Corrigendum: "Incorporating quantum dots into polymer microspheres via a spray-drying and thermal-denaturizing approach". Nanotechnology 17 (2006) 1791-1796".

Corrigendum.

[Valid constructing method of three-dimensional finite element human foot model and experimental analysis on its rationality].

To provide a digital simulation platform for foot-ankle biomechanics research, a 3-D finite element model was established through helical CT images under the principle of RE (reverse engineering) and meshed in FEM software. In the process of modeling cartilage, ligaments, tendons and plantar soft tissue, many anatomic data and results of cadaver specimen experiment were referenced; LINE elements and SHELL elements were used skillfully to simplify the model and resemble the physiological state. The model was then validated by specimen experimentation, which was done on seven fresh cadaver foot specimens, and digital speckle correlation method (DSCM) was used to measure their displacements. Upon the comparison with experimentation and others models, this study also testified that the model, of which the plantar fascia is linked to the heads of metatarsus, is more reasonable to clinical application.

Genetic diversity and structure of Cordyceps sinensis populations from extensive geographical regions in China as revealed by inter-simple sequence repeat markers.

Cordyceps sinensis is one of the most valuable medicinal caterpillar fungi native to China. However, its productivity is extremely limited and the species is becoming endangered. The genetic diversity of eighteen C. sinensis populations across its major distributing regions in China was evaluated by inter-simple sequence repeat (ISSR) markers. A total of 141 markers were produced in 180 individuals from the 18 populations, of which 99.3% were polymorphic. The low average of Shannon (0.104) and Nei index (0.07) of the 18 populations indicates that there are little genetic variations within populations. For all 18 populations, estimates of total gene diversity (H(T)), gene diversity within populations (H(S)), coefficient of genetic differentiation (G(ST)), and gene flow (Nm) were 0.170, 0.071, 0.583, and 0.357, respectively. This pattern suggests that the genetic diversity of C. sinensis is low and most of the ISSR variations are found among populations with little gene exchange. The 18 populations are divided into five groups based on the genetic distance and the grouping pattern matches with the geographic distribution along the latitudinal gradient. The five groups show obvious difference in the G(ST) and Nm values. Therefore, the genetic diversification of C. sinensis populations may be determined by geographic isolation and the combined effects of life history characters and the interaction with host insect species. The information illustrated by this study is useful for selecting in situ conservation sites of C. sinensis.

A finite element analysis of the pelvic reconstruction using fibular transplantation fixed with four different rod-screw systems after type I resection.

BACKGROUND: The pelvis often needs to be reconstructed after bone tumor resection. A major challenge here for the orthopedic surgeons is to choose a method that gives the best performance which depends upon its biomechanical properties. In this study, a 3-dimensional finite element analysis (FEA) was used to analyze the biomechanical properties of reconstructed pelvis using fibula transplant fixed by four commonly used rod-screw systems. METHODS: A total pelvic finite-element model including the lumbar-sacral spine and proximal femur was constructed based on the geometry of CT image from a healthy volunteer. Three-dimensional finite element models of different implants including fibula, rod and screw were simulated using ways of solid modeling. Then various reconstructed finite element models were assembled with different finite element implant model and type I resected pelvic finite element model. The load of 500 N was imposed vertically onto the superior surface of L3 vertebral body, and the pelvis was fixed in bilateral leg standing positions. FEA was performed to account for the stress distribution on the bones and implants. The pelvis displacement of the different rod-screw fixation methods and the maximum equivalent stress (max EQV) on all nodes and element were figured out to evaluate the advantages and disadvantages of different reconstructive methods. RESULTS: Stress concentration in the fibula transplant was extremely high in the reconstructed pelvis, but could be substantially decreased by internal fixation, which partially transferred the stress from the fibula to the rod-screw systems. High stress concentration was also found in the implants, especially in the connection sites between screw and rod. Among the four methods of fixation, a double rod system with L5-S1 pedicle and ilium screws (L5-S1 HR) produced the best performance: least stress concentrations and least total displacement. CONCLUSION: According to the stability and stress concentration, the method of L5-S1 HR fixation combined with fibula transplantation is better than other fixation methods in pelvic reconstruction after type I resection.

[Analysis of the pelvic stability after type I resection of iliac tumor].

OBJECTIVE: To analyze the pelvic stability after type I resection of iliac tumor. METHODS: Six adult cadaveric specimens were tested. The iliac subtotal resection models were established according to Ennecking's type I resection. Markers were affixed to the key region of the pelves. Axial loading from the proximal lumbar was applied by MTS load cell in the gradient of 0-500 N in the double feet standing state. Images in front view were obtained using CCD camera. Based on Image J software, displacements of the first sacral vertebrae (S1) of the resected pelves and the intact pelves were calculated using digital marker tracing method with center-of-mass algorithm. RESULTS: Serious instabilities were found in the resected pelves. S1 rotational movements around the normal side femoral head of the resected pelvis were found. The average vertical displacement of S1 of the resected pelvis was (7 +/- 3) mm under vertical load of 500 newtons, which were 8.3 times compared to the intact pelvis. The average angle of S1 rotation around the normal side femoral head of the resected pelvis was (4.0 +/- 1.8) degrees, which were 12.5 times compared to the intact pelvis. CONCLUSIONS: Biomechanical model of type I resection of iliac tumor are established. Essential pelvic reconstruction must be introduced because of the serious instability of the bone defection after tumor resection.

