bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring the Effects of Initiating Body Checking at the Atom Age Level
Authors: Montelpare WJ , McPherson MN
Published: April 2008

The purpose of this study was to determine the effects of initiating body checking at the Atom age level. The study used an experimental design in which teams from the Ottawa District Minor Hockey Association (ODMHA) represented the control group, while teams from the Ontario Hockey Federation (OHF) represented the treatment group. The study was conducted over a three-year period from 1998 to 2001. The comparison sampling between the two leagues was as follows: ODMHA Yr1 = 69 teams versus OHF Yr1 = 74 teams, ODMHA Yr2 = 59 teams versus OHF Yr2 = 101 teams, ODMHA Yr3 = 46 teams versus OHF Yr3 = 90 teams. Measures of interest reported here included player selection bias, injury incidence, and variables that describe the characteristics of the flow of the game such as goals for, goals against, and number of penalties. Athlete exposures for each league by year were computed using 15 players per team for a 20 game plus 20 practice schedule.

Statistical analysis of the difference in proportions of injuries reported by the two leagues based on the CHA injury insurance dataset showed that no significant difference occurred per year of the study. In addition, the rates of injuries were lower in each year than those reported by previously published studies.

Body checking, which includes body contact is considered by many to be a skill within the game of ice hockey that can be taught at the younger age levels in a manner that does not lead to a higher incidence of injuries, or unfavorable changes in the game. The results of this study support that contention. In the present study, it was assumed that education was an essential component of the introduction process and that coaches were provided the necessary background to enable them to teach the introduction of body checking as a skill.
Adherence to Return-to-Play Guidelines Following a Sport-Induced Concussion
Authors: Goodman D , Gall B , Miller A
Published: April 2008

Two studies were conducted in which compliance to Canadian Hockey Association concussion management guidelines was assessed via response to questionnaires. The first study, conducted in both the 2001 and 2002 hockey seasons, involved elite male and female youth hockey players in the British Columbia Best Ever Program. Over 40% of the under 16-year-old males and 37% of the under 18-year-old females reported having sustained a concussion. In the 2001 male cohort, 18% of the concussions resulted in loss of consciousness (LOC), yet 50% of those indicated they returned to the same game. The second study, involving athletes in the Pacific International Junior Hockey League, indicated that 24% of the 163 athletes sustained a concussion within the last year. Out of the 12 who reported LOC, three of those returned to the same game, while only three were seen by a medical doctor prior to return to play. The results suggest that there remains considerable room for improvement with respect to adherence to return to play guidelines.
Perceptions of Equipment on On-Ice Attitudes and Performances of Hockey Players
Authors: Janski RA , Meyer BB
Published: April 2008

The purpose of this study was to examine if and how the perception of protective sporting equipment influences the on-ice attitudes and behaviors of ice hockey players. Interviews were conducted with ice hockey players at the Junior level of competition. A series of open-ended questions pertaining to participants' development in ice hockey, attitudes towards ice hockey, and their use of equipment guided the interviews. Data were organized by themes and results provided evidence for the creation of norms of violence within ice hockey as well as alluded to the idea that creation is an ongoing process engaged in throughout a player's career. Attitude towards the game of ice hockey was found to influence performance, but at the same time, attitude was influenced by aggression. Finally, the results indicated that ice hockey players do perceive their equipment as a source of confidence and security.
Rediscovering Youth Sportsmanship
Authors: Mariconda J , Mariconda A
Published: April 2008

There is a growing concern about the misbehavior of parents at youth sporting events. To address this issue, the Rediscovering Youth Sportsmanship Program has been produced by the St. Barnabas Health Care System in New Jersey. The program offers parents a better understanding of the developmental needs of young athletes so that the parents can provide proper support while avoiding the pitfalls of player burnout and forcing their youngsters into injury-potential situations. Rediscovering Youth Sportsmanship builds awareness of the negative effects of poor sportsmanship by adults on young athletes, offers parents behavioral strategies for maintaining good sportsmanship, helps leagues set rules and guidelines for parental behavior and informs parents of sanctions for parental misbehavior.
Structuring the Ice Hockey Environment to Promote Development of Positive Values
Authors: Roy M , Bernard D
Published: April 2008

Important modifications in the sport structure are required to promote the learning of positive values. As an example of some changes, in the Quebec city area, the Cardinal Roy High School Ice Hockey program is designed to develop the young individuals in five dimensions, i.e., the physical, mental, emotional, social and moral dimensions. The program's philosophy also focuses its coaches' behaviors on the participants. This study describes first how the program was implemented. Second, results highlighting the high level of satisfaction of the 38 participants, junior and senior, regarding their coaches' leadership are presented. Implementing a philosophy that places the emphasis on the individual's multidimensional development rather than on the “win-at-all-costs” approach is realistic and a promising avenue to coaching young individuals.
Comparison of Ice Versus Treadmill Skating — Plantar Force Distribution Patterns
Authors: Turcotte RA , Pearsall DJ , Montgomery DL , Lefebvre R , Ofir D , Loh JJ
Published: April 2008

