Initial contact shapes the perception of friction.

Humans efficiently estimate the grip force necessary to lift a variety of objects, including slippery ones. The regulation of grip force starts with the initial contact and takes into account the surface properties, such as friction. This estimation of the frictional strength has been shown to depend critically on cutaneous information. However, the physical and perceptual mechanism that provides such early tactile information remains elusive. In this study, we developed a friction-modulation apparatus to elucidate the effects of the frictional properties of objects during initial contact. We found a correlation between participants' conscious perception of friction and radial strain patterns of skin deformation. The results provide insights into the tactile cues made available by contact mechanics to the sensorimotor regulation of grip, as well as to the conscious perception of the frictional properties of an object.

Biomechanical characteristics of the meniscocapsular junction of the posterior segment of the medial meniscus.

PURPOSE: Despite extensive literature available on the mechanical properties of knee ligaments and menisci, research on the mechanical properties of the meniscus-capsular junction (MCJ) is lacking. This study aims to investigate the biomechanical behavior of the MCJ of the medial meniscus using a tensile failure test. MATERIALS AND METHODS: Seven dissected cadaveric knees were used for biomechanical analysis. Tensile failure tests were performed using an INSTRON ElectroPuls E1000 stress system to measure stress/strain curves, maximum load at failure, elastic limit load, elongation at break, elongation at the elastic limit, and linear stiffness, were collected and analyzed. RESULTS: All ruptures occurred at the MCJ. The MCJ displayed similar mechanical properties to knee ligaments. Average values were: maximum load at failure (63.9 ± 3.2 N), yield load (52.9 N ± 2.6 N), elongation at break (2.5 mm ± 0.3 mm), elongation at the elastic limit (1.25 mm ± 0.15 mm), strain at break (47.0% ± 3.5%), strain at yield (23.2% ± 2.3%), and stiffness (56.6 ± 9. N/mm-1). CONCLUSION: The meniscus-capsular junction's mechanical properties are similar to other knee ligaments and may play a role in knee stability. The findings provide insights into the the behavior of the meniscus-capsular junction could have clinical implications for diagnosing and surgical treatment of meniscocapsular lesions.

Influences of Molecular Weights on Physicochemical and Biological Properties of Collagen-Alginate Scaffolds.

For tissue engineering applications, biodegradable scaffolds containing high molecular weights (MW) of collagen and sodium alginate have been developed and characterized. However, the properties of low MW collagen-based scaffolds have not been studied in previous research. This work examined the distinctive properties of low MW collagen-based scaffolds with alginate unmodified and modified by subcritical water. Besides, we developed a facile method to cross-link water-soluble scaffolds using glutaraldehyde in an aqueous ethanol solution. The prepared cross-linked scaffolds showed good structural properties with high porosity (~93%) and high cross-linking degree (50-60%). Compared with collagen (6000 Da)-based scaffolds, collagen (25,000 Da)-based scaffolds exhibited higher stability against collagenase degradation and lower weight loss in phosphate buffer pH 7.4. Collagen (25,000 Da)-based scaffolds with modified alginate tended to improve antioxidant capacity compared with scaffolds containing unmodified alginate. Interestingly, in vitro coagulant activity assay demonstrated that collagen (25,000 Da)-based scaffolds with modified alginate (C25-A63 and C25-A21) significantly reduced the clotting time of human plasma compared with scaffolds consisting of unmodified alginate. Although some further investigations need to be done, collagen (25,000 Da)-based scaffolds with modified alginate should be considered as a potential candidate for tissue engineering applications.

Poly(Vinyl Alcohol) Cryogel Membranes Loaded with Resveratrol as Potential Active Wound Dressings.

