5.7 Efficacy of PLD Coatings In Vivo
5.7.5 Studies in Beagle Dogs
Although the PLD method does not need a grit-blasting step to achieve strong coating adherence to the substrate, as has been shown, the thin coating can follow any surface topography achieved through predeposition machining, cleaning, or grit-blasted roughening. Hence, PLD constitutes a suitable method to evaluate the contribution of the CaP chemistry to osseointegration, with least interference of the roughness. Therefore, Peraire et al. [119] used dog jaws to demonstrate the bone response for ArF laser-deposited coatings in an in vivo model similar to human oral implantation. It was considered of special interest to assess the contribution of roughness and the chemistry of the coatings to the Fig. 5.22 Scanning electron
microscopy cross-section micrograph of the ArF laser-deposited implant surface in contact with surrounding bone. The almost intact original 2 mm thick PLD coating could still be observed in extended areas after 24 weeks of implantation in rabbit tibia.
From [118], with permission from Wiley Interscience
osseointegration of the implants, not only from the histological point of view but also with regard to their mechanical bonding after implantation.
Hence, 3 months after teeth extraction, five materials were implanted in Beagle dogs: (1) smooth, as-machined, titanium plugs (Ti-s); (2) grit-blasted titanium plugs (Ti-g); (3) grit-blasted titanium plugs with HA-PS coating (HA-PS); (4) smooth, as-machined titanium plugs with HA-PLD coat-ing (HA-PLDs); and (5) grit-blasted titanium plugs with HA-PLD coatcoat-ing (HA-PLDg). The PLD coating was the same 2 mm thick, dense, and fully crystalline coating as previously tested in rabbit tibia [118]. The implantation period was 12 weeks, at the end of which the radiographic study revealed that sham holes were not completely healed. This indicated that the bone had not finished its maturation process, and remodeling was still ongoing. Qualitative and quantitative analyses were performed on samples prepared for histology, whereby % bone apposition, % lacunae apposition, and % bone surface were measured. To assess bone bonding, a push-in test was used to evaluate the mean shear strength. For all the implanted materials, the central zone of the implant was surrounded by trabecular bone, whereas cortical bone was associated with the apical zone. Table 5.4 shows the results for bone apposition and mean shear strength. The mean roughness (Ra) of the surfaces was also included. No statistical differences were detected when the three coated surfaces were com-pared—the plasma-sprayed samples (PSg), the pulsed laser-deposited HA coat-ings on grit-blasted surfaces (PLDg), and those deposited on as-machined titanium (PLDs)—despite their very different roughness. However, these coated surfaces could be significantly differentiated from their corresponding uncoated counterparts. The PLDs implants improved bone apposition com-pared to the uncoated titanium smooth surfaces (Ti-s) (Scheffe´ Test) (P < 0.05), as the plasma-sprayed surface could be differentiated from the grit-blasted titanium surface (Ti-g). Remarkably, rough surfaces (Ti-g and PLDg) did not increase bone apposition when compared to their respectively ‘‘smooth’’
Table 5.4 Bone apposition and mean shear strength of ArF laser coatings on titanium smooth and grit-blasted surfaces
