Design characteristics for temporomandibular joint disc tissue engineering: learning from tendon and articular cartilage

Tissue engineering of chondrocytic or fibroblastic musculoskeletal tissues has been relatively well studied compared with that of the temporomandibular joint (TMJ) disc. Early attempts at tissue engineering the disc have been misguided owing to a lack of understanding of the composition and function of the TMJ disc. The objective of this review is to compare the TMJ disc with a chondrocytic tissue (hyaline articular cartilage) and a fibroblastic tissue (tendon) to understand better the properties of this fibrocartilaginous tissue. The TMJ disc has 25 times more glycosaminoglycan (GAG) per dry weight than tendon but half that of articular cartilage. The disc's tensile modulus is six times more than cartilage but orders less than tendon. The GAG content and tensile modulus suggest that the TMJ disc is characterized as a tissue between hyaline cartilage and tendon, but the disc appears more tendon like when considering its collagen make-up and cell content. Like tendon, the TMJ disc contains primarily collagen type I at 85 per cent per dry weight, while articular cartilage has 30 per cent less collagen, which is type II. Knowledge of quantitative comparisons between joint tissues can give extensive insight into how to improve tissue engineering of the TMJ disc.     

胶接技术在工程中的应用

简要介绍胶接技术,在实例的基础上详细阐述它的特性,以及在现代工程中的应用和未来发展前景。     

高效液相色谱法测定水果中的抗坏血酸

用高效液相色谱法测定了几种水果中的维生素C,并研究了不同的色谱条件、不同的提取液对测定结果的影响,结果表明用0.25%的偏磷酸浸提样品以及作为流动相效果较好,测得Vc的保留时间为4.35,回收率为92%～98%,线性范围0.0001～1.68mg/ml.     

Tissue engineering of the synovial joint: the role of cell density

The ultimate goal in the tissue engineering of the synovial joint is to fabricate biologically derived analogues that can replace severely degenerated or traumatized synovial joint components. A number of challenges must be addressed before reaching this ultimate goal. In this report, the relevance of cell seeding density in the synthesis of chondrogenic and osteogenic matrices from human mesenchymal stem cells is explored. Human mesenchymal stem cells (hMSCs) were differentiated into chondrogenic cells and osteogenic cells ex vivo and encapsulated in poly(ethylene glycol) diacrylate (PEGDA) hydrogel at densities of 5 x 106 cells/ml, 40 x 10(6) cells/ml, and 80 x 10(6) cells/ml, in addition to a cell-free poly(ethylene glycol) (PEG) control group (0 x 10(6) cells/ml). Cell-seeded or cell-free PEG constructs were separately incubated in vitro for 4 weeks or implanted in vivo in the dorsum of immunodeficient rats for 4 weeks. In-vitro data demonstrated that hMSC-derived chondrocytes or hMSC-derived osteoblasts maintained their lineages per Safranin O and von Kossa staining after incubation for 4 weeks. The general pattern of initial cell seeding densities of 5 x 10(6) cells/ml, 40 x 10(6) cells/ml, and 80 x 10(6) cells/ml were preserved following in-vitro cultivation. Similarly, in-vivo data revealed that hMSC-derived chondrocytes and hMSC-derived osteoblasts maintained their respective lineages and the pattern of cell-seeding densities. An attempt was made to fabricate a composite construct with PEGDA hydrogel and polycaprolactone (PCL) with designed internal porosity for an osteochondral graft. Various cell-seeding densities as delineated in this report can be realized in the composite PEG-PCL graft. The findings demonstrate that cell-seeding density is likely a key parameter to consider in tissue-engineering design. The source of cells can either be transplanted cells or internally recruited cells.     

组织工程支架的快速成形制备方法

这篇文章介绍了组织工程的概念及组织工程支架的重要性.与传统的组织工程支架制备方法相比,提出了新的快速成形技术.主要阐述了3维打印技术、熔融沉积技术及选择性激光烧结技术的原理及其在构建组织工程支架的应用及特点.     

Investigation of polyelectrolyte for electrochemical detection of uric acid in presence of ascorbic acid

Uric acid (UA) was detected in the presence of ascorbic acid (AA) at GC electrode by cyclic voltametry (CV) and differential pulse voltametry (DPV) in aqueous media of cationic polyelectrolyte (poly(diallyldimethylammonium chloride) (PDDA)). Both, UA and AA are anionic nature and electro-static attraction with cationic solution. This lowered their oxidation potentials and increased anodic current. In CV studies, the UA oxidation potential was decreased by 400 mV in the presence of PDDA along with increase in peak current. Effect of PDDA and pH on E_pa and I_pa were also studied. About 360 mV difference in oxidation peak potentials was observed for AA and UA in PDDA media, which established a quick method for their simultaneous determination. The detection limit of UA in the presence of 200 folds AA was found as 1 μM with correlation coefficient of 0.994 and sensitivity of 0.05 μA μM⁻¹. The proposed method has been also applied for determining the UA in human urine without any pretreatment, and found to be satisfactory.     