Dynamic plantar foot force measurements were compared between skating on ice (ICE) versus on a skating treadmill (TM). Four subjects skated at three forward speeds of 22, 24, 26 kph (or 6.1, 6.7, 7.2 m/s, respectively). Plantar force measures were obtained by using FScan™ sensors taped to the insole of a subject's right skate. In general, results indicate that the whole foot force-time patterns were similar between ICE and TM for equivalent speeds except for consistent differences during heel strike i.e., TM heel loading force values were approximately 30% greater than those observed during ICE skating (P>0.05). As skating speed increased, the latter differences diminished. Thus, with the exception of the heel loading, the skating TM replicates the overall pattern during forward skating, particularly during mid-support and toe-off phases of propulsion.
Task Analysis (Hitting, Shooting, Passing, and Skating) of Professional Hockey Players
Authors: Montgomery DL , Nobes K , Pearsall DJ , Turcotte RA
Published: April 2008

Task analysis data were summarized for ten NHL hockey teams based on nine home games played against the Montreal Canadiens. Approval for filming was obtained from the Montreal Canadiens Hockey Club. Three camera views were obtained. One camera followed the puck, while cameras two and three were fixed on opposite halves of the ice surface. The sample included 62 defensemen (D), 74 wingers (W), 44 centers (C) and 10 goalies (G). Frequencies of starts, stops, crossovers, sharp turns, and direction changes were recorded as well as total forward and backwards skating. Defensemen and forwards were analyzed for the following skills: hitting (on boards and open-ice), shooting (slap, wrist, backhand, snap), passing (forehand, backhand, sweep and snap), and pass reception (forehand, backhand, other). For the goaltenders, only passing and pass reception were investigated. Task analysis data were summarized by position. Average shift times were 44.7 s, 43.1 s, and 47.6 s for the C, W, and D, respectively. The percentage of time spent in backward skating was 4.8% for the C, 5.7% for the W, and 19.2% for the D. Skating movements were totaled for the following movements: starts, stops, crossovers, sharp turns, and front-to-back or back-to-front. The total forward skating activities were 258, 227, and 270 for the C, W, and D, respectively. The total backward skating activities were 43, 44, and 146 for the C, W, and D, respectively. Skating patterns of the forwards and defense are significantly different and probably warrant the design of different skates for these positions. The frequency of hitting, battles for the puck, and battles for position were not high when average values were recorded; however, the most active players totaled 25–28 contacts per game.
Measurement of Pore Size and Porosity of Tissue Scaffolds
Authors: Tomlins P , Grant P , Mikhalovsky S , James S , Mikhalovska L
Published: April 2008

Tissue engineering involves seeding the patient's cells on to a three dimensional temporary scaffold. It is becoming increasingly obvious that cells used to seed the scaffold have very specific requirements concerning the morphology and chemistry of the surface of the scaffold and its interconnectivity. A range of techniques has been examined in relation to key measurements such as pore size and porosity. Since capillary flow porometry measures a pore solely at its most constricted point, the method is unable to provide characterisation of other aspects of the pore.

Scanning Electron Microscopy is limited to examining surface pores in ‘stiff’ scaffolds. Although cryo-SEM reduces the amount of ice-induced damage generated in ‘soft’ scaffolds upon freezing, the technique is limited to the same constraints. Imagesproduced via scanning confocal microscopy are probably more representative of the truestructure of the scaffold than that implied by cryo-SEM, although due to the diffuse nature of the image it is difficult to measure pore sizes.
Development and Validation of a Detection Method for a Broad Range of Human Papillomavirus Types
Authors: Galbraith DN , Collins T , Black J , McManus B , McMutrie D , Lovatt A
Published: April 2008

Human papillomaviruses (HPVs) are viruses that are almost unique in their tropism for human skin cells; they also have the potential to cause severe pathology. These viruses present a significant risk to contaminate tissue engineered skin replacement products that use human-derived skin cells as part of their manufacture. Eight pairs of primers and appropriate DNA oligonucleotide probes were designed from a relatively conserved region of the LI open reading frame of HPV. TaqMan® PCR using these primer/probe sets was found to be capable of detecting HPV-DNA in a background of cellular material likely to be present in skin replacement products. The assay is more sensitive than any currently described in the scientific literature and can be completed in a single working day making it suitable for testing the short shelf life that many of these products have.
NIST and Standards for Tissue Engineered Medical Products
Authors: Tesk JA , Karam LR
Published: April 2008

On June 13–14, 2001, the National Institute of Standards and Technology (NIST) convened a workshop of high level representatives from industry, federal agencies, and standards organizations to identify standards-related needs of the biomedical materials and devices industry. There were individual breakout sessions on standards for: Biomaterials, Therapeutic and Drug Delivery Devices, Auditory Diagnostic and Prosthetic Devices, Manufacturing of Prostheses, and Tissue Engineered Medical Products (TEMPs). Cross-cutting issues of Harmonization of Standards, Data, and Sterilization were also addressed. The session on Standards for TEMPs placed its most significant needs on the development of test methods and materials characterization. Action items for NIST to consider were separated into those relative to the Food and Drug Administration (FDA) approval process and those relative to industry needs not directly related to the FDA approval process. This paper summarizes the needs identified for TEMPs and the status of NIST-related activities.
Mechanical Evaluation of Allograft Bone
Authors: Summitt MC , Squillace DMK , Bianchi JR
Published: April 2008

