Development of in situ forming implants for controlled delivery of punicalagin.

Due to efficient drainage of the joint, the development of intra-articular depots for long-lasting drug release is a difficult challenge. Moreover, a disease-modifying osteoarthritis drug (DMOAD) that can effectively manage osteoarthritis has yet to be identified. The current study was undertaken to explore the potential of injectable, in situ forming implants to create depots that support the sustained release of punicalagin, a promising DMOAD. In vitro experiments demonstrated punicalagin's ability to suppress production of interleukin-1ß and prostaglandin E2, confirming its chondroprotective properties. Regarding the entrapment of punicalagin, it was demonstrated by LC-MS/MS to be stable within PLGA in situ forming implants for several weeks and capable of inhibiting collagenase upon release. In vitro punicalagin release kinetics were tunable through variation of solvent, PLGA lactide:glycolide ratio, and polymer concentration, and an optimized formulation supported release for approximately 90 days. The injection force of this formulation steadily increased with plunger advancement and higher rates of advancement were associated with greater forces. Although the optimal formulation was highly cytotoxic to primary chondrocytes if cells were exposed immediately or shortly after implant formation, upwards of 70 % survival was achieved when the implants were first allowed to undergo a 24-72 h period of phase inversion prior to cell exposure. This study demonstrates a PLGA-based in situ forming implant for the controlled release of punicalagin. With modification to address cytotoxicity, such an implant may be suitable as an intra-articular therapy for OA.

Laser microgrooving and resorbable blast texturing for enhanced surface function of titanium alloy for dental implant applications.

Long-term dental implant success is dependent on biocompatibility and osseointegration between the bone and the implant. Surface modifications such as laser-induced microgrooving which increase contact area can enhance osseointegration by establishing and directing a stable attachment between the implant surface and peri-implant bone. The objective of this study was to evaluate pre-osteoblast proliferation, morphology, and differentiation on titanium alloy (Ti64) surfaces-Laser-Lok© (LL), resorbable blast textured (RBT), and machined (M)-compared to tissue culture plastic (TCP) control. We hypothesized the LL surfaces would facilitate increased cellular alignment compared to all other groups, and LL and RBT surfaces would demonstrate enhanced proliferation and differentiation compared to M and TCP surfaces. Surface roughness was quantified using a surface profilometer, and water contact angle was measured to evaluate the hydrophilicity of the surfaces. Cellular function was assessed using quantitative viability and differentiation assays and image analyses, along with qualitative fluorescent (viability and cytoskeletal) imaging and scanning electron microscopy. No differences in surface roughness were observed between groups. Water contact angle indicated LL was the least hydrophilic surface, with RBT and M surfaces exhibiting greater hydrophilicity. Cell proliferation on day 2 was enhanced on both LL and RBT surfaces compared to M, and all three groups had higher cell numbers on day 2 compared to day 1. Cell orientation was driven by the geometry of the surface modification, as cells were more highly aligned on LL surfaces compared to TCP (on day 2) and RBT (on day 3). At day 21, cell proliferation was greater on LL, RBT, and TCP surfaces compared to M, though no differences in osteogenic differentiation were observed. Collectively, our results highlight the efficacy of laser microgrooved and resorbable blast textured surface modifications of Ti64 for enhancing cellular functions, which may facilitate improved osseointegration of dental implants.

Comparison of the Capacitance of a Cyclically Fatigued Stretch Sensor to a Non-Fatigued Stretch Sensor When Performing Static and Dynamic Foot-Ankle Motions.