Histomorphometry Push-in test
Group Ra (mm) % Bone apposition Bone contact (mm)
Mean Shear Strength (MPa)
Ti-s 0.40 38– 18 2900– 1500 3.19– 0.74
PLDs 1.44 66– 27* 4400– 1800 5.14– 1.89
PLDg 4.25 64– 15 4600– 1100 6.76– 1.41
Ti-g 5.43 52– 14 3900– 1000 5.05– 1.08
PS 8.86 81– 16* 6100– 1100* 4.21– 1.32
From ref. 119, with permission
Ti-s, as-machined titanium, Ti-g, grit-blasted titanium; PLDs, pulsed laser-deposited coating on smooth Ti; PLDg, pulsed laser-deposited coating on grit-blasted Ti; PS, plasma-sprayed coating
* P< 0.05 Scheffe´ test
Table 5.5 List of articles published on pulsed laser deposition of calcium phosphate coatings
Specificity of the particular system
Physico-chemical
characterization techniques
used Testing
Laser type Nd:YAG
Year Author(s) ArF KrF SHG THG FHG Modifications FTIR Raman XRD SEM EDS TEM AFM RBS=SIMS XPS=AES Mechanical Invitro Invivo
1992 Baeri [21] x x x x
1992 Cotell [20] x x x x x x
1993 Cotell [34] x x x x x
1993 Torrisi. [36] x x x x
1994 Sardin [22] x x x x x
1994 Singh [23] x x x x x x
1994 Torrisi [35] x x x x x
1995 Bagratashvili [26] x x x x
1995 Jelı´nek [25] x x x x x
1995 Serra [24] x
1996 Antonov [127] x x x x x
1996 Cotell [113] x x x x x x
1996 Guillot-Noe¨l [29] x x x x
1996 Hontsu [28] x x x x
1996 Parker [104] x x x x
1996 Serra [59] x x
1996 Tucker [27] x x x x
1997 Antonov [128] x x x
1997 Arias [31] x x x
1997 Garcı´a-Sanz [43] x x x x x
1997 Hontsu [82] x x x x
1997 Serra [58] x
1997 Wang [30] x x x x x x x x
1998 Antonov [37] x x x x x
1998 Arias [49] x x x
1998 Cle´ries [100] x x x x x
1998 Dosta´lova´ [115] x x x
1998 Ferna´ndez-Pradas [32] x x x x x
1998 Garcı´a [129] x x x
1998 Himmlova´ [110] x x x
1998 Hontsu [125] x x x x x
1998 Mayor [72] x x x x x
1998 Mayor [130] x x
1998 Serra [56] x
1998 Serra [131] x
1998 Serra [57] x
1999 Cle´ries [101] x x x x x x
1999 Craciun [33] x x x x x
1999 Craciun [132] x x x x x
Table 5.5 (continued)
Specificity of the particular system
Physico-chemical
characterization techniques
used Testing
Laser type Nd:YAG
Year Author(s) ArF KrF SHG THG FHG Modifications FTIR Raman XRD SEM EDS TEM AFM RBS=SIMS XPS=AES Mechanical Invitro Invivo
1999 Serra [60] x
1999 Serra [69] x
2000 Arias [66] x x x x
2000 Cle´ries [133] x x x x x x
2000 Cle´ries [93] x x x x x x
2000 Cle´ries [105] x x x x x
2000 Lo [134] x x x x x
2000 Ferna´ndez-Pradas [124]
x x x x x x x
2000 Nelea [135] x x x x
2000 Zeng [42] x x x x x
2000 Zeng [65] x x x x
2000 Zeng [136] x x x x x
2001 Antonov [84] x x x x
2001 Antonov [67] x x x x
2001 Ball [85] x x x
2001 Dosta´lova´ [117] x
2001 Ferna´ndez-Pradas [94] x x x x
2001 Ferna´ndez-Pradas [68] x x
2002 Arias [71] x x x x x
2002 Arias [61] x x x x
2002 Jelı´nek [116] x x
2002 Ferna´ndez-Pradas [44] x x x x x
2002 Ferna´ndez-Pradas [96] x x x x x
2002 Katto [88] x x x x x
2002 Nelea [87] x x x x x
2002 Nelea [137] x x x x
2003 Antonov [81] x x x x x
2003 Arias [95] x x x x x x x x x
2003 Arias,J.L. [62] x
2003 Ferna´ndez-Pradas [70] x x x x x
2003 Katto [89] x x x x x x
2003 Nelea [98] x x x x x x
2004 De Aza [138] x x x x x
2004 Ferraz [52] x x x x x
2004 Gyorgy [54] x x x x x
2004 Iliescu [79] x x x x x
2004 Iliescu [139] x x x
2004 Jime´nez [78] x x x x x
surfaces (Ti-s and PLDs) after 12 weeks of implantation. This experiment seems to indicate that the chemical effect of the HA coatings in promoting bone response has a greater contribution than topography.
