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Biomedical subjects

J B Brunski

Publications and source records attributed to J B Brunski.

At least 19 recordsLinked to original sources
PubMed2005

Microstrain fields for cortical bone in uniaxial tension: optical analysis method.

This study employed an optical strain measurement method, called microdisplacements by machine vision photogrammetry (DISMAP), to measure both the global and local strain fields in microtensile specimens of cortical bone subjected to controlled uniaxial tension. The variation of local maximum principal strains was measured within the gauge region of samples as a function of applied tensile stress during testing. High gradients of local strain appeared around microstructural features in stressed bone even while the global strain for the entire gauge region showed a strong linear correlation with increasing tensile stress (r2 = 0.98, p < 0.0001). The highest local strain around microstructural features in bone was 11.5-79.5 times higher than the global strain.

Animals↗
PubMed2000

Real-time in vivo loading in the lumbar spine: part 1. Interbody implant: load cell design and preliminary results.

STUDY DESIGN: Instrumented interbody implants were placed into the disc space of a motion segment in two baboons. During the animal's activities, implants directly measured in vivo loads in the lumbar spine by telemetry transmitter. OBJECTIVES: Develop and test an interbody implant-load cell and use the implant to measure directly loads imposed on the lumbar spine of the baboon, a semiupright animal. SUMMARY OF BACKGROUND DATA: In vivo forces in the lumbar spine have been estimated using body weight calculations, moment arm models, dynamic chain models, electromyogram measurements, and intervertebral disc pressure measurements. METHODS: An analytical model was used to determine the force-strain relation in a customized interbody implant. After validation by finite element modeling, strain gauges were mounted onto the implant and connected to a telemetry transmitter. Implants were placed surgically into the L4-L5 disc space of skeletally mature baboons and the transmitter in the flank. After surgery, load data were collected from the animals during activities. Radiographs were taken monthly to assess fusion. RESULTS: The implant-load cell is sufficiently sensitive to monitor dynamic changes in strain and load. During extreme activity, highest measurable strain values were indicative of loads in excess of 2.8 times body weight. CONCLUSIONS: The study technique and technology are efficacious for measuring real-time in vivo loads in the spine. Measuring load on an intradiscal implant over the course of healing provides key information about the mechanics of this process. Loads may be used to indicate performance demands on the intervertebral disc and interbody implants for subsequent implant design.

Animals↗
PubMed1999

In vivo bone response to biomechanical loading at the bone/dental-implant interface.

Since dental implants must withstand relatively large forces and moments in function, a better understanding of in vivo bone response to loading would aid implant design. The following topics are essential in this problem. (1) Theoretical models and experimental data are available for understanding implant loading as an aid to case planning. (2) At least for several months after surgery, bone healing in gaps between implant and bone as well as in pre-existing damaged bone will determine interface structure and properties. The ongoing healing creates a complicated environment. (3) Recent studies reveal that an interfacial cement line exists between the implant surface and bone for titanium and hydroxyapatite (HA). Since cement lines in normal bone have been identified as weak interfaces, a cement line at a bone-biomaterial interface may also be a weak point. Indeed, data on interfacial shear and tensile "bond" strengths are consistent with this idea. (4) Excessive interfacial micromotion early after implantation interferes with local bone healing and predisposes to a fibrous tissue interface instead of osseointegration. (5) Large strains can damage bone. For implants that have healed in situ for several months before being loaded, data support the hypothesis that interfacial overload occurs if the strains are excessive in interfacial bone. While bone "adaptation" to loading is a long-standing concept in bone physiology, researchers may sometimes be too willing to accept this paradigm as an exclusive explanation of in vivo tissue responses during experiments, while overlooking confounding variables, alternative (non-mechanical) explanations, and the possibility that different types of bone (e.g., woven bone, Haversian bone, plexiform bone) may have different sensitivities to loading under healing vs. quiescent conditions.

Adaptation, Physiological↗
PubMed1997

Mechanical and morphologic investigation of the tensile strength of a bone-hydroxyapatite interface.