Hydrogel wound dressings are highly effective in the therapy of wounds. Yet, most of them do not contain any active ingredient that could accelerate healing. The aim of this study was to prepare hydrophilic active dressings loaded with an anti-inflammatory compound - trans-resveratrol (RSV) of hydrophobic properties. A special attention was paid to select such a technological strategy that could both reduce the risk of irritation at the application site and ensure the homogeneity of the final hydrogel. RSV dissolved in Labrasol was combined with an aqueous sol of poly(vinyl) alcohol (PVA), containing propylene glycol (PG) as a plasticizer. This sol was transformed into a gel under six consecutive cycles of freezing (-80 °C) and thawing (RT). White, uniform and elastic membranes were successfully produced. Their critical features, namely microstructure, mechanical properties, water uptake and RSV release were studied using SEM, DSC, MRI, texture analyser and Franz-diffusion cells. The cryogels made of 8 % of PVA showed optimal tensile strength (0.22 MPa) and elasticity (0.082 MPa). The application of MRI enabled to elucidate mass transport related phenomena in this complex system at the molecular (detection of PG, confinement effects related to pore size) as well as at the macro level (swelling). The controlled release of RSV from membranes was observed for 48 h with mean dissolution time of 18 h and dissolution efficiency of 35 %. All in all, these cryogels could be considered as a promising new active wound dressings.

The Meniscus in Normal and Osteoarthritic Tissues: Facing the Structure Property Challenges and Current Treatment Trends.

The treatment of meniscus injuries has recently been facing a paradigm shift toward the field of tissue engineering, with the aim of regenerating damaged and diseased menisci as opposed to current treatment techniques. This review focuses on the structure and mechanics associated with the meniscus. The meniscus is defined in terms of its biological structure and composition. Biomechanics of the meniscus are discussed in detail, as an understanding of the mechanics is fundamental for the development of new meniscal treatment strategies. Key meniscal characteristics such as biological function, damage (tears), and disease are critically analyzed. The latest technologies behind meniscal repair and regeneration are assessed.

Chitinase-like1 Plays a Role in Stalk Tensile Strength in Maize.

Stalk lodging in maize (Zea mays) causes significant yield losses due to breaking of stalk tissue below the ear node before harvest. Here, we identified the maize brittle stalk4 (bk4) mutant in a Mutator F2 population. This mutant was characterized by highly brittle aerial parts that broke easily from mechanical disturbance or in high-wind conditions. The bk4 plants displayed a reduction in average stalk diameter and mechanical strength, dwarf stature, senescence at leaf tips, and semisterility of pollen. Histological studies demonstrated a reduction in lignin staining of cells in the bk4 mutant leaves and stalk, and deformation of vascular bundles in the stalk resulting in the loss of xylem and phloem tissues. Biochemical characterization showed a significant reduction in p-coumaric acid, Glc, Man, and cellulose contents. The candidate gene responsible for bk4 phenotype is Chitinase-like1 protein (Ctl1), which is expressed at its highest levels in elongated internodes. Expression levels of secondary cell wall cellulose synthase genes (CesA) in the bk4 single mutant, and phenotypic observations in double mutants combining bk4 with bk2 or null alleles for two CesA genes, confirmed interaction of ZmCtl1 with CesA genes. Overexpression of ZmCtl1 enhanced mechanical stalk strength without affecting plant stature, senescence, or fertility. Biochemical characterization of ZmCtl1 overexpressing lines supported a role for ZmCtl1 in tensile strength enhancement. Conserved identity of CTL1 peptides across plant species and analysis of Arabidopsis (Arabidopsis thaliana) ctl1-1 ctl2-1 double mutants indicated that Ctl1 might have a conserved role in plants.

Environmentally Friendly Films Combining Bacterial Cellulose, Chitosan, and Polyvinyl Alcohol: Effect of Water Activity on Barrier, Mechanical, and Optical Properties.

The interest in developing new materials intended for food packaging based on bacterial cellulose is growing in the recent years. Flexible and transparent films from bacterial cellulose-chitosan-polyvinyl alcohol have shown excellent UV-barrier properties. However, this material interacts with ambient moisture modifying its water activity due to its hydrophilic nature. In this work, a study was carried out to evaluate the changes caused by the water activity. Results showed a plasticizing effect of water molecules increasing the water vapor permeability of the samples from 1.86 × 10-12 to 1.17 × 10-11 g/m·s·Pa, percentage of elongation from 3.25 to 36.55%, and distance to burst from 0.64 to 5.12 mm. The increase of the water activity decreased the Young's modulus and tensile strength. The values of the UV-barrier were maintained at the wide range of water activity. Consequently, water molecules do not affect the UV-barrier properties of the films.