Standard test methods to evaluate the material properties of cortical bone do not exist. A test methodology that accounts for the anisotropy of cortical bone by subjecting the material to multiple modes of loading is proposed. The four test included are axial compression parallel to the longitudinal axis, tensile load perpendicular to the long axis (diametral compression), double lap shear, and three-point bend. These methods provide a means of documenting the biomechanical changes that may occur as a result of unique attributes inherent to a donor or the processes that the donor tissue is exposed. Several examples illustrate how these methodologies demonstrate the relationship between process and mechanical properties.
Method to Determine Germicidal In activation in Allograft Processing
Authors: Mills CR , Roberts MR , Chang JY , Bianchi JR , Summitt MC
Published: April 2008

Because the risk of disease transmission remains even though stringent requirements for selecting and screening allograft donors have been adopted, processing methods capable of sterilizing tissue are needed. This test method discusses a means of evaluating the efficacy of allograft processing methods to eliminate bacterial contamination within the matrix of cortical bone. A Bacillus stearothermophilus biological indicator is inserted into a cavity drilled into the cortex of a long bone and the bone is processed under different treatment methods. A similar set of soft tissue specimens was prepared by inserting the spore strip into the soft tissue matrix and stitching it closed. After treatment the spore strips are aseptically removed and evaluated for growth. This test method allows for the evaluation of sterilization processes of tissue-based products with complex matrices.
Cartilage Mechanical Properties after Injury
Authors: D'Lima DD , Steklov N , Bergula A , Chen PC , Colwell CW , Lotz M
Published: April 2008

Cartilage injury often results in matrix degradation and in secondary osteoarthritis. This study was designed to correlate cell death and matrix degradation with biomechanical properties of cartilage. Full-thickness mature bovine femoral articular cartilage was harvested as 5 mm diameter cylindrical disk explants. Explants were divided into three groups: control, injury, and IL-1. The injury group was subjected to mechanical compression of 40% strain for five minutes. The IL-1 group was cultured in media containing 10 ng/mL of IL-1 beta. The control group was not injured or exposed to IL-1 beta. Chondrocyte viability, glycosaminoglycan release in media, and equilibrium creep were measured ten days after injury. A reduction in cell viability was seen after injury. A significant increase in glycosaminoglycan release and in equilibrium creep was detected in injured explants and in explants exposed to IL-1 beta. A correlation was also found between the equilibrium creep and glycosaminoglycan content after injury and IL-1 beta stimulation.
A Comparative Study of Biomarkers of Oxidative DNA Damage Used to Detect Free Radical Damage in Tissue-Engineered Skin
Authors: Rodriguez H , Jaruga P , Birincioglu M , Barker PE , O'Connell C , Dizdaroglu M
Published: April 2008

The process of tissue engineering often involves the mixing of cells with polymers that may elevate the level of endogenous free radicals and thus cause genetic damage to the cell. In order to assure that such composite materials are free of genetic damage, our laboratory is responding to the need for test methods used to assess the safety and performance of tissue-engineered materials. Specifically, we are identifying cellular biomarkers that could be used to ensure that the cells of tissue-engineered materials have not undergone any oxidative DNA damage from the production of free radicals by oxidative stress during the development, storage or shipment of the product. Using the technique of gas chromatography/mass spectrometry, we have screened for the xidatively modified DNA base 8-hydroxyguanine in tissue-engineered skin and compared the levels to those in control cells, neonatal fibroblasts and neonatal keratinocytes. No significant level of damage was detected compared to control cells. The technique of liquid chromatography/mass spectrometry was also used in the validation of this biomarker by measuring its nucleoside form. The results obtained with this technique were nearly identical to those obtained with gas chromatography/mass spectrometry. Biomarker programs such as this can provide the basis for an international reference standard of cellular biomarkers that can aid in the development and safety of tissue-engineered medical products.
A New Method for Real-Time and In-Situ Characterization of the Mechanical and Material Properties of Biological Tissue Constructs
Authors: Zhang G , Gilbert JL
Published: April 2008

