethyl fumarate (DEF) scaffolds fabricated with MSTL and biomimetic apatite coating can be potentially used in bone tissue engineering.     

热处理对二硅酸锂微晶玻璃结构和强度的影响

以SiO_2-Li_2O-K_2O-B_2O_3-P_2O_5为基础组成,P_2O_5为形核剂,采用传统熔体冷却法制备了该系统基础玻璃.利用DSC、XRD、SEM等检测手段研究了热处理制度对玻璃析晶行为、析出晶相种类、晶粒尺寸、晶粒分布及微晶玻璃力学性能的影响.结果表明,当引入P_2O_5为形核剂时,玻璃在核化温度范围内发生分相,并诱导Li_2SiO_3的异相成核.随温度的升高,亚稳态的Li_2SiO_3最终转变成Li_2Si_2O_5稳定相.基础玻璃经核化处理后,分两步晶化比一步晶化更有利于Li_2Si_2O_5的生长,并在一定程度上提高了微晶玻璃的抗弯强度.延长晶化时间能使Li_2Si_2O_5晶体进一步生长,联锁微观结构聚集体的尺寸增大,晶粒与晶粒间交联程度更高,晶粒间有更牢固的化学键合,抗弯强度有所提高.     

Formation of a bioactive calcium titanate layer on gum metal by chemical treatment

The so-called gum metal with the composition Ti–36Nb–2Ta–3Zr–0.3O is free from cytotoxic elements and exhibits a low elastic modulus as well as high mechanical strength. In the present study, it was shown that this alloy exhibited a high capacity for apatite formation in a simulated body fluid when subjected to 1 M NaOH treatment, 100 mM CaCl₂ treatment, heat treatment at 700°C, and then hot water treatment. The high apatite formation was attributed to the CaTi₂O₅ which was precipitated on its surface, and found to be maintained even in a humid environment over a long period. The treated surface exhibited high scratch resistance, which is likely to be useful in clinical applications. The surface treatment had little effect on the unique mechanical properties described above. These results show that gum metal subjected to the present surface treatments exhibits a high potential for bone-bonding, which will be useful in orthopedic and dental implants.     

Devitrification and microstructural coarsening of a fluoride-containing barium aluminosilicate glass

Barium aluminosilicate (BAS) glass-ceramics have the potential to be used in the production of cast prostheses for biomedical applications because of their radiopacity and increased strength compared with traditional feldspathic porcelains. It is essential to understand the crystallization kinetics of these materials in order to fabricate products with increased fracture resistance rapidly. It was hypothesized that the addition of fluoride (F) to the composition of BAS glass would reduce the necessary processing time and temperatures by obviating the need for a separate crystal nucleation treatment. BASF glass was subjected to both linear non-isothermal and one-stage isothermal crystallization treatments, and the resulting glass-ceramics were characterized using x-ray diffraction, differential thermal analysis, and stereology. BASF glass had a low energy barrier to crystallization (397 kJ/mol) and transformed to 76 ± 2% crystallinity within 30 min at 975°C. A fine-grained microstructure was produced by bulk crystallization without the need for a separate crystal nucleation stage. After the initial crystal precipitation, the mean crystal size and mean free path between crystals increased over time at elevated temperature by a diffusion rate-limited coarsening mechanism.