Mechanical strain attenuates cytokine-induced ADAMTS9 expression via transient receptor potential vanilloid type 1.

The synovial fluids of patients with osteoarthritis (OA) contain elevated levels of inflammatory cytokines, which induce the expression of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) and of the matrix metalloproteinase (MMP) in chondrocytes. Mechanical strain has varying effects on organisms depending on the strength, cycle, and duration of the stressor; however, it is unclear under inflammatory stimulation how mechanical strain act on. Here, we show that mechanical strain attenuates inflammatory cytokine-induced expression of matrix-degrading enzymes. Cyclic tensile strain (CTS), as a mechanical stressor, attenuated interleukin (IL)-1ß and tumor necrosis factor (TNF)-α-induced mRNA expression of ADAMTS4, ADAMTS9, and MMP-13 in normal chondrocytes (NHAC-kn) and in a chondrocytic cell line (OUMS-27). This effect was abolished by treating cells with mechano-gated channel inhibitors, such as gadolinium, transient receptor potential (TRP) family inhibitor, ruthenium red, and with pharmacological and small interfering RNA-mediated TRPV1 inhibition. Furthermore, nuclear factor κB (NF-κB) translocation from the cytoplasm to the nucleus resulting from cytokine stimulation was also abolished by CTS. These findings suggest that mechanosensors such as the TRPV protein are potential therapeutic targets in treating OA.

Improved tendon healing by a combination of Tanshinone IIA and miR-29b inhibitor treatment through preventing tendon adhesion and enhancing tendon strength.

Background: Despite significant advances in the materials and methods development used in surgical repair and postoperative rehabilitation, the adhesion formation remains the most common clinical problem in tendon injuries. Therefore, the development of novel therapies is necessary for targeting at preventing tendon adhesion formation and improving tendon strength. Methods: We used rat fibroblasts for in vitro experiments to determine the optimal concentration of TSA in rats, and then set up negative control group, TSA intervention group, mir-29b interference adenovirus intervention group and TSA and mir-29b interference adenovirus co-intervention group. By comparing cell proliferation and protein expression in different group, we verified the effect and mechanism of drugs on fibroblast function. At the same time, the Sprague-Dawley rat Achilles tendon model in vivo was established in this study, which was divided into sham operation group and operation group. Afterwards in the operation group, mir-29b inhibitor and placebo were injected every 3 days respectively. Then the injection inhibitor group was divided into 5 groups which mean TSA was injected into the marked area at 0, 6, 24 and 72 hours after operation for 1 week, finally all of the rats were died at 3 weeks after operation. Through the observation of general properties, histological observation of Achilles tendon injury, biomechanical test and cell and protein expression in rats' tendon cell, the effect of drugs on tendon adhesion formation was analyzed. Results: We demonstrated that the combination of miR-29b inhibitor and tanshinone IIA(TSA) could prevent tendon adhesion and also enhance tendon strength. Mechanically, the miR-29b inhibitor could activate the TGF-ß/Smad3 pathway to trigger endogenous pathways and induce a high proliferation of fibroblast. Subsequently, we also found adding TSA after 6 hours of miR-29b treatment gave less cell cytotoxicity in our rat model with better outcome of less tendon adhesion and enhanced strength. Conclusion: We conclude that the use of miR-29b inhibitor at the end of the tendon break could initiate endogenous repair mechanism and subsequently use of TSA should be able to inhibit the exogenous repair mechanism. Therefore, the combination of both treatments could prevent tendon adhesion and ensure tendon strength. Our findings suggested that this approach would be a feasible approach for tendon repair.

The femoral posterior fan-like extension of the ACL insertion increases the failure load.

