一种新型仿生骨小梁的摩擦系数

许奎雪; 刘伟; 程曦; 潘超; 王振国; 袁志山; 王吕武; Xu Kuixue; Liu Wei; Cheng Xi; Pan Chao; Wang Zhenguo; Yuan Zhishan; Wang Lvwu

网刊加载中。。。

使用Chrome浏览器效果最佳，继续浏览，你可能不会看到最佳的展示效果，

确定继续浏览么?

复制成功，请在其他浏览器进行阅读

Friction Coefficient of a Novel Bionic Trabecular Bone PDF

- ORCID：
Xu Kuixue ¹
✉
- ORCID：
Liu Wei ¹
- ORCID：
Cheng Xi ¹
- ORCID：
Pan Chao ¹
- ORCID：
Wang Zhenguo ¹
✉
- ORCID：
Yuan Zhishan ²
- ORCID：
Wang Lvwu ²

1. Beijing Chunlizhengda Medical Instruments Co., Ltd, Beijing 101100, China； 2. GRIMED Medical (Beijing) Co., Ltd, Beijing 102200, China

Updated：2021-09-06

DOI：XX.XXXX/j.issn.1002-185X.2021.08.017

Abstract

The coefficient of friction (COF) of a novel bionic trabecular structure that was manufactured through 3D printing with Ti-6Al-4V power was investigated. Cortical and spongy bones were used as counterparts. The contact angle results show that the bionic structure has better surface wettability than the homogeneous structure at the early-stage. However, the two structures have highly hydrophilic surface. For homogeneous trabeculae, the average values of COF range from 0.71 to 0.82, which are significantly lower than the values of 0.82~0.99 for the bionic trabeculae. The static COF values range from 1.52 to 1.96 for the bionic trabeculae and 0.99 to 1.26 for the homogeneous trabeculae. The maximum static COF value of 1.96 is acquired at 10 N for the cortical bone against the bionic trabeculae. The results indicate that the bionic trabecular structure has a higher COF than the homogeneous trabeculae and other components. Hence, the novel bionic trabecular structure can provide sufficient friction at the bone-implant interface, thus achieving primary stability.

Keywords

biomaterials; COF; bionic trabecular bone; 3D printing

Science Press

The primary stability of implants is an important factor for the successful implantation, and it is critical for osseointe-gration in primary and revision hip arthroplasty for acetabular components. It is affected by the architecture of the bone surrounding the implant, surgical technique, and implant geometry (length, diameter and surface characteristics)^[

1]. For implant manufacturers, there are ways to design and realize implant geometry. Additively manufactured porous metallic structures have recently received much attention in bone implant applications^{[Reference 2-4}2-4]. Electron beam melting (EBM) is one of the additive manufacturing technology for orthopedic implants, which is of interest for the fabrication of intricate geometries for cellular materials in areas where complex architectures are needed^{[Reference 5

Baidu Scholar}5,6].

Natural bones are porous materials with interconnected voids and consist of outer cortical bone and inner trabecular bone. Porous titanium materials with interconnected pores and porosities similar to those of natural bones are of particular interest for orthopedic implant applications^[

7]. And the pore interconnectivity is very important for the implants to show positive influence on osteoconductive properties of metallic implants^{[Reference 8

Baidu Scholar}8].

The mechanical properties of porous implants are close to those of host bone, which is expected to reduce the stress-shielding effect^[

9]. The porous structure is conducive to the adhesion, differentiation and growth of osteoblasts, promoting the growth of new bone into the pores, enhancing the combination of implant and bone, and achieving the fixation of implant and bone tissue. Moreover, the internal pores are conducive to vascularization and metabolic material transpor-tation^{[Reference 10

Baidu Scholar}10]. In addition, the porous structure has different coeffi-cients of friction (COFs). The COF influences the mechanical stability of the implant, its relative motion, and the reaming and seating of the implant in the bone^{[Reference 11

Baidu Scholar}11]. Harrison et al indicated that a higher COF is considered to be an advantage in providing improved primary fixation for orthopaedic implants^{[Reference 12

Baidu Scholar}12]. For porous titanium acetabular components, to provide even greater interface friction for further improving initial mechanical stability, the surface roughness was increased^{[Reference 13

Baidu Scholar}13]. Studies have also indicated that a highly porous acetabular cup with COFs between 0.8 and 1.2 is less influential given the plethora of other surgical implantation factors^{[Reference 14

Baidu Scholar}14].

