The use of air-flow impedance to control fiber deposition patterns during electrospinning

Electrospun non-woven structures have the potential to form bioresorbable vascular grafts that promote tissue regeneration in situ as they degrade and are replaced by autologous tissue. Current bioresorbable grafts lack appropriate regeneration potential since they do not have optimal architecture, and their fabrication must be altered by the manipulation of process parameters, especially enhancing porosity. We describe here an air-impedance process where the solid mandrel is replaced with a porous mandrel that has pressurized air exiting the pores to impede fiber deposition. The mandrel design, in terms of air-flow rate, pore size, and pore distribution, allows for control over fiber deposition and scaffold porosity, giving greater cell penetration without a detrimental loss of mechanical properties or structural integrity.     

方形孔结构细胞支架非线性流固耦合数值计算

目的讨论三维方形孔细胞支架不同孔隙率和不同孔半径的对细胞表面固体场和流体场的影响,以及将多孔支架视为刚性体和非线性变形体对计算结果的影响。方法采用一种直接耦合解法和和两种间接耦合解法,两种间接耦合解法分别是有限原法(固体模型)与有限差分法(流体模型)耦合、有限原法(固体模型)与有限体积法(流体模型)耦合。对3种流固耦合计算方法的可靠性进行验证。结果通过对构建的12种模型的计算(50、100和150μm三种边长和61%、65%、77%和84%四种孔隙率),获得了固体模型的应力场、应变场和位移场和流体模型的静压、速度、壁面剪应力和切变率,并对结果进行了比较分析。结论将多孔支架视为刚性体和非线性变形体计算结果有一定差别;孔隙率一定时不同孔半径以及孔半径一定时不同孔隙率条件下对固体场和流体场都有不同程度的影响。     

Hierarchical pore structure of calcium phosphate scaffolds by a combination of gel-casting and multiple tape-casting methods

The objective of this work was to design hierarchical pore structure scaffolds with potential applications in bone tissue regeneration. For that purpose, a bioceramic material such as biphasic calcium phosphate, which consists of a mixture of hydroxyapatite and beta-tricalcium phosphate, was selected. Multilayer pieces (MLP) with hierarchical pore structure were developed employing a new technique that combines gel casting and adding porogens, using multiple tape-casting methods. Pieces with functionally graded porosity were fabricated using porogens with different sizes. The porogens used were Porlat K85 and Porlat K86 with diameters <150 microm and 150-300 microm, respectively. Two types of sintered tapes, with different porosity, no cracking and enough interconnection size were selected. MLP with hierarchical pore structure were designed by the multiple tape-casting method. Interconnected pores whose sizes increase from interior tapes (1.6-3.6 microm) towards exterior tapes (20-51.5 microm) and interpenetration between tapes were achieved. Delamination or cracking were not observed after heat treatment. The flexural strength of pieces was investigated by the three-point bending test. This new combination of methods offers the possibility of manufacturing scaffolds with interconnected pore sizes ranging from 1.6 to 51.5 microm.     

The relationship between porosity, collagen fiber orientation and strength of plated bone after rigid plate fixation and removal

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Ultrasound Parameters for Human Osteoarthritic Subchondral Bone ex Vivo: Comparison with Micro-Computed Tomography Parameters

The aim of this study was to identify ultrasound parameters reflecting subchondral porosity (P_o), subchondral plate thickness (T_pl) and bone volume fraction at the trabecular bone region (BV/TV_Tb). Sixteen osteoarthritic human lateral femoral condyles were evaluated ex vivo using a 15-MHz pulsed-echo ultrasound 3-D scanning system. The cartilage–subchondral bone (C-B) surface region (layer 1) and inner subchondral bone region (layer 2) were analyzed; we newly introduced entropy (ENT) and correlation (COR) of ultrasound texture parameters of the parallel (x) or perpendicular (z) direction to the C-B interface for this analysis. P_o, T_pl and BV/TV_Tb were evaluated as reference measurements using micro-computed tomography. ENT_L1x (ENT of layer 1, x-direction) and ENT_L1z were significantly correlated with P_o (both r values?=?0.58), COR_L2x with T_pl (r?=?–0.73) and COR_L2z with BV/TV_Tb (r?=?–0.66). These are efficient indicators of the characteristics of osteoarthritis-related subchondral bone; the other texture parameters were not significant.     