PURPOSE: To examine the role of the posterior fan-like extension of the ACL's femoral footprint on the ACL failure load. METHODS: Sixteen (n = 16) fresh frozen, mature porcine knees were used in this study and randomized into two groups (n = 8): intact femoral ACL insertion (ACL intact group) and cut posterior fan-like extension of the ACL (ACL cut group). In the ACL cut group, flexing the knees to 90°, created a folded border between the posterior fan-like extension and the midsubstance insertion of the femoral ACL footprint and the posterior fan-like extension was dissected and both areas were measured. Specimens were placed in a testing machine at 30° of flexion and subjected to anterior tibial loading (60 mm/min) until ACL failure. RESULTS: The intact ACL group had a femoral insertion area of 182.1 ± 17.1 mm2. In the ACL cut group, the midsubstance insertion area was 113.3 ± 16.6 mm2, and the cut posterior fan-like extension portion area was 67.1 ± 8.3 mm2. The failure load of the ACL intact group was 3599 ± 457 N and was significantly higher (p < 0.001) than the failure load of the ACL cut group 392 ± 83 N. CONCLUSION: Transection of the posterior fan-like extension of the ACL femoral footprint has a significant effect on the failure load of the ligament during anterior loading at full extension. Regarding clinical relevance, this study suggests the importance of the posterior fan-like extension of the ACL footprint which potentially may be retained with remnant preservation during ACL reconstruction. Femoral insertion remnant preservation may allow incorporation of the fan-like structure into the graft increasing graft strength.

Load-deformation properties of the ligament of the head of femur in situ.

The ligament of the head of femur (LHF) or ligamentum teres has been reported to tense during hip adduction and also to provide mechanical stability to the joint. LHF injury is more common in females and also in right hip joints compared with left ones. Although this could be due to leg dominance, pelvic size or muscle strength, there is no study that has looked into these differences. This cadaveric biomechanical study aimed to compare potential differences in the mechanical behavior of the LHF between neutral and 20° adducted hip joints, sex, and sides. Tensile tests of the LHF were performed on 25 hip joints (mean age at death of 85.7 ± 7.5 years; 9 females, 4 males; 13 left, 12 right), positioned either neutrally or in adduction. The maximum force required to rupture the ligament, its strain at failure, tensile strength, linear stiffness, and elastic modulus were obtained and statistically compared between analysis groups. The maximum force the LHF could withstand before rupture averaged 57 ± 37 N, strain at failure of 59 ± 33%, tensile strength of 2.9 ± 1.8 MPa, linear stiffness of 5.4 ± 3.5 N/mm, and elastic modulus of 7.2 ± 3.8 MPa. The LHF length at failure was significantly greater in males compared with females (P = 0.02). Irrespective of joint position, there were no statistical differences in the stress-strain properties of the LHF between females and males, or sides. There may be other anatomical, functional, and demographic factors that could render the ligament tissue vulnerable to injury in these groups. Clin. Anat., 33:705-713, 2020. © 2019 Wiley Periodicals, Inc.

The Specific Molecular Composition and Structural Arrangement of Eleutherodactylus Coqui Gular Skin Tissue Provide Its High Mechanical Compliance.

A male Eleutherodactylus Coqui (EC, a frog) expands and contracts its gular skin to a great extent during mating calls, displaying its extraordinarily compliant organ. There are striking similarities between frog gular skin and the human bladder as both organs expand and contract significantly. While the high extensibility of the urinary bladder is attributed to the unique helical ultrastructure of collagen type III, the mechanism behind the gular skin of EC is unknown. We therefore aim to understand the structure-property relationship of gular skin tissues of EC. Our findings demonstrate that the male EC gular tissue can elongate up to 400%, with an ultimate tensile strength (UTS) of 1.7 MPa. Species without vocal sacs, Xenopus Laevis (XL) and Xenopus Muelleri (XM), elongate only up to 80% and 350% with UTS~6.3 MPa and ~4.5 MPa, respectively. Transmission electron microscopy (TEM) and histological staining further show that EC tissues' collagen fibers exhibit a layer-by-layer arrangement with an uninterrupted, knot-free, and continuous structure. The collagen bundles alternate between a circular and longitudinal shape, suggesting an out-of-plane zig-zag structure, which likely provides the tissue with greater extensibility. In contrast, control species contain a nearly linear collagen structure interrupted by thicker muscle bundles and mucous glands. Meanwhile, in the rat bladder, the collagen is arranged in a helical structure. The bladder-like high extensibility of EC gular skin tissue arises despite it having eight-fold lesser elastin and five times more collagen than the rat bladder. To our knowledge, this is the first study to report the structural and molecular mechanisms behind the high compliance of EC gular skin. We believe that these findings can lead us to develop more compliant biomaterials for applications in regenerative medicine.

