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- A comparative study of orthotropic and isotropic bone adaptation in the femur. [JOURNAL ARTICLE]
- Int j numer method biomed eng 2014 Apr 21.
Functional adaptation of the femur has been studied extensively by embedding remodelling algorithms in finite element models, with bone commonly assumed to have isotropic material properties for computational efficiency. However, isotropy is insufficient in predicting the directionality of bone's observed microstructure. A novel iterative orthotropic 3D adaptation algorithm is proposed and applied to a finite element model of the whole femur. Bone was modelled as an optimised strain-driven adaptive continuum with local orthotropic symmetry. Each element's material orientations were aligned with the local principal stress directions and their corresponding directional Young's moduli updated proportionally to the associated strain stimuli. The converged predicted density distributions for a coronal section of the whole femur were qualitatively and quantitatively compared with the results obtained by the commonly used isotropic approach to bone adaptation and with ex vivo imaging data. The orthotropic assumption was shown to improve the prediction of bone density distribution when compared with the more commonly used isotropic approach, whilst producing lower comparative mass, structurally optimised models. It was also shown that the orthotropic approach can provide additional directional information on the material properties distributions for the whole femur, an advantage over isotropic bone adaptation. Orthotropic bone models can help in improving research areas in biomechanics where local structure and mechanical properties are of key importance, such as fracture prediction and implant assessment. Copyright © 2014 John Wiley & Sons, Ltd.
- Delivering stem cells to the healthy heart on biological sutures: effects on regional mechanical function. [JOURNAL ARTICLE]
- J Tissue Eng Regen Med 2014 Apr 21.
Current cardiac cell therapies cannot effectively target and retain cells in a specific area of the heart. Cell-seeded biological sutures were previously developed to overcome this limitation, demonstrating targeted delivery with > 60% cell retention. In this study, both cell-seeded and non-seeded fibrin-based biological sutures were implanted into normal functioning rat hearts to determine the effects on mechanical function and fibrotic response. Human mesenchymal stem cells (hMSCs) were used based on previous work and established cardioprotective effects. Non-seeded or hMSC-seeded sutures were implanted into healthy athymic rat hearts. Before cell seeding, hMSCs were passively loaded with quantum dot nanoparticles. One week after implantation, regional stroke work index and systolic area of contraction (SAC) were evaluated on the epicardial surface above the suture. Cell delivery and retention were confirmed by quantum dot tracking, and the fibrotic tissue area was evaluated. Non-seeded biological sutures decreased SAC near the suture from 0.20 ± 0.01 measured in sham hearts to 0.08 ± 0.02, whereas hMSC-seeded biological sutures dampened the decrease in SAC (0.15 ± 0.02). Non-seeded sutures also displayed a small amount of fibrosis around the sutures (1.0 ± 0.1 mm(2) ). Sutures seeded with hMSCs displayed a significant reduction in fibrosis (0.5 ± 0.1 mm(2) , p < 0.001), with quantum dot-labelled hMSCs found along the suture track. These results show that the addition of hMSCs attenuates the fibrotic response observed with non-seeded sutures, leading to improved regional mechanics of the implantation region. Copyright © 2014 John Wiley & Sons, Ltd.
- Collagen Gel Contraction as a Measure of Fibroblast Function in Carpal Tunnel Syndrome. [JOURNAL ARTICLE]
- J Biomed Mater Res A 2014 Apr 20.
Non-inflammatory subsynovial connective tissue (SSCT) fibrosis with nerve compression is a prominent feature of carpal tunnel syndrome (CTS). Studies have shown that SSCT matrix synthesis and material property changes in CTS are associated with increased activity of transforming growth factor β (TGF-β1). This study's aims were to 1) investigate the ability of SSCT fibroblasts from CTS patients and unaffected individuals to contract a collagen gel ring and 2) determine how the addition of TGF-β1 affects this ability. SSCT fibroblasts from 3 normal cadavers and 3 age-matched female patients who had undergone surgery for CTS were used. Results showed patient cell seeded gels had a significantly higher contraction rate (p<0.001) than control cells and fully contracted gel rings possessed a significantly higher tensile strength (p=0.003) and stiffness (p<0.001). Furthermore, TGF-β1 significantly intensified contraction rate (p<0.001), tensile strength (p<0.001) and stiffness (p<0.001). In conclusion, SSCT cells from normal donors and CTS patients contract collagen gel rings differently, and this ability is affected by TGF-β1 treatment. This cell-seeded collagen gel model may be useful for developing methods of stopping or eliminating the effect of TGF-β1 effects on the SSCT fibroblasts and surrounding matrix, which might aid identification of medical treatments of CTS.
