Biomedical subjects

Zong-Ping Luo

Publications and source records attributed to Zong-Ping Luo.

32 records · Page 2Linked to original sources

PubMed2004

Stretching type II collagen with optical tweezers.

Collagens are the most abundant proteins of vertebrates and they provide mechanical and supportive functions in a wide range of connective tissues. Knowledge of the mechanical properties of single collagen molecules is essential in studying the self-assembly of collagen, the interaction between cells and extracellular matrix, the etiology of tissue degeneration and mechanism of regeneration, and the relationship between the structures and mechanical properties of tissues. Here we stretched single type II collagen molecules in neutral pH solution using optical tweezers. The molecular parameters of collagen were obtained by fitting force-extension curves into worm-like chain elasticity model. The molecule length of type II collagen monomer was 295.8 nm. The persistence length of type II collagen monomer was 11.2 nm. These observations indicate that collagen molecules are flexible rather than rigid rod molecules at neutral pH solution.

Collagen Type II↗

PubMed2004

The combined regulation of estrogen and cyclic tension on fibroblast biosynthesis derived from anterior cruciate ligament.

Female athletes are two to eight times more likely to suffer a knee or ankle ligament injury than male athletes, and sex hormones have been considered to play an important role in the injury. Because ligaments are always under mechanical loading during sports, mechanical force is also a critical factor in ligament injuries. In this study, the effects of estrogen and mechanical loading on the gene expression of three major components of ligament--collagen type I, type III, and biglycan--in primary cultured porcine anterior cruciate ligament (ACL) fibroblasts were investigated individually and collectively using reverse transcript-polymerase chain reaction (RT-PCR). The results revealed that cyclic tensile loading alone increased the messenger RNA expression of collagen I but did not affect that of collagen III and biglycan, and estrogen alone increased the gene expression of collagen I and III but not of biglycan. However, combined administration of estrogen and cyclic loading inhibited the mRNA expression of all the three genes. These results suggested that the inhibition of the gene expression of major extracellular matrix component molecules caused by the combined effects of estrogen and mechanical loading, unique to females, might be responsible for the increased incidence of ligaments injury in female athletes.

Animals↗

PubMed2004

Flexibility of type I collagen and mechanical property of connective tissue.

The hierarchical organization of the connective tissue, more specifically, the musculoskeletal soft tissue, has been extensively studied. With advancements in experimental methodology, investigation of the structure-function relationship has provided more insight into how the mechanical integrity of the tissue is created. Such information is essential in the linking the macroscopic loading environment of the tissue to the microscopic level of the tissue to be experienced by the cell. The flexibility and elastic modulus of gross connective tissue, the fascicle, the fiber and then the collagen molecule are compared based on the data available in the literature.

Adaptation, Physiological↗

PubMed2004

Single molecule mechanical properties of type II collagen and hyaluronan measured by optical tweezers.

Type II collagen and hyaluronan are the two major components of extracellular molecules in cartilage and play an important role in mechanical functions of extracellular matrix. Currently, their mechanical properties have been investigated only at the gross-level. In this study, the mechanical properties of single type II collagen and hyaluronan molecules were directly measured using optical tweezers technique. The persistence length was found to be 11.2+/-8.4 nm in type II collagen and 4.5+/-1.2 nm in hyaluronan. This result suggested that type II collagen is stiffer than hyaluronan at the individual molecule level, which supports the general concept that collagen is responsible for resisting tensile force. The experimental system developed here also provides a powerful tool for quantifying mechanical properties of extracellular matrix at the single molecule level.

Animals↗

PubMed2003

A method for testing compressive properties of single proteoglycan aggregates.

This study presents a method for direct measurement of the compressive properties of single molecules of proteoglycan aggregate using a state-of-the-art laser tweezers/interferometer system previously developed to test the tensile properties of single molecules. A typical molecule of proteoglycan aggregate showed a highly non-linear resistance to compression after being compressed to about 25% of its original molecule length.

Compressive Strength↗

PubMed2003

Correlation between rotator cuff tear and glenohumeral degeneration.

We studied the occurrence and correlation between a rotator cuff tear and glenohumeral degeneration. 44 cadaveric shoulders (22 right) were obtained from 32 subjects (18 females), mean age 73 (62-86) years and without a history of systemic diseases. Rotator cuffs were exposed and tear size (14 shoulders) was measured after removal of soft tissue and deltoid. Articular cartilage damage of the glenoid and humeral head was recorded by photography. A grading system of 1 (intact), 2 (mild) and 3 (severe) was used to determine the severity of cartilage damage. The area of articular cartilage damage was calculated using the Sonic Digitizer Analyzing System. The area of articular cartilage damage to the glenoid and the humeral head in the rotator cuff tear group was 32% and 36%, respectively. It was greater than that in the groups without a tear, which was 6% in the glenoid and 7% in the humeral head. However, it was not correlated with the size of the tear. Most of the articular cartilage damage in massive and large rotator cuff tears was located in the anterior-inferior portion of the glenoid and in the posterior portion of the humeral head. The articular cartilage damage area of the glenoid was correlated with that of the humeral head. In conclusion, the area of glenohumeral degeneration was greater in the rotator cuff tear group and was located in a specific site.