Motion capture is the current gold standard for assessing movement of the human body, but laboratory settings do not always mimic the natural terrains and movements encountered by humans. To overcome such limitations, a smart sock that is equipped with stretch sensors is being developed to record movement data outside of the laboratory. For the smart sock stretch sensors to provide valuable feedback, the sensors should have durability of both materials and signal. To test the durability of the stretch sensors, the sensors were exposed to high-cycle fatigue testing with simultaneous capture of the capacitance. Following randomization, either the fatigued sensor or an unfatigued sensor was placed in the plantarflexion position on the smart sock, and participants were asked to complete the following static movements: dorsiflexion, inversion, eversion, and plantarflexion. Participants were then asked to complete gait trials. The sensor was then exchanged for either an unfatigued or fatigued plantarflexion sensor, depending upon which sensor the trials began with, and each trial was repeated by the participant using the opposite sensor. Results of the tests show that for both the static and dynamic movements, the capacitive output of the fatigued sensor was consistently higher than that of the unfatigued sensor suggesting that an upwards drift of the capacitance was occurring in the fatigued sensors. More research is needed to determine whether stretch sensors should be pre-stretched prior to data collection, and to also determine whether the drift stabilizes once the cyclic softening of the materials comprising the sensor has stabilized.

Effects of short-duration treatment of cartilage with punicalagin and genipin and the implications for treatment of osteoarthritis.

Punicalagin (PA) not only binds type II collagen, but also blocks its MMP-13-mediated degradation, and genipin (GNP) is a collagen cross-linking agent. We hypothesized that these drugs could mitigate the loss of cartilage if administered in the early phase of osteoarthritis, and experiments were designed to provide proof-of-concept. Porcine cartilage was exposed to both drugs in a manner designed to simulate intra-articular (IA) injection. Based on penetration of PA into cartilage, the rate of drug diffusion was conservatively estimated at 2 µm per minute. GNP caused a measurable degree of cross-linking, increased compressive resistance and coefficient of friction, and substantially inhibited degradation by collagenase, but not by hyaluronidase. Pre-incubation of GNP with collagenase had no effect on enzymatic activity. PA did not cross-link collagen nor affect the mechanical properties of cartilage. It did, however, increase resistance to degradation by collagenase and hyaluronidase. Furthermore, it reacted with collagenase in solution and inhibited its subsequent enzymatic activity. Effects of PA and GNP were not additive. The chondroprotective effect of semi-weekly IA injections was investigated in the monoiodoacetate-induced model of OA in rats. Quantitative histology suggested that injection of PA decreased the amount of cartilage lost compared to saline-injected controls, and the addition of GNP made no difference. This study supports the notion that IA delivery of PA could mitigate OA-induced cartilage erosion.

Assessment of erythrocyte damage and in-line pressure changes associated with simulated transfusion of canine blood through microaggregate filters.

OBJECTIVE: To determine whether passage of whole blood through a microaggregate filter by use of a syringe pump would damage canine erythrocytes. SAMPLE: Blood samples obtained from 8 healthy client-owned dogs. PROCEDURES: Whole blood was passed through a standard microaggregate filter by use of a syringe pump at 3 standard administration rates (12.5, 25, and 50 mL/h). Prefilter and postfilter blood samples were collected at the beginning and end of a simulated transfusion. Variables measured at each time point included erythrocyte osmotic fragility, mean corpuscular fragility, RBC count, hemoglobin concentration, RBC distribution width, and RBC morphology. In-line pressure when blood passed through the microaggregate filter was measured continuously throughout the simulated transfusion. After the simulated transfusion was completed, filters were visually analyzed by use of scanning electron microscopy. RESULTS: Regardless of administration rate, there was no significant difference in mean corpuscular fragility, RBC count, hemoglobin concentration, or RBC distribution width between prefilter and postfilter samples. Additionally, there were no differences in in-line pressure during the simulated transfusion among administration rates. Echinocytes were the erythrocyte morphological abnormality most commonly observed at the end of the transfusion at administration rates of 12.5 and 25 mL/h. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that regardless of the administration rate, the microaggregate filter did not alter fragility of canine RBCs, but may have altered the morphology. It appeared that the microaggregate filter would not contribute to substantial RBC damage for transfusions performed with a syringe pump.

Effects of short- and long-term administration of nonsteroidal anti-inflammatory drugs on osteotomy healing in dogs.