For load-bearing calcium-phosphate biomaterials, it is important to understand the relative contributions of direct physical-chemical bonding vs. mechanical interlocking to interfacial strength. In the limit of a perfectly smooth hydroxyapatite (HA) surface, a tensile test of the bone-HA interface affords an opportunity to isolate the bonding contribution related to HA surface chemistry alone. This study measured the bone-HA interfacial tensile strength for highly polished (approximately 0.05 micron alumina) dense HA disks (5.25 mm in diameter, 1.3 in mm thickness) in rabbit tibiae. Each of five rabbits received four HA disks, two per proximal tibia. Pull-off loads ranged from 3.14 +/- 2.38N at 55 days after implantation to 18.35 +/- 11.9N at 88 days; nominal interfacial tensile strengths were 0.15 +/- 0.11 MPa and 0.85 +/- 0.55 MPa, respectively. SEM of failed interfaces revealed failures between HA and bone, within the HA itself and within adjacent bone. Tissue remnants on HA were identified as mineralized bone with either a lamellar or trabecular structure. Oriented collagen fibers in the bone intricately interdigitated with the HA surface, which frequently showed breakdown at material grain boundaries and a rougher surface than originally implanted. Mechanical interlocking could not be eliminated as a mode of tissue attachment and contribution to bone-HA bonding, even after implanting an extremely smooth HA surface.

Alloys↗
PubMed1992

Biomechanical factors affecting the bone-dental implant interface.

While it is known that dental implants can 'work'--the success of the Branemark 'osseointegrated' implant is a prime example--implants can also fail. The challenge is to develop a basic science understanding of all aspects which contribute to implant performance. In designing a successful dental implant, the main objective is to ensure that the implant can support biting forces and deliver them safely to interfacial tissues over the long term. Biomechanics are central in this design problem. Key topics include: (1) the nature of the biting forces on the implants; (2) how the biting forces are transferred to the interfacial tissues; (3) how the interfacial tissues react, biologically, to stress transfer conditions. For biting forces on dental implants, the basic problem is to determine the in-vivo loading components on implants in various prosthetic situations, e.g. for implants acting as single tooth replacements or as multiple supports for loaded bridgework. Significant progress has been made; several theoretical models have been presented for determining the partitioning of forces among dental implants supporting bridgework. However, more work will be needed to clarify how well these models match reality. Interfacial stress transfer and interfacial biology represent more difficult, interrelated problems. One problem is that the multitude of different shapes, sizes, materials, surgical sites and animal models for dental implants has precluded any generally accepted rules for biologically 'favorable' vs 'unfavorable' interfacial stress transfer conditions. While many engineering studies have shown that variables such as implant shape, elastic modulus, extent of bonding between implant and bone, etc., can affect the stress transfer conditions, the unresolved question is whether there is any biological significance to such differences. Recent research suggests that, at the very least, our search for a more detailed hypothesis regarding the relationship between interface mechanics and biology should take account of basic bone physiology, e.g. wound healing after implantation plus basic processes of bone modeling and remodeling.

Animals↗
PubMed1988

Biomechanics of oral implants: future research directions.

Biomechanical principles are relevant in dental implant design because all implants share a common biomechanical purpose: the restoration of masticatory function. Key problems confronting implant designers are: What are the in vivo loadings that dental implants must support? What factors govern interfacial stress transfer? How do biomechanical factors influence tissue reactions at the interface? Dental implant designers are currently in the position of trying to design implants without complete or accurate data to answer these biomechanical questions. These three questions and suggestions for future research are answered in this paper.

Biomechanical Phenomena↗
PubMed1987

Method for histological preparation of bone sections containing titanium implants.

