The roles of knitted mesh-reinforced collagen–chitosan hybrid scaffold in the one-step repair of full-thickness skin defects in rats

Full-thickness skin defects represent a significant and urgent clinical problem. Dermal substitutes serving as a regenerative template to induce dermal reconstruction provide a promising method to treat serious skin defects. Although collagen–chitosan dermal scaffolds display good biocompatibility and a suitable porous structure for angiogenesis and tissue regeneration, their poor mechanical properties compromise their application. To develop a well-supported dermal substitute, a poly(l-lactide-co-glycolide) (PLGA) knitted mesh was fabricated and integrated with collagen–chitosan scaffold (CCS) to obtain a PLGA knitted mesh-reinforced CCS (PLGAm/CCS). The morphology of this PLGAm/CCS was investigated in vitro. To characterize the tissue response, specifically angiogenesis and tissue regeneration, the PLGAm/CCS was transplanted in combination with thin split-thickness autografts to repair full-thickness skin wounds using a one-step surgical procedure in Sprague–Dawley rats. These results were then compared with CCSs. At weeks 2, 4 and 8 after the operation, the healing wounds were imaged to analyse wound changes, and tissue specimens were harvested for histology, immunohistochemistry, real-time quantitative polymerase chain reaction and Western blot analysis. The results demonstrated that collagen–chitosan sponge in the PLGAm/CCS remained porous, interconnected and occupied the openings of PLGA mesh, and the incorporation of the PLGA knitted mesh into CCS improved the mechanical strength with little influence on its mean pore size and porosity. Following transplantation, PLGAm/CCS inhibited wound contraction, and effectively promoted neotissue formation and blood vessel ingrowth. In conclusion, the mechanical strength of the scaffolds plays an important role in the process of tissue regeneration and vascularization. The ability of PLGAm/CCS to promote angiogenesis and induce in situ tissue regeneration demonstrates its potential in skin tissue engineering.     

Effects of multiple firings on the mechanical properties and microstructure of veneering ceramics for zirconia frameworks

Objectives

The purpose of this study is to evaluate the effects of multiple firings on the mechanical properties and microstructure of veneering ceramics used with zirconia frameworks.

Methods

Five different veneering ceramics for zirconia frameworks were used: Vintage ZR (ZR), Cerabien ZR (CZR), Vita VM9 (VM9), Cercon ceram KISS (KISS), IPS e.max ceram (e.max), and one veneering ceramic used for PFM frameworks: Vintage MP (MP). Twenty specimens were fabricated of each veneering ceramic. Ten specimens were fired twice and another ten specimens were fired ten times. Three-point flexural strength following the ISO 6872 and Vickers hardness were measured, and fracture toughness (K_IC) was calculated. Density and porosity were determined. Specimens were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM).

Results

For all materials, density increased and porosity decreased after 10 firings. Significant differences in density and porosity were observed between 2 and 10 firings, with the exception of VM9 (P < 0.05). There were no significant differences in flexural strength between 2 and 10 firings except for MP. The Vickers hardness of ZR, VM9, KISS and MP increased significantly after 10 firings (P < 0.001). There were no significant differences in fracture toughness for ZR, CZR, VM9 and MP between 2 and 10 firings. However, e.max underwent a significant increase in fracture toughness (P = 0.000), and there was a significant decrease in the toughness of KISS after 10 firings (P = 0.007).

Conclusion

Multiple firings could be effective for improving the densification and the hardness of veneering ceramics for zirconia restorations.

Clinical significance

By 10 firings, the density and hardness of the veneering ceramics used with zirconia frameworks were raised, and porosity was reduced. However, no significant changes occurred in flexural strength, fracture toughness or microstructure.     

