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Biomedical subjects

Huub Maas

Publications and source records attributed to Huub Maas.

14 recordsLinked to original sources
PubMed2006

Photoisomerization of azobenzene derivatives in nanostructured silica.

A series of derivatized azobenzene molecules are synthesized such that one of the phenyl groups can be chemically bonded to mesostructured silica and the other, derivatized with dendrons, is free to undergo large-amplitude light-driven motion. The silica frameworks on which the motion takes place are either 150 nm thick films containing ordered hexagonal arrays of tubes (inner diameter about 2 nm) containing the bonded azobenzenes, or particles (about 500 nm in diameter) containing the same ordered arrays of functionalized tubes. The photoisomerization yields and the rate constants for the thermal cis to trans back-reaction of the azobenzenes in the tubes are measured and compared to those of the molecules in solution. The rate constants decrease with increasing size of the dendrons. Fluorescence spectra of the cis and trans isomers in the pores show that the photoisomerization in the nanostructured materials is selectively driven by specific wavelengths of light and is reversible.

Journal Article↗
PubMed2005

Controlled intermittent shortening contractions of a muscle-tendon complex: muscle fibre damage and effects on force transmission from a single head of rat EDL.

This study was performed to examine effects of prolonged (3 h) intermittent shortening (amplitude 2 mm) contractions (muscles were excited maximally) of head III of rat extensor digitorum longus muscle (EDL III) on indices of muscle damage and on force transmission within the intact anterior crural compartment. Three hours after the EDL III exercise, muscle fibre damage, as assessed by immunohistochemical staining of structural proteins (i.e. dystrophin, desmin, titin, laminin-2), was found in EDL, tibialis anterior (TA) and extensor hallucis longus (EHL) muscles. The damaged muscle fibres were not uniformly distributed throughout the muscle cross-sections, but were located predominantly near the interface of TA and EDL muscles as well as near intra- and extramuscular neurovascular tracts. In addition, changes were observed in desmin, muscle ankyrin repeat protein 1, and muscle LIM protein gene expression: significantly (P<0.01) higher (1.3, 45.5 and 2.3-fold, respectively) transcript levels compared to the contralateral muscles. Post-EDL III exercise, length-distal force characteristics of EDL III were altered significantly (P<0.05): at high EDL III lengths, active forces decreased and the length range between active slack length and optimum length increased. For all EDL III lengths tested, proximal passive and active force of EDL decreased. The slope of the EDL III length-TA+EHL force curve decreased, which indicates a decrease of the degree of intermuscular interaction between EDL III and TA+EHL. It is concluded that prolonged intermittent shortening contractions of a single head of multi-tendoned EDL muscle results in structural damage to muscle fibres as well as altered force transmission within the compartment. A possible role of myofascial force transmission is discussed.

Animals↗
PubMed2005

Mechanisms causing effects of muscle position on proximo-distal muscle force differences in extra-muscular myofascial force transmission.

Certain recent studies showed that extra-muscular myofascial force transmission affects the length-force characteristics of rat extensor digitorium longus (EDL) muscle significantly after distal or proximal lengthening. This suggested that the relative position of a muscle with respect to its surrounding connective tissues is a co-determinant of muscle force in addition to muscle length, and indicated major effects on muscular mechanics. The specific goal of the present study is to investigate such effects by studying: (1) distributions of lengths of sarcomeres within muscle fibres and (2) the relative contributions of muscle fibres and the extra-cellular matrix to muscle total force, using a finite element model. The length of the muscle modelled was kept constant at a high and at a low muscle length whereas the relative position of the muscle was altered exclusively. For both muscle lengths, the forces exerted at distal and proximal tendons were unequal at almost all muscle relative positions. The proximo-distal force difference was enhanced as the muscle was repositioned away from its reference position. This confirmed the role of relative position of a muscle as a co-determinant of muscle force. At higher muscle lengths, distributions of lengths of sarcomeres arranged in series within muscle fibres were substantial. The force transmitted by the muscles' extra-cellular matrix comprised a sizable part of muscle total force. At lower muscle lengths distribution of sarcomere lengths was relatively limited indicating that the extra-cellular matrix is bearing the extra-muscular force. However, minor sarcomere length changes were shown to accumulate to sizable effects on the summed forces exerted by the muscle fibres. In addition, the extra-muscular load was shown to manipulate the force exerted by the extra-cellular matrix. We conclude that the relative position of a muscle has substantial effects on intra-muscular mechanics and the importance of the role of the extra-cellular matrix in determining the proximo-distal force differences is comparable to that of the intra-cellular domain.