Aged↗

PubMed2002

Direct quantification of the flexibility of type I collagen monomer.

Collagens are the most abundant structural proteins found in the extracellular matrix of vertebrates. Knowledge of the mechanical behavior of collagen monomers is essential for understanding the mechanical properties of collagen fibrils that constitute the main architectural framework of skin, bone, cartilage, and other connective tissues. In this study, the flexibility of type I collagen monomer was studied by stretching type I collagen monomers directly. The force-extension relationship was measured and analyzed by fitting the data into a worm-like chain elasticity model. The persistence length of collagen I monomer was determined to be 14.5 nm and the contour length was 309 nm. The results confirm that type I collagen monomer is flexible rather than rigid, rod-like molecule. Such flexibility may possibly be a consequence of the micro-unfolding of discrete domains of single collagen molecule.

Collagen Type I↗

PubMed2002

Mechanical properties of single hyaluronan molecules.

Hyaluronan (HA) is a major component of the extracellular matrix. It plays an important role in the mechanical functions of the extracellular matrix and stabilization of cells. Currently, its mechanical properties have been investigated only at the gross level. In this study, the mechanical properties of single HA molecules were directly measured with an optical tweezer technique, yielding a persistence length of 4.5 +/- 1.2 nm. This information may help us to understand the mechanical roles in the extracellular matrix infrastructure, cell attachment, and to design tissue engineering and drug delivery systems where the mechanical functions of HA are essential.

Biomechanical Phenomena↗

PubMed2002

Effect of foot orthoses on 3-dimensional kinematics of flatfoot: a cadaveric study.

OBJECTIVE: To test in cadaveric feet the hypothesis that prefabricated foot orthoses will improve arch alignment in flatfoot deformity. DESIGN: Experimental, paired comparisons. SETTING: Biomechanics laboratory. CADAVERS: Nine cadaveric lower-extremity specimens with no abnormalities. INTERVENTIONS: To evaluate the performance of 2 orthoses specimens were tested in 4 combinations: intact, flatfoot, flatfoot with shoe and orthosis 1, and flatfoot with shoe and orthosis 2. To simulate the midstance phase of gait, loads were applied to 5 tendons and an axial load equivalent to two thirds of the standing load was applied to the foot's plantar surface. MAIN OUTCOME MEASURES: Arch height and tarsal bone positions before and after a flatfoot deformity created by ligament sectioning; tarsal bone positions determined with a magnetic tracking system. RESULTS: After ligament sectioning, the average decrease in arch height with a shoe applied was 4.6+/-1.6mm (8%); with orthosis 1, mean arch height increased 0.7+/-0.6mm (P=.008); with orthosis 2, it increased 0.3+/-0.5mm (P=.05). With both orthoses, arch height after sectioning was significantly less than that of the normal arch. Compared with the flatfoot condition, metatarsal-talar alignment improved in plantar flexion and inversion with both orthoses but did not approximate normal with either orthosis. Calcaneal-tibial position did not improve with either orthosis and was markedly different from that in the intact foot with either orthosis. No difference was found between the 2 orthoses except for metatarsal-talar motion in external rotation (P=.014) and eversion (P=.026). CONCLUSIONS: Arch alignment improved significantly but to a limited degree (<2%) in cadaveric feet with the use of orthoses. Hindfoot valgus malalignment did not consistently improve by the use of shoe inserts.

Aged↗

PubMed2002

An in vitro study of glenohumeral performance after suprascapular nerve entrapment.

PURPOSE: The functional performance of athletes with suprascapular nerve entrapment remains unaddressed biomechanically. The purpose of this study was to investigate the glenohumeral joint kinematics, stability, and characteristics of joint contact. METHODS: The investigation used an in vitro model simulating muscle palsy due to the suprascapular nerve entrapment. The experiment was performed in three clinically relevant positions: inferior, one by sulcus test; posterior, one with 90 degrees flexion and maximal internal rotation; and anterior, one with 90 degrees abduction and 90 degrees external rotation (which is critically involved in several sports activities). RESULTS: Simulated palsy due to suprascapular nerve entrapment had effects on glenohumeral joint stability and contact characteristics. Changes in the humeral head displacement and the glenohumeral joint contact characteristics were the most significant in the anterior direction when the arm in 90 degrees abduction and 90 degrees external rotation. CONCLUSION: Glenohumeral function is affected by muscle weakness at the position that is critical in sports activities. Because the infraspinatus supplies 90% of the external rotation power of the shoulder and the supraspinatus stabilizes the humeral head in the glenoid during elevation, residual weakness due to suprascapular nerve entrapment may preclude a safe return to athletics.

Aged↗

PubMed1998

Measurement of surface contact area of the ankle joint.

