Using PEG as Progen to Preparate Chitosan Scaffold for Tissue Engineering

Tissue engineering basically made up growing the relevant cell in vitro and extracellular matrix. A major goal of tissue engineering is to preparate porous three dimension scaffold for cell proliferate, migrate, differention and to form the structure of desirable tissue and organ. In this study, the effects of various content and macromolecular weight of PEG to chitosan were investigated and evaluated. The pore morphology of chitosan was controlled by changing the concentration and macromolecular weight of PEG. Chitosan porous scaffold has interconecting porosity. The pore morphology can be controlled with varying PEG concentration and macromolecular weight. The pore size is between 10～50 urn, the degree of swelling in water is 85.70 % .     

软组织建模中的有限元模型

用求解弹性力学问题的经典方法一有限元方法进行物理建模，并根据人体软组织的生物力学特性，对有限元模型进行修改。实验结果表明：修改后的有限元模型在形变逼真的情况下稳定性更强。     

采用生物反应器体外构建大面积组织的接种技术

目的　采用培养袋生物反应器进行大面积支架材料细胞接种技术的研究。方法　以人体成纤维细胞和PET无纺布支架材料为模型,考察水平摇床的转速和起始细胞悬液密度对细胞接种动力学、细胞接种率、支架中细胞密度以及细胞分布的影响。结果　在实验条件范围内,成纤维细胞接种大面积PET支架材料的过程基本符合一级反应动力学;低细胞悬液密度接种时,接种率和支架中细胞密度随转速的增加而下降,高细胞悬液密度接种时则反之;细胞分布均匀度都随着转速的增加而下降,起始细胞悬液密度对细胞分布影响较小。结论　采用培养袋生物反应器进行大面积支架材料的细胞接种是可行的,研究结果为进一步优化适合大面积支架材料接种的方法奠定基础。     

旋转生物反应器用于提高组织工程气管软骨力学强度的实验研究

针对体外静态培养方法的缺点,采用旋转生物反应器培养组织工程气管软骨,探讨工程化软骨合适的体外培养条件.选用大鼠剑突软骨细胞种植到DegraPol管状支架上,然后分别于传统静态培养和生物反应器内培养.于体外培养3周和6周后,取出软骨细胞-DegraPol支架复合物,以噻唑蓝(MTT)法测定细胞增殖活性,GAG浓度测定细胞外基质分泌情况,应力-应变机械力学方法测定最大应变和应力的变化,并制备扫描电镜标本观察软骨细胞在DegraP01支架中培养后的超微结构.体外培养3周应用MTT法测定A值分别为:静态培养的细胞-支架复合物组0.12±0.01,生物反应器组0.17±0.05(每组n=6).GAG浓度测定静态培养组为(0.14±0.03) μg/mg,生物反应器组为(0.22±O.03) μg/mg(每组n=6).应力-应变机械力学测定结果为,体外培养3周应变值:生物反应器组为(3.53±0.91),静态培养组为(1.71±0.13).应力值生物反应器组为(0.33±0.04) MPa,静态培养组为(0.26±0.01) MPa.体外培养6周应变值:生物反应器组为(0.57±0.10),静态培养组为(0.48±0.07),应力值生物反应器组为(0.16±0.02) MPa,静态培养组为(0.09±0.02) MPa(每组n=4).扫描电镜观察显示生物反应器组获得更好的软骨样结构和更多的细胞外基质.应用旋转生物反应器能够提供适宜的机械应力刺激,可作为体外构建组织工程化气管软骨的可行的培养方法.     