Animals↗
PubMed2005

Myofascial force transmission in dynamic muscle conditions: effects of dynamic shortening of a single head of multi-tendoned rat extensor digitorum longus muscle.

This study investigated the effects of myofascial force transmission during dynamic shortening of head III of rat extensor digitorum longus muscle (EDL III). The anterior crural compartment was left intact. Force was measured simultaneously at the distal EDL III tendon, the proximal EDL tendon and the distal tendons of tibialis anterior and extensor hallucis longus muscles (TA + EHL). Two types of distal shortening of EDL III were studied: (1) sinusoidal shortening (2 mm) and (2) isokinetic shortening (8 mm). Sinusoidal shortening of EDL III caused a decrease in force exerted at the distal tendon of EDL III: from 0.58 (0.08) N to 0.26 (0.04) N. In contrast, hardly any changes in proximal EDL force and distal TA+EHL force were found. Maximal concentric force exerted at the distal tendon of EDL III was higher than maximal isometric force expected on the basis of the physiological cross-sectional area of EDL III muscle fibers (Maas et al. 2003). Therefore, a substantial fraction of this force must originate from sources other than muscle fibers of EDL III. Isokinetic shortening of EDL III caused high changes in EDL III force from 0.97 (0.15) N to zero. In contrast, changes in proximal EDL force were much smaller: from 2.44 (0.25) N to 1.99 (0.19) N. No effects on TA + EHL force could be shown. These results are explained in terms of force transmission between the muscle belly of EDL III and adjacent tissues. Thus, also in dynamic muscle conditions, muscle fiber force is transmitted via myofascial pathways.

Animals↗
PubMed2005

Intermuscular interaction between synergists in rat originates from both intermuscular and extramuscular myofascial force transmission.

The purpose of the present study is to investigate the origin of mechanical interactions between the rat extensor digitorum longus (EDL) muscle and the grouped tibialis anterior and extensor hallucis longus muscles (TA+EHL). The proximal and distal tendons of EDL as well as the tied distal tendons of TA+EHL were transected and connected to force transducers. Connective tissues at the muscle bellies of the anterior crural compartment were left intact. Supramaximal stimulation of the common peroneal nerve activated all muscles maximally and simultaneously. Length-isometric force characteristics of distal TA+EHL were assessed. Simultaneously, forces exerted at the proximal and distal tendons of EDL, kept at constant muscle-tendon complex length and position, were measured. Intermuscular interaction was tested in two conditions: (a) after full longitudinal compartmental fasciotomy, and (b) after blunt dissection of the intermuscular connective tissue linkages between EDL and TA+EHL. Note that in the latter condition, intermuscular myofascial pathways were eliminated. In the initial condition, lengthening TA+EHL by 12 mm increased proximal (by 0.14 N, i.e. 9.5%) and decreased distal EDL force (by 0.21 N, i.e. 11.8%), despite the fact that EDL muscle-tendon complex length was kept constant. Blunt dissection decreased TA+EHL and distal EDL forces at low TA+EHL lengths only, while proximal EDL force decreased for all TA+EHL lengths tested. The dissection caused no changes in the TA+EHL length effects on proximal EDL force. In contrast, the amplitude of change in the distal EDL force curve decreased significantly (by 39%) subsequent to blunt dissection. It is concluded that mechanical interaction between synergists originates from both intermuscular as well as extramuscular connective tissues. The highest contribution, however, should be ascribed to the extramuscular pathway.

