Low Force Requirements Research Articles

A novel porous hydrogel based on hybrid gelation for injectable and tough scaffold implantation and tissue engineering applications

Although there have been many advances in injectable hydrogels as scaffolds for tissue engineering or as payload-containing vehicles, the lack of adequate microporosity for the desired cell behavior, tissue integration, and successful tissue generation remains an important drawback. Herein, we describe an effective porous injectable system that allows in vivo formation of pores through conventional syringe injection at room temperature. This system is based on the differential melting profiles of photocrosslinkable salmon gelatin and physically crosslinked porogens of porcine gelatin (PG), in which PG porogens are solid beads, while salmon methacrylamide gelatin remains liquid during the injection procedure. After injection and photocrosslinking, the porogens were degraded in response to the physiological temperature, enabling the generation of a homogeneous porous structure within the hydrogel. The resultant porogen-containing formulations exhibited controlled gelation kinetics within a broad temperature window (18.5 ± 0.5–28.8 ± 0.8 °C), low viscosity (133 ± 1.4–188 ± 16 cP), low force requirements for injectability (17 ± 0.3–39 ± 1 N), robust mechanical properties after photo-crosslinking (100.9 ± 3.4–332 ± 13.2 kPa), and favorable cytocompatibility (>70% cell viability). Remarkably, in vivo subcutaneous injection demonstrated the suitability of the system with appropriate viscosity and swift crosslinking to generate porous hydrogels. The resulting injected porous constructs showed favorable biocompatibility and facilitated cell infiltration for desirable potential tissue remodeling. Finally, the porogen-containing formulations exhibited favorable handling, easy deposition, and good shape fidelity when used as bioinks in 3D bioprinting technology. This injectable porous system serves as a platform for various biomedical applications, thereby inspiring future advances in cell therapy and tissue engineering.

Joint Strength of Low Carbon Steel Joints and its Selection Guide of Friction Welding Conditions for Low Force Requirements made by Friction Stud Welding Method

Joint Strength of Low Carbon Steel Joints and its Selection Guide of Friction Welding Conditions for Low Force Requirements made by Friction Stud Welding Method

Effects of reinforcement value on instruction following under schedules of negative reinforcement

The effects of reinforcement value and social control on instruction following under a negative-reinforcement (escape) schedule were studied. Initially, responding produced timeouts from pressing a force cell under a low and a high force requirement on a fixed-ratio 1 schedule of reinforcement. Next, participants were reexposed to the low and high force requirements, but were instructed that the experimenter expected them to decrease the number of timeouts relative to the previous exposures to the procedure. Even though following the instruction led to a decrease in number of timeouts and to an increase in effort (i.e., was non-efficient), instruction following occurred consistently for each participant and was modulated by reinforcement value. That is, the decrease in the number of timeouts (i.e., instruction following) was lower under the high force requirement than under the low force requirement. These results replicate and extend previous findings that instructions interact with social and nonsocial contingencies in controlling human behavior.

Methodology for the evaluation of 3D surface topography in multiple indentation processes

Elementary indentation processes are relatively simple compression processes and they are quite extended in many fields of the industry. Nevertheless, the concatenation of these processes is a new approach and has interest from a technological point of view. Incremental forming processes can be carried out in CNC machines with more flexibility, lower force requirements and simpler tools than in conventional forging processes. The purpose of this work is the analysis of the three-dimensional geometry resulting from the multiple indentation process. Based on the surface rugosity parameters defined in the specification standard ISO 4287, the state of the 3D-formed surface by several types of tools is studied and a predictive evaluation model has been developed in order to quantify, by means of shape parameters Sa and SM, the topography of the expected surface and the amount of material displaced depending on the technological and geometrical characteristics of the process.

Specific Metabolic Properties of Rat Oculorotatory Extraocular Muscles Can Be Linked to Their Low Force Requirements

To gain insight into the metabolic pathways of oculorotatory extraocular muscle (EOM) fiber types at the cellular level to explain their high fatigue resistance, rapid contraction, and low force output. In consecutive sections of adult rat EOMs, the cross-sectional area (CSA) was calculated, and the activities of succinate-dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPDH) were measured by quantitative histochemistry of different fiber types classified by the myofibrillar adenosine triphosphatase (mATPase) staining pattern. In the orbital regions, type 1 (fast) fibers were present, showing small CSA, medium SDH, and low GPDH activity. The type 2 (slow) fibers exhibited extremely small CSA and low SDH and GPDH activity. In the global region, fast types 3 to 5 fibers were found, forming a continuum with an inverse correlation between CSA and enzyme activity. SDH and GPDH activity showed an unusual positive relationship in contrast to the skeletal muscle fiber types. The type 6 fibers were slow forming a close and clearly separated group with medium CSA and extremely low SDH and low GPDH activity. Muscle fibers in adult rat EOMs show unique metabolic properties not seen in other skeletal muscles, covering their extraordinary functional demands. It can be speculated that the EOMs embedded within the orbit material do not need to perform with high force, and therefore they could develop extensive systems that ensure both fatigue resistance (many mitochondria) and fast contraction with high mATPase activity (a well-developed sarcotubular system).