OBJECTIVE: To determine the influence of short-term administration of carprofen on bone healing in dogs. STUDY DESIGN: Randomized controlled experimental study. ANIMALS: Eighteen purpose-bred sexually mature hound dogs. METHODS: Tibial osteotomies were performed, and dogs were divided into three groups: no carprofen (n = 6), 2-week administration of carprofen at 2.2 mg/kg twice daily (n = 6), and 8-week administration of carprofen at 2.2 mg/kg twice daily (n = 5). Bone healing was evaluated radiographically at 4 and 8 weeks postoperatively. Postmortem, fracture healing was assessed via biomechanical testing (three-point bending), histological cartilage:callus ratio, and bone mineral density (BMD) with quantitative computed tomography. RESULTS: No biomechanical difference was detected between dogs that received no carprofen and those that received 2 weeks of carprofen or between those that received 2 weeks vs 8 weeks of carprofen. Stiffness (P = .035) and maximum stress (P = .042) were higher in dogs that received no carprofen than in those that received 8 weeks of carprofen. Radiographic healing did not differ between dogs without carprofen and those with 2-week administration of carprofen (P = .9923). However, tibias of dogs without carprofen and those with 2-week administration of carprofen were more healed compared with those in the 8-week-carprofen group at 4 and 8 weeks after surgery (P = .0011). No treatment effect was detected by cartilage:callus ratio or BMD. CONCLUSION: Long-term administration of carprofen had a negative effect on bone healing compared with short-term or no administration of carprofen. CLINICAL SIGNIFICANCE: Nonsteroidal anti-inflammatory drugs should be used cautiously in dogs at risk for delayed bone healing, and administration should be discontinued beyond the perioperative period in dogs with fractures or osteotomies.

A biomechanical comparison of conventional dynamic compression plates and string-of-pearls™ locking plates using cantilever bending in a canine Ilial fracture model.

BACKGROUND: Fracture of the ilium is common orthopedic injury that often requires surgical stabilization in canine patients. Of the various methods of surgical stabilization available, application of a lateral bone plate to the ilium is the most common method of fixation. Many plating options are available, each having its own advantages and disadvantages. The purpose of this study was to evaluate the biomechanical properties of a 3.5 mm String-of-Pearls™ plate and a 3.5 mm dynamic compression plate in a cadaveric canine ilial fracture model. Hemipelves were tested in cantilever bending to failure and construct stiffness, yield load, displacement at yield, ultimate load, and mode of failure were compared. RESULTS: The mean stiffness of dynamic compression plate (116 ± 47 N/mm) and String-of-Pearls™ plate (107 ± 18 N/mm) constructs, mean yield load of dynamic compression plate (793 ± 333 N) and String-of-Pearls™ plate (860 ± 207 N) constructs, mean displacement at yield of dynamic compression plate (8.6 ± 3.0 mm) and String-of-Pearls™ plate (10.2 ± 2.8 mm) constructs, and ultimate load at failure of dynamic compression plate (936 ± 320 N) and String-of-Pearls™ plate (939 ± 191 N) constructs were not significantly different. No differences were found between constructs with respect to mode of failure. CONCLUSIONS: No significant biomechanical differences were found between String-of-Pearls™ plate and dynamic compression plate constructs in this simplified cadaveric canine ilial fracture model.

Biomechanical Testing and Histologic Examination of Intradermal Skin Closure in Dogs Using Barbed Suture Device and Non-Barbed Monofilament Suture.

OBJECTIVE: To compare the biomechanical strength and histologic features of 3-0 Glycomer™ 631 barbed suture (V-LOC™ 90 Absorbable Wound Closure Device, Covidien, Mansfield, MA) to non-barbed 3-0 Glycomer™ 631 suture (Biosyn™, Covidien) for intradermal skin wound closure in the dog. STUDY DESIGN: Randomized, factorial, in vivo. ANIMALS: Eighteen purpose-bred, mature male, and female hound dogs. METHODS: Eighteen adult hound dogs were randomly assigned to 1 of 3 groups designated by postoperative day of assessment. Six skin incisions were made along the dorsum in the thoracolumbar region of each dog with an equal number (n=3) randomly assigned to closure with barbed or non-barbed suture. Six dogs were euthanatized on postoperative days 3, 10, and 14, respectively. Two additional incisions were made on each dog after euthanasia for baseline data (Day 0). The skin incision specimens were harvested for biomechanical testing and histologic evaluation. RESULTS: Non-barbed closure had significantly higher maximum load at failure (P<.001) and stiffness (P<.001) than barbed closure regardless of day. The average tissue reaction score was significantly higher for barbed closure (P=.008), regardless of day. Suturing time for barbed closures was significantly shorter. There was no significant difference in frequency of complications between closures. CONCLUSION: Barbed Glycomer™ 631 closures had a significantly lower maximum load at failure and stiffness, and higher average tissue reaction scores, but showed no difference in short term outcome for intradermal closure of dorsally located skin incisions in dogs.

