The purpose of this study was to investigate the effect of biaxial tensile strain on the osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs) in vitro. The rBMSCs were isolated from tibia and femur of 4 weeks-old Sprague-Dawley (SD) rats. The rBMSCs were cultured in DMEM-LG complete culture medium and grew to subconfluence in the cell culture device for loading tensile strain. The biaxial tensile strain was applied to the rBMSCs for periods of 2, 4 and 6 hours every day, respectively, lasting 3 days. The amplitude of biaxial tensile strain applied to the rBMSCs were 1%, 2% and 5% respectively, at a frequency of 1 Hz. Unstrained rBMSCs were used as blank control (control group). The rBMSCs cultured with DMEM-LG complete culture medium containing 100 nmol/L β-Estradiol (E2) were used as positive control. The mRNA expression of alkaline phosphatase (ALP), collagen typeⅠ (ColⅠ), Runt-related transcription factor 2 (Runx2) and osteocalcin (OCN) was examined with real-time quantitative PCR and the protein expression of ALP, ColⅠ, Runx2 and OCN was detected with Western blot method. The results showed as follws: (1) The mRNA and protein expression of the ALP, ColⅠ, Runx2, OCN were significantly higher in rBMSCs of the E2 group than those in the control group (P＜0.05). (2) The mRNA and protein expression level of the ALP, Runx2 were higher markedly in the 1% tensile strain groups than those in the control group (P＜0.05), but lower than those in the E2 group (P＜0.05). (3) The mRNA and protein expression level of the ALP, ColⅠ, Runx2, OCN were significantly higher in the 2% tensile strain groups than those in the control group (P＜0.05), and the mRNA and protein expression level of ColⅠ and Runx2 in the group applied with 2% amplitude of tensile strain for 4 h/d was significantly higher than those in E2 group (P＜0.05). (4) The mRNA and protein expression level of the ALP, ColⅠ, Runx2 were significantly higher in the groups applied with 5% amplitude of tensile strain for 2 h/d or for 4 h/d than those in the control group (P＜0.05). In our study, E2 and mechanical stimulation played an important role in the regulation of differentiation of rBMSCs into osteoblasts, and the manner applied with the 2% amplitude of tensile strain for 4 h/d, lasting 3 days was an optimal stimulus for up-regulating the mRNA and protein expression of ALP, ColⅠ, Runx2, OCN of rBMSCs.
ObjectiveTo discuss the effectiveness of limited open reduction via sinus tarsi approach using medial distraction technique in the treatment of intra-articular calcaneus fractures by comparing with open reduction and internal fixation via extensile L-shaped incision. MethodsA retrospective analysis was made on the clinical data of 21 patients with intra-articular calcaneus fractures treated by sinus tarsi approach combined with medial distraction technique between April 2013 and November 2014 (minimally invasive group), and 32 patients treated by extensile L-shaped incision approach between June 2012 and September 2014 (extensile incision group). No significant difference was found in gender, age, injury pattern, fracture classification, time from injury to operation, preoperative Böhler angle, Gissane angle, calcaneal varus angle, the ankle and hind-foot score of American Orthopaedic Foot and Ankle Society (AOFAS), and visual analogue scale (VAS) score between 2 groups (P>0.05), which was comparable. The operation time, wound complications, and bone healing time were recorded. The postoperative function was also evaluated by AOFAS score and VAS score. The pre-and post-operative Böhler angle, Gissane angle, and calcaneal varus angle were measured on the X-ray films, and the corrective angle was calculated. ResultsSixteen patients were followed up 6-18 months (mean, 11.5 months) in the minimally invasive group, and 23 patients for 6-24 months (mean, 13.5 months) in the extensile incision group. Difference was not significant in operation time between 2 groups (t=0.929, P=0.796). No complication occurred in the minimally invasive group; partial skin flap necrosis occurred in 3 cases of the extensile incision group, was cured after dressing change. There was no loosening of implants or reduction loss in 2 groups at last follow-up. Subtalar joint stiffness occurred in 1 case of the minimally invasive group and 4 cases of the extensile incision group, and 1 patient had discomfort for the implants in the extensile incision group. The bone healing time was (9.9±0.8) weeks in the minimally invasive group, and was (10.1±0.7) weeks in the extensile incision group, showing no significant difference (t=0.613, P=0.845). Böhler angle, Gissane angle, calcaneal varus angle, AOFAS score, and VAS score were significantly improved at last follow-up when compared with preoperative values in 2 groups (P < 0.05), but there was no significant difference between 2 groups (P>0.05), and the corrective value of angle showed no significant difference between 2 groups (P>0.05). ConclusionLimited open reduction via sinus tarsi approach for intra-articular calcaneus fractures could reduce the incidence of wound complications effectively. Meanwhile, the medial distraction technique is helpful to correct the heel varus deformity.
Suture broken, knot slipping and tissue tearing are the main reasons of wound closure failure in clinical operation. Based on this, we simulated the suturing and healing operation by using a biological materials testing machine and investigated the tensile properties before and after knotting, relaxation property and friction property of three common sutures: silk, polyglactin 910 and polypropylene. Results show that the tensile property decreased after knotting. The tensile strength of polyglactin 910 and elongation of polypropylene were the largest. During the relaxation process, the sutures relaxed the most in the first 2 hours. The relaxation from less to more was: polyglactin 910, silk and polypropylene. Coating or monofilament could obviously reduce the surface roughness of sutures, and thus reduce the friction force of the suture-suture interface. The friction force of the suture-suture interface increased with the increasing load but did no change with the increasing velocity. The results can provide an important theoretical basis for the optimizations of suture design and knotting operation.