On the origin of the tensile strength of insect swarms.

Traditionally animal groups have been characterized by the macroscopic patterns that they form. It is now recognised that such patterns convey limited information about the nature of the aggregation as a whole. Aggregate properties cannot be determined by passive observations alone; instead one must interact with them. One of the first such dynamical tests revealed that swarms of flying insects have macroscopic mechanical properties similar to solids, including a finite Young's modulus and yield strength. Here I show, somewhat counterintuitively, that the emergence of these solid-like properties can be attributed to centre-of-mass movements (heat). This suggests that perturbations can drive phase transitions.

Poly-ε-caprolactone scaffold for the reinforcement of stapled small intestinal anastomoses: a randomized experimental study.

BACKGROUND: Anastomotic leakage is a severe complication in gastrointestinal surgery. Different methods have been evaluated for anastomotic reinforcement to prevent anastomotic leakage. The aim of this study was to investigate the effect of a poly-ε-caprolactone (PCL) scaffold incorporated in the staple-line, on the anastomotic strength and histological wound healing, of small intestinal anastomoses in piglets. METHOD: This randomized experimental trial included 17 piglets. In each piglet, three end-to-end anastomoses were performed in the small intestine with a circular stapler, i.e. one control and two interventional anastomoses. On postoperative day 5, the anastomoses were resected and subjected to tension stretch test and histological examination. RESULTS: No anastomotic leakage occurred. In the interventional anastomoses, the mean value for maximal tensile strength was 15.7 N, which was significantly higher than control anastomoses 12.7 N (p = 0.01). No statistically significant differences were found between the two groups in the histopathological parameters. CONCLUSION: To conclude, this study has shown that the incorporation of a PCL scaffold in the staple-line was feasible and significantly increased the maximal tensile strength of small intestine anastomoses in piglets on postoperative day 5. The difference in histological parameters was not significantly distinct.

Nuclear envelope proteins modulate proliferation of vascular smooth muscle cells during cyclic stretch application.

Cyclic stretch is an important inducer of vascular smooth muscle cell (VSMC) proliferation, which is crucial in vascular remodeling during hypertension. However, the molecular mechanism remains unclear. We studied the effects of emerin and lamin A/C, two important nuclear envelope proteins, on VSMC proliferation in hypertension and the underlying mechano-mechanisms. In common carotid artery of hypertensive rats in vivo and in cultured cells subjected to high (15%) cyclic stretch in vitro, VSMC proliferation was increased significantly, and the expression of emerin and lamin A/C was repressed compared with normotensive or normal (5%) cyclic stretch controls. Using targeted siRNA to mimic the repressed expression of emerin or lamin A/C induced by 15% stretch, we found that VSMC proliferation was enhanced under static and 5%-stretch conditions. Overexpression of emerin or lamin A/C reversed VSMC proliferation induced by 15% stretch. Hence, emerin and lamin A/C play critical roles in suppressing VSMC hyperproliferation induced by hyperstretch. ChIP-on-chip and MOTIF analyses showed that the DNAs binding with emerin contain three transcription factor motifs: CCNGGA, CCMGCC, and ABTTCCG; DNAs binding with lamin A/C contain the motifs CVGGAA, GCCGCYGC, and DAAGAAA. Protein/DNA array proved that altered emerin or lamin A/C expression modulated the activation of various transcription factors. Furthermore, accelerating local expression of emerin or lamin A/C reversed cell proliferation in the carotid artery of hypertensive rats in vivo. Our findings establish the pathogenetic role of emerin and lamin A/C repression in stretch-induced VSMC proliferation and suggest mechanobiological mechanism underlying this process that involves the sequence-specific binding of emerin and lamin A/C to specific transcription factor motifs.