烧结温度对牙科氧化锆增韧氧化铝陶瓷力学性能及微观结构的影响

目的 探讨烧结温度对牙科氧化锆增韧氧化铝（ZTA)陶瓷的力学性能及微观结构的影响。方法 在不同烧结温度下（1100℃、1200℃、1350℃、1450℃、1550℃）制备牙科ZTA陶瓷,在烧结完成后测定不同烧结温度下ZTA陶瓷硬度、脆性、线收缩率,并观察微观结构的变化。〖HTH〗结果 随着烧结温度的升高,ZTA陶瓷的硬度、脆性及线收缩率逐渐升高,且比较各温度间ZTA陶瓷的硬度、脆性及线收缩率,差异均有统计学意义（P＜0.05）。 结论 不同烧结温度对ZTA陶瓷脆性、硬度、线收缩率及微观结构的影响不同,当烧结温度在1350℃的条件下时,ZTA陶瓷的上述性能处于最佳状态。     

Microstructural and histomorphological features of osteophytes in late-stage human knee osteoarthritis with varus deformity

ObjectivesTo illustrate the microstructural and histomorphological characteristics of osteophytes in the human knee osteoarthritis (OA).MethodsTibial plateau specimens, including osteophytes and subchondral trabecular bone (STB) from weight-bearing and non-weight-bearing regions, were obtained from 81 patients with OA after total knee arthroplasty surgery. All the patients had varus deformity of the knee. Micro-CT was applied to evaluate the microstructure characteristics of the tibial plateau, which was segmented into 6 regions of interest (ROIs). After micro-CT scanning, decalcified and undecalcified bone histology were performed to assess histological features and bone remodeling status in these different ROIs.ResultsIn both medial and lateral plateaus, osteophytes exhibited a less sclerotic microstructure and higher bone remodeling level compared with STB from weight-bearing and non-weight-bearing regions. Moreover, the medial osteophyte tended to have a more sclerotic microarchitecture and a relatively low level of bone metabolism than its lateral counterpart. Osteophyte, which consists of mesenchymal connective tissue cap, cartilage and mineralized bone tissue, demonstrated evident chondrocyte hypertrophy and endochondral ossification in the cartilage-to-bone interface. Compared with the non-weight-bearing region, the weight-bearing region showed more severely deteriorated cartilage, and more sclerotic subchondral bone with high remodeling status.ConclusionOsteophytes exhibited a sparse microstructure and high bone remodeling level in knee OA, but demonstrating region-dependent variations. In addition, the microstructure, bone metabolism status and pathological alterations of osteochondral complex were distinct between weight-bearing and non-weight-bearing regions in the tibial plateau. Biomechanical stress might play a pivotal role in osteophyte formation and deterioration of osteochondral complex.     

Experimental characterisation for micromechanical modelling of CoCr stent fatigue

Fatigue of CoCr alloy stents has become a major concern in recent times, owing to cases of premature fracture, often driven by microstructural phenomena. This work presents the development of a micromechanical framework for fatigue design, based on experimental characterisation of a biomedical grade CoCr alloy, including both microscopy and mechanical testing. Fatigue indicator parameters (FIPs) within the micromechanical framework are calibrated for the prediction of microstructure-sensitive fatigue crack initiation (FCI). A multi-scale CoCr stent model is developed, including a 3D global J₂ continuum stent-artery model and a 2D micromechanical sub-model. Several microstructure realizations for the stent sub-model allow assessment of the effect of crystallographic orientations on stent fatigue crack initiation predictions. Predictions of FCI are compared with traditional Basquin-Goodman total life predictions, revealing more realistic scatter of data for the microstructure-based FIP approach. Comparison of stent predictions with performance of a 316L stent for the same generic design exposes the design as over-conservative for the CoCr alloy. In response, the micromechanical framework is used to modify the stent design for the CoCr alloy, improving design efficiency.     