With regard to bone bonding, and in agreement with the fact that surface roughness gives higher shear strength due to mechanical interlocking, the two grit-blasted surfaces resulted in higher values than their smooth counterparts (Ti-g versus Ti-s, PLDg versus PLDs). Surprisingly, the plasma-sprayed coating did not improve bonding compared to grit-blasted titanium owing to cohesion failure on shear loading. Despite these plasma-sprayed coatings yielding the highest percentage of bone contact in this experiment, under shear loading in an orthopedic device the debonding of the osseointegrated coating from the implant can end up catastrophically; the metallic implant would become loose, and revision would be necessary. The highest mean shear strength was
Table 5.5 (continued)
Specificity of the particular system
Physico-chemical
characterization techniques
used Testing
Laser type Nd:YAG
Year Author(s) ArF KrF SHG THG FHG Modifications FTIR Raman XRD SEM EDS TEM AFM RBS=SIMS XPS=AES Mechanical Invitro Invivo
2004 Jime´nez [78] x x x x x
2004 Nelea [140] x x x x x
2004 Nelea [99] x x x
2004 Nistor [141] x x x x x
2004 Pelletier [142] x x x
2004 Pelletier [143] x x x
2004 Pelletier [144] x x x
2004 Pelletier [145] x x x
2004 Socol [80] x x x x
2005 Beltrano [146] x x x x
2005 Bigi [112] x x x x x
2005 Blind [48] x x x x x x
2005 Borrajo [147] x x x x
2005 Ferro [51] x x x x
2005 Ferna´ndez-Pradas [77] x x x x x x
2005 Katto [50] x x x x x
2005 Kim [148] x x
2005 Kusunoki [83] x x
2005 Mihailescu [149] x x x x
2005 Solla [90] x x x x x
2006 Peraire [118] x x x
2006 Seydlova [111] x x x x
2006 Suda [55] x x x x
obtained for the PLD coating on the grit-blasted surface, but both PLD-coated samples (grit-blasted and smooth) improved bone bonding with regard to their corresponding uncoated counterparts, substantiating the histomorphometric findings. In agreement with the 6-month rabbit tibia results, after implantation for 12 weeks in dog jaws large areas of the nearly intact PLD coating were observed by SEM.
It is interesting to compare the bone response to the ArF laser-deposited coatings (PLDg), after implantation during 24 weeks in rabbit tibias [118] and during half of this time (12 weeks) in dog jaws [119]. The percentage of bone apposition on the laser-deposited coating has been higher and more differen-tiated from the other materials in the rabbit than in the dog despite the facts that: (1) in the rabbit tibia, the implants were in contact with both cortical and trabecular bone; and (2) alveolar bone from dog jaw is dense and in general regenerates faster than trabecular bone. Thus, one would expect faster osseoin-tegration in the dog jaw. Generally, it is assumed that in the longer term all biocompatible materials implanted in the body tend to osseointegrate, and the difference in bone response between diverse materials is likely to disappear. In fact, for sputtered coatings, Mohammadi et al. [121, 122] found less differentia-tion between coated and uncoated materials in a long-term study (9 months) than in the short-term investigation (up to 6 weeks) after implantation in cortical and trabecular bone of rabbits. This result is in opposition to our findings, wherein after the longer implantation time the PLD coating showed more significantly differentiated bone apposition with regard to the reference material than in the shorter experiment, where bone was still remodeling.
Concerning the differences in response between trabecular and cortical bone, Mohammadi et al. found that trabecular bone differentiated better between the different materials than cortical bone, in agreement with our findings.