Natural ECM as Biomaterial for Scaffold Based Cardiac Regeneration Using Adult Bone Marrow Derived Stem Cells

Cellular therapy using stem cells for cardiac diseases has recently gained much interest in the scientific community due to its potential in regenerating damaged and even dead tissue and thereby restoring the organ function. Stem cells from various sources and origin are being currently used for regeneration studies directly or along with differentiation inducing agents. Long term survival and minimal side effects can be attained by using autologous cells and reduced use of inducing agents. Cardiomyogenic differentiation of adult derived stem cells has been previously reported using various inducing agents but the use of a potentially harmful DNA demethylating agent 5-azacytidine (5-azaC) has been found to be critical in almost all studies. Alternate inducing factors and conditions/stimulant like physical condition including electrical stimulation, chemical inducers and biological agents have been attempted by numerous groups to induce cardiac differentiation. Biomaterials were initially used as artificial scaffold in in vitro studies and later as a delivery vehicle. Natural ECM is the ideal biological scaffold since it contains all the components of the tissue from which it was derived except for the living cells. Constructive remodeling can be performed using such natural ECM scaffolds and stem cells since, the cells can be delivered to the site of infraction and once delivered the cells adhere and are not “lost”. Due to the niche like conditions of ECM, stem cells tend to differentiate into tissue specific cells and attain several characteristics similar to that of functional cells even in absence of any directed differentiation using external inducers. The development of niche mimicking biomaterials and hybrid biomaterial can further advance directed differentiation without specific induction. The mechanical and electrical integration of these materials to the functional tissue is a problem to be addressed. The search for the perfect extracellular matrix for therapeutic applications including engineering cardiac tissue structures for post ischemic cardiac tissue regeneration continues.     

Peculiarities of Using Stem Cells for Regeneration of the Bone and Cartilage Tissue

Scientific literature about the use of MSC contains clinical and experimental data on the efficiency of cell technologies for restoration of the osteoarticular apparatus. The use of MSC immobilized in the appropriate carriers and differentiation of these cells towards the bone cells and chondrocytes are of crucial importance. However, the use of MSC, both individual and in combination with other preparations and substances has a number of drawbacks and advantages. The absence of published reports on contraindications and complications of cell therapy is worthy of note, because the analysis of unsuccessful application of MSC will help to determine the indication for this treatment, and hence, to improve the efficiency of cell technologies in the future. Wider use of MSC in clinical practice and experimental studies for acceleration of reparative processes in the bone and cartilage tissue seems to be promising.     

软骨组织工程用材料进展

对近年来软骨组织工程用材料及其制备技术作了较系统的综述,指出了当前软骨组织工程所面临的问题,并针对此问题对未来软骨组织工程用材料的研究作出了展望。     

Agarose Gel as Biomaterial or Scaffold for Implantation Surgery: Characterization,Histological and Histomorphometric Study on Soft Tissue Response

Maxillofacial, orthopedic, oral, and plastic surgery require materials for tissue augmentation, guided regeneration, and tissue engineering approaches. In this study, the aim was to develop and characterize a new extrudable hydrogel, based on agarose gel (AG; 1.5% wt) and to evaluate the local effects after subcutaneous implantation in comparison with collagen and hyaluronic acid. AG chemical–physical properties were ascertained through Fourier transform infrared (FT-IR) spectroscopy and rheological analysis. In vivo subcutaneous implants were performed, and histological and histomorphometric evaluations were done at 1, 4, 12, and 16 weeks. FT-IR confirmed that spectroscopic properties were the same for the baseline agarose and rheological characterization established that AG is a weak hydrogel. Subcutaneous AG implants induced new vessels and fibrous tissue formation rich in neutrophils; the capsule thickness around AG increased until the 12th week but remained thinner than those around hyaluronic acid and collagen. At 16 weeks, the thickness of the capsule significantly decreased around all materials. This study confirmed that 1.5% wt AG possesses some of the most important features of the ideal biocompatible material: safety, effectiveness, costless, and easily obtained with specific chemical and geometrical characters; the AG can represent a finely controllable and biodegradable polymeric system for cells and drug delivery applications.     