- Branching morphology of decapitated arborescent monocotyledons with secondary growth. [JOURNAL ARTICLE]
- Am J Bot 2014 Apr 21.
Dragon trees (Dracaenaceae) are arborescent monocotyledons with anomalous secondary growth and are able to branch, exhibiting a treelike habit. Studies of the morphology and anatomy of ramifications allow for a better understanding of the complex course and arrangement of the vascular bundles in the stem-branch attachment region for Dracaena and other arborescent monocots with anomalous secondary growth.Morphological and anatomical analyses of ramifications induced in decapitated specimens of D. marginata and D. reflexa included serial sectioning, maceration, staining, and bleaching techniques as well as high and low resolution optical microscopy and three-dimensional (3D)-visualization techniques.The use of innovative 3D reconstruction and high-resolution imaging revealed the extent of connections between branch and stem on various hierarchical levels in Dracaena. A stem-clasping attachment of the side shoot was observed, which in more detail shows a strong regional dependence of course and connectivity of individual vascular bundles to the main stem. Consequently, the attachment of branch tissue is strongly limited to the outer periphery of the main stem.Our results indicate that the observed course of vascular bundles with fiber caps cannot only be a result of physiological need for water and nutrient supply but are interpreted in terms of mechanical constraints acting on the branching region. In addition, the used 3D cine technique and coupled 3D reconstruction provide a valuable tool for botanists working in the field of anatomy.
- Current concepts on trochleoplasty procedures for the surgical treatment of trochlear dysplasia. [JOURNAL ARTICLE]
- Knee Surg Sports Traumatol Arthrosc 2014 Apr 22.
Trochleoplasty is a surgical procedure, whose goal is to change the abnormal shape of the femoral trochlea in patients with recurrent patellar dislocation. Such surgeries that aim to reshape the articular surface of a bone without damaging it are quite unique in orthopaedic surgery. Although in the beginning, trochleoplasty was reserved for the refractory cases where previous surgery has failed, the last years it became more and more popular because of a better knowledge of anatomy and biomechanics and a greater availability of instruments. The roots of the deepening trochleoplasty could be found in the previous century when the first surgeons tried to directly remove the dysplastic bone with pioneer interventions but with devastating consequences. Since then, multiple procedures have been described and are analysed in this review; each one with its unique features, advantages and pitfalls. Regardless of the technique used, the very recent bibliography presents very encouraging results from the application of trochleoplasty with other procedures in a selected population with severe trochlear dysplasia and recurrent patellar dislocation, in whom the benign neglect of dysplasia would lead to unfavourable results. Level of evidence IV.
- Corneal Collagen Crosslinking: A Systematic Review. [JOURNAL ARTICLE]
- Ophthalmologica 2014 Apr 17.
Keratoconus (KCN) is an ectatic disorder with progressive corneal thinning and a clinical picture of corneal protrusion, progressive irregular astigmatism, corneal fibrosis and visual deterioration. Other ectatic corneal disorders include: post-LASIK ectasia (PLE) and pellucid marginal degeneration (PMD). Corneal crosslinking (CXL) is a procedure whereby riboflavin sensitization with ultraviolet A radiation induces stromal crosslinks. This alters corneal biomechanics, causing an increase in corneal stiffness. In recent years, CXL has been an established treatment for the arrest of KCN, PLE and PMD progression. CXL has also been shown to be effective in the treatment of corneal infections, chemical burns, bullous keratopathy and other forms of corneal edema. This is a current review of CXL - its biomechanical principles, the evolution of CXL protocols in the past, present and future, indications for treatment, treatment efficacy and safety. © 2014 S. Karger AG, Basel.
- Heterogeneity of rectus femoris muscle architectural adaptations after two different 14-week resistance training programmes. [JOURNAL ARTICLE]
- Clin Physiol Funct Imaging 2014 Apr 21.
This study aimed to determine the architectural changes of rectus femoris muscle at distinctive sites of the thigh length after two different 14-week resistance training programmes.Thirty-five untrained men were randomly allocated into three different groups: conventional resistance training (n = 12), isokinetic training (n = 12) and control (n = 11). Rectus femoris cross-sectional area, thickness and fascicle angle at two specific thigh sites (30% and 50% of the length) were assessed before and after 14 weeks of unilateral knee extension exercise or control. The isometric peak torque of the knee extensors was estimated as a muscle strength index.Conventional (30% = 47·4% versus 50% = 14·4%) and isokinetic (30% = 31·8% versus 50% = 11·4%) training induced significant increases on thickness at both rectus femoris sites. While conventional training resulted in substantial increments on cross-sectional area (30% = 62·1%, 50% = 19·5%), isokinetic training provoked a significant increase only at the distal site (50% = 64·7%). The isometric peak torque increased (22·4 and 29·6%, for conventional and isokinetic groups, respectively) after training independently of the training mode, although no significant changes were observed for any dependent variable in the control group.In general, the training modes resulted in similar changes on rectus femoris architecture, whereas their magnitude depended on the thigh site.