The role of hind limb flexor muscles during swimming in the toad, Bufo marinus

Most work examining muscle function during anuran locomotion has focused largely on the roles of major hind limb extensors during jumping and swimming. Nevertheless, the recovery phase of anuran locomotion likely plays a critical role in locomotor performance, especially in the aquatic environment, where flexing limbs can increase drag on the swimming animal. In this study, I use kinematic and electromyographic analyses to explore the roles of four anatomical flexor muscles in the hind limb of Bufo marinus during swimming: m. iliacus externus, a hip flexor; mm. iliofibularis and semitendinosus, knee flexors; and m. tibialis anticus longus, an ankle flexor. Two general questions are addressed: (1) What role, if any, do these flexors play during limb extension? and (2) How do limb flexors control limb flexion? Musculus iliacus externus exhibits a large burst of EMG activity early in limb extension and shows low levels of activity during recovery. Both m. iliofibularis and m. semitendinosus are biphasically active, with relatively short but intense bursts during limb extension followed by longer and typically weaker secondary bursts during recovery. Musculus tibialis anticus longus becomes active mid way through recovery and remains active through the start of extension in the next stroke. In conclusion, flexors at all three joints exhibit some activity during limb extension, indicating that they play a role in mediating limb movements during propulsion. Further, recovery is controlled by a complex pattern of flexor activation timing, but muscle intensities are generally lower, suggesting relatively low force requirements during this phase of swimming.

Close-die forging of large Cu-lids by a method of low force requirement

This paper presents a FE-analysis and experimental results of a hot forging method for fabrication of large copper canister lids with a low forging load. The forging sequence is carried out in two parts, namely axisymmetric and cogging. The cogging tool is used to bite off small areas of the workpiece periphery surface at the same time as the outer material is forced into the deep die cavity of the bottom die. During this process, the bottom tool is rotated about 45° after each pressing before a new bite is taken. As a result the main part of the cavity is filled at the same time as a protrusion develops at the central part of the workpiece. The cogging tool works on it later. Due to the small contact surface between the upper tool and the workpiece, the forging load needed to complete die filling is small and does not exceed the maximum load of the press. The process was earlier optimised so that no flash was needed for complete die filling. Process parameters affecting the evolution of the microstructure are analysed. Material flow and forging load in different stages of the process are studied. Microstructures obtained in the final product are presented for different locations along the radius of a vertical symmetry plane of the circular lid. Grain size evaluations are roughly co-related to the accumulated effective strain distribution obtained during the different manufacturing operations and to the temperature distribution obtained at the end of the forming process. It is concluded from the simulations that a 4600-t press is sufficient to achieve complete die filling and from experiments that an acceptably small grain size is obtained throughout the lid. From the simulation results the whole volume of the lid has experienced high strains after the manufacturing steps. No regions of low strain were found which according to experience is coincidental with a coarse-grained microstructure.

Strength demands of line handlers on the Panama canal

Vessels transiting the Panama Canal are guided through the locks using locomotives attached by means of towlines (made of wire rope), which are fastened to bitts on the deck by line handlers. The latter activity requires high pulling strength demands and is thought to be a cause of the high incidence of low back disorders in these workers. At the invitation of the Panama Canal Commission, NIOSH researchers evaluated the strength demands of line handlers and the strength capabilities of a line handling crew. Strength demands measured during a transit indicated high pulling force demands for attaching ropes to the bow and stern bitts (< 1000 N), but lower force requirements for midships bitts (< 400 N). Tests of pulling strength capabilities of a line handling crew suggest that at least 4–5 line handlers are needed to perform the most demanding tasks. When pulling upwards or downwards on a rope in a team effort, ordering the crew according to stature appears important. Simulation of slippery deck conditions resulted in a 13% decrease in team pulling strength. Though the short duration of the study prevented an extensive evaluation, the data obtained provides insight into the design aspects of occupations where team-pulling activities are required.

Response Difficulty: Response Rate Relation and Sex of Subjects

Past research on the relation between response effort and response rate in humans has not considered the effect of subjects' sex. Subjects (22 men and 23 women) were asked to pull a trigger repeatedly when the force required to pull the trigger was varied for each subject at 5, 10, 15, or 20 lb. At the lower force requirements, combined, women made more responses than at the combination of the two higher force requirements. For men, however, this relation was reversed. Possible implications of these findings are discussed.

Variation of Isometric Response Force in the Rat.