Animals↗
PubMed2004

Muscle force is determined also by muscle relative position: isolated effects.

Effects on force of changes of the position of extensor digitorum longus muscle (EDL) relative to surrounding tissues were investigated in rat. Connective tissue at the muscle bellies of tibialis anterior (TA), extensor hallucis longus (EHL) and EDL was left intact, to allow myofascial force transmission. The position of EDL muscle was altered, without changing EDL muscle-tendon complex length, and force exerted at proximal and distal tendons of EDL as well as summed force exerted at the distal tendons of TA and EHL muscles (TA+EHL) were measured. Proximal and distal EDL forces as well as distal TA+EHL force changed significantly on repositioning EDL muscle. These muscle position-force characteristics were assessed at two EDL lengths and two TA+EHL lengths. It was shown that changes of muscle force with length changes of a muscle is the result of the length changes per se, as well as of changes of relative position of parts of the muscle. It is concluded that in addition to length, muscle position relative to its surroundings co-determines isometric muscle force.

Animals↗
PubMed2003

Host-guest antenna materials.

The focus of this review is on host-guest composites with photonic antenna properties. The material generally consists of cylindrical zeolite L crystals the channels of which are filled with dye molecules. The synthesis is based on the fact that molecules can diffuse into individual channels. This means that, under the appropriate conditions, they can also leave the zeolite by the same way. In some cases, however, it is desirable to block their way out by adding a closure molecule. Functionalization of the closure molecules allows tuning of, for example, wettability, refractive index, and chemical reactivity. The supramolecular organization of the dyes inside the channels is a first stage of organization. It allows light harvesting within a certain volume of a dye-loaded nanocrystalline zeolite and radiationless transport to both ends of the cylinder or from the ends to the center. The second stage of organization is the coupling to an external acceptor or donor stopcock fluorophore at the ends of the channels, which can trap or inject electronic excitation energy. The third stage of organization is the coupling to an external device through a stopcock molecule. The wide-ranging tunability of these highly organized materials offers fascinating new possibilities for exploring excitation-energy-transfer phenomena, and challenges for developing new photonic devices.

Journal Article↗
PubMed2003

Myofascial force transmission between a single muscle head and adjacent tissues: length effects of head III of rat EDL.

Force transmission from muscle fibers via the connective tissue network (i.e., myofascial force transmission) is an important determinant of muscle function. This study investigates the role of myofascial pathways for force transmission from multitendoned extensor digitorum longus (EDL) muscle within an intact anterior crural compartment. Effects of length changes exclusively of head III of rat EDL muscle (EDL III) on myofascial force transmission were assessed. EDL III was lengthened at the distal tendon. For different lengths of EDL III, isometric forces were measured at the distal tendon of EDL III, as well as at the proximal tendon of whole EDL and at the distal tendons of tibialis anterior and extensor hallucis longus (TA+EHL) muscles. Lengthening of EDL III caused high changes in force exerted at the distal tendon of EDL III (from 0 to 1.03 +/- 0.07 N). In contrast, only minor changes were found in force exerted at the proximal EDL tendon (from 2.37 +/- 0.09 to 2.53 +/- 0.10 N). Increasing the length of EDL III decreased TA+EHL force significantly (by 7%, i.e., from 5.62 +/- 0.27 to 5.22 +/- 0.32 N). These results show that force is transmitted between EDL III and adjacent tissues via myofascial pathways. Optimal force exerted at the distal tendon of EDL III (1.03 +/- 0.07 N) was more than twice the force expected on the basis of the physiological cross-sectional area of EDL III muscle fibers (0.42 N). Therefore, a substantial fraction of this force must originate from sources other than EDL III. It is concluded that myofascial pathways play an important role in force transmission from multitendoned muscles.