Therefore, the key characteristics to design porous metallic implants include the selection of porosity, pore size, and pore interconnectivity, aiming to achieve satisfactory clinical outcomes^[

15]. As a novel concept for bone implant prostheses, porous trabecular bone implants have become a focus of research and clinical attention, especially the bio-inspired design.

However, fabrication of porous titanium implants with mechanical properties suitable to mimic natural bones, especially the bionic trabecular structure, is still a challenge. Hence, in this study, a novel bionic trabecular structure was designed by CAD molding to natural bones, which was 3D-printed with Ti-6Al-4V power by EBM. The COFs between the bionic trabecular structure and bone were investigated.

1 Experiment

Small specimens (10 mm×10 mm×10 mm) used as sub-strates were cut from 2D-C/C composites with a density of 1.78 g/cm³. The specimens were hand-polished using 400 grit sand paper, then cleaned with alcohol and dried in air. Powder compositions in mass fraction for pack cementation process were as follows: 75%~80% Si (45 µm) and 20%~25% graphite (45 µm) for SiC coating, 60%~75% Si (45 µm), 20%~30% Ta (45 µm) and 5%~10% graphite (45 µm) for TaSi₂ coating. The pack mixtures were weighed and mixed by tumbling in a ball mill up to 10 h. For comparison, homo-geneous and bionic trabecular structures were designed by research engineers. The three-dimensional structures of both the homogeneous and bionic trabecular structure were first drawn using 3D-CAD software 3-matic. When using the 3D-CAD design, the default parameters were entered, and the 3D-CAD design drawings are shown in Fig.1a and 1c. Fig.1a is the homogeneous structure and Fig.1c is the bionic structure. The drawings were fabricated by Ti-6Al-4V powder using an Arcam Q10 plus EBM machine. The particle size of Ti-6Al-4V powder distribution is between 45 and 106 μm. Fig.1b and 1d show the 3D-printed samples produced via EBM. Table 1 presents the porosity, pore size and trabecular thickness for the homogeneous and bionic trabecular structures.

Fig.1 Homogeneous (a, b) and bionic (c, d) trabecular bone structures: (a, c) 3D-CAD design and (b, d) 3D-printed

Table 1 Porosity, pore size and trabecular thickness

Structure	Porosity/%	Pore size/μm	Trabecular thickness/mm
Homogeneous	~62.5	~300	~2
Bionic	50~80	200~400	300~700

Initial contact angle analysis was performed to characterize the variation of surface wettability through an optical contact angle measuring instrument (DSA 100S, Germany). Digital images were taken perpendicular to the 5 μL droplets of ultrapure water placed on the surface, and the angle tangential to the water-surface interface was directly measured from each image.

The friction tests were carried out on a commercial reciprocating tribotester (Cetr UMT-2). All the experimental tests were performed at an ambient temperature of approxi-mately 25 °C. The reciprocating stroke was 15 mm, which corresponds to a sliding frequency of 1/60 Hz. Normal loads of 5, 10 and 15 N were used. The counterparts employed during the test were 6 mm in diameter and 15 mm in height and made of cortical bone and spongy bone. The cortical and spongy bones were obtained through a milling machine from pork bones, and the contact surface was polished by 3000# SiC abrasive paper. The surface roughness was 0.82±0.11 and 0.91±0.15 μm for the cortical bone and spongy bone, respectively. To prevent bone breakage during testing, the clamped position for the bone was packed by waterproof adhesive tape. The lubricating fluid in this procedure was newborn calf serum at a concentration of 20 g/L. In order to ensure the consistency of the tests, the samples were com-pletely immersed in the lubricating fluid in the testing process. During the tests, the COFs were recorded by the computer. Experiments were performed in triplicate for each test under different conditions.

2 Results and Discussion

The surface wettability of biomaterials is one of the most decisive aspects governing the cell adhesive properties. Droplet images taken during the measurements are shown in Fig.2. Fig.2a shows that the initial contact angle is about 96.9° for the homogeneous structure, while the bionic structure has a lower initial contact angle of 87.7°, as shown in Fig.2b. The result shows that the bionic structure has better surface wettability than the homogeneous structure at the early-stage. The contact angles are reported to be zero due to inherent surface roughness for the two different structures. That is, the two structures has highly hydrophilic surface, and it will increase the early-stage bone tissue integration or osseointe-gration^[

16]. It has been reported that implants exhibiting a higher degree of surface wettability can promote adhesion of proteins, interstitial fluid, and blood macromolecules, which can further improve biological integration and result in faster healing for patients^{[Reference 17

Baidu Scholar}17,18].

