Comparison of the early production of extracellular matrix on dense hydroxyapatite and hydroxyapatite-coated titanium in cell and organ culture

Alternative methods for assessing biocompatibility and function of implant materials

Biocompatibility testing is used to evaluate the host response to implantable materials and to assess their ability to perform in applications in which they are intended to interact with biological systems. In compliance with international and/or national standards, such assessment is based mainly on the results of experimental implantation into animal tissues. However, the development of in vitro experimental techniques creates new opportunities to observe and to understand the interaction of biomaterials with host tissue. The state-of-the-art application of alternative methods in biocompatibility testing is presented in this review article. It is discussed with respect to the Three Rs concept (reduction, refinement, replacement) of Russell & Burch. Perspectives on alternative methods in biocompatibility studies are discussed with regard to the possible role of biomaterials in tissue engineering.

Biomimetic surface modification of titanium surfaces for early cell capture by advanced electrospinning

The time required for osseointegration with a metal implant having a smooth surface ranges from three to six months. We hypothesized that biomimetic coating surfaces with poly(lactic-co-glycolic acid) (PLGA)/collagen fibers and nano-hydroxyapatite (n-HA) on the implant would enhance the adhesion of mesenchymal stem cells. Therefore, this surface modification of dental and bone implants might enhance the process of osseointegration. In this study, we coated PLGA or PLGA/collagen (50:50 w/w ratio) fiber on Ti disks by modified electrospinning for 5 s to 2 min; after that, we further deposited n-HA on the fibers. PLGA fibers of fiber diameter 0.957 ± 0.357 µm had a contact angle of 9.9 ± 0.3° and PLGA/collagen fibers of fiber diameter 0.378 ± 0.068 µm had a contact angle of 0°. Upon n-HA incorporation, all the fibers had a contact angle of 0° owing to the hydrophilic nature of n-HA biomolecule. The cell attachment efficiency was tested on all the scaffolds for different intervals of time (10, 20, 30 and 60 min). The alkaline phosphatase activity, cell proliferation and mineralization were analyzed on all the implant surfaces on days 7, 14 and 21. Results of the cell adhesion study indicated that the cell adhesion was maximum on the implant surface coated with PLGA/collagen fibers deposited with n-HA compared to the other scaffolds. Within a short span of 60 min, 75% of the cells adhered onto the mineralized PLGA/collagen fibers. Similarly by day 21, the rate of cell proliferation was significantly higher (p ⩽ 0.05) on the mineralized PLGA/collagen fibers owing to enhanced cell adhesion on these fibers. This enhanced initial cell adhesion favored higher cell proliferation, differentiation and mineralization on the implant surface coated with mineralized PLGA/collagen fibers.

In vitro testing of Nd:YAG laser processed calcium phosphate coatings

Nd:YAG laser cladding is a new method for deposition of a calcium phosphate onto metallic surfaces of interest in implantology. The aim of this study was to compare the biologic response of MG-63 human osteoblast-like cells grown on Ti-6Al-4V substrates coated with a calcium phosphate layer applied using different methods: plasma spraying as reference material and Nd:YAG laser cladding as test material. Tissue culture polystyrene was used as negative control. The Nd:YAG laser clad material showed a behaviour similar to the reference material, plasma spray, respective to cell morphology (SEM observations), cell proliferation (AlamarBlue assay) and cytotoxicity of extracts (MTT assay). Proliferation, as measured by the AlamarBlue assay, showed little difference in the metabolic activity of the cells on the materials over an 18 day culture period. There were no significant differences in the cellular growth response on the test material when compared to the ones exhibited by the reference material. In the solvent extraction test all the extracts had some detrimental effect on cellular activity at 100% concentration, although cells incubated in the test material extract showed a proliferation rate similar to that of the reference material. To better understand the scope of these results it should be taken into account that the Nd:YAG clad coating has recently been developed. The fact that its in vitro performance is comparable to that produced by plasma spray, a material commercially available for more than ten years, indicates that this new laser based method could be of commercial interest in the near future.

Physico-chemical characteristics and protein adsorption potential of hydroxyapatite particles: Influence on in vitro biocompatibility of ceramics after sintering

Through the example of two HA ceramics prepared from two HA powders (HAD and HAL), we explored the relation between the physico-chemical qualities of the initial HA powder and the final HA ceramic and their influence on the protein adsorption and cell response to the final HA ceramics. The powders were characterized by XRD, FT-IR, zeta potential, and specific surface area (SSA). Their protein adsorption potential was tested after immersion in culture medium +15% of fetal calf serum. These results were correlated with the protein adsorption potential of the two ceramics (cHAD and cHAL) prepared from the HAD and HAL powders respectively and to the cell attachment after 4, 24 and 72 h on the ceramics. From our results, it appears that a relation can be established between the physico-chemical characteristics of the initial HA powders and the final biological response to the sintered ceramics prepared from these powders. An inverse relation exists between the SSA and the protein adsorption capacity of HA powders and the protein adsorption and cell attachment on HA ceramics. This inverse relation is related to phenomenon occurring during the sintering phase and the formation of inter-granular micro-porosity.