骨组织工程支架材料聚磷酸钙生物陶瓷研究进展

为修复创伤及病理因素导致的骨缺损,骨组织工程是一项迅速发展、不断革新的课题。多孔聚磷酸钙生物陶瓷是可吸收生物陶瓷的一种,具有良好的生物相容性以及可降解性,在骨组织工程中日益被人们所认识。骨组织工程中细胞生长速率与材料的降解速率相匹配一直是有待解决的问题,聚磷酸钙由于具有独特的结构及降解性能,因此有望解决这个问题。本文对作为骨组织工程支架材料之一的聚磷酸钙生物陶瓷的理化性质、制备方法、研究进展、骨结合机理等进行了综述,并对其研究和发展作出了展望。     

Localized Mycobacterium genavense Soft Tissue Infection in an Immunodeficient HIV-Negative Patient

 An HIV-negative woman with chronic lymphopenia related to past sarcoidosis situated in the bone marrow presented with an inflammatory lesion in the iliac region due to a localized Mycobacterium genavense soft tissue infection. The lesion resolved after 12 months of antibiotic therapy with clarithromycin, ethambutol and ciprofloxacin. The patient had no recurrence of the subcutaneous abscess during a follow-up period of 14 months after the end of the treatment.     

灌流式生物反应器内支架材料孔隙流场和壁面剪应力的数值分析

为获得支架材料孔隙受到的壁面剪应力的大小及分布、孔隙内压力分布以及支架材料与灌流小室之间不同缝隙时的灌流率。根据有限元方法建立了灌流式生物反应器小室内3种支架材料孔隙模型，用ansys软件分析了各种模型在不同工况下的灌流情况。结果表明，支架材料与灌流小室之间的孔隙决定灌流率，缝隙大于0.5mm时灌流率小于60％；支架材料孔隙壁面剪应力大小主要受灌流流量的影响，调节灌流流量是控制剪应力水平的主要手段。孔壁剪应力和孔内流体压力的分布均由支架材料孔隙的形状特征所决定。     

In Situ Fabrication of Nano-hydroxyapatite in a Macroporous Chitosan Scaffold for Tissue Engineering

A chitosan (CS)/hydroxyapatite (HAP) nanohybrid scaffold with high porosity and homogeneous nanostructure was fabricated through a bionic treatment combined with thermally-induced phase separation. The nano-HAP particles were formed in situ in the scaffold at room temperature instead of mechanically mixing the powders with the polymer component. The scaffold was macroporous with a pore size of about 100–136 μm. The nano-sized HAP particles with diameters of 90–200 nm were scattered homogeneously in the interactively connective pores. Both the improvement of the compressive modulus and yield strength of the scaffolds showed that the in situ nano-HAP particles reinforced the microstructure of the scaffold. The in vitro bioactivity study carried out in simulated body fluid (SBF) indicated good mineralization activity. The crystallization phenomenon suggested that the nano-HAP particles have positive impacts on directing apatite crystallization in the scaffold and led to the good bioactivity of the nanohybrid scaffold.     

Development of Biodegradable Polyurethane Scaffolds Using Amino Acid and Dipeptide-Based Chain Extenders for Soft Tissue Engineering

The inherent flexibility of polyurethane (PU) chemistry allows the incorporation of specific chemical moieties into the backbone structure conferring a unique biological function to these synthetic polymers. We describe here the synthesis and characterization of a PU containing a Gly–Leu linkage, the cleavage site of several matrix metalloproteinases. A Gly–Leu dipeptide was introduced into the chain extender of the polyurethane through the reaction with 1,4-cyclohexane dimethanol. PUs synthesized with the Gly–Leu-based chain extender had a high weight-average molecular weight (M _w > 125 × 10³) and were phase segregated, semi-crystalline polymers with a low soft-segment glass-transition temperature (T _g < –50°C). Uniaxial tensile testing of PU films indicated that the polymer could withstand high ultimate tensile strengths (approx. 13 MPa) and were flexible with breaking strains of approx. 900%. The Gly–Leu PU had a significantly higher initial modulus, yield stress and ultimate stress compared to a PU previously developed in our laboratory containing a phenylalanine-based chain extender (Phe PU). The Gly–Leu-based chain extender allowed for better hard segment packing and hydrogen bonding leading to enhanced mechanical properties. Electrospinning was used to form scaffolds with randomly organized fibers and an average fiber diameter of approx. 3.6 μm for both the Gly–Leu and Phe PUs. Mouse embryonic fibroblasts were successfully cultured on the PU scaffolds out to 28 days. Further investigations into cell-mediated polymer degradation will help to identify the suitability of this new biomaterial as scaffolds for soft tissue applications.     