To capture the transient, nonlinear and time-dependent characteristics of the mechanical and material properties of biomaterials and biological tissue constructs, we developed a real-time based evaluation method. This method measures the paired transient stress and strain as a function of time for a given material, and calculates instantaneously its complex modulus measurements as a function of frequency. Because the measured complex moduli contain not only the mechanical properties (magnitude of the modulus curves) but also the material characteristics (shape of the modulus curves), this method allows us to link directly the mechanical properties to the material characteristics in a real-time and in-situ manner. The significance of this capability is that the changes in both mechanical property and material structure can be correlated repeatedly during the growing or aggregating processes of the biological tissues or constructs.
Biomolecules in Tissue Engineered Medical Products (TEMPs): A Case Study of Recombinant Human Bone Morphogenetic Protein-2 (rhBMP-2)
Authors: Porter TJ , Rathore S , Rouse J , Denton M
Published: April 2008

rhBMP-2 is an osteoinductive protein that, when administered locally, results in the induction of new bone tissue at the site of implantation. The osteoinductive properties of rhBMP-2 first were demonstrated by implantation at ectopic (nonbony) sites in rodents. BMPs are the only protein factors known to induce new, ectopic bone. rhBMP-2/Absorbable Collagen Sponge (ACS) is a TEMP that combines rhBMP-2 with a matrix for implantation. rhBMP-2/ACS is used in long bone fracture repair and spinal fusion. The development of rhBMP-2 protein as the active ingredient in the rhBMP-2/ACS product is summarized. Four aspects of rhBMP-2 development are covered: protein structural characterization, functional characterization, purity analysis and design of comparability studies to support changes in the manufacturing process. Topics discussed include rhBMP-2 as a “biologic” and as a constituent of a combination TEMP. The lessons learned during the development of rhBMP-2/ACS may allow general insight into the development of future standards for TEMPs that contain biologically active proteins.
Microbiological Safety and Adventitious Agents Standards for TEMPS
Authors: Sofer G
Published: April 2008

Microbiological contamination and adventitious virus contamination can be introduced into TEMPs from source materials, such as cells, cell culture media, scaffolds, and growth factors. Contamination can occur during isolation and expansion of cells, production of scaffolds and growth factors, and product manufacturing. Contamination may also arise during storage due to the inability to use sufficiently stringent preservation and storage methods without destroying the TEMPs' function.

Standard safety testing for pathogens may not be suitable for TEMPs. New rapid microbiological detection methods and PCR assays for mycoplasma and virus may enable preliminary product release. Cleaning and sanitization of equipment can be validated using a combination of traditional and new, more rapid methods. When there are significant processing steps, clearance studies can provide a further assurance of freedom from unwanted adventitious agents.
The European Situation on Standards for Tissue Engineering Products
Authors: Schutte E
Published: April 2008

Human tissue engineered medical products are not regulated on a European level. This means that, to date, various national approaches exist to regulation of Tissue Engineered Products in Europe. In general, diversity exists how these products should be regulated. Some Member States wait for the European Commission to take a position and fill in the gap of regulation. Other countries develop specific regulation on human tissue products, and use elements on tissue banking principles; other countries use the pharmaceutical approach, whereas others use the medical device regulation as a basis.

The industry favors a new regime based on a risk/benefit based approach. The Directive should define essential requirements, and to demonstrate compliance to these requirements, harmonized standards should be used.

Recently, some new initiatives have started, concerning future harmonized European regulation, such as the draft Directive as “Setting high standards of quality and safety for the procurement, testing, processing, storage and distribution of human tissues and cells”, in order to ensure a high level of human health protection. At the same time the European Commission solicited input for a framework to solve free trade amongst Member States.
Molecular Biomarkers Used to Detect Cellular/Genetic Damage in Tissue-Engineered Skin
Authors: O'Connell C , Barker PE , Marino M , McAndrew P , Atha DH , Jaruga P , Birincioglu M , Rodriguez H
Published: April 2008

In this study, tissue-engineered skin (TestSkin II) was obtained, separated into its two cellular layers (epidermis and dermis) and DNA was extracted. The first biomarker tested consisted of screening for DNA point mutations in exons 5 and 6 of the TP53 gene, the most commonly mutated gene in skin cancer. To ensure the accuracy of the results, two measurement technologies that incorporate internal calibration standards were used. It was shown that tissue-engineered skin did not contain mutations in this gene at the level of sensitivity of SSCP-capillary electrophoresis and Denaturing High Performance Liquid Chromatography. Results were compared to control cells (neonatal fibroblasts and neonatal keratinocytes) and fibroblasts that were obtained from a 55-year-old and 96-year-old human donor. The second set of biomarkers tested looked at the loss of the Y-chromosome. Using Fluorescent In Situ Hybridization technology, no detectable loss of Y-chromosome was found in the tissue-engineered skin and neonatal control cells. Y-chromosome loss was found in the fibroblasts from the 96-year-old donor. Biomarkers such as TP53 mutations and chromosome loss can provide the basis for an international reference standard of cellular biomarkers that can aid in the development and safety of tissue engineered medical products.
A Useful Marker for Evaluating the Safety and Efficacy of Tissue Engineered Products
Authors: Tsuchiya T
Published: April 2008

We propose a survey of the function of the gap-junctional intercellular communication (GJIC) as a useful marker for evaluating the safety and efficacy of tissue-engineered products.
Characterizing Dynamic Fracture Behavior of Adhesive Joints under Quasi-Static and impact Loading
Authors: Simón JC , Johnson E , Dillard DA
Published: April 2008