土壤物理性质对土壤氡浓度及地表氡析出率的影响

目的探讨土壤性质对土壤氡浓度及地表氡析出率的影响。方法在北京、贵阳、呼和浩特的31个测量点进行土壤氡浓度及析出率的现场实测。采集土壤样品，在实验室进行土壤镭含量、含水量、孔隙度和粒径分布等物理性质测量。用线性拟合方法分析了实测土壤氡、析出率数据之间的相关性，以及它们与土壤镭含量的关系。结果地表氡析出率与土壤氡浓度和土壤镭含量有正相关关系；土壤含水饱和度过高或过低均会使析出率和土壤氡浓度降低；贵阳地区土壤镭含量较高，但其粉砂黏土壤的特性使土壤氡浓度很难准确采样，导致结果偏低。结论地表氡析出率和土壤氡浓度虽然与土壤镭含量有正相关关系，但在实际环境中易受含水量等多因素影响，而且土壤氡浓度的准确测量受土壤特性限制较大。     

GI-Ⅱ型渗透陶瓷中氧化铝坯体和烧结体的孔隙分析

目的　研究 GI- 型渗透陶瓷氧化铝坯体和烧结体的孔隙特征 ,分析其氧化铝多孔结构的形成机理和在渗透陶瓷增强补韧中的作用。方法　用 BI- XDC粒度分析仪分析氧化铝粉体粒度的质量组成 ,压汞法测试氧化铝坯体和 112 5℃烧结的氧化铝烧结体的开孔孔隙分布特征 ,扫描电镜观察氧化铝烧结前后的微观结构。结果　氧化铝粉体细颗粒分布在 0 .0 9～ 0 .1μm,0 .2～ 0 .5 μm,粗颗粒主要分布在 1.5～ 4.5 μm,在质量上以粗颗粒为主。氧化铝坯体中孔隙在烧结后增大。坯体中孔隙半径集中在 0 .2 5 31μm,烧结体中孔隙半径集中在 0 .30 81μm;平均半径由 0 .0 95 6 μm变为 0 .110 2 μm。扫描电镜观察烧结后的氧化铝中的小颗粒相互部分融合 ,而大颗粒无此现象。结论　氧化铝粒度组成有利于形成多孔可渗透氧化铝结构。这种多孔结构既是 GI- 型渗透陶瓷的形态骨架 ,也是力学骨架 ,是提高渗透陶瓷复合体力学性能的关键。     

A broadband viscoelastic spectroscopic study of bovine bone: implications for fluid flow

To explore the hypothesis that mechanical excitation-induced fluid flow and/or fluid pressure are potential mechanical transduction mechanisms in bone adaptation, a complementary experimental and analytical modeling effort has been undertaken. Experimentally, viscoelastic tan properties of saturated cortical bovine bone were measured in both torsion and bending, and significant tan values in the 10⁰-10⁵Hz range were observed, although the nature of the damping is not consistent with a fluid pressure hypothesis. Analytically, micromechanically based poroelasticity models were exercised to quantify energy dissipation associated with load-induced fluid flow in large scale channels. The modeling results indicate that significant damping due to fluid flow occurs only above 1 MHz frequencies. Together, the experimental and analytical results indicate that at excitation frequencies presumed to be physiological (1–100 Hz), mechanical loading of bone generates extremely small pore fluid pressures, making the hypothesized fluid-pressure transduction mechanism upon osteocytes untenable. © 2001 Biomedical Engineering Society. PAC01: 8380Lz, 8710+e, 8385Cg     

Development and Optimization of a Solid Dispersion Hot-Melt Fluid Bed Coating Method

ABSTRACT

A new hot-melt fluid bed coating process has been developed, characterized, and optimized. Polyethylene glycol served as the model coating agent and was charged with substrate into the fluid bed chamber in the solid state. The processing stages included: (A) warm-up, (B) preheating, (C) melting-spreading, and (D) cooling-congealing. A central composite design was utilized to characterize and optimize the process. Substrate porosity and density evaluations were conducted by mercury intrusion. The method proved capable of coating nonpareils from 10 to 35 mesh (0.500 to 2.00 mm) and tablets up to 1 g. The nonpareils were coated as individual particles, while particle sizes significantly smaller than 40 mesh (0.420 mm) tended to agglomerate. The porosity-and density values of dissimilar nonpareil batches showed a large degree of variation, affecting the method's reproducibility. Additive coatings were achieved by sequential runs using coating agents of diminishing melting points. The method is a viable alternative to hot-melt spray-coating processes. Organic solvents, spraying equipment, steam jackets, and/or heating tape are eliminated from the process.     

Engineering multi-stage nanovectors for controlled degradation and tunable release kinetics

Nanovectors hold substantial promise in abating the off-target effects of therapeutics by providing a means to selectively accumulate payloads at the target lesion, resulting in an increase in the therapeutic index. A sophisticated understanding of the factors that govern the degradation and release dynamics of these nanovectors is imperative to achieve these ambitious goals. In this work, we elucidate the relationship that exists between variations in pore size and the impact on the degradation, loading, and release of multistage nanovectors. Larger pored vectors displayed faster degradation and higher loading of nanoparticles, while exhibiting the slowest release rate. The degradation of these particles was characterized to occur in a multi-step progression where they initially decreased in size leaving the porous core isolated, while the pores gradually increased in size. Empirical loading and release studies of nanoparticles along with diffusion modeling revealed that this prolonged release was modulated by the penetration within the porous core of the vectors regulated by their pore size.