Biomechanics of Additively Manufactured Metallic Scaffolds-A Review.

This review paper is related to the biomechanics of additively manufactured (AM) metallic scaffolds, in particular titanium alloy Ti6Al4V scaffolds. This is because Ti6Al4V has been identified as an ideal candidate for AM metallic scaffolds. The factors that affect the scaffold technology are the design, the material used to build the scaffold, and the fabrication process. This review paper includes thus a discussion on the design of Ti6A4V scaffolds in relation to how their behavior is affected by their cell shapes and porosities. This is followed by a discussion on the post treatment and mechanical characterization including in-vitro and in-vivo biomechanical studies. A review and discussion are also presented on the ongoing efforts to develop predictive tools to derive the relationships between structure, processing, properties and performance of powder-bed additive manufacturing of metals. This is a challenge when developing process computational models because the problem involves multi-physics and is of multi-scale in nature. Advantages, limitations, and future trends in AM scaffolds are finally discussed. AM is considered at the forefront of Industry 4.0, the fourth industrial revolution. The market of scaffold technology will continue to boom because of the high demand for human tissue repair.

Demonstration of pressure reduction in a new proof of concept spine board.

Pressure injuries are a significant problem following spinal cord injury (SCI). High interface pressures while lying on a spine board during emergency transport appear to play a major role in their formation. The aim of the present study was to assess the interface pressures and sensing area between the body and the standard spine board (SSB) and a proof of concept spine board prototype (P-5). Twenty-one able-bodied subjects were assessed on each board. Interface pressures and sensing area were recorded every minute over 15 min. The mean peak pressure was higher on the SSB at the head, scapulothoracic (S-T), sacroiliac (S-I), and heels (227.6 mmHg, 148.9 mmHg, 360.3 mmHg, and 179.3 mmHg) compared to P-5 (51.9 mmHg, 60.1 mmHg, 66.8 mmHg, and 60.2 mmHg). The peak pressure index (PPI) at the head, S-T and S-I was higher on the SSB (100.2 mmHg, 101.6 mmHg, and 270.6 mmHg) compared to P-5 (41.6 mmHg, 51.9 mmHg and 58.7 mmHg). An analysis using pairwise comparisons for repeated measures showed that interface pressures (p < .05) and PPI (p < .001) were reduced at all locations. Modifications of a spine board incorporated in P-5 can dramatically reduce interface pressures and reduce pressure injury formation.

Redesign of a spine board: Proof of concept evaluation.

Sacral pressure ulcers are a significant problem in individuals following spinal cord injury (SCI) and are felt to be in part due to the high interface-pressures applied to the body while lying on a standard spine board (SSB) during emergency transport. The aim of the present study was to assess the interface pressures and sensing areas between the body and the SSB and two proof of concept spine board prototypes (P-1 and P-2). Ten able-bodied individuals were assessed on each board. Interface pressures and sensing area were recorded every minute over 15 minutes. The highest pressure was generated at the sacral-iliac region. The mean of the peak pressures on the SSB, P-1, and P-2 was 288.6, 202.8, and 102.8 mmHg, respectively. The mean of the sensing areas on the SSB, P-1, and P-2 was 78.2, 98.5, and 109.4 in(2), respectively. An analysis using pairwise comparisons test showed the interface pressures were significantly reduced (p = 0.003) and the sensing area was significantly increased (p < 0.001) on P-2 in the sacral-iliac location. This study's procedures can be used when determining critical factors to guide the redesign of an SSB that reduces interface pressure and increases sensing area.

The Effect of a Liner on the Dispersion of Sacral Interface Pressures During Spinal Immobilization.

Sacral pressure ulcers are a significant problem following spinal cord injury and are felt to be in part due to the high interface-pressures generated while strapped to the spine board. The objective of this study was to determine sacral interface-pressure and sensing area in healthy volunteers on a spine board and the effects of a gel pressure dispersion liner. Thirty-seven volunteers were placed on a pressure-sensing mat between the subject and the spine board. Measurements were carried out with and without a gel liner. Pressures and sensing area were recorded every minute for 40 minutes. The highest pressure was generated at the sacral prominence of each subject. Mean interface-pressures were higher on the spine board alone than with the gel liner (p < .0001). Overall, mean sensing area was lower on the spine board than with the gel liner (p < .0001). Standard spinal immobilization causes high sacral interface-pressures. The addition of a gel liner on the spine board decreased overall mean sacral pressures and increased mean sensing area. Generation of sacral pressure ulcers may be related to the initial interface-pressures generated while the patient is strapped to the spine board. The addition of a gel liner may reduce the incidence of sacral pressure ulcers.

