Steven H. Elder

Potential use of chitosan as a cell scaffold material for cartilage tissue engineering.

One of the most important factors in any tissue-engineering application is the cell substrate. The purpose of this study was the initial evaluation of chitosan, a derivative of the abundant, naturally occurring biopolymer chitin, as a cell scaffold for cartilage tissue engineering. Chitosan scaffolds having an interconnecting porous structure were easily fabricated by simple freezing and lyophilization of a chitosan solution. After rehydration of scaffolds, porcine chondrocytes were seeded onto scaffolds and cultured for up to 28 days in a rotating-wall bioreactor. Chitosan scaffolds supported cell attachment and maintenance of a rounded cell morphology. After 18 days, cells within the scaffolds had synthesized extracellular matrix in which proteoglycan and type II collagen were detected by toluidine blue staining and immunohistochemistry, respectively. Abundant extracellular matrix was found almost exclusively in the periphery of the scaffolds, as scaffold microstructure prevented cells from penetrating to interior regions. Nonetheless, the results suggest that chitosan scaffolds may be a useful alternative to synthetic cell scaffolds for cartilage tissue engineering.

Contact angle, protein adsorption and osteoblast precursor cell attachment to chitosan coatings bonded to titanium.

Chitosan, a derivative of the bio-polysaccharide chitin, has shown promise as a bioactive material for implant, tissue engineering and drug-delivery applications. The aim of this study was to evaluate the contact angle, protein adsorption and osteoblast precursor cell attachment to chitosan coatings bonded to titanium. Rough ground titanium (Ti) coupons were solution cast and bonded to 91.2% de-acetylated chitosan (1 wt% chitosan in 0.2% acetic acid) coatings via silane reactions. Non-coated Ti was used as controls. Samples were sterilized by ethylene oxide gas prior to experiments. Contact angles on all surfaces were measured using water. 5 × 104 cells/ml of ATCC CRL 1486 human embryonic palatal mesenchyme (HEPM) cells, an osteoblast precursor cell line, were used for the cell attachment study. SEM evaluations were performed on cells attached to all surfaces. Contact angles and cell attachment on all surfaces were statistically analyzed using ANOVA. The chitosan-coated surfaces (76.4 ± 5.1°) exhibited a significantly greater contact angle compared to control Ti surfaces (32.2±6.1°). Similarly, chitosan-coated surfaces exhibited significantly greater (P < 0.001) albumin adsorption, fibronectin adsorption and cell attachment, as compared to the control Ti surfaces. Coating chitosan on Ti surfaces decreased the wettability of the Ti, but increased protein adsorption and cell attachment. Increased protein absorption and cell attachment on the chitosan-coated Ti may be of benefit in enhancing osseointegration of implant devices.

The integration of chitosan-coated titanium in bone: an in vivo study in rabbits.

Procedure:Much research is directed at surface modifications to enhance osseointegration of implants. A new potential coating is the biopolymer, chitosan, the deacetylated derivative of the natural polysaccharide, chitin. Chitosan is biocompatible, degradable, nontoxic, and exhibits osteogenic properties. The aim of this research was to investigate the hypothesis that chitosan-coated titanium supports bone formation and osseointegration. Materials and Methods:Chitosan (1wt% of 92.3% deacetylated chitosan in 1% acetic acid) was solution cast and bonded to rough ground titanium pins (2-mm diameter × 4-mm long) via silane reactions. Calcium phosphate sputter-coated titanium and uncoated titanium pins were used as controls. Two chitosan-coated pins, and 1 each of calcium phosphate coated and uncoated pins were implanted unilaterally in the tibia of 16 adult male New Zealand white rabbits. At 2, 4, 8, and 12 weeks, undecalcified sections were histologically evaluated for healing and bone formation. Results:Histological evaluations of tissues in contact with the chitosan-coated pins indicated minimal inflammatory response and a typical healing sequence of fibrous, woven bone formation, followed by development of lamellar bone. These observations were similar to those for tissues interfacing the control calcium phosphate-coated and uncoated titanium implants. Quantitative comparisons of the bone-implant interface were not possible since 31% of the implants migrated into the tibial marrow space after implantation due to insufficient cortical bone thickness to hold pins in place during healing. Conclusion:These data support the hypothesis that chitosan-coatings are able to develop a close bony apposition or the osseointegration of dental/craniofacial and orthopedic implants.

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. Biotechnol. Bioeng. 2011; 108:1421–1429.