Structural constitutive modeling of the anisotropic mechanical properties of human vocal fold lamina propria.

The anisotropic mechanical properties of the vocal fold lamina propria play an important role in voice production and control. The goal of this study is to develop a constitutive model capable of predicting lamina propria elastic moduli along both the longitudinal and transverse directions under different conditions of vocal fold elongation, which can be used as input to reduced-order phonation models based on linear elasticity. A structurally-based constitutive model that links microstructural characteristics of the lamina propria to its macromechanical properties is proposed. The model prediction has been shown to agree reasonably well with recent biaxial tensile testing results.

An Automatic Suturing Machine for Intestinal Anastomosis: Advantages Compared With Hand-Suturing Technique.

One of the main procedures in intestinal surgery is anastomosis, which is mostly performed by stapling or hand suturing. Due to limitations of these methods, a novel automatic suturing machine was designed and fabricated in this study, equipped with a needle-driving system; a thread control mechanism, and a linear mechanism, which is applicable in intestinal anastomosis by making continuous sutures. The main advantages of the fabricated machine are employing biocompatible suture, from the tissue's adaptation point of view, and making a uniform suturing pattern, independent of surgeon's skill, and thus offering a greater strength than the hand-sutured specimen. In order to evaluate the capability of the fabricated machine and investigate the validity of the hypothesis made in this study, that is, a more uniform suture will result in a greater mechanical strength of the sutured tissue, in vitro tests were performed on human intestine specimens, which were manually sutured by an expert surgeon and by the automatic suturing machine. The tensile tests with an elongation rate of 5 mm/min were done for 90 specimens, in 9 groups with various suturing configurations. The optimum pattern, from the mechanical strength point of view, was found to be the same in both manual and automatic suturing methods, that is, h7 d6 ( h = distance of suture from the edge of the tissue = 7 mm, and d = distance between stitches = 6 mm). It was also shown that the maximum breaking strength, for the best suturing pattern, h7 d6, is significantly greater when the automatic suturing machine was employed, compared with the hand-sutured tissue ( P < .001).

Do-It-Yourself Microsuture from Human Hair for Basic Microsurgical Training.

BACKGROUND: Microsuture is an essential material for basic microsurgical training. However, it is consumable, expensive, and sometimes unavailable in the microsurgical laboratory. To solve this problem, we developed a microsuture made from human hair and needle gauge. METHODS: Do-It-Yourself (DIY) microsuture is made from human hair and needle gauge 32G (BD Ultra-Fine Pen Needles 4 mm × 32G). Methods are explained step by step. This DIY microsuture (labeled as "test microsuture") and nylon 8-0 (Ethilon suture 8-0, labeled as "standard microsuture") were used for teaching orthopaedic residents to perform arterial anastomosis in chicken thighs. All residents practiced without knowing that "test microsuture" was made from the DIY method. After completing the training, quality of both microsutures was evaluated by questionnaire in topics of (1) thread quality (size, strength, elasticity, handing, knot perform, and knot security), (2) needle quality (size, curve, shape, sharpness, handling, and strength), (3) needle-thread interface (size, strength, and smoothness), and (4) overall quality of microsuture. Each category was evaluated by Likert score (5 = excellent, 4 = good, 3 = fair, 2 = poor, and 1 = very poor). RESULTS: The DIY microsuture was performed in three steps: (1) insert human hair into needle gauge by microforceps, (2) bend needle into smooth curve, and (3) disconnect needle and create needle-hair interface. The questionnaire was completed by 30 orthopaedic residents and showed that thread quality of DIY and standard microsuture had "good" and "good-to-excellent" quality (mean Likert score: 3.77-4.23 and 3.80-4.27, respectively, with no statistical difference). Thread-needle interface quality of DIY and standard microsuture also had "good" and "good-to-excellent" quality (Likert score: 3.73-4.20 and 4.07-4.33, respectively, with no statistical difference). Needle part of DIY microsuture had lower quality than standard suture (fair-to-good compared with good-to-excellence quality, score 3.30-3.67 vs. 4.20-4.27, respectively, with a statistically significant difference, p-value < 0.05). However, overall quality of DIY suture and standard microsuture had "good" and "good-to-excellent" (mean Likert score: 3.73 and 4.00, respectively, with no statistical difference). CONCLUSION: The DIY microsuture from human hair and needle gauge could be an alternative for basic microsurgical training with lower cost, easy production, and more availability for use in practice with acceptable quality compared with that of standard microsuture.