Hungry, unrestrained rats (N = 7) were rewarded for pressing a response beam in excess of 11 different force requirements. Changes in peak force production as a function of peak force requirement were examined by analyses of the first four moments of distributions of peak response forces: constant error, the within-subject standard deviation, skewness, and kurtosis. Results were similar to those previously obtained with human subjects: Constant error was positive at low and negative at high force requirements, the within-subject standard deviation increased as a negatively accelerating function of force requirement, and skewness and kurtosis were positive at low force requirements and decreased to negative values at the highest increments. Additional analyses of response kinetics indicated that rats, like humans, meet increasing force requirements by altering the rate of rise of force. The performance similarities suggest that common processes are engaged by the human and rat motor control systems to solve the problem of generating forces that are appropriate to the prevailing environmental constraints.

Knee Extensor Mechanics After Subtotal Excision of the Patella

Two sets of six fresh frozen autopsy specimens were used to test the quadriceps force requirements for knee extension after sequential distal-to-proximal and proximal-to-distal excisions of the patella. The quadriceps force as a function of knee flexion angle was recorded for varying amounts of excision and compared with the results for total patellectomy. Excision of the proximal one half or less resulted in lower force requirements when compared with total patellectomy. The effects of removal of the proximal three-fourths length of patella were inconsistent and actually increased the force requirements in three knees. The effects of distal to proximal excisions indicate a biomechanical advantage to maintaining a fragment equal to at least three fourths the length of the proximal patella. Retaining a fragment of adequate size preserves at least some of the mechanical advantage provided by the intact patella.

CONFIRMATION OF LINEAR SYSTEM THEORY PREDICTION: RATE OF CHANGE OF HERRNSTEIN'S k AS A FUNCTION OF RESPONSE‐FORCE REQUIREMENT

Four human subjects worked on all combinations of five variable-interval schedules and five reinforcer magnitudes ( cent/reinforcer) in each of two phases of the experiment. In one phase the force requirement on the operandum was low (1 or 11 N) and in the other it was high (25 or 146 N). Estimates of Herrnstein's kappa were obtained at each reinforcer magnitude. The results were: (1) response rate was more sensitive to changes in reinforcement rate at the high than at the low force requirement, (2) kappa increased from the beginning to the end of the magnitude range for all subjects at both force requirements, (3) the reciprocal of kappa was a linear function of the reciprocal of reinforcer magnitude for seven of the eight data sets, and (4) the rate of change of kappa was greater at the high than at the low force requirement by an order of magnitude or more. The second and third findings confirm predictions made by linear system theory, and replicate the results of an earlier experiment (McDowell & Wood, 1984). The fourth finding confirms a further prediction of the theory and supports the theory's interpretation of conflicting data on the constancy of Herrnstein's kappa.

The Effects of Force Training and Reinforcement Schedules on Human Performance

Instrumental behaviors were conditioned in college students under partial (PRF) or continuous (CRF) reinforcement with either a high or low response force requirement. Half the subjects in the resulting four conditions were transferred to a similar task (shuttle) where they received 20 CRF trials. Remaining subjects were transferred to a dissimilar task where they solved (CRF) five anagrams. A subsequent persistence test (extinction) for similar-task subjects consisted of 70 nonreinforced shuttle trials; a persistence test for dissimilar-task subjects was 10 insoluble anagrams. Phase 1 yielded results that showed that training with either partial reinforcement or a high force requirement occasioned greater instrumental responding than training with continuous reinforcement or a low force requirement did. Differential effort effects were found in both shuttle and anagram acquisition, as subjects previously trained under high force requirements responded significantly faster than those trained under low force requirements. The findings from extinction indicated that partial reinforcement training increased resistance to shuttle extinction, as did training with a high force requirement. Further, the effects of schedules and force were found to be additive. Nondifferential effects were found for anagram extinction. Results were discussed in the context of Amsel's frustration theory of persistence and Eisenberger's learned effort hypothesis.

EFFECTS OF EFFORT ON RESPONSE RATE.

Pigeons were trained to peck for food reinforcement, and the minimum effective force for a peck was varied. In a single-key situation, the response rate was unaffected up to a certain force value, beyond which increments caused a proportional decrement in response rate. Transient enhancement and suppression effects were observed following a change in the force requirement. A change from a high force requirement to a low force requirement resulted in a temporary enhancement of response rate above the stable performance level, whereas a change from a low to a high requirement produced a temporary suppression of the rate below the stable rate. In a two-key situation, the response rate on a key with a given force remained unaffected by the force requirement on the other key. When the rate of response was plotted against the required force, the resultant function was remarkably similar to that obtained from the single-key experiment. When the rates of reinforcement on the two keys differed, the decrement in response rate produced by an increase in the force requirement was proportionally greater on the key with the lower rate of reinforcement.