Pullout strength of monocortical and bicortical screws in metaphyseal and diaphyseal regions of the canine humerus.

OBJECTIVE: Monocortical screws are commonly employed in locking plate fixation, but specific recommendations for their placement are lacking and use of short monocortical screws in metaphyseal bone may be contraindicated. Objectives of this study were to evaluate axial pullout strength of two different lengths of monocortical screws placed in various regions of the canine humerus compared to bicortical screws, and to derive cortical thickness and bone density values for those regions using quantitative computed tomography analysis (QCT). METHODS: The QCT analysis was performed on 36 cadaveric canine humeri for six regions of interest (ROI). A bicortical, short monocortical, or 50% transcortical 3.5 mm screw was implanted in each ROI and axial pullout testing was performed. RESULTS: Bicortical screws were stronger than monocortical screws in all ROI except the lateral epicondylar crest. Short monocortical metaphyseal screws were weaker than those placed in other regions. The 50% transcortical screws were stronger than the short monocortical screws in the condyle. A linear relationship between screw length and pullout strength was observed. CLINICAL SIGNIFICANCE: Cortical thickness and bone density measurements were obtained from multiple regions of the canine humerus using QCT. Use of short monocortical screws may contribute to failure of locking plate fixation of humeral fractures, especially when placed in the condyle. When bicortical screw placement is not possible, maximizing monocortical screw length may optimize fixation stability for distal humeral fractures.

Structural and biomechanical characterizations of porcine myocardial extracellular matrix.

Extracellular matrix (ECM) of myocardium plays an important role to maintain a multilayered helical architecture of cardiomyocytes. In this study, we have characterized the structural and biomechanical properties of porcine myocardial ECM. Fresh myocardium were decellularized in a rotating bioreactor using 0.1 % sodium dodecyl sulfate solution. Masson's trichrome staining and SEM demonstrated the removal of cells and preservation of the interconnected 3D cardiomyocyte lacunae. Movat's pentachrome staining showed the preservation of cardiac elastin ultrastructure and vascular elastin distribution/alignment. DNA assay result confirmed a 98.59 % reduction in DNA content; the acellular myocardial scaffolds were found completely lack of staining for the porcine α-Gal antigen; and the accelerating enzymatic degradation assessment showed a constant degradation rate. Tensile and shear properties of the acellular myocardial scaffolds were also evaluated. Our observations showed that the acellular myocardial ECM possessed important traits of biodegradable scaffolds, indicating the potentials in cardiac regeneration and whole heart tissue engineering.

A comparative biomechanical analysis of term fetal membranes in human and domestic species.

OBJECTIVE: The purpose of this study was to biomechanically characterize and compare human, porcine, equine, and ovine fetal membranes. STUDY DESIGN: Noncontact metrology was used for topographic analyses. Uniaxial tensile testing was performed to resolve specific biomechanical values. Puncture force and radial stresses were determined with biaxial puncture testing. Microstructure and surface tortuosity were analyzed histologically. RESULTS: Equine and human membranes sustained larger magnitude loading, but ovine and porcine membranes exhibited stronger material properties. Biaxial puncture validated uniaxial results; human and equine groups accommodated the largest loads but lowest stresses. Equine membranes were mostly vascularized; tortuosity was highest in porcine membranes. Species' gestation length was correlated positively with membrane thickness. CONCLUSION: The anatomy of placentation and length of species gestation show distinct relationships to membrane biomechanics. Unlike other species, human fetal membranes do not compensate for structural weakness with a thicker membrane. This finding may explain the high incidence of preterm premature rupture of membranes in humans.

Effect of a mechanical stimulation bioreactor on tissue engineered, scaffold-free cartilage.