Fig.2 Initial surface contact angle of homogeneous (a) and bionic (b) structures

Fig.3 presents the COFs of the homogeneous/bionic trabe-culae under different experimental conditions. The average COFs are listed in Table 2. The average COF increases with increasing the load. This may be due to the increase in area of contact between the sample and bone surface. Due to the increased area of contact, there is more interaction between bone trabeculae or asperities, which results in increased COF^[

11]. For the homogeneous trabeculae, the values ranging from 0.71 to 0.82 are obviously lower than the values of 0.82~0.99 for bionic trabeculae. The max average COF of 0.99 is obtained for the cortical bone against the bionic trabeculae at 15 N. Some studies have shown that high COF between implant and bone enhances the initial stability with small micro motions at the interface^{[Reference 9

Baidu Scholar}9,11,13]. The trabecular structure has a larger attachment surface of bone cells and greater surface energy, which is conducive to adsorption of macromolecules on cells and bone tissue, leading to bony on-growth^{[Reference 12

Baidu Scholar}12].

Table 2 Average and static COFs

Bone	Structure		5 N	10 N	15 N
Spongy	Homogeneous	Average	0.71	0.72	0.76
	Homogeneous	Static	1.04	0.99	1.26
	Bionic	Average	0.82	0.85	0.88
	Bionic	Static	1.52	1.68	1.53
Cortical	Homogeneous	Average	0.77	0.79	0.82
	Homogeneous	Static	1.07	1.03	1.16
	Bionic	Average	0.88	0.99	0.91
	Bionic	Static	1.71	1.96	1.76

The static COF between the sample and bone is needed, and it is more representative for the tribological properties of the trabeculae structure. As shown in Fig.3, the first COF peak value is defined as the static COF^[

19]; the values are also listed in Table 2. The first COF peak value increases with increasing the load. The values range from 1.52 to 1.96 for the bionic trabeculae, larger than the values from 0.99 to 1.26 for the homogeneous trabeculae. When the friction pair is the cortical bone and bionic trabeculae, the maximum static COF value of 1.96 is acquired at 10 N. The first COF peak values are significantly larger than those of trabecular structures that were designed by other companies, such as the values of 0.8~1.2 for DePuy products^{[Reference 20

Baidu Scholar}20] and 0.93~1.08 for the 3D ACT trabecular structure. The higher COF is attributed to the uneven trabecular structure at the interface hindering the motion of the mating surface along the surface ^{[Reference 21

Baidu Scholar}21]. The results indicate that the bionic trabeculae can enhance the initial stability of implants, effectively prevent the prosthesis from fretting and sinking and promote long-term stability. Previous research has shown that a higher COF enhances interference fit and ultra-porous surfaces enhance osseointegration^{[Reference 22

Baidu Scholar}22]. Another study showed that high friction and porosity can minimize micro motion and diminish possible fibrous texture formation around the revision implant^{[Reference 23

Baidu Scholar}23].

However, it is reported that a higher COF does not necessarily translate to greater stability, and the COF affects the final position of the implant under a given implantation force^[

24]. A study pointed out that the COF of the acetabula cup plays a limited role compared with the factor of bone quality in resisting relative micro motion in the cup-pelvis interface^{[Reference 25

Baidu Scholar}25].

It is evident in Fig.3 that there are large fluctuations in all the curves. The curves are related to the implant surfaces with different structures. One study found that by introducing gradient variation in surface microstructures, more novel materials with tunable frictional properties can be designed and fabricated^[

26], and the trabecular structures used in this study are based on this consideration. The variation in the curves in Fig.3 reflects the changes in the trabecular structure. Although the fluctuation in the curves is large, the friction remains at a high level. Sufficient frictional stability enables bone in-growth into the surface of the implant, resulting in a long-lasting mechanical interlock of the implant and optimal secondary mechanical stability^{[Reference 13

Baidu Scholar}13].

Fig.4 shows the bone debris on the homogeneous/bionic trabecular surface after the tests. There is significantly more spongy bone debris than cortical bone debris. This is dependent on the structure and density of the bone. In addition, the amount of bone debris on the bionic trabecular surface is larger than on the homogeneous trabecular surface. This is mainly due to different trabecular structures. The results indicate that the bionic trabeculae results in more friction than the homogeneous trabeculae. In other words, the bionic trabecular has a higher COF than homogeneous trabeculae.

Fig.4 Bone debris on the trabecular surface: (a) homogeneous and (b) bionic

3 Conclusions

1) The COFs of the bionic and homogeneous trabecular structures are investigated in a newborn calf serum fluid. The initial contact angle is about 96.9° for the homogeneous structure, which is higher than that of the bionic structure (87.7°). The bionic structure has better surface wettability than the homogeneous structure at the early-stage.