制备PDLLA组织工程支架的致孔剂研究

为了制备孔隙呈球形、孔隙间相互连通的高孔隙率三维细胞支架,研究了一种新型水溶性球形致孔剂及性质。探讨了间歇离心湿度粘技术与水溶性球形致孔剂相结合,制备聚乳酸(PDLLA)三维多孔细胞支架,获得了高度为5·0mm±0·5mm,直径为8·3±0·4mm的三维多孔支架。实验结果表明,致孔剂颗粒呈球形、水溶性良好,在三维支架中无残留;并且支架的孔隙结构均匀、孔隙率高(94·68%±0·52%)、孔隙呈球形、孔隙间相互完全连通,孔隙的大小可以人为控制。由此表明,在组织工程细胞支架制备中,这类水溶性球形致孔剂具有广泛的潜在应用价值。     

Semi-Automated Needle Steering in Biological Tissue Using an Ultrasound-Based Deflection Predictor

The performance of needle-based interventions depends on the accuracy of needle tip positioning. Here, a novel needle steering strategy is proposed that enhances accuracy of needle steering. In our approach the surgeon is in charge of needle insertion to ensure the safety of operation, while the needle tip bevel location is robotically controlled to minimize the targeting error. The system has two main components: (1) a real-time predictor for estimating future needle deflection as it is steered inside soft tissue, and (2) an online motion planner that calculates control decisions and steers the needle toward the target by iterative optimization of the needle deflection predictions. The predictor uses the ultrasound-based curvature information to estimate the needle deflection. Given the specification of anatomical obstacles and a target from preoperative images, the motion planner uses the deflection predictions to estimate control actions, i.e., the depth(s) at which the needle should be rotated to reach the target. Ex-vivo needle insertions are performed with and without obstacle to validate our approach. The results demonstrate the needle steering strategy guides the needle to the targets with a maximum error of 1.22 mm.     

膝关节置换术中软组织平衡测量技术的发展

骨性关节炎是世界上最常见的关节病之一,随年龄增大,患病率迅速上升,人工膝关节置换术已成为治疗膝关节严重病变的主要手段之一。在人工关节置换术中,生物力线测量和软组织平衡调节是两个主要问题,本文主要针对膝关节置换手术中的软组织平衡测量技术的发展做了归纳和分析,认为随着传感技术的不断发展和计算机辅助手术导航技术的不断完善,膝关节置换术中的软组织平衡测量技术将会得到不断提高,使得人工关节的寿命不断延长。     

How to Optimize Maturation in a Bioreactor for Vascular Tissue Engineering: Focus on a Decision Algorithm for Experimental Planning

Bioreactors may become essential tools for developing tissue-engineered organs from cells, with or without scaffolds. Cells seeded in these devices are expected to grow and form a tissue. Up to now, one of the main challenges to successfully develop functional organs is the structural organization of the cells into the scaffold during maturation in the bioreactor. The maturation step is affected by a set of highly interlinked dynamical variables (flow, stress, pH, temperature, and growth factors) in such a way that fixing the optimal environmental conditions becomes very complex. This work focuses on how the experimental parameters in the bioreactor can be optimized through numerical modeling to maximize tissue growth. Genetic programming (GP) and Markov decision processes (MDPs) were used in synergy to generate and take full advantage of a model of the vascular construct growth. The approach consists in formulating a model through GP to explain the growth of the construct and using MDPs to come up with a strategy to yield the best results in the experimental runs. Construct growth was improved, and the regeneration process was better understood in numerical simulations that relied on this control system. Therefore, an advanced numerical controller of this type could become an effective and inexpensive tool for planning experimental work in tissue engineering.