Progress 10/01/02 to 09/30/07
Outputs
Outputs: Investigations of torsional properties of bone have initiated, work has focused on set-up or torsional testing system and specimen preparation. Data from torsional tests and axial compression tests which have been completed will permit computation of Poisson¿s ratio for the material. Variations in bone age, mineral composition and moisture content along with applied strain rates affect measured material properties, and these effects on axially loaded specimens has been noted. Torsional testing, followed by Mohr¿s analysis of stress data from both types of tests will aid in quantifying the degree of non-isotropic behavior as well as practical effects of clamping torsional specimens and contact friction in compression tests. A study of cricoid cartilage-suture interaction relevant to equine laryngoplasty has been completed. Strength, elasticity, and creep behavior of 5 different commercial suture materials (FiberWire #2, FiberWire #5, Securos, Ethibond¿, and Stainless Steel were quantified, along with the force-displacement behavior of a suture/cartilage combination representative of the surgical repair. Using force and displacement rates comparable to those found in independent dynamic in vivo studies of equine cadaver structures. Preloading by stretching of woven synthetic sutures before surgery was discovered to be a feasible way for the surgeon to reduce the post-surgery collapse of repaired structures. High modulus sutures (stainless steel) obviously did not require stretching, and were more likely to tear the soft tissues in the postoperative phase. Creep of woven sutures coupled with creep of soft tissue in post-op period was quantified. Steel suture materials exhibited no measurable creep at the surgical loads observed, but loss of tensile support did occur if the geometry of the wire prosthesis .was altered after the surgical repair was completed.
Impacts
Outcomes/Impacts: Soft tissue properties have been evaluated for the problem of suture- cricoid cartilage interaction in tension. Tensile tests indicated that all five suture materials tested are capable of supporting the load required to abduct the arytenoids cartilage. The most important properties describing the effectiveness of the suture used for laryngoplasty include the suture-tissue interactions, the peak load withstood by the suture, and the creep of the suture under physiologic loading. Both FiberWire ¿ sutures (#2 and #5) demonstrated the the most creep (largest time-dependent strain) and for these reasons are not recommended for use in laryngoplasty. The initial rapid creep in FiberWire ¿ sutures immediately following the application of physiologic loads may be controlled by the surgeon holding the suture in the tightened position for at least 30 seconds prior to use.. Steel exhibited the least creep but showed a tendency for cutting cartilage and equine laryngoplasty should be done with less rigid suture materials. The Securos sutures expressed the next highest resistance to creep at physiologic loads and produced the least tissue tearing.. Ethibond¿ and Securos sutures exhibited low creep and demonstrated the best mechanical properties and superior tissue interactions for use in equine laryngoplasty with Securos being the top recommendation. Hard tissue (bone) behavior under torsional loading is being investigated. Development of suitable torsion grips and accounting for small but mathematically significant displacements in the torsional loading fixtures is ongoing. Participants:
A Master of engineering graduate student completed their research of cartilage-suture properties and developed recommendations for suture use for surgical repair of equine laryngeal heniplegia. Undergraduates have worked on the set-up and sample preparation of torsion tests. Design, construction and evaluation of torsion test fixtures and procedures for testing long bones continues.
Target Audiences: Audiences include surgeons, biomechanics and structural biomaterials researchers, and materials scientists. Project Modifications: New developments include the torsional testing capabilities, specimen preparation and gripping and the work on mechanical properties of bone using independent compression and torsion testing and analysis of duplicate samples.
Publications
- No publications reported this period
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Progress 01/01/06 to 12/31/06
Outputs
Sutures are used as prosthetic repairs for equine laryngeal hemiplegia. The effectiveness of suture prosthetic repairs was investigated previously, and the static and dynamic tension in the suture material was measured in-vivo. It was determined from in-vivo measurements that the sutures were subjected to a cyclic tensile load varying on average, from 25.8 to 26.5 N. Mechanical tests were performed to determine the creep behavior of the suture and equine laryngeal cartilage. Sutures were looped through sections of cartilage and the suture-cartilage system was subjected to a creep load of 25.0 N. Creep displacement was measured for a period of 10 minutes to simulate the post operative condition. Immediately following the creep experiment, the system was loaded to failure to determine the maximum allowable load. Stainless steel monofiliment sutures exhibited the least creep, 0.83 mm after 10 minutes, Braided polymer suture showed a significantly higher creep of 1.10 to
1.33 mm. The suture contribution to total creep was lowest for steel monofiliment, 0.24 mm, and greatest for 'fiberWire #5', 1.33 mm. Steel monofiliment displayed the lowest failure force of 109 N, tearing the cartilage. Thicker, braided polymer suture, 'Ethibond' showed highest failure force of 154.6 N.