- Modulating hair follicle size with Wnt10b/DKK1 during hair regeneration. [JOURNAL ARTICLE]
- Exp Dermatol 2014 Apr 21.
Hair follicles have characteristic sizes corresponding to their cycle specific stage. However, how the anagen hair follicle specifies its size remains elusive. Here, we show that in response to prolonged ectopic Wnt10b-mediated β-catenin activation, regenerating anagen hair follicles grow larger in size. In particular, the hair bulb, dermal papilla and hair shaft become enlarged. While the formation of different hair types (Guard, Awl, Auchene, and Zigzag) is unaffected. Interestingly, we found the effect of exogenous WNT10b was mainly on Zigzag and less on the other kinds of hairs. We observed dramatically enhanced proliferation within the matrix, DP and hair shaft of the enlarged AdWnt10b-treated hair follicles compared with those of normal hair follicles at P98. Furthermore, expression of CD34, a specific hair stem cell marker, was increased in its number to the bulge region after AdWnt10b treatment. Ectopic expression of CD34 throughout the ORS region was also observed. Many CD34 positive hair stem cells were actively proliferating in AdWnt10b-induced hair follicles. Importantly, subsequent co-treatment with the Wnt inhibitor, DKK1, reduced hair follicle enlargement, decreased proliferation and ectopic localization of hair stem cells. Moreover, injection of DKK1 during early anagen significantly reduced the width of prospective hairs. Together, these findings strongly suggest that Wnt10b/DKK1 can modulate hair follicle size during hair regeneration. This article is protected by copyright. All rights reserved.
- Impact of heating on passive and active biomechanics of suspended cells. [Journal Article]
- Interface Focus 2014 Apr 6; 4(2):20130069.
A cell is a complex material whose mechanical properties are essential for its normal functions. Heating can have a dramatic effect on these mechanical properties, similar to its impact on the dynamics of artificial polymer networks. We investigated such mechanical changes by the use of a microfluidic optical stretcher, which allowed us to probe cell mechanics when the cells were subjected to different heating conditions at different time scales. We find that HL60/S4 myeloid precursor cells become mechanically more compliant and fluid-like when subjected to either a sudden laser-induced temperature increase or prolonged exposure to higher ambient temperature. Above a critical temperature of 52 ± 1°C, we observed active cell contraction, which was strongly correlated with calcium influx through temperature-sensitive transient receptor potential vanilloid 2 (TRPV2) ion channels, followed by a subsequent expansion in cell volume. The change from passive to active cellular response can be effectively described by a mechanical model incorporating both active stress and viscoelastic components. Our work highlights the role of TRPV2 in regulating the thermomechanical response of cells. It also offers insights into how cortical tension and osmotic pressure govern cell mechanics and regulate cell-shape changes in response to heat and mechanical stress.
- Asymmetric facial skin viscoelasticity during climacteric aging. [Journal Article]
- Clin Cosmet Investig Dermatol 2014.:111-8.
Climacteric skin aging affects certain biophysical characteristics of facial skin. The purpose of the present study was to assess the symmetric involvement of the cheeks in this stage of the aging process.Skin viscoelasticity was compared on both cheeks in premenopausal and post-menopausal women with indoor occupational activities somewhat limiting the influence of chronic sun exposure. Eighty-four healthy women comprising 36 premenopausal women and 48 early post-menopausal women off hormone replacement therapy were enrolled in two groups. The tensile characteristics of both cheeks were tested and compared in each group. A computerized suction device equipped with a 2 mm diameter hollow probe was used to derive viscoelasticity parameters during a five-cycle procedure of 2 seconds each. Skin unfolding, intrinsic distensibility, biological elasticity, and creep extension were measured.Both biological elasticity and creep extension were asymmetric on the cheeks of the post-menopausal women. In contrast, these differences were more discrete in the premenopausal women.Facial skin viscoelasticity appeared to be asymmetric following menopause. The possibility of asymmetry should be taken into account in future studies of the effects of hormone replacement therapy and any antiaging procedure on the face in menopausal women.