State of the art review of knee-ankle-foot orthoses.

Knee-ankle-foot orthoses (KAFOs) are used to assist in ambulation. The purpose of this paper is to review existing KAFO designs which can be grouped into passive KAFOs, stance control (SC) KAFOs, and dynamic KAFOs. The conventional passive KAFOs do not provide any active control for knee motions. SCKAFOs lock the knee joint during the stance phase and allow free rotations during the swing phase. Some SCKAFOs switch between the stance and swing phases using body posture, while others use some kind of a control system to perform this switch. Finally, dynamic KAFOs control the knee joint during both stance and swing phases. Four dynamic systems are identified in the literature that use pneumatics, linear springs, hydraulics, and torsional rods made of superelastic alloys to control the knee joint during the gait cycle. However, only the two systems that use linear springs and torsional rods can reproduce the normal knee stiffness pattern which has two distinct characteristics: a soft stiffness during the swing phase and a hard stiffness during the stance phase. This review indicates that there is a need to conduct research regarding new KAFO designs that duplicate normal knee function during the whole gait cycle.

3-D anatomically based dynamic modeling of the human knee to include tibio-femoral and patello-femoral joints.

An anatomical dynamic model consisting of three body segments, femur, tibia and patella, has been developed in order to determine the three-dimensional dynamic response of the human knee. Deformable contact was allowed at all articular surfaces, which were mathematically represented using Coons' bicubic surface patches. Nonlinear elastic springs were used to model all ligamentous structures. Two joint coordinate systems were employed to describe the six-degrees-of-freedom tibio-femoral (TF) and patello-femoral (PF) joint motions using twelve kinematic parameters. Two versions of the model were developed to account for wrapping and nonwrapping of the quadriceps tendon around the femur. Model equations consist of twelve nonlinear second-order ordinary differential equations coupled with nonlinear algebraic constraint equations resulting in a Differential-Algebraic Equations (DAE) system that was solved using the Differential/Algebraic System Solver (DASSL) developed at Lawrence Livermore National Laboratory. Model calculations were performed to simulate the knee extension exercise by applying non-linear forcing functions to the quadriceps tendon. Under the conditions tested, both "screw home mechanism" and patellar flexion lagging were predicted. Throughout the entire range of motion, the medial component of the TF contact force was found to be larger than the lateral one while the lateral component of the PF contact force was found to be larger than the medial one. The anterior and posterior fibers of both anterior and posterior cruciate ligaments, ACL and PCL, respectively, had opposite force patterns: the posterior fibers were most taut at full extension while the anterior fibers were most taut near 90 degrees of flexion. The ACL was found to carry a larger total force than the PCL at full extension, while the PCL carried a larger total force than the ACL in the range of 75 degrees to 90 degrees of flexion.

Biomechanics of the knee joint in deep flexion: a prelude to a total knee replacement that allows for maximum flexion.

A two-dimensional anatomically based mathematical model of the human knee joint was developed to understand its biomechanics in deep flexion. The model was used to determine the internal knee loads as it simulates isometric quadriceps and hamstring co-contractions at different flexion angles during deep squat. It was found that in order to achieve deep flexion, large muscle forces are required, resulting in large tibio-femoral contact forces. In deep flexion, the femoral contact point was located on the most proximal point of the posterior condyle, location which was not affected by the level of quad activation. Conversely, the location of the tibial contact point was highly affected by the level of quad activation. Both anterior and posterior fiber bundles of the posterior cruciate ligament were found to carry high loads when the knee is maximally flexed. These results point to the important role of the posterior cruciate ligament in this position, and suggest the necessity of retaining this ligament during total knee replacement (TKR) procedures that allows for maximum flexion angles. Furthermore, the present data provide an explanation why most TKR's do not allow deep flexion: while contact occurs on the most proximal points of the posterior condyles in normal knees, this portion of the condyles is not presently resurfaced when performing a TKR.