[Development and validating of a three-dimensional finite element model of total human pelvis].

OBJECTIVE: To develop a three-dimensional finite element model of normal total adult human pelvis and to establish a platform for biomechanical research of human pelvis. METHODS: 186 series of traverse CT images of the pelvis, from the third lumbar vertebra (L3) to the upper third of femur, obtained with spiral CT scanning on a healthy man, aged 42, without diseases of lumbar vertebrae and pelvis, were processed. A three-dimensional finite element model of pelvis was constructed directly by producing the units and nodes with the pixels of the original CT films, using ANSYS finite analytical system. RESULT: A three-dimensional finite element model of normal human pelvis was constructed including lumbar and proximal femur, which could be divided into 207,248 nodes and 721,820 units. CONCLUSION: The established three-dimensional finite element model of normal adult is valid and reasonable, and can be used for biomechanical analysis.

3D finite element mesh generation of complicated tooth model based on CT slices.

An interactive three-dimensional finite element generation method is presented for modelling a multi-connected teeth and mandible structure. The tetrahedron is chosen as the basic element type due to its rigorous adaptability to structures with geometric complexities. The mesh generation is implemented by allocating two quadrangles in adjacent CT image slices to form a set of tetrahedrons. By examining all the possible allocations and their degradations, an algorithm is developed for interactive mesh generation, resulting in a series of tetrahedrons consistent with all the others without overlapping and spacing. The developed system was applied to a tooth-mandibular structure, generating a complicated 3D FEM model consisting of 4762 nodes and 18,534 tetrahedral elements with nine different materials. This 3D model was successfully used to evaluate different tooth restoration strategies, which proved the viability and effectiveness of the proposed method.

The strain at bone-implant interface determines the effect of spinopelvic reconstruction following total sacrectomy: a strain gauge analysis in various spinopelvic constructs.

PURPOSE: There is still some controversy regarding the optimal biomechanical concept for spinopelvic stabilization following total sacrectomy for malignancy. Strains at specific anatomical sites at pelvis/sacrum and implants interfaces have been poorly investigated. Herein, we compared and analyzed the strains applied at key points at the bone-implant interface in four different spinopelvic constructs following total sacrectomy; consequently, we defined a balanced architecture for spinopelvic fusion in that situation. METHODS: Six human cadaveric specimens, from second lumbar vertebra to proximal femur, were used to compare the partial strains at specific sites in a total sacrectomy model. Test constructs included: (1) intact pelvis (control), (2) sacral-rod reconstruction (SRR), (3) bilateral fibular flap reconstruction (BFFR), (4) four-rods reconstruction (FRR), and (5) improved compound reconstruction (ICR). Strains were measured by bonded strain gauges onto the surface of three specific sites (pubic rami, arcuate lines, and posterior spinal rods) under a 500 N axial load. RESULTS: ICR caused lower strains at specific sites and, moreover, on stress distribution and symmetry, compared to the other three constructs. Strains at pubic rami and arcuate lines following BFFR were lower than those following SRR, but higher at the posterior spinal rod construct. The different modes of strain distribution reflected different patient's parameter-related conditions. FRR model showed the highest strains at all sites because of the lack of an anterior bracing frame. CONCLUSIONS: The findings of this investigation suggest that both anterior bracing frame and the four-rods load dispersion provide significant load sharing. Additionally, these two constructs decrease the peak strains at bone-implant interface, thus determining the theoretical surgical technique to achieve optimal stress dispersion and balance for spinopelvic reconstruction in early postoperative period following total sacrectomy.

Structural stability of different reconstruction techniques following total sacrectomy: a biomechanical study.

BACKGROUND: The biomechanical stability of spino-pelvis structure after varying reconstruction methods following total sacrectomy remains poorly defined. The objective of this study was to compare the structural stability of different reconstruction techniques. METHODS: Six fresh human cadavers (L2-pelvis-femora) were used to compare biomechanical stability after reconstruction using four different techniques: (1) sacral rod reconstruction; (2) bilateral fibular flap reconstruction; (3) four-rod reconstruction; and (4) improved compound reconstruction. After total sacrectomy, the construction was carried out using each method once in each cadaver. Structural stiffness was evaluated by linear and angular ranges of motion. L5 relative shift-down displacement, abduction angle on the coronal plane and rotation angle on the sagittal plane, were calculated based on displacement of the identification point under 500N axial loading. Overall stiffness was estimated using load displacement curve. FINDINGS: Improved compound reconstruction resulted in significantly higher stiffness than all three other techniques. The structural stability following bilateral fibular flap reconstruction was superior to that after sacral rod reconstruction. Four-rod reconstruction achieved worst stability due to the lack of anterior bracing applied in three other methods. INTERPRETATION: Improved compound reconstruction produces optimal structural stability after total sacrectomy. This finding suggests that both anterior bracing and alternation of screw trajectory are important in achieving optimal structural stability.