Impacts
While the working load of a prosthetic suture system is well below the failure load of either suture or cartilage, the creep of the prosthetic repair reduces it effectiveness. Steel creep is negligible, due mainly to the wire straightening after surgery. Polymer materials creep more than steel, indicating these should be pre-stressed by the surgeon prior to application. Surgical procedures need go be carefully done, especially with monofiliment steel to avoid tearing cartilage during surgery.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
Static and dynamic tension in sutures inserted during equine laryngoplasty were measured in-vivo in cadaver specimens under simulated conditions of vigorous respiration activity. An inhalation device was used to duplicate respiratory peak volumetric flow amplitudes of 60 L/s at 120 hz and corresponding peak inhalation pressure drops of 25 mm Hg through the cadaver larynx. A loop of an Ethibond(tm) suture stabilized the collapsed arytenoid cartilage (prostetic laryngoplasty treatment) and the free ends together were tethered to a load cell. The suture was first preloaded in a static configuration without airflow to represent initial surgical treatment of the disease. The statically applied tension without airflow was 28 N, the average tensile force needed to stabilize the collapsed arytenoid cartilage. When the cyclic air flow was applied to the larynx, the average suture loads varied between the static load of 28 N to an average peak load of 28.5 N, well below the
suture failure load of 155 N. Failure loads for various Polymer and steel sutures were also determined.
Impacts
This study provides quantative data on the suture forces necessary to stabilize the collapsed arytenoid cartilage in equine laryngoplasty. The study investigated the effects of the age of the animal and sex of the animal on the suture loads needed to make the surgical repair. Although a small number of tests were conducted, it appears the braided polymer sutures are preferable because these appear to produce less tearing of cartilage in cyclic tests, and also because they flex slightly along with the larynx in simulated exercise tests. Steel sutures do not stretch appreciably, braided polymer sutures may be most effective if these are preloaded to a level well above 28 N but less than their yield point before insertion for the corrective surgery.
Publications
- Ducharme, R. 2005. An examination of sutures as prosthetic devices for treatment of laryngeal hemipegia. Master of Engineering Report, Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY.
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Progress 01/01/04 to 12/31/04
Outputs
Testing of suture materials and suture/tissue/structure interraction in suture application in Equine larynx. Equine Larynx structures from cadavers were evaluated under cyclic airflow (Peak flow and Peak volume) conditions to simulate vigorous exercise conditions. Air was inhaled and exhaled through the Larynx using tandum 1.5hp ShopVac arrangement to create flow and a computer controled switching valve to regulate total flow, and create reverse flow direction at a pre-determined cyclic rate. At the same time, the tensile forces in the sutures in the Larynx structure were monitored using an Instron 4502 universal testing machine. Air flow and peak velocity paramaters were varied in the tests, and the suture tension was monitored before, during and after the tests to determine creep and relaxation behavior of the suture and cartilage 'system'. This work continues at the time of this update. Sepatate creep and relaxation of suture materials have been completed using the
Instron 4502. Creep tests of suture are based on loads determined during the previous cyclic flow tests. Relaxation properties of laryangel cartilage are in progress. Relaxation tests are being performed with the Instron 4502 and those tests will include a final destructive test where the suture/cartilage connection is loaded to failure at a displacement rate similar to that found in the cyclic air flow tests.
Impacts
Larynx tissue and suture tests are intended to identify best practices for repair of defects and injury. Previous clinical work at the Cornell Vet Clinic and elsewhere has involved several techniques to create a stabile suture repair and a optimal pre-stress of the suture during surgery to give optimal performance and life expectancy of the patient. Little quantative data is available to guide the surgeon in placement of the sutures and there is no agreed-to method for pre-stressing or even for quantifying the level of pre-stressing that is achieved during surgery. The loss of suture function after surgery may be related to pre-stress levels in sutures during surgery. The 'fatigue' life of repairs may also be related to the pre-stress levels, level of animal activity and suture-cartilage mechanics, variables this work is aimed at investigating. Soft tissue materials testing in this project supports a broader long term effort at Cornell and elsewhere in tissue
engineering to develop replacement tissues for animal and human trachea reconstruction.
Publications
- Tsai, C. 2004. Etiology of Tendon Damage Accumulation, Master of Engineering Project Report, Biological and Environmental Engineering.
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Progress 01/01/03 to 12/31/03
Outputs
Two projects are in progress. One involves mechanical testing of Equine Laryngeal tissue and evaluation of suture methods and suture materials suitable to repair Laryngeal damage. A second project underway is to determine the elastic properties of tracheatissue and tracheal structures with a goal of using this information to tissue engineer replacement tissue of compatible mechanical properties with the natural tissues.
Impacts
Larynx tissue and suture tests are intended to identify best practices for repair of defects and injury. Trachea materials testing is part of a larger effort in tissue engineering to develop replacement tissues for animal and human trachea reconstruction.
Publications
- No publications reported this period
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