A biomechanical comparison of 3.5 locking compression plate fixation to 3.5 limited contact dynamic compression plate fixation in a canine cadaveric distal humeral metaphyseal gap model.

3.5 locking compression plate (LCP) fixation was compared to 3.5 limited contact dynamic compression plate (LC-DCP) fixation in a canine cadaveric, distal humeral metaphyseal gap model. Thirty paired humeri from adult, large breed dogs were separated into equal groups based on testing: static compression, cyclic compression, and cyclic torsion. Humeral constructs stabilised with LCP were significantly stiffer than those plated with LC-DCP when loaded in static axial compression (P = 0.0004). When cyclically loaded in axial compression, the LCP constructs were significantly less stiff than the LC-DCP constructs (P = 0.0029). Constructs plated with LCP were significantly less resistant to torsion over 500 cycles than those plated with LC-DCP (P<0.0001). The increased stiffness of LCP constructs in monotonic loading compared to constructs stabilised with non-locking plates may be attributed to the stability afforded by the plate-screw interface of locking plates. The LCP constructs demonstrated less stiffness in dynamic testing in this model, likely due to plate-bone offset secondary to non-anatomic contouring and occasional incomplete seating of the locking screws when using the torque-limiting screw driver. Resolution of these aspects of LCP application may help improve the stiffness of fixation in fractures modeled by the experimental set-up of this investigation.

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.

Comparison of a Suture Anchor and a Toggle Rod for Use in Toggle Pin Fixation of Coxofemoral Luxations

The mechanical characteristics of toggle rods and Bone Biter anchors inserted through the medial acetabular wall for toggle pin repair of coxofemoral luxations were compared in 16 canine cadaver pelves. No differences were detected in maximum load to failure, displacement at failure, or energy to failure between the two constructs. Toggle rod constructs failed primarily by breakage of the suture at the rod eyelet. All of the Bone Biter anchor constructs failed when the anchors pulled through the medial acetabular wall.

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.

Postoperative Integrity of Veterinary Surgical Gloves

A multicenter, prospective study was performed to document the incidence of defective gloves postoperatively in veterinary surgery and to correlate defects with a variety of influencing factors. Gloves were collected after surgical procedures performed by the small animal clinical services at two veterinary teaching hospitals and one institutions student surgery laboratories. Gloves were evaluated for defects using electrical resistance testing. The overall incidence of glove defects was 23.3%. Significantly more defects occurred in gloves used for nonsoft-tissue procedures and in gloves worn on the nondominant hand. Eighty-four percent of all defects occurred in procedures lasting >60 minutes. No differences were detected in the brands of gloves used nor among surgeons of different experience levels. The individuals performing the surgery were not able to accurately predict the presence of a defect in their gloves. Surgeons should remain alert for possible glove defects and consider measures such as changing gloves every 60 minutes or double-gloving to minimize potential complications.

The effect of tibial tuberosity advancement and meniscal release on kinematics of the cranial cruciate ligament-deficient stifle during early, middle, and late stance

OBJECTIVES To evaluate the effect of tibial tuberosity advancement (TTA) and meniscal release on cranial-caudal and axial rotational displacement during early, middle and late stance phases in the canine cranial cruciate ligament- (CCL) deficient stifle. STUDY DESIGN In vitro biomechanical study. METHODS Eighteen pelvic limbs were evaluated for the effects of TTA on cranial-caudal displacement and axial rotation under a load equivalent to 30% bodyweight, and under the following treatment conditions: normal (intact CCL), CCL deficient, TTA-treated (CCL deficient + TTA), and meniscal release (TTA treated + meniscal release). The limbs were evaluated in the early, middle, and late stance phases using electromagnetic tracking sensors to determine cranial tibial displacement and tibial rotation relative to the femur. RESULTS Transection of the CCL resulted in significant cranial tibial displacement during early, middle, and late stance (p < 0.0001) and significant internal rotation during early (p = 0.049) and middle stance (p = 0.0006). Performance of TTA successfully eliminated cranial tibial displacement in early, middle, and late stance (p <0.0001); however, the TTA was unsuccessful in normalizing axial rotation in middle stance (p = 0.030). Meniscal release had no effect on cranial-caudal or rotational displacement when performed in conjunction with the TTA. CLINICAL SIGNIFICANCE Tibial tuberosity advancement effectively eliminates cranial tibial displacement during early, middle and late stance; however, TTA failed to provide rotational stability in mid-stance.