[A finite element analysis of pelvic ring reconstruction with fibular autograft following periacetabular tumor resection].

OBJECTIVE: To establish sophisticated three-dimensional finite element model of reconstructing the whole pelvis and defects in pelvis caused by the resection of periacetabular tumor, and to research the stress distribution regularity of the pelvis reconstructed by the fibular transplantation through three different internal fixation techniques. METHODS: The CT datasets including L3 to middle-femur, unilateral fibular and internal fixation system from 1 healthy 35-year-old male volunteer were collected to establish finite element models of reconstructing the pelvis after the resection of periacetabular tumors through 3 different internal fixation means, namely fibular with plates, pedicle-rods and sacral-iliac rods. Bilateral leg standing position was simulated, then vertical load of 500 N was imposed on the surface of L3, the stress distribution regularity of reconstructed pelvis, transplanted fibular and internal fixation system were evaluated. RESULTS: The finite element models of the pelvis reconstruction after resection of periacetabular tumors were established. The stress concentration of transplanted fibular was extremely high in the vicinity of the host junction sites. For the three internal fixation systems, the connection between steel plate and screw or between titanium bar and screw inclined to have stress concentration; and when the titanium bar was adopted to reconstruct, the transplanted fibular and the healthy side of femoral neck had less stress concentration, while sacral-iliac rods had the most obvious stress concentration. CONCLUSION: For the reconstruction pelvis, the three fibula transplantation and steel plate internal fixation are consistent with intact state of pelvis in terms of the stress distribution, which is a relatively good method for the treatment of bone defect after periacetabular tumor. The finite element model can be used as a tool for the pelvis biomechanics research.

[Construction of platform on the three-dimensional finite element model of the dentulous mandibular body of a normal person].

OBJECTIVE: To develop a method to construct a three-dimensional finite element model of the dentulous mandibular body of a normal person. METHODS: A series of pictures with the interval of 0.1 mm were taken by CT scanning. After extracting the coordinates of key points of some pictures by the procedure, we used a C program to process the useful data, and constructed a platform of the three-dimensional finite element model of the dentulous mandibular body with the Ansys software for finite element analysis. RESULTS: The experimental results showed that the platform of the three-dimensional finite element model of the dentulous mandibular body was more accurate and applicable. The exact three-dimensional shape of model was well constructed, and each part of this model, such as one single tooth, can be deleted, which can be used to emulate various tooth-loss clinical cases. CONCLUSION: The three-dimensional finite element model is constructed with life-like shapes of dental cusps. Each part of this model can be easily removed. In conclusion, this experiment provides a good platform of biomechanical analysis on various tooth-loss clinical cases.

[Elastic modulus of small intestinal submucosa].

OBJECTIVE: to determine the modulus of elasticity (E) of small intestinal submucosa (SIS), a new biological graft material. METHODS: The longitudinal tensile testing was performed on 21 specimens of canine jejunum with the electronic material test machine. RESULTS: Stress (sigma)-strain (epsilon) data were obtained. It was found that the stress (sigma)-strain (epsilon) data fitted the expression sigma = Kiepsilon(alpha) very well, the mean correlation coefficients R2 was 0. 991 6. Then the expression of the modulus of elasticity (E) of SIS was E=K(1/alpha)sigma(1-1/alpha). The mean values of alpha and K were 3.966 9 and 374.55, so E = 4.3992sigma(0.75). CONCLUSION: The modulus of elasticity was found to increase with increasing stress. The variations law is similar to that of the vessels. Furthermore when sigma is 0.01333 MPa (100 mmHg), E is about 0.16 MPa, which is similar to that of the vessels.

Incorporating quantum dots into polymer microspheres via a spray-drying and thermal-denaturizing approach.

Bovine serum albumin (BSA) microspheres incorporated with CdTe quantum dots (QDs) have been prepared via a spray-drying and thermal-denaturizing approach. The results show that the morphology of the composites obtained was greatly affected by the inlet temperature and the initial concentration of BSA in the precursor. Most of the composites prepared with 0.6 mM BSA in the precursor at 40 °C were spherical in shape and hollow. The thermal-denaturized microspheres were water-insoluble, and separated from each other after dispersing in water. Each microsphere had bright fluorescence with pure colour. The microspheres without thermal-denaturation dissolved easily in water, and released nanospheres (>8 nm) that consisted of many CdTe nanoparticles (<3 nm). This approach opens the possibility of rapidly preparing QDs microspheres with controlled fluorescence intensity or with separated multiemission peaks for biomedical applications.