Animals↗
PubMed2003

Compartmental fasciotomy and isolating a muscle from neighboring muscles interfere with myofascial force transmission within the rat anterior crural compartment.

Muscles within the anterior crural compartment (extensor digitorum longus, EDL; tibialis anterior, TA; and extensor hallucis longus, EHL) and within the peroneal compartment were excited simultaneously and maximally. All muscles were kept at constant length with the exception of EDL, for which muscle length was changed by moving its proximal tendon. Active and passive force was measured at proximal as well as distal EDL tendons and at the combined distal tendons of TA and EHL (TA+EHL). In the initial experimental condition, a difference (F(proximal) > F(distal)) in EDL force, amounting to 0-14% of proximal force, was confirmed for most EDL lengths. This is interpreted as a clear proof of extramuscular myofascial force transmission, as no significant EDL length effects could be shown on TA+EHL force. Repeated measurements were confirmed to cause marked changes of both proximal and distal length-force characteristics, such as a shift of the whole ascending limb of the active curve, including optimum length, to higher lengths without decreasing optimum force, and decreasing active force at low lengths (by approximately 57%). Repeated measurements also lowered proximal and distal EDL passive force (by up to 35%). The proximo-distal difference in passive as well as active EDL force was decreased, but persisted. At most lengths, this difference for active force amounted to a constant fraction (14%) of proximal force. TA+EHL force was not affected significantly. Subsequently, acute effects of experimental surgical alterations were studied: The first manipulation was full lateral fasciotomy of the anterior crural compartment that caused a further decrease in active force at the proximal EDL but not at the distal EDL tendon. Passive forces showed no further significant changes. The proximo-distal EDL active force difference decreased to 0-5% of proximal force. After fasciotomy, TA+EHL force increased by 30%. This was interpreted as evidence of increased intramuscular and decreased extramuscular myofascial force transmission. The second manipulation was full isolation of EDL from TA+EHL, but not from extramuscular connective tissues, which caused a further decrease of the EDL proximo-distal force differences, indicating a stiffening effect of the presence of TA+EHL on the extramuscular matrix. For EDL active force the difference was no longer significantly different from zero. In contrast, for EDL passive force the proximo-distal force difference persisted. It is concluded that extramuscular myofascial force transmission is an important feature of the anterior crural compartment. The magnitude of this force transmission requires that it be considered in analysis of muscular function.

Analysis of Variance↗
PubMed2003

The relative position of EDL muscle affects the length of sarcomeres within muscle fibers: experimental results and finite-element modeling.

BACKGROUND: Effects of extramuscular connective tissues on muscle force (experimentally measured) and lengths of sarcomeres (modeled) were investigated in rat. It was hypothesized that changes of muscle-relative position affect the distribution of lengths of sarcomeres within muscle fibers. METHOD OF APPROACH: The position of extensor digitorum longus muscle (EDL) relative to intact extramuscular connective tissues of the anterior crural compartment was manipulated without changing its muscle-tendon complex length. RESULTS: Significant effects of EDL muscle relative position on proximal and distal EDL forces were found, indicating changes of extramuscular myofascial force transmission. EDL isometric force exerted at its proximal and distal tendons differed significantly. Finite-element modeling showed that the distribution of lengths of sarcomeres is altered by changes of muscle-relative position. CONCLUSIONS: It is concluded that forces exerted on a muscle via extramuscular myofascial pathways augment distributions of lengths of sarcomeres within that muscle.

Animals↗
PubMed2002

Synthesis of new molecules containing head, spacer, and label moieties.

We describe the synthesis and characterization of novel molecules containing head with precise shape, spacer, and label moieties. The protocol is based on a Pd(0)-catalyzed cross-coupling reaction between ethynylphenyl/bromide to obtain a rigid head followed by the attachment of a flexible spacer possessing two reactive functional groups on the termini. The final step consists of forming a covalent bond between spacer and label. In addition, monosubstituted soluble labels were synthesized in good yields.

Journal Article↗