A thin sectioning technique involving hand grinding has been developed to produce 20-40-microns-thick sections of bone-titanium implant sites. Components include: 1) surface staining of sections prior to mounting on slides so bone labels (oxytetracycline-HCl and 2,4-bis(N,N-dicarbomethyl)aminomethylfluorescein (DCAF] can be seen in sections viewed with transmitted light, 2) a pneumatic sample press for bonding sections to slides with a thin, uniform glue line and without trapped air bubbles, and 3) bonding methyl methacrylate embedded sections to clear acrylic slides with methyl methacrylate monomer to provide enhanced bond strength and grinding properties compared to those obtainable with glass slides. Sample cracking and distortion is minimized and the tissue-implant interface can be kept intact. The expense of start-up equipment for this technique is minimal.

Bone and Bones↗
PubMed1986

Development of a modular wheelchair cushion for spinal cord injured persons.

This paper discusses a modular wheelchair cushion system intended for patients at moderate or low risk for developing pressure sores. With the use of components with different mechanical and physical properties the modular cushion produces improved performance compared with cushions comprising the individual components alone. In addition to achieving clinically acceptable interface pressures, this approach to wheelchair cushion prescription helps to accommodate individual preferences associated with stability, temperature dissipation, and resiliency. Mechanical tests were performed to demonstrate the underlying principles of the modular cushion. Tests with able-bodied subjects identified specific cushion configurations for different weight groups, offering alternative material configurations that may be selected at the discretion of the therapist or patient.

Body Weight↗
PubMed1984

In vivo forces on dental implants: hard-wiring and telemetry methods.

Methods are presented for measuring vertical force components on bridged titanium dental implants in dog mandibles. These methods have included custom-made strain-gauge transducers, plus hard-wiring and telemetric schemes for data collection. The essential components of the measurement system are described, and typical bite force data are illustrated.

Animals↗
PubMed1983

Stresses in a Harrington distraction rod: their origin and relationship to fatigue fractures in vivo.

As illustrated by the case study described in this paper, in-vivo fractures of distraction rods often occur by metallurgical fatigue at the junction between the smooth and ratcheted parts of the rod (i.e., at the first ratchet junction, FRJ). To clarify causative factors of fatigue at the FRJ, stresses are analyzed in a standard 11-in. rod using both experimental and theoretical methods. The analyses reveal how distraction force, eccentricity of loading, rod geometry and material determine the stresses at the FRJ. These stresses can exceed the fatigue endurance limit for certain clinically encountered conditions.

Adult↗
PubMed1982

Model experiments to study the stress distributions in a seated buttock.

Mechanical stress states that develop in the buttock during sitting may exceed tissue tolerance and lead to decubitus ulcer formation in susceptible patients, such as those with spinal cord injury. The danger of this complication can be reduced by using suitable cushions to minimize stress magnitudes and gradients within soft tissues. In this investigation, a two-dimensional physical model of the buttock-cushion system was developed to aid in cushion design. The model consists of PVC gel simulating flesh, cast around a wooden core simulating the ischium bone. A grid etched on the gel permits measurement of strains via photographs of the undeformed and deformed model buttock supported by various cushion materials. The displacement field is analyzed, using a finite strain theory and a strain energy function, to obtain the "tissue stresses'. In this manner, the performances of five clinically used cushion materials were compared with respect to the high stress regimes developed in the model buttock.

Buttocks↗
PubMed1979

The influence of functional use of endosseous dental implants on the tissue-implant interface. I. Histological aspects.

The tissue-implant interfaces of functional and non-functional endosseous dental implants were compared histologically for up to one year post-operatively. Nonmineralized connective tissue zones (a "fibrous capsule") existed in all functional interfaces. Direct, or nearly direct, bone apposition to implants occurred in non-functional interfaces. The origin of this result and its significance in dental implantology is discussed.

Alveolar Process↗
PubMed1979

The influence of functional use of endosseous dental implants on the tissue-implant interface. II. Clinical aspects.

Functional and non-functional endosseous dental implants were clinically compared in beagle mandibles for up to one year post-operatively. Differing biomechanical conditions led to clinical differences between functional and non-functional implants. Typical clinical tests, however, did not always reveal detailed histological differences between implant-tissue interfaces of functional and non-funcional implants.

Alveolar Process↗