Spectrofluorometric determination of ascorbic acid using thiamine and potassium ferricyanide

A simple and sensitive spectrofluorometry method for the determination of ascorbic acid was reported. In alkaline solution, the nonfluorescent thiamine was oxidized by potassium ferricyanide and formed the fluorescent thiochrome with an excitation maximum at 367?nm and an emission peak at 441?nm. However, the fluorescence intensity gradually decreased in the presence of ascorbic acid. The decreased fluorescence was linearly dependent under the optimum conditions with the concentration of ascorbic acid from 0.086–1.5?µmol?L^?1 with a correlation coefficient of 0.9996. The detection limit of 0.026?µmol?L^?1 was lower than many other methods. Additionally, the mechanism underlying the enhancement and quenching of this method was discussed. The protocol was used to determine ascorbic acid in tablets and juice with satisfactory results.     

组织工程支架的低温沉积制造工艺参数研究

低温沉积制造是一种新的快速成形技术。为了将这项技术更好地应用于组织工程支架的制造,根据支架孔隙率的要求,按照一定比例将PLGA和珍珠粉混合,配制成浆料,然后利用低温沉积制造工艺制备了网格型的组织工程支架,并得出了适于加工这种材料的一组工艺参数。主要从软件设定、浆料性质、温控调节和速度匹配4个方面入手,研究了在材料配制、分层和成形机制造等一系列工艺过程中参数对成形结果的影响。实验结果表明,制造出的支架结构规则能满足孔隙率的要求。     

基于逆向工程的个性化人工关节三维CAD数模的建立

通过螺旋CT扫描人体股骨关节,得到二维断层图像数据,利用数据处理软件将二维图片转换成三维点云数据,继而依据点云数据,采用计算机三维重构技术,构建了股骨的三维CAD数字模型.     

Stem cells for tissue engineering of articular cartilage

Articular cartilage injuries are one of the most common disorders in the musculo-skeletal system. Injured cartilage tissue cannot spontaneously heal and, if not treated, can lead to osteoarthritis of the affected joints. Although a variety of procedures are being employed to repair cartilage damage, methods that result in consistent durable repair tissue are not yet available. Tissue engineering is a recently developed science that merges the fields of cell biology, engineering, material science, and surgery to regenerate new functional tissue. Three critical components in tissue engineering of cartilage are as follows: first, sufficient cell numbers within the defect, such as chondrocytes or multipotent stem cells capable of differentiating into chondrocytes; second, access to growth and differentiation factors that modulate these cells to differentiate through the chondrogenic lineage; third, a cell carrier or matrix that fills the defect, delivers the appropriate cells, and supports cell proliferation and differentiation. Stem cells that exist in the embyro or in adult somatic tissues are able to renew themselves through cell division without changing their phenotype and are able to differentiate into multiple lineages including the chondrogenic lineage under certain physiological or experimental conditions. Here the application of stem cells as a cell source for cartilage tissue engineering is reviewed.     

Effects of joint on dynamics of space deployable structure

Joints are necessary components in large space deployable truss structures which have significant effects on dynamic behavior of these joint dominated structures.Previous researches usually analyzed effects of one or fewer joint characters on dynamics of jointed structures.Effects of joint stiffness,damping,location,number,clearance and contact stiffness on dynamics of jointed structures are systematically analyzed.Cantilever beam model containing linear joints is developed based on finite element method,influence of joint on natural frequencies and mode shapes of the jointed system are analyzed.Analytical results show that frequencies of jointed system decrease dramatically when peak mode shapes occur at joint locations,and there are cusp shapes present in mode shapes.System frequencies increase with joint damping increasing,there are different joint damping to achieve maximum system damping for different joint stiffness.Joint nonlinear force-displacement is described by describing function method,one-DOF model containing nonlinear joints is established to analyze joints freeplay and hysteresis nonlinearities.Analysis results show that nonlinear effects of freeplay and hysteresis make dynamic responses switch from one resonance frequency to another frequency when amplitude exceed demarcation values.Joint contact stiffness determine degree of system nonlinearity,while exciting force level,clearance and slipping force affect amplitude of dynamic response.Dynamic responses of joint dominated deployable truss structure under different sinusoidal exciting force levels are tested.The test results show obvious nonlinear behaviors contributed by joints,dynamic response shifts to lower frequency and higher amplitude as exciting force increasing.The test results are further compared with analytical results,and joint nonlinearity tested is coincident with hysteresis nonlinearity.Analysis method of joint effects on dynamic characteristics of jointed system is proposed,which can be used in optimal design of joint parameters     