An experimental evaluation of the dynamic fracture properties of an automotive epoxy is presented. Pronounced stick-slip behavior was observed in both quasi-static and impact tests of aluminum and composite adherends bonded with this adhesive. An experimental technique for conducting low speed impact of adhesively bonded automotive composite joints is presented. Based on the use of a modified drop tower, mode I, II, and mixed mode values for critical energy release rate were determined to create a fracture envelope for the composite/epoxy system. Because load measurements are erratic and unreliable at higher test rates, displacement-based relationships were used to quantify these energy release rates. Displacement data were collected with an imaging system that utilizes edge detection to determine displacement profiles, end displacements, and opening displacements where applicable. Because of the resolution of the image-based approach being used, determining crack length experimentally is difficult. As a result, numerical methods based on edge detection algorithms were developed to objectively determine the crack length based on the available experimental data in mode I, II, and mixed mode I/II configurations.
Fracture Mechanics Applied to Adhesive Joints
Authors: Wheeler GE , Madsen BS , DeVries KL
Published: April 2008

Since the advent of synthetic adhesives in the middle of the last century, the growth in their usage has been so phenomenal that a handbook, the International Plastics Selector-Adhesives. published by D.A.T.A. in 1991, lists some 5000 different adhesive formulations that are commercially available. Despite their wide usage, much is not well understood about adhesives and adhesive joint failure. A few observations relevant to this discussion of Fracture Mechanics Analysis of Adhesive Joints are: (a) The stress distribution in such joints is never as simple as often assumed, and the usually reported “standard test results” often completely ignore the most important aspects of the stress distribution. (b) Crack growth does not always initiate at the point of maximum stresses in an adhesive joint. (c) The locus of adhesive crack growth is often somewhat removed from the adhesive-substrate bond-line, but there are instances where it closely follows this bond-line. (d) Adhesive Fracture Mechanics analysis can provide significant information on the resolution of questions raised in these observations. This presentation will review some of the work in these areas by graduate students in our laboratory. Some of the cited work was accomplished by previous lab students. Other parts of the cited work are from ongoing research by current students. The presentation will endeavor to demonstrate that: (a) Adhesive Fracture Mechanics can be used to quantitatively predict the strength of adhesive joints and, more particularly, to elucidate the effects of such factors as adherend thickness, adhesive thickness (and variation), amount of overlap, geometric configuration, material discontinuities, etc. (b) Other factors being equal, crack growth tends to initiate at locations of maximum energy release rate irrespective of whether or not these are points of maximum stresses. (c) The preferred locus of crack growth is along those paths for which the energy release rate is a maximum. In each of these cases, results of a fracture mechanics analysis will be presented along with experimental verification of the analyses.
Generalized Size and Shape Description of UHMWPE Wear Debris — A Comparison of Cross-Linked, Enhanced Fused, and Standard Polyethylene Particles
Authors: Sprecher CM , Schneider E , Wimmer MA
Published: April 2008

Released wear debris of implants causes local inflammation of the host tissue if it is in a phagocytosable size. The purpose of this study was to compare particle size, shape, and number of three different types of UHMWPE. After wear testing, particles were isolated from the serum and analyzed using SEM. The parameters ‘equivalent circle diameter’ (ECD) and ‘equivalent shape ratio’ (ESR) were determined. Most of the generated debris was sub-micron in size. Classifying the particles into size groups demonstrated a non-linear correlation between size and shape for all three types of polyethylene: small particles were more round, large particles were more elongated. Based on this relationship, the generated number of particles and their total surface area were estimated and compared with calculations based on size alone.
Microscopy of Highly Cross-Linked UHMWPE Wear Surfaces
Authors: Rieker CB , Konrad R , Schön R , Schneider W , Abt NA
Published: April 2008

Highly cross-linked ultra high molecular weight polyethylenes (UHMWPEs) were developed to reduce UHMWPE wear in arthroplasty. These UHMWPEs have manifested a significant improvement in the in-vitro adhesive — abrasive wear resistance of total joint prostheses.

Examination of the first clinically retrieved liners revealed surface features not usually observed on previous retrievals. A flattening of the machining marks is evident, together with the presence of ripples with micro-fissures. To evaluate these features, examinations were performed on a cup-on-ball device, an AMTI hip simulator, and a Stanmore knee simulator, as well as on retrieved components with a maximum follow-up of 15 months. The surface features of the components were investigated with light microscopy, by scanning electron microscopy (SEM), and also by transmission electron microscopy (TEM).

Ripples with micro-fissures were observed on the loaded areas perpendicular to the principal directions of motion. The transverse examinations of all sections of these specimens, which were made with optical microscopy and by TEM, showed that the ripples with micro-fissures may be described as folds. With all the investigated samples, the depth of the micro-cracks at the tip of the folds extended to a maximum of 5 μm below the surface. The folds experienced with UHMWPE were already described in the late 1970s.