2) The COF increases as the load increases. For the bionic trabeculae, the average COFs range from 0.82 to 0.99, which are higher than the values of 0.71~0.82 for the homogeneous trabecular. Similarly, the static COF values are 1.52~1.96 for the bionic trabeculae, which are significantly higher than the values of 0.99~1.26 for the homogeneous trabeculae. The maximum static COF of 1.96 is acquired at 10 N in the test between the cortical bone and bionic trabecular. The bionic trabecular structure has a higher COF.

3) The newly developed bionic trabecular structure can provide sufficient friction at the bone-implant interface, thus achieving primary stability due to a higher friction coefficient.

References

Ovesy M, Indermaur M, Zysset P K. Journal of the Mechanical Behavior of Biomedical Materials[J], 2019, 98: 301 [Baidu Scholar]

Thomas D, Singh D. International Journal of Surgery[J], 2017, 46: 195 [Baidu Scholar]

Weißmann V, Bader R, Hansmann H et al. Materials and Design [J], 2016, 95: 188 [Baidu Scholar]

Bartolomeua F, Douradoa N, Pereira F et al. Materials Science & Engineering C[J], 2020, 107: 110 342 [Baidu Scholar]

Ibrahim E, Ola Harrysson Harvey We et al. Additive Manu-facturing[J], 2017, 17: 169 [Baidu Scholar]

Hernández-Navaa E, Smitha C J, Derguti F et al. Acta Materialia[J], 2016, 108: 279 [Baidu Scholar]

Yan C Z, Hao L, Hussein A et al. Journal of the Mechanical Behavior of Biomedical Materials[J], 2015, 51: 61 [Baidu Scholar]

Bandyopadhyay A, Espana F, Balla V K et al. Acta Biomaterialia[J], 2010, 6(4): 1640 [Baidu Scholar]

Hu Y B, Li J Z. Journal of Materials Processing Technology[J], 2017, 249: 426 [Baidu Scholar]

Kang C W, Fang F Z. Advances in Manufacturing[J], 2018, 6: 137 [Baidu Scholar]

Aziz R, Haq M I U, Raina A. Polymer Testing[J], 2020, 85: 106 434 [Baidu Scholar]

Harrison N, McHugh P E, Curtin W et al. Journal of the Mecha-nical Behavior of Biomedical Materials[J], 2013, 21: 37 [Baidu Scholar]

Small S R, Berend M E, Howard L A et al. Journal of Arthroplasty[J], 2013, 28(3): 510 [Baidu Scholar]

Goldman A H, Armstrong L C, Owen J R et al. Journal of Arthroplasty[J], 2016, 31(3): 721 [Baidu Scholar]

Wang Xiaojian, Xue Shanqing, Zhou Shiwei et al. Biomaterials [J], 2016, 83: 127 [Baidu Scholar]

Sartoretto S C, Alves A T, Resende R F et al. Journal of Applied Oral Science[J], 2015, 23(3): 279 [Baidu Scholar]

Rupp F, Gittens R A, Scheideler L et al. Acta Biomaterialia[J], 2014,10(7): 2894 [Baidu Scholar]

Sabetrasekh R, Tiainen H, Reseland J E et al. Biomedical Materials[J], 2010, 5(1): 15 003 [Baidu Scholar]

Luo Y, Yang L, Tian M C. Biomaterials and Medical Tribology [J], 2013: 181 [Baidu Scholar]

Biemond J E, Aquarius R, Verdonschot N et al. Archives of Orthopaedic and Trauma Surgery[J], 2011, 131(5): 711 [Baidu Scholar]

Majumdar D D, Ghosh M, Mondal D P et al. Procedia Manu-facturing[J], 2019, 35: 833 [Baidu Scholar]

Carli A V, Warth L C, Bentley K L M et al. Journal of Arthroplasty [J], 2017, 32(2): 463 [Baidu Scholar]

Zhang C Q, Zhang L, Liu L et al. Journal of Orthopaedic Surgery and Research [J], 2020, 15: 40 [Baidu Scholar]

Damm N B, Morlock M M, Bishop N E. Journal of Biomechanics[J], 2015, 48(12): 3517 [Baidu Scholar]

Hsu J T, Chang C H, Huang H L et al. Medical Engineering and Physics[J], 2007, 29(10): 1089 [Baidu Scholar]

Yuan W F, Yao Y, Keer L et al. Extreme Mechanics Letters[J], 2019, 26: 46 [Baidu Scholar]

Home

Introduction

Editorial Board

Submission Guideline

Contact Us