Achieving sufficient functional properties prior to implantation remains a significant challenge for the development of tissue engineered cartilage. Many studies have shown chondrocytes respond well to various mechanical stimuli, resulting in the development of bioreactors capable of transmitting forces to articular cartilage in vitro. In this study, we describe the production of sizeable, tissue engineered cartilage using a novel scaffold-free approach, and determine the effect of perfusion and mechanical stimulation from a C9-x Cartigen bioreactor on the properties of the tissue engineered cartilage. We created sizable tissue engineered cartilage from porcine chondrocytes using a scaffold-free approach by centrifuging a high-density chondrocyte cell-suspension onto an agarose layer in a 50 mL tube. The gross and histological appearances, biochemical content, and mechanical properties of constructs cultured in the bioreactor for 4 weeks were compared to constructs cultured statically. Mechanical properties were determined from unconfined uniaxial compression tests. Constructs cultured in the bioreactor exhibited an increase in total GAG content, equilibrium compressive modulus, and dynamic modulus versus static constructs. Our study demonstrates the C9-x CartiGen bioreactor is able to enhance the biomechanical and biochemical properties of scaffold-free tissue engineered cartilage; however, no additional enhancement was seen between loaded and perfused groups.

Vasoactive agents alter the biomechanical properties of aortic heart valve leaflets in a time-dependent manner.

BACKGROUND AND AIM OF THE STUDY: Although the vasoactive agents, angiotensin II (Ang II) and 5-hydroxytryptamine (5-HT) are implicated in aortic heart valve disease, it is unclear how these compounds alter the biomechanical properties of valve leaflet tissue. The study aim was to characterize temporal changes in the elastic modulus of tissues incubated with these compounds. METHODS: Valve leaflets were excised from fresh porcine aortic heart valves. Leaflet tissue was incubated with 10(-6) M 5-HT, or 10(-6) M Ang II. The stress and elongation of the tissue in the circumferential and radial directions was measured using a stepper motor-driven micromechanical testing machine at 0.5, 6, and 24 h, followed by calculations of strain and elastic modulus of each sample. RESULTS: Tissue samples incubated with Ang II showed a significant increase in stiffness with time in the radial direction, but not in the circumferential direction. Regression analysis showed a correlation between time and elastic modulus for the tissue (R2 = 0.84). Conversely, leaflets incubated in 5-HT did not show any significant change in elastic modulus over time in the radial direction; however, significant increases in stiffness were observed after 24 h in the circumferential direction. A strong correlation between the elastic modulus in the circumferential direction and time was also noted (R2 = 0.99). CONCLUSION: The study results showed that vasoactive agents are capable of increasing the elastic modulus of aortic valve tissue in a time-dependent manner. Furthermore, the biomechanical changes induced by vasoactive agents are direction-specific, indicating different modes of action.

Production of hyaline-like cartilage by bone marrow mesenchymal stem cells in a self-assembly model.

A scaffoldless or self-assembly approach to cartilage tissue engineering has been used to produce hyaline cartilage from bone marrow-derived mesenchymal stem cells (bMSCs), but the mechanical properties of such engineered cartilage and the effects the transforming growth factor (TGF) isoform have not been fully explored. This study employs a cell culture insert model to produce tissue-engineered cartilage using bMSCs. Neonatal pig bMSCs were isolated by plastic adherence and expanded in monolayer before being seeded into porous transwell inserts and cultured for 4 or 8 weeks in defined chondrogenic media containing either TGF-beta1 or TGF-beta3. Following biomechanical evaluation in confined compression, colorimetric dimethyl methylene blue and Sircol dye-binding assays were used to analyze glycosaminoglycan (GAG) and collagen contents, respectively. Histological sections were stained with toluidine blue for proteoglycans and with picrosirius red to reveal collagen orientation, and immunostained for detection of collagen types I and II. Neocartilage increased in thickness, collagen, and GAG content between 4 and 8 weeks. Proteoglycan concentration increased with depth from the top surface. The tissue contained much more collagen type II than type I, and there was a consistent pattern of collagen alignment. TGF-beta1-treated and TGF-beta3-treated constructs were similar at 4 weeks, but 8-week TGF-beta1 constructs had a higher aggregate modulus and GAG content compared to TGF-beta3. These results demonstrate that bMSCs can generate functional hyaline-like cartilage through a self-assembling process.