Due to the extreme wear resistance of highly cross-linked UHMWPEs, these folds accumulate on the surface of components manufactured in this new generation of UHMWPEs. In view of their depth stability with the number of cycles, we believe that these folds have no influence on the fatigue behavior of such components.
Improved Resistance to Wear, Delamination and Posterior Loading Fatigue Damage of Electron Beam Irradiated, Melt-Annealed, Highly Crosslinked UHMWPE Knee Inserts
Authors: Yao JQ , Blanchard CR , Lu X , Laurent MP , Johnson TS , Gilbertson LN , Swarts DF , Crowninshield RD
Published: April 2008

Recently, a knee prosthesis containing an electron beam irradiated (58 – 72 kGy, nominal dose of 65 kGy), melt-annealed, highly crosslinked UHMWPE (HXPE) tibial insert has been developed. In the present study, the wear and delamination resistance of the HXPE tibial insert and its fatigue performance under a posterior loading condition have been evaluated against its conventional gamma-sterilized UHMWPE counterpart (37kGy, in nitrogen). The test methodologies used were newly developed with the aim to evaluate this new material under severe testing conditions.

In comparison to the gamma controls, the HXPE inserts: (a) wore significantly less (achieving wear reductions of 81% and 73% over 5 and 20 million cycles, respectively); (b) exhibited significantly improved delamination resistance; and (c) exhibited significantly improved posterior loading fatigue resistance.
The Effect of Crosslinking UHMWPE on In Vitro Wear Rates of Fixed and Mobile Bearing Knees
Authors: McNulty DE , Swope SW , Auger DD , Smith T
Published: April 2008

This study evaluated the wear performance of conventional (gamma irradiation at 4Mrads in low oxygen) and moderately crosslinked (gamma irradiation at 5Mrads and melt-annealed) ultra high molecular weight polyethylene (UHMWPE) materials in fixed and mobile knee bearing designs. Kinematic and load inputs corresponding to the gait cycle outlined in the ISO displacement controlled knee simulation draft standard, ISO/CD 14243-3, were maintained in all simulations. Wear rates were determined gravimetrically. Surface finish changes and worn surface characteristics were also noted. Moderately crosslinked fixed bearing knee component wear rate was 74% lower than conventional fixed bearing components. There was no discernable difference in wear rate for the mobile bearing knee for the two materials. However, the mobile bearing knee wear rates were 94% and 79% lower than fixed bearing conventional and fixed bearing moderately crosslinked materials, respectively. In the fixed bearing knee, the majority of the wear reduction of the moderately crosslinked material compared to the conventional material was attributed to enhanced crosslinking due to the melt-annealing process rather than the dose difference. The reduction in wear rate of the mobile bearing knee compared to the fixed bearing was attributed to the reduced cross shear motion at the tibio-femoral articulation since mobile bearing wear was independent of material.
Multiaxial Fatigue Behavior of Oxidized and Unoxidized UHMWPE During Cyclic Small Punch Testing at Body Temperature
Authors: Villarraga ML , Edidin AA , Herr M , Kurtz SM
Published: April 2008

We hypothesized that oxidation would influence the resistance to fatigue crack initiation and propagation of Ultra-High molecular weight polyethylene (UHMWPE). We subjected tibial insert surrogates (ram extruded GUR 1050) to accelerated aging protocols following ASTM F 2003-00 (14, 21 and 28 days). Subsurface disc specimens from the control and aged materials at each time period were subjected to cyclic small punch loading to failure (modification of ASTM F 2183-02). A significant decrease in fatigue loading was observed, relative to the un-aged controls, starting at three weeks of accelerated aging. Furthermore, SEM examination of the failed aged specimens revealed a network of multiple secondary initiation sites, which was also confirmed by observation with endoscopy, and microCT. Thus, in contrast to the unoxidized highly crosslinked conventional materials evaluated previously, the oxidized materials failed by the initiation and propagation of cracks from numerous initiation sites with the brittle appearance increasing with oxidation time. These results suggest that oxidized UHMWPE exhibits a different fatigue crack initiation and propagation behavior compared to unoxidized virgin, and crosslinked UHMWPE. Future studies will be needed to increase our understanding of the clinically acceptable fatigue properties for new tibial bearing materials, such as highly crosslinked UHMWPEs.
Wear and Structural Fatigue Simulation of Crosslinked Ultra-High Molecular Weight Polyethylene For Hip and Knee Bearing Applications
Authors: Wang A , Manley M , Serekian P
Published: April 2008