The mechanical properties of the aorta tissue is not only important for maintaining the cardiovascular health, but also is closely related to the development of cardiovascular diseases. There are obvious differences between the ventral and dorsal tissues of the descending aorta. However, the cause of the difference is still unclear. In this study, a biaxial tensile approach was used to determine the parameters of porcine descending aorta by analyzing the stress-strain curves. The strain energy functions Gasser-Ogden-Holzapfel was adopted to characterize the orthotropic parameters of mechanical properties. Elastic Van Gieson (EVG) and Sirius red stain were used to observe the microarchitecture of elastic and collagen fibers, respectively. Our results showed that the tissue of descending aorta had more orthotropic and higher elastic modulus in the dorsal region compared to the ventral region in the circumferential direction. No significant difference was found in hyperelastic constitutive parameters between the dorsal and ventral regions, but the angle of collagen fiber was smaller than 0.785 rad (45°) in both dorsal and ventral regions. The arrangement of fiber was inclined to be circumferential. EVG and Sirius red stain showed that in outer-middle membrane of the descending aorta, the density of elastic fibrous layer of the ventral region was higher than that of the dorsal region; the amount of collagen fibers in dorsal region was more than that of the ventral region. The results suggested that the difference of mechanical properties between the dorsal and ventral tissues in the descending aorta was related to the microstructure of the outer membrane of the aorta. In the relatively small strain range, the difference in mechanical properties between the ventral and dorsal tissues of the descending aorta can be ignored; when the strain is higher, it needs to be treated differently. The results of this study provide data for the etiology of arterial disease (such as arterial dissection) and the design of artificial blood vessel.
Objective To compare the biomechanical properties of two ultra-strong sutures and suturing methods in panda rope bridge technique (PRBT) application, and provide guidance for clinical selection of suture threads and suture methods. Methods Forty Achilles tendons from bulls were randomly divided into 4 groups (n=10) and transected at the 4 cm proximal to the tendon insertion. Groups A and B used Ethibond sutures (USP 5), the proximal end was fixed at the myotendious junction with Krackow sutures and the distal end was fixed through a calcaneus canal. Groups A and B had 4 and 8 threads through the stump plane, respectively. Groups C and D used Ultrabraid sutures (USP 2), the proximal end was fixed at the myotendious junction with Krackow sutures and the distal end was fixed in the calcaneus with two anchors. Groups C and D had 4 and 8 threads through the stump plane, respectively. The dynamic tensile forces of 20-100, 20-200, 20-300, and 20-400 N were tested respectively by using a dynamic tensile testing machine at 0.5 Hz for 250 cycles. After each stage of testing, the gap between stumps was measured with a caliper and the type of suture failure was recorded. Results After dynamic tensile forces of 20-100 N and 20-200 N, the gaps of the four groups arranged from small to large were groups D, B, C, and A. The differences between groups A and B and groups C and D were significant (P<0.05). But after dynamic tensile forces of 20-300 N and 20-400 N, the gaps were more than 5 mm in all groups. The suture retention rates of the four groups after dynamic tensile forces of 20-100 N and 20-200 N were all 100%. The suture retention rates of groups A, B, C, and D were 0, 80%, 60%, and 100%, respectively after dynamic tensile forces of 20-300 N. The differences of suture retention rates between group A and groups B and D were significant (P<0.05). There was no significant difference between groups B, C, and D (P>0.05). After dynamic tensile forces of 20-400 N, the suture retention rates of groups A, B, C, and D were 0, 50%, 0, and 70%, respectively. There were significant differences between groups A and B and groups C and D (P<0.05). Conclusion Repairing Achilles tendon rupture via PRBT with 8 ultra-strong sutures through the stump plane can meet the mechanical requirements for walking by using ankle boots and heel pads in the early accelerated rehabilitation after operation.
In order to understand how the biomechanical properties of rabbit cornea change over time after corneal ablation, 21 healthy adult rabbits were used in this study, with the left eye as experimental side and the right eye as the control side. Firstly, a lamellar knife was used to remove a portion of the anterior corneal surface tissue (30%~50% of the original corneal thickness) from the left eye of each rabbit, as an animal model simulating corneal refractive surgery. Secondly, postoperative experimental rabbits were kept for one, three, or six months until being euthanized. Strip specimens were produced using their corneas in vitro to perform a uniaxial tensile test with an average loading-unloading rate of approximately 0.16 mm/s. Finally, the visco-hyperelastic material constitutive model was used to fit the data. The results showed that there was a significant difference in the viscoelastic parameters of the corneas between the experimental and the control eyes at the first and third postoperative months. There was a difference in tangential modulus between the experimental and the control eyes at strain levels of 0.02 and 0.05 at the third postoperative month. There was no significant difference in biomechanical parameters between the experimental and the control eyes at the sixth postoperative month. These results indicate that compared with the control eyes, the biomechanical properties of the experimental eyes vary over postoperative time. At the third postoperative month, the ratio of corneal tangential modulus between the experimental and the control eyes significantly increased, and then decreased. This work lays a preliminary foundation for understanding the biomechanical properties of the cornea after corneal refractive surgery based on rapid testing data obtained clinically.