Surface engineering and the application of laser-based processes to stents - A review of the latest development

Abstract

Late in-stent thrombus and restenosis still represent two major challenges in stents' design. Surface treatment of stent is attracting attention due to the increasing importance of stenting intervention for coronary artery diseases. Several surface engineering techniques have been utilised to improve the biological response in vivo on a wide range of biomedical devices. As a tailorable, precise, and ultra-fast process, laser surface engineering offers the potential to treat stent materials and fabricate various 3D textures, including grooves, pillars, nanowires, porous and freeform structures, while also modifying surface chemistry through nitridation, oxidation and coatings. Laser-based processes can reduce the biodegradable materials' degradation rate, offering many advantages to improve stents' performance, such as increased endothelialisation rate, prohibition of SMC proliferation, reduced platelet adhesion and controlled corrosion and degradation. Nowadays, adequate research has been conducted on laser surface texturing and surface chemistry modification. Laser texturing on commercial stents has been also investigated and a promotion of performance of laser-textured stents has been proved. In this critical review, the influence of surface texture and surface chemistry on stents performance is firstly reviewed to understand the surface characteristics of stents required to facilitate cellular response. This is followed by the explicit illustration of laser surface engineering of stents and/or related materials. Laser induced periodic surface structure (LIPSS) on stent materials is then explored, and finally the application of laser surface modification techniques on latest generation of stent devices is highlighted to provide future trends and research direction on laser surface engineering of stents.

Keywords: Cell response; Laser surface engineering; Laser textured stents; Stent; Surface engineering.

Graphical abstract

Fig. 1

AFM images of five surface with different roughness made by Chung et al. [44]: (a) PU surface, Ra: 1.53 ± 0.20 nm; (b) PU-PEG (2000 PEG length) surface, Ra: 20.10 ± 7.87 nm;(c) PU-PEG (mixing PEG length) surface, Ra: 39.79 ± 10.48 nm; (d) PU-PEG (mixing PEG length) surface coated with peptide, Ra: 18.63 ± 5.30 nm;(e) PU-PEG (mixing PEG length) surface coated with peptide, Ra: 34.58 ± 9.89 nm.

Fig. 2

SEM images of Mg surface with gradient roughness engineered by chemical etching, from Zhou et al. [48]. Scale bar is 50 μm.

Fig. 3

Different shape of smooth muscle cells under different condition, replotted from Chang et al. [56].

Fig. 4

Nanopillar surface structure on CoCr made through RF plasma from Loya et al. [61] at (a) low magnification (b) high magnification.

Fig. 5

Platelet adhesion results showed the different attachment mode and different activation condition: (a) Bridging mode of platelet, pillar interspace and diameter are 0.5 μm; (b) Full-contact mode of platelet, pillar interspace and diameter are 4 μm. From Ding et al. [57].

Fig. 6

SEM images: (a, c) 20 nm porous alumina surface; (b, d) 200 nm porous alumina surface after whole blood contact test, from Ferraz et al. [69]. The arrows and circles indicate the platelets.

Fig. 7

Nanowire structures fabricated by CVD from (a) Aktas et al. [71] (b) Mohan et al. [73].

Fig. 8

SEM image of hierarchical surface texture with pores and grooves fabricated from chemical pickling and grinding, from Shen et al. [74].

Fig. 9

Schematic pictures of nanowire/nanopits hierarchical texture fabricated by CVD with laser ablation [77]: (a) SEM of the nanowire/nanopit texture; (b)SEM images of nanowire texture; (c) SEM images of pores inside nanopits.

Fig. 10

Comparison of original stents surface, laser ablated surface and luminal surface of rat aorta. (a) untextured stents surface (b) textured stents surface (c) biomimetic grooved surface on 316L in nitrogen made by Li et al. [120]; (d) the inner luminal surface of rat aorta.

Fig. 11

SEM images of plain CoCr and DLIP textured samples fabricated by Schieber et al. [134] with different periodicities (valley to valley distance, 3 μm, 10 μm, 20 μm, 32 μm) and depth (<40 nm, L; >600 nm, H).

Fig. 12

Different surface structure created by laser at different condition: (a–d) different spot size at scanning speed of 0.8 mm/s and pulse energy at 200 μJ; (e–h) different feed speed at spot size of 150 μm and pulse energy at 200 μJ; (i–l) different pulse energy at spot size of 150 μm and feed speed at 0.8 mm/s, from Liang et al. [140].

Fig. 13

LIPSS structure at different pulse energy and speed (a) Speed-Pulse energy plot for spot size 150 μm and (b–e) related SEM images, from Liang et al. [140].

Fig. 14

Three types of LIPSS structures: (a) As-polished surface; (b) nano-LIPSS surface; (c) micro/nano LIPSS surface, from Nozaki et al. [79]. E is the laser electric field polarisation vector. Scale bar (long white line) is 100 μm.

Fig. 15

Platelet adhesion on (a) as-polished; (b)nano-LIPSS; (c) micro/nano-LIPSS surface, from Nozaki et al. [79].

Fig. 16

FE-SEM images of different LIPSS surface structures (a) scanning speed is 2 mm/s; (b) scanning speed is 2 mm/s (c) scanning speed is 0.85 mm/s; (d) scanning speed is 0.85 mm/s. Laser fluence for all samples is 6.8 J/cm², from Lin et al. [141]. E is the polarisation direction. Scan shows the direction of scanning direction.

Fig. 17

Chain scission degradation mechanism of biodegradable polymers plotted by Wee et al. [167].

Fig. 18

Crater fabricated on PLGA by Shibata et al. [174] through (a) mechanical milling, (b)800 nm laser, (c)400 nm laser.

Fig. 19

The filament structure underneath the laser (1030 nm) treated surface from Stępak et al. [175].

Fig. 20

Schematic and figures SEM images of three types of texture designs. (a) (d) (g) (j) two-steps: circle with grooves scanning; (b) (e) (h) (k) one-step circle scanning; (c) (f) (i) (l) on-step half circle scanning, from Li et al. [178].

Fig. 21

SEM images of LIPSS produced at different polarisation conditions, replotted from Skoulas et al. [23].

Fig. 22

SEM images of two scanning with different pulse delay from −10ps to 10ps. XP: cross-polarisation. CP: circular polarisation. Replotted from Fraggelakis et al. [179].

Fig. 23

Lotus leaf-like structure created by Zorba et al. through femtosecond laser irradiation under reactive SF₆ atmosphere [180].