There have been increasing concerns about the structural fatigue resistance of crosslinked UHMWPE devices due to deterioration of certain mechanical properties. However, due to the lack of clear correlation between specific mechanical properties and clinical performance, these concerns remain theoretical. In order to evaluate the potential benefits and risks of various crosslinked polyethylene materials for hip and knee bearing applications, two clinically relevant worst-case scenarios were simulated on functional devices. In the first worst-case scenario, cemented all-poly patellar components were tested under simulated stair-climbing conditions with rotational misalignment. In the second worst-case scenario, metal-backed thin acetabular liners were tested in a hip joint simulator under rim-loading conditions. Various types of crosslinked UHMWPE were prepared according to published process descriptions of commercial materials. While significant levels of volumetric wear reduction were confirmed by both the patellar and hip simulator tests, mixed results were obtained on the structural integrity of the devices. The latter was more significantly affected by the post-irradiation thermal treatment history than by the total dose of irradiation. Re-melting following irradiation led to catastrophic fractures of both rim-loaded liners and rotational-malaligned patellar pegs. The key mechanical property that was positively identified to correlate with the structural fatigue performance of crosslinked polyethylene materials was the ultimate tensile strength, whereas tensile elongation within 250% and 400% range had no effect on structural integrity. However, the results presented in this study should not be misconstrued with respect to the potential clinical performance of irradiation crosslinked and re-melted polyethylene liners with proper designs. In fact, the true outcome of all the crosslinked materials can only be revealed by long-term clinical follow-up.
The Flow Ratio Effect on Oriented, Crosslinked Ultra-High Molecular Weight Polyethylene (UHMWPE)
Authors: King RS , Young SK , Greer KW
Published: April 2008

The compression molding process is known to produce UHMWPE components of improved oxidation resistance [1] and quality surface finish. Induction of molecular orientation in non-crosslinked UHMWPE was demonstrated by using a slot drawing process [2]. The objective of this study was to assess the effect of flow ratio on wear and mechanical properties of crosslinked UHMPWE. Pre-irradiated GUR 1020 preforms, corresponding to flow ratios from 1.06 to 1.40, were evaluated in this study. Molecular orientation was shown by Thermal Mechanical Analysis and crossed polarizer microphotographs. Tensile (Type V), double notched Izod and pin on disk wear data were generated. The degree of molecular orientation was correlated with the flow ratio and was reflected by the enhancement of the mechanical properties. Pin on disk wear data show that there was no significant difference in wear resistance between oriented, crosslinked UHMWPE and its machined counterpart.
The Effects of Raw Material, Irradiation Dose, and Irradiation Source on Crosslinking of UHMWPE
Authors: Greer KW , King RS , Chan FW
Published: April 2008

Four Ultra-High Molecular Weight Polyethylene (UHMWPE) materials were evaluated after various irradiation crosslinking processes to determine the effects of the materials and processes on their properties for orthopaedic applications. The materials and processes included two molecular weight materials (GUR 1020 and GUR 1050), two fabricated forms (ram extruded bar and compression-molded sheet), two irradiation sources (gamma and e-beam) and multiple irradiation doses ranging from 30–120 kGy. Increasing irradiation dose led to increased crosslinking, decreased wear, and decreased toughness. The molecular weight of the starting material and the irradiation source both had effects on the final properties while the fabricated form did not. Wear testing of selected groups indicated that there was a direct correlation with irradiation dose but not with the crosslink density (as calculated from the swell ratio).
Characterization of the Wear Performance of Crosslinked UHMWPE and Relationship to Molding Procedures
Authors: St.John KR , Poggie RA
Published: April 2008

Using an eight-station hip wear simulator, radiation-crosslinked polyethylenes were tested for their resistance to wear-related weight loss and the results compared to results for studies conducted on the same machine using polyethylene that was being implanted at the time. The testing results showed that the wear rate of crosslinked (60 kGy) Slab Compression Molded (SCM) polymer was about 63% lower than standard (30 kGy) SCM cups and 69% less than Ram Extruded 4150 (30 kGy) cups. The Near-net Final Shape molded (NFS) crosslinked (60 kGy) specimens had an 89% reduction in wear rate over the standard (30 kGy) NFS cups, regardless of whether GUR 1020 or GUR 1050 crosslinked cups were tested. All wear rates for nitrogen packaged materials were significantly superior to those for cups sterilized in air and for earlier generation GUR 4150 products sterilized and stored in contact with oxygen.

The results confirm that both the SCM and NFS molding processes produce acetabular cups with excellent wear properties as compared to previous processes. The additional crosslinking process, described herein, provided a major improvement in the wear resistance with either molding process with greater improvement occurring in the NFS specimens.
Influence of Electron Beam Irradiation Dose on the Properties of Crosslinked UHMWPE
Authors: Abt NA , Schneider W , Schön R , Rieker CB
Published: April 2008

The purpose of this study was to investigate the influence of a dose of e-beam irradiation on the mechanical and tribological properties of crosslinked UHMWPE.

Specimens of UHMWPE were irradiated at different dose levels between 0 and 110 kGy using the WIAM e-beam process. Irradiation was followed by melt annealing and slow cooling.

In general, the mechanical properties of irradiated UHMWPE decrease with increasing irradiation dose. Increasing the irradiation dose from 50 to 95 kGy results in a loss of 4% yield strength, 16% elongation, 15% tensile strength and 18% impact strength. Crystallinity does not change significantly.