The use of acellular matrices for the tissue engineering of cardiac valves

Tissue-engineering approaches to cardiac valve replacement have made considerable advances over recent years and it is likely that this application will realize clinical success in the near future. Research in this area has been driven by the inadequacy of the currently available cardiac valve prostheses for younger patients who require multiple reoperations as they grow and develop. Tissue engineering has the potential to provide a valve capable of the same growth, repair, and regeneration as a natural valve and could improve outcomes for patients of all ages. Owing to the function and physical environment of the cardiac valve, the development of tissue-engineered replacements is unusual in that the biomechanical properties of the construct must dominate the biological properties in order for the valve to be functional at the time of implantation. As a result of this, conventional tissue-engineering scaffolds based on biodegradable polymers or collagen may not at present be suitable in this situation because of their initial limited strength. Research into the use of acellular xenogeneic and allogeneic matrices for tissue-engineered heart valves has consequently become extremely popular since the biomechanical properties of the valve can potentially be preserved with an optimal decellularization technique that removes the cells without damaging the matrix. A number of acellular scaffolds have already been tested clinically both unseeded and preseeded with cells and these have met with variable results. This article reviews the concepts involved and the advantages and disadvantages of the different approaches to tissue engineering a living cardiac valve.     

Mechanisms of fluid-flow-induced matrix production in bone tissue engineering

Matrix production by tissue-engineered bone is enhanced when the growing tissue is subjected to mechanical forces and/or fluid flow in bioreactor culture. Cells deposit collagen and mineral, depending upon the mechanical loading that they receive. However, the molecular mechanisms of flow-induced signal transduction in bone are poorly understood. The hyaluronan (HA) glycocalyx has been proposed as a potential mediator of mechanical forces in bone. Using a parallel-plate flow chamber the effects of removal of HA on flow-induced collagen production and NF-kappaB activation in MLO-A5 osteoid osteocytes were investigated. Short periods of fluid flow significantly increased collagen production and induced translocation of the NF-kappaB subunit p65 to the cell's nuclei in 65 per cent of the cell population. Enzymatic removal of the HA coat and antibody blocking of CD44 (a transmembrane protein that binds to HA) eliminated the fluid-flow-induced increase in collagen production but had no effect on the translocation of p65. HA and CD44 appear to play roles in transducing the flow signals that modulate collagen production over long-term culture but not in the short-term flow-induced activation of NF-kappaB, implying that multiple signalling events are initiated from the commencement of flow. Understanding the mechanotransduction events that enable fluid flow to stimulate bone matrix production will allow the optimization of bioreactor design and flow profiles for bone tissue engineering.     

SolidWorks对工科学校机械专业教学的重大影响--有感于SolidWorks2001plus的教学

随着教学的改革,SolidWorks对工科机械专业课程产生很大冲击。本文通过对SolidWorks的介绍,以及其在机械制图、机械原理、毕业设计等课程中的实际应用,讨论了SolidWorks在教学过程中的重要作用和意义。     

Effects of MoS2 concentration on friction

The effects of MoS₂ concentration on friction were investigated by using the ring compression test. An optimum concentration was found for friction. The optimum value is affected by specimen hardness and surface finish. A second optimum value also seems to exist for annealed (softer) 2011 aluminium alloy specimens.     

Effects of electroacupuncture on a degenerated intervertebral disc using an in-vivo rat-tail model

Electroacupuncture (EA) has long been used as conservative treatment for low back pain (LBP). Its effect on relief of back pain has been demonstrated in many clinical studies. However, whether it has any effect on the biological properties of an intervertebral disc, which is one of the major causes of LBP, is still unclear. The aim of this study was, therefore, to investigate the effects of EA with different simulation frequencies on an intervertebral disc with simulated degeneration using an in-vivo rat-tail model. In this study, 33 rats were used. Disc degeneration was simulated in the rat caudal 8-9 disc via continuous static compressive loading of 11 N for 2 weeks. EA with a frequency of 2 or 100 Hz was then applied to the degenerated disc for 3 weeks with 3 sessions/week and 20 min/session. The intervertebral disc height was measured before and after compression as well as after EA intervention for 3 weeks. The static compression was found to result in a reduction in the disc height of about 22 per cent. There was no evidence that this change could be reversed after resting or the EA intervention. However, EA at 100 Hz was found to induce a further decrease in disc height, which was not shown for the rats after resting or EA at 2 Hz. The results of this study showed that effects of EA on disc degeneration are frequency dependent and adverse effects could result if EA at a certain frequency was used.     

Modeling of porous structures for rapid prototyping of tissue engineering scaffolds

Rapid prototyping techniques are increasingly used to build porous scaffolds for the regeneration of biological tissues. This paper deals with one of the most critical tasks involved by this option, i.e., the preparation of geometric data for layered fabrication. Compared to other existing approaches, this work aims at both reducing the required effort in interactive modeling and allowing a standard use of commercial prototyping systems without resorting to special treatments. The proposed method adds a porous structure to the geometric model of tissue surface in polygon format. The structure is of the Cartesian type and consists of an interconnected network of rectilinear channels, whose dimensions can be varied according to desired porosity and pore size. The algorithmic procedures needed for the generation of the porous structure have been implemented in a demonstrative software tool. Sample models of scaffolds have been generated and used to build prototype parts by different fabrication processes and systems.