Making yttria-stabilized tetragonal zirconia translucent

ObjectiveThe aim of this study was to provide a design guideline for developing tetragonal yttria-stabilized zirconia with improved translucency.MethodsThe translucency, the in-line transmission in particular, of 3 mol.% yttria-stabilized tetragonal zirconia (3Y-TZP) has been examined using the Rayleigh scattering model. The theory predicts that the in-line transmission of 3Y-TZP can be related to its thickness with grain size and birefringence the governing parameters. To achieve a threshold value of translucency, the critical grain size of 3Y-TZP was predicted for various thicknesses (0.3–2.0 mm). The threshold value was defined by a measured average in-line transmission value of a suite of dental porcelains with a common thickness of 1 mm. Our theoretical predictions were calibrated with one of the very few experimental data available in the literature.ResultsFor a dense, high-purity zirconia, its in-line transmission increased with decreasing grain size and thickness. To achieve a translucency similar to that of dental porcelains, a nanocyrstalline 3Y-TZP structure was necessitated, due primarily to its large birefringence and high refractive index. Such a grain size dependence became more pronounced as the 3Y-TZP thickness increased. For example, at a thickness of 1.3 mm, the mean grain size of a translucent 3Y-TZP should be 82 nm. At 1.5 mm and 2 mm thicknesses, the mean grain size needed to be 77 nm and 70 nm, respectively.SignificanceA promising future for zirconia restorations, with combined translucency and mechanical properties, can be realized by reducing its grain size.     

烧结温度对二硅酸锂玻璃陶瓷析晶和微结构的影响

目的:观察烧结温度改变对二硅酸锂玻璃陶瓷的析晶行为和微结构的影响.方法:采用两段式烧结法烧结陶瓷,改变烧结终温度,XRD和SEM分别观察烧结前后陶瓷物相和表面微结构的变化.结果:经不同温度烧结后陶瓷呈现不同的析晶行为和微结构改变,以800 ℃时的改变最为显著,经840 ℃烧结后的陶瓷具有较高结晶度(P<0.05)和均匀致密的表面微结构.结论:二硅酸锂玻璃陶瓷烧结中的温度控制至关重要,800 ℃ 和840 ℃为陶瓷晶相和微结构改变的关键温度.     

茶多酚对胃缺血再灌注致黏膜毛细血管内皮超微结构损伤的保护作用

目的观察茶多酚（polyphenols of tea，PPT）对胃缺血再灌注致胃黏膜毛细血管内皮超微结构损伤的保护作用。方法将30只雄性sD大鼠随机分成6组（n=5）：空白对照组、手术组、20mg／kg PPT组、40mg／kg PPT组、80mg／kg PPT组、160mg／kg PPT组。在成功制作胃缺血动物模型的基础上，观察大鼠胃缺血30min后再灌注12h胃黏膜组织毛细血管内皮细胞超微结构的变化。结果茶多酚可显著减轻胃黏膜组织毛细血管内皮细胞超微结构的损伤。结论茶多酚对胃缺血再灌注致胃黏膜毛细血管内皮损伤具有保护作用，且存在剂量关系。     

房颤患者心房肌细胞凋亡水平的变化

目的:研究心房颤动(房颤)患者心房肌细胞凋亡指数的变化,探讨房颤与心房肌细胞重构的关系. 方法:38例风湿性心脏病二尖瓣狭窄换瓣术者,其中窦性心律者13例(A组)、阵发性房颤及房颤持续时间＜6个月者8例(B组)、房颤持续时间＞6个月者17例(C组).外科手术时取3组病人右心耳组织少许,利用TUNEL法观察心房肌细胞凋亡指数. 结果:房颤患者(B、C组)心房肌细胞凋亡指数比窦性心律者(A组)显著增高,分别为44.53%±11.08%,67.96%±16.09%对19.68%±15.36%,P均＜0.05;凋亡指数与房颤持续时间成正相关. 结论:心房肌细胞重构可能在房颤的发生或维持中起重要作用,是慢性房颤转复为窦性心律后心房收缩功能延迟恢复的主要原因.