Scleraxis and osterix antagonistically regulate tensile force-responsive remodeling of the periodontal ligament and alveolar bone.

The periodontal ligament (PDL) is a mechanosensitive noncalcified fibrous tissue connecting the cementum of the tooth and the alveolar bone. Here, we report that scleraxis (Scx) and osterix (Osx) antagonistically regulate tensile force-responsive PDL fibrogenesis and osteogenesis. In the developing PDL, Scx was induced during tooth eruption and co-expressed with Osx. Scx was highly expressed in elongated fibroblastic cells aligned along collagen fibers, whereas Osx was highly expressed in the perialveolar/apical osteogenic cells. In an experimental model of tooth movement, Scx and Osx expression was significantly upregulated in parallel with the activation of bone morphogenetic protein (BMP) signaling on the tension side, in which bone formation compensates for the widened PDL space away from the bone under tensile force by tooth movement. Scx was strongly expressed in Scx(+)/Osx(+) and Scx(+)/Osx(-) fibroblastic cells of the PDL that does not calcify; however, Scx(-)/Osx(+) osteogenic cells were dominant in the perialveolar osteogenic region. Upon BMP6-driven osteoinduction, osteocalcin, a marker for bone formation was downregulated and upregulated by Scx overexpression and knockdown of endogenous Scx in PDL cells, respectively. In addition, mineralization by osteoinduction was significantly inhibited by Scx overexpression in PDL cells without affecting Osx upregulation, suggesting that Scx counteracts the osteogenic activity regulated by Osx in the PDL. Thus, Scx(+)/Osx(-), Scx(+)/Osx(+) and Scx(-)/Osx(+) cell populations participate in the regulation of tensile force-induced remodeling of periodontal tissues in a position-specific manner.

UVA/riboflavin collagen crosslinking stiffening effects on anterior and posterior corneal flaps.

The UVA/riboflavin collagen crosslinking (CXL) is one of the treatment procedure for stopping the progression of keratoconus. The inclusion criterion for this procedure is a minimum corneal thickness of 400 µm, which is not often met in patients with advanced keratoconus. Preoperatively swelling thin corneas was shown to stabilize the keratectasia without any postoperative endothelial damage. Recently, we have shown that swelling porcine corneas prior to the CXL treatment had no significant effect on the resulting improvement in their tensile properties. In the present study, we extended this previous study and characterized the stiffening effects of CXL on anterior and posterior flaps as a function of their hydration. A DSAEK system was used to excise 10 mm corneal flaps from 80 porcine corneas. Individual flaps were crosslinked at different initial hydration levels by using riboflavin solutions composed of different dextran concentrations; the thickness was taken as a measure of flap hydration. A DMA machine was used to measure the tensile properties either immediately after the CXL treatment or after the thickness (hydration) of the crosslinked samples was brought down to a specific value. The average thickness of anterior groups was 670 µm, 540 µm, and 410 µm, and the average thickness of posterior groups was 845 µm, 650 µm, and 440 µm. It was found that although CXL significantly increased the tensile properties of all anterior groups, it had an insignificant effect on the stiffness of posterior flaps. Furthermore, except for the posterior flaps in 845 µm and 650 µm thickness groups, decreasing the hydration significantly increased the tensile modulus (p < 0.05). Finally, the anterior flaps that were crosslinked at higher hydration, i.e. swollen before CXL, showed significantly less amount of stiffening in comparison with those crosslinked at lower hydration when the tensile property measurement was done at similar hydration (p < 0.05).