In comparison with conventional material, irradiation with 50 kGy reduces the wear rate by 73%. A further reduction of 56% can be realized by increasing the dose from 50 to 95 kGy.
Elevated Crosslinking Alone Does Not Explain Polyethylene Wear Resistance
Authors: Furman BD , Maher SA , Morgan TG , Wright TM
Published: April 2008

New ultra high molecular weight polyethylene (UHMWPE) materials have been introduced that utilize elevated radiation doses combined with post-irradiation heat treatments. The elevated radiation dose creates higher levels of crosslinking and is reported to cause improved abrasive wear resistance. The heat treatment quenches free radicals that result from irradiation, thus preventing oxidative degradation. Although abrasive wear occurs between conforming bearing surfaces, macroscopic wear damage is more commonly cited than abrasive wear as a limiting factor with non-conforming surfaces such as occur in knee replacements. Though these new materials demonstrate reduced mechanical properties compared to conventional UHMWPE gamma irradiated in air, recent studies revealed that some of these materials performed well under non-conforming in vitro wear conditions. Our aim was to understand why materials with reduced fracture toughness and yield strength would be more resistant to wear damage.

Polyethylene materials with varying radiation doses and heat treatments were examined. We compared modulus, yield strength, ultimate stress, and ductility, J-integral fracture toughness, density and wear. Crystalline morphology was evaluated using transmission electron microscopy. A relation was found between modulus, morphology and wear behavior. Materials with modulus equal to or less than 850 MPa and the majority of lamellae measuring less than 200 nm demonstrated no pitting, delamination or cracking in wear tests, regardless of the level of crosslinking. Even though elevated crosslinked materials showed reduced toughness, they demonstrated good damage resistance, but elevated crosslinking alone does not explain wear damage resistance.
Selecting a Suite of Ecological Indicators for Resource Management
Authors: Dale VH , Mulholland PJ , Olsen LM , Feminella JW , Maloney KO , White DC , Peacock A , Foster T
Published: April 2008

We discuss the use of ecological indicators as a natural resource management tool, focusing on the development and implementation of a procedure for selecting and monitoring indicators. Criteria and steps for the selection of ecological indicators are presented. The development and implementation of indicators useful for management are applied to Fort Benning, Georgia, where military training, controlled fires (to improve habitat for the endangered red cockaded woodpecker), and timber thinning are common management practices. A suite of indicators is examined that provides information about understory vegetation, soil microorganisms, landscape patterns, and stream chemistry and benthic macroinvertebrate populations and communities. For example, plants that are geophytes are the predominant life form in disturbed areas, and some understory species are more common in disturbed sites than in reference areas. The set of landscape metrics selected (based upon ability to measure changes through time or to differentiate between land cover classes) included percent cover, total edge (with border), number of patches, mean patch area, patch area range, coefficient of variation of patch area, perimeter/area ratio, Euclidean nearest neighbor distance, and dumpiness. Landscape metrics indicate that the forest area (particularly that of pine) has declined greatly since 1827, the date of our first estimates of land cover (based on witness tree data). Altered management practices in the 1990s may have resulted in further changes to the Fort Benning landscape. Storm sediment concentration profiles indicate that the more highly disturbed catchments had much greater rates of erosion and sediment transport to streams than less disturbed catchments. Disturbance also resulted in lower richness of EPT (i.e., number of taxa within the aquatic insect orders Ephemeroptera, Plecoptera, and Trichoptera) than in reference streams but similar total richness of invertebrate species. Each indicator provides information about the ecological system at different temporal and spatial scales.
Integrating Mineral Development and Biodiversity Conservation into Regional Land-Use Planning
Authors: Richards DG
Published: April 2008

A major independent multi-stakeholder analysis of how the mining industry can maximize its role in the transition to sustainable patterns of development — the Mining, Minerals and Sustainable Development (MMSD) project — concluded in 2001. Prominent among the recommendations in the MMSD report were the need for the mining industry to improve its performance in biodiversity assessment and management, and the need for all parties to commit to better models for decision-making processes in land use and access.

Mining is a temporary use of land, but history teaches us that the net effect of mining in a landscape is usually negative for biodiversity. There are benefits to human society in health, wealth and education, but society increasingly demands that environmental values be protected without compromising economic and social foundations. These expectations are captured in the concept of sustainable development.

Often, the most prospective areas for future mines will also be those with the greatest biodiversity value and with the greatest need for poverty alleviation. Many governments lack the capacity, will or resources to reconcile these conflicting needs equitably. Corruption in government and oppression of local populations have accompanied some mine developments.

Leading companies in the mining industry believe that these negative experiences are not inevitable, that better decisions on land use and access can be achieved and that sustainable benefits can be delivered through mineral development. One key to achieving these outcomes is the regional landscape-scale analysis of projects and conservation priorities, supported by fair, transparent and consistent decisionmaking processes.

Rio Tinto is a large diversified mining company which played a leading role in the actions leading to the commissioning of the MMSD project and participated fully in it. Examples from recent projects in Rio Tinto, illustrating aspects of regional planning and conservation actions, are presented in support of the case outlined above.