Effect of collagen hydrolysate on chondrocyte-seeded agarose constructs.

The mechanical properties of engineered cartilage are strongly dependent on collagen content, but the collagen to glycosaminoglycan ratio in engineered cartilage is often much lower than that of the native tissue. Therefore culture medium supplements which increase collagen production by chondrocytes are of interest. It had previously been reported that collagen hydrolysate stimulated type II collagen biosynthesis in short-term, high density monolayer chondrocyte cultures. It was hypothesized that collagen hydrolysate added to the culture medium of three dimensional chondrocyte-agarose constructs would enhance their mechanical properties. Porcine articular chondrocytes were embedded in 2% agarose and cultured for up to 6 weeks with and without 1 mg/ml collagen hydrolysate. The instantaneous compressive modulus and equilibrium compressive modulus were significantly lower in the collagen hydrolysate-treated constructs, consistent with the finding of lower collagen and GAG content. Contrary to our hypothesis, our results indicate that 1 mg/ml collagen hydrolysate may actually inhibit macromolecule biosynthesis and be detrimental to the mechanical properties of long term chondrocyte-agarose constructs.

Biomechanical and molecular characteristics of hereditary equine regional dermal asthenia in Quarter Horses.

Hereditary equine regional dermal asthenia (HERDA) is an autosomal recessive skin disorder that has yet to be fully characterized. HERDA is predominately expressed in Quarter Horses, with the majority of these disseminating from elite cutting horse bloodlines, leading to the increased incidence of HERDA in recent years. Affected horses have loose, hyper-extensible, fragile skin and are frequently euthanized due to poor wound healing and disfiguring scars. This study sought to better characterize HERDA by analysis of the biomechanical parameters of tensile strength, modulus of elasticity, energy to failure and thickness of skin from 10 affected and 6 unaffected horses using an Instron Universal Testing Instrument. In addition, total soluble collagen and glycosaminoglycan concentrations of skin were analysed from 13 affected and 12 unaffected horses using Sircol Soluble Collagen and Blyscan Sulfated Glycosaminoglycan assays respectively. Affected horses exhibited a two to threefold reduction in tensile strength versus unaffected horses with statistically significant differences at six of seven sample locations (P < or = 0.05). The modulus of elasticity proved to be significantly different at six of seven sample locations, energy to failure at six of seven sample locations, and skin thickness at one of seven sample locations (P < or = 0.05). Affected horses exhibited significantly higher amounts of total soluble collagen than unaffected horses (P < or = 0.05). No significant difference was demonstrated between groups for glycosaminoglycan concentration. Affected horses demonstrated uniformly weaker skin across sample locations, indicating the biomechanical properties of HERDA are not regionally confined to specific areas of the horses' skin.

The anisotropic compressive mechanical properties of the rabbit patellar tendon.

In this study, we examine the transverse and longitudinal compressive mechanical behavior of the rabbit patellar tendon. The anisotropic compressive properties are of interest, because compression occurs where the tendon attaches to bone and where the tendon wraps around bone leading to the development of fibro-cartilaginous matrices. We quantified the time dependent viscoelastic and anisotropic behavior of the tendon under compression. For both orientations, sections of patellar tendon were drawn from mature male white New Zealand rabbits in preparation for testing. The tendons were sequentially compressed to 40% strain at strain rates of 0.1, 1 and 10% strain(s) using a computer-controlled stepper motor driven device under physiological conditions. Following monotonic loading, the tendons were subjected to stress relaxation. The tendon equilibrium compressive modulus was quantified to be 19.49+/-11.46 kPa for the transverse direction and 1.11+/-0.57 kPa for the longitudinal direction. The compressive modulus at applied strain rates of 0.1, 1 and 10% strain(s) in the transverse orientation were 13.48+/-2.31, 18.24+/-4.58 and 20.90+/-8.60 kPa, respectively. The compressive modulus at applied strain rates of 0.1, 1 and 10% strain/s in the longitudinal orientation were 0.19+/-0.11, 1.27+/-1.38 and 3.26+/-3.49 kPa, respectively. The modulus values were almost significantly different for the examination of the effect of orientation on the equilibrium modulus (p=0.054). Monotonic loading of the tendon showed visual differences of the strain rate dependency; however, no significant difference was shown in the statistical analysis of the effect of strain rate on compressive modulus. The statistical analysis of the effect of orientation on compressive modulus showed a significant difference. The difference shown in the orientation analysis validated the anisotropic nature of the tendon.

