Controlling and testing anisotropy in additively manufactured stochastic structures

Hossain, Umar; Ghouse, Shaaz; Nai, Kenneth; Jeffers, Jonathan R.T.

doi:10.1016/j.addma.2021.101849

Cited by 22 publications

(19 citation statements)

References 31 publications

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“…Other research groups have found that lattice-based stem designs are effective for reducing strain shielding [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ], with innovations including the inclusion of fatigue life constraints during the optimisation process [ 7 , 8 , 9 ]. The use of a trabecular-like stochastic porous structure in this study is potentially advantageous compared to more regular lattice designs as stochastic structures enable control of anisotropy [ 42 ], which may result in an implant that is more tolerant to unanticipated load cases. Other researchers have optimised the outer shape of hip implants [ 5 , 43 , 44 , 45 , 46 , 47 , 48 ], or optimised the modulus/density distribution within implants [ 49 , 50 ], with similar proposed benefits for preventing strain shielding.…”

Section: Discussionmentioning

confidence: 99%

Topology Optimisation for Compliant Hip Implant Design and Reduced Strain Shielding

Tan

Arkel

2021

Materials

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Stiff total hip arthroplasty implants can lead to strain shielding, bone loss and complex revision surgery. The aim of this study was to develop topology optimisation techniques for more compliant hip implant design. The Solid Isotropic Material with Penalisation (SIMP) method was adapted, and two hip stems were designed and additive manufactured: (1) a stem based on a stochastic porous structure, and (2) a selectively hollowed approach. Finite element analyses and experimental measurements were conducted to measure stem stiffness and predict the reduction in stress shielding. The selectively hollowed implant increased peri-implanted femur surface strains by up to 25 percentage points compared to a solid implant without compromising predicted strength. Despite the stark differences in design, the experimentally measured stiffness results were near identical for the two optimised stems, with 39% and 40% reductions in the equivalent stiffness for the porous and selectively hollowed implants, respectively, compared to the solid implant. The selectively hollowed implant’s internal structure had a striking resemblance to the trabecular bone structures found in the femur, hinting at intrinsic congruency between nature’s design process and topology optimisation. The developed topology optimisation process enables compliant hip implant design for more natural load transfer, reduced strain shielding and improved implant survivorship.

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Section: Discussionmentioning

confidence: 99%

Topology Optimisation for Compliant Hip Implant Design and Reduced Strain Shielding

Tan

Arkel

2021

Materials

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“…[16][17][18][19][20][21][22][23] Furthermore, combinations of such materials and structures have produced varying mechanical anisotropies. 24,25 In animal models, these lattices can accelerate bone formation and increase bone density compared to solid metal controls. 18,21,26,27 AM titanium structures have also been shown to offer improved long-term fixation which could prove beneficial in cementless arthroplasty.…”

Section: Introductionmentioning

confidence: 99%

Total and partial knee arthroplasty implants that maintain native load transfer in the tibia

Munford

Stoddart

Liddle

et al. 2022

Bone & Joint Research

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Aims Unicompartmental and total knee arthroplasty (UKA and TKA) are successful treatments for osteoarthritis, but the solid metal implants disrupt the natural distribution of stress and strain which can lead to bone loss over time. This generates problems if the implant needs to be revised. This study investigates whether titanium lattice UKA and TKA implants can maintain natural load transfer in the proximal tibia. Methods In a cadaveric model, UKA and TKA procedures were performed on eight fresh-frozen knee specimens, using conventional (solid) and titanium lattice tibial implants. Stress at the bone-implant interfaces were measured and compared to the native knee. Results Titanium lattice implants were able to restore the mechanical environment of the native tibia for both UKA and TKA designs. Maximum stress at the bone-implant interface ranged from 1.2 MPa to 3.3 MPa compared with 1.3 MPa to 2.7 MPa for the native tibia. The conventional solid UKA and TKA implants reduced the maximum stress in the bone by a factor of 10 and caused > 70% of bone surface area to be underloaded compared to the native tibia. Conclusion Titanium lattice implants maintained the natural mechanical loading in the proximal tibia after UKA and TKA, but conventional solid implants did not. This is an exciting first step towards implants that maintain bone health, but such implants also have to meet fatigue and micromotion criteria to be clinically viable. Cite this article: Bone Joint Res 2022;11(2):91–101.

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“…The samples were compressed at a quasi-static axial loading speed rate at 1.5 mm/min. To exclude the influence of the build printing orientation on the mechanical responses, all samples were loaded in the perpendicular upright direction with printing orientation (Bai et al, 2020;Hossain et al, 2021;Zeng et al, 2021). The samples were compressed just enough until yielding occurrence can be discerned graphically in stress-strain plots during the compression test.…”

Section: Compression Testmentioning

confidence: 99%

Lattice structure design parameters optimization for the structural integrity of passive vibration isolator

Azmi¹,

Ismail²,

Abdollah³

2022

Manufacturing Technology

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Passive vibration isolator with lower natural frequency has always been a challenge due to structural integrity issues. This study presents the use of RSM statistical tool to analyze and optimize the mechanical responses of BCC lattice structure for structural integrity in a passive vibration isolator application. The optimization was done to obtain low stiffness for low natural frequency but high yield stress for optimum load-bearing capability with unit cell size and strut diameter design parameters tweak. From the results, the significance and contribution of each design parameter on each mechanical response through compression test can be understood. Results indicated changes in strut diameter produced linear growth while changes in the unit cell size produced inverse exponential responses. From optimization, a combination of 3.9 mm strut diameter with 10 mm unit cell size produced the optimum result. Therefore, it was demonstrated that RSM can provide statistical importance and contribution between input factors and their influence on each mechanical response with minimal test and cost.

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Controlling and testing anisotropy in additively manufactured stochastic structures

Cited by 22 publications

References 31 publications

Topology Optimisation for Compliant Hip Implant Design and Reduced Strain Shielding

Topology Optimisation for Compliant Hip Implant Design and Reduced Strain Shielding

Total and partial knee arthroplasty implants that maintain native load transfer in the tibia

Lattice structure design parameters optimization for the structural integrity of passive vibration isolator

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