OBJECTIVE: To determine the distribution of contact area of the ankle joint with axial loading and in positions of maximal dorsiflexion, plantar flexion, supination, and pronation. We also tested the effects of extrinsic tendon loading and arch instability. DESIGN: Nine cadaveric feet were studied in the intact condition and following transection of ligaments to create arch instability. BACKGROUND: Assessment of ankle contact in various joint positions and degrees of instability is difficult to accomplish with conventional methods. METHODS: Displacement of the talus relative to the tibia was measured with a magnetic tracking device and tibiotalar joint contact from proximity calculations of digitized joint surfaces. RESULTS: Contact area did not change significantly from unloaded condition to 667 N load condition in the medial, central, and lateral zones. Central zone contact area decreased in plantar flexion by an average of 324 mm(2) (SD, 165 mm(2)) (P = 0.0004). Medial zone contact area decreased in plantar flexion by a mean of 55 mm(2) (SD, 28 mm(2)) (P = 0.0004), decreased in pronation by an average of 42 mm(2) (SD, 36 mm(2)) (P = 0.0086), and increased in supination by an average of 20 mm(2) (SD, 26 mm(2)) (P = 0.0430). Lateral zone contact decreased in plantar flexion by a mean of 124 mm(2) (SD, 57 mm(2)) (P = 0.0002). CONCLUSIONS: In plantar flexion, there was a decrease in contact area. Loading extrinsic tendons to the foot did not significantly increase ankle contact area, but arch instability caused a decrease in central and lateral zone contact area. RELEVANCE: This technique was used to assess joint contact characteristics in various loading conditions and will be useful for evaluating the extent to which treatment for ankle or hindfoot problems such as bracing or reconstruction operations restores normal joint contact.

Journal Article↗

PubMedDate not supplied

The structure of proteoglycan aggregate determined by atomic force microscopy.

Proteoglycan aggregate is the major extracellular matrix component in cartilage, comprising about 18% of the dry weight of hyaline cartilage. The proteoglycan aggregate is the major substance in cartilage which resists compression in the joint. The purpose of this study was to utilize the newly developed imaging technique, Atomic force Microscopy (AFM), to visualize the ultrastructure of proteoglycan aggregates. The proteoglycan aggregate molecules were imaged in air using the tapping mode of the AFM. The images illustrated the ultrastructure of the aggregates, especially the individual proteoglycan and the core hyaluronic acid. In addition to the length and width of each molecule, the height of the proteoglycan aggregates and the individual proteoglycans could be directly measured. The images of the ultrastructures of proteoglycan aggregates visualized from the AFM are comparable with those using conventional electron microscopy approaches. Nevertheless, the sample preparation for AFM imaging does not involve fixation, staining, coating, and other routine procedures required for traditional electron microscopy imaging. Thus, this technique could be a simple alternative approach for future analysis of proteoglycan aggregate and its assembly.

Animals↗

PubMedDate not supplied

Comminuted olecranon fractures: a comparison of plating methods.

The relative strength of posterior plating and dual medial-lateral plating for comminuted olecranon fractures has not been evaluated. Fifteen male cadaveric elbows with simulated highly comminuted olecranon fractures were tested to failure via cantilever bending. The strength of dual medial-lateral plates and a single posterior plate with and without an intramedullary screw was evaluated. The mean bending moment at failure for the dual-plated specimens was 30.0 +/- 7.5 Nm. The mean bending moment at failure for specimens with a posterior plate without an intramedullary screw was 34.5 +/- 9.1 Nm. The mean bending moment at failure for specimens with a posterior plate and an intramedullary screw was 44.5 +/- 6.9 Nm; this was significantly greater than for dual-plated specimens (P < .05) but not for specimens with a posterior plate without an intramedullary screw. The posterior plate with an intramedullary screw was the most stable construct tested and may, therefore, be the preferred method of fixation for comminuted olecranon fractures. This construct was significantly (48%) stronger than dual medial and lateral plating.

Biomechanical Phenomena↗

PubMedDate not supplied

Force-mediated dissociation of proteoglycan aggregate in articular cartilage.

Proteoglycan aggregate is the primary component in articular cartilage responsible for resisting compressive loading. It consists of a core molecule of hyaluronan and a number of side chains of aggrecan bound to hyaluronan non-covalently. The loss of aggrecan from articular cartilage is considered to be a major factor in the development of osteoarthritis. Though enzymatic digestion of aggrecan is believed to be responsible for the release of aggrecan from osteoarthritic cartilage, other mechanisms, such as direct force-mediated detachment of aggrecan from hyaluronan may also be involved. In this study, the rupture force of the single bond between hyaluronan and aggrecan in articular cartilage was directly quantified using experimental measurement and Monte Carlo simulation. Low rupture force of this bond, as determined in this study suggested a possible direct force-mediated detachment of aggrecan from proteoglycan aggregate in osteoarthritic cartilage.

Aggrecans↗