Influence of hydrostatic and distortional stress on chondroinduction.

Undifferentiated connective tissue that arises during embryonic development and some healing processes contains pluripotent mesenchymal stem cells. It is becoming increasingly evident that the mechanical environment is an important differentiation factor for these cells. In our laboratory, we have focused on the potential for mechanical signals to induce chondrogenic differentiation of mesenchymal stem cells. Using C3H10T1/2 cells as a model, we have investigated the influence of hydrostatic pressure, equibiaxial contraction, and centrifugal pressure on chondroinduction. Cells responded to cyclic hydrostatic compression (5 MPa at 1 Hz) and cyclic contractile strain (15% at 1 Hz) by upregulating aggrecan and collagen type II gene expression. In addition, a preliminary study of the effects of centrifugal pressure (4.1 MPa for 30 min) suggests that it may increase cell proliferation and stimulate proteoglycan and collagen type II production. We speculate that compression, whether it is distortional or hydrostatic in nature, applied to undifferentiated connective tissue triggers differentiation toward a chondrocyte-like phenotype and production of a less permeable extracellular matrix which is capable of sustaining increasingly higher hydrostatic fluid pressure for compressive load support.

Variation of diameter distribution, number density, and area fraction of fibrils within five areas of the rabbit patellar tendon.

The purpose of this investigation is to show microstructural information at various regions within the rabbit patellar tendon. The properties of the rabbit patellar tendon are well documented mechanically, but detailed information at the microscopic level is not available. Increasing attention has been directed to soft tissue microscopy as the demand for development of biologically inspired materials increases. Microstructural examination of the tendon fibrils is performed to provide further insight into understanding of the structure to function relations within the rabbit patellar tendon. Limited studies on rabbit patellar tendon collagen fibrils at the microscopic level have been computed. Furthermore, evaluation of structure-function relations in multiple regions of any given specimen of a particular tissue type has not been conducted. In this study the number density, area fraction, and diameter distribution of collagen fibrils have been determined. Overall, this examination showed considerable variation within each section of the tendon. Correlating these structural results with mechanical tests of the tendon portions in the various regions could provide additional information on the mechanics of the rabbit tendon as well as insight into development of artificial tissue constructs.

Effect of Cytoskeletal Disruption on Mechanotransduction of Hydrostatic Pressure by C3H10T1/2 Murine Fibroblasts.

Cyclic hydrostatic pressure of physiological magnitude (< 10 MPa) stimulates chondrogenic differentiation of mesenchymal stem cells, but mechanotransduction mechanisms are not well understood. It was hypothesized that an intact cytoskeleton would be required for uninhibited mechanotransduction of hydrostatic pressure. Therefore we examined the effects of drugs which selectively interfere with actin and tubulin polymerization on pressure-induced upregulation of aggrecan and col2a1 (type II collagen) mRNA expression. C3H10T1/2 cells were cultured as pellets in either 4microM cytochalasin D or 4microM nocodazole and subjected to 3 days of cyclic hydrostatic compression (1 Hz, 5 MPa, 2 h per day). Phalloidin staining and indirect immunostaining with anti alpha-tubulin antibody confirmed disruption of microfilament and microtubule assemblies, respectively. Real time RT-PCR revealed that both drugs substantially lowered the basal level of aggrecan and col2a1 mRNA, but that neither drug prevented a pressure-stimulated increase in gene expression relative to the altered basal state. Thus upregulation of macromolecular gene expression by cyclic hydrostatic pressure did not require a completely intact cytoskeleton.