The attachment and growth behavior of osteoblast-like cells on microtextured surfaces

In previous studies, we showed that the application of microgrooves on a surface can direct cellular morphology and the deposition of mineralized matrix of osteoblast-like cells (Biomaterials 20 (1999) 1293; Clin. Oral Impl Res. 11 (2000) 325). In this study, we evaluated the attachment and growth behavior of these cells, using scanning- and transmission electron microscopy (SEM/TEM). Smooth and microgrooved polystyrene substrates were made (groove depth 0.5-1.5 microm, groove- and ridge width 1-10 microm). On these substrates, osteoblast-like cells were cultured for periods up to 16 days. SEM showed that the cells, and their extensions, closely followed the surface on smooth and wider grooved (>5 microm) substrates. In contrast, narrow grooves (<2 microm) were bridged. After 16 days of incubation, the matrix showed extensive deposition of collagen fibrils, and the formation of calcified nodules. With TEM it was shown that on the smooth and wider grooved substrates, focal adhesions were spread throughout the surface. However, on narrow grooves focal adhesions were always positioned on the edges of surface ridges only. Apparently, most extracellular matrix (ECM) was produced by the cells that directly adhered to the substrate. Deposition of ECM was seen in the surface grooves, as well as in between the cell layers. On basis of the current study and previous experiments, we conclude that microgrooves are able to influence bone cell behavior by (1) determining the alignment of cells and cellular extensions, (2) altering the formation and placement of cell focal adhesions, and (3) altering ECM production. Therefore, microgrooved surfaces seem interesting to be applied on bone-anchored implants.

Effect of chemical composition on hydrophobicity and zeta potential of plasma sprayed HA/CaO-P2O5 glass coatings

Multilayered plasma sprayed coatings on the surface of Ti-6Al-4V alloys have been prepared, which were composed of an underlayer of HA and a surface layer of a CaO-P2O5 glass-HA composite, with 2 or 4wt% of glass. Contact angle and surface tension variation with time, for both water and a protein solution, were determined by the sessile and pendent drop methods respectively using the ADSA-P software. Wettability studies showed that hydrophobicity of the coatings increase with the glass addition. The work of adhesion of albumin was also altered in a controlled manner by the addition of the CaO-P2O5 glass, being lower on the composite coatings than on HA. Zeta potential (ZP) results showed that composite coatings presented a higher net negative charge than HA coatings and that ZP values were also influenced by the content of the glass. This study demonstrated that the surface properties of those coatings may be modified by the addition of CaO-P2O5 glass.

Osteogenic evaluation of glutaraldehyde crosslinked gelatin composite with fetal rat calvarial culture model

The cytotoxicity of the synthetic bone substitute composed of tricalcium phosphate and glutaraldehyde crosslinked gelatin (GTG) were evaluated by osteoblast cell culture. In a previous study, the GTG composites were soaked in distilled water for 1, 2, 4, 7, 14, 28, and 42 days, and then the solutions (or extracts) were cocultured with osteoblasts to evaluate the cytotoxicity of GTG composites by alive cell counting. In this study, the extracts were cocultured with the osteoblasts; thereafter, the concentration of transforming growth factor-beta (TGF-beta1) and prostaglandin E2 (PGE2) in the medium was analyzed to strictly reflect the biological effects of GTG composites on the growth of osteoblasts. In order to investigate the osteoconductive potential of the GTG composites on new bone formation in a relative short term, a model of neonatal rat calvarial organ culture was designed prior to animal experiments. Three experimental materials of 4, 8, and 12% GTG composites were evaluated by fetal rat calvarial organ culture for their ability for bone regeneration. Deproteinized bovine and porcine cancellous bone matrixes were used as the controlled materials. All the organ culture units were maintained in cultured medium for 5 weeks. Following the culture period, the morphology of tissue was observed under an optical microscope, and the quantitative evaluation of the new generation bone was determined by using a semiautomatic histomorphometeric method. Except in the initial 4 days, the concentration of TGF-beta1 of 4% and 8% GTG composites was higher than that of the blank group for all the other experimental time periods. The PGE2 concentration for 4% and 8% GTG composites was lower than that of the blank group. It revealed that the 4% and 8% GTG composites would not lead to inflammation and would promote osteoblast growth. The morphology and activity of the osteoblasts were not transformed or changed by the 2 GTG composites. For the 12% GTG composite, the performance of the in vitro condition was inferior to the blank group and the other 2 GTG composites. Although the concentration of TGF-beta1 and PGE2 was gradually back to normal after 14 days, the morphology of the osteoblasts was abnormal with features such as contracted cytoplast structures. The osteoblast was damaged perhaps in the initial stage. We suggested that the 4% and 8% GTG composites should be soaked in distilled water at least for 4 days before medical applications. The 12% GTG composite and the composites with a concentration of glutaraldehyde solution higher than 12% were not recommended as a medical prostheses in any condition. The fetal rat calvaria culture also showed the same results with the analysis of TGF-beta1 and PGE2. From the study, we could predict the results of animal experiments in the future.

Osteoblast growth on titanium foils coated with hydroxyapatite by pulsed laser ablation

Pulsed laser ablation is a new method for deposition of thin layers of hydroxyapatite (HA) on to biomaterial surfaces. In this paper, we report activity and morphology of osteoblasts grown on HA surfaces fabricated using different laser conditions. Two sets of films were deposited from dense HA targets, at three different laser fluences: 3, 6 and 9 Jcm(-2). One set of the surfaces was annealed at 575 degrees C to increase the crystallinity of the deposited films. Primary human osteoblasts were seeded onto the material surfaces and cytoskeletal actin organisation was examined using confocal laser scanning microscopy. The annealed surfaces supported greater cell attachment and more defined cytoskeletal actin organisation. Cell activity, measured using the alamar Blue assay, was also found to be significantly higher on the annealed samples. In addition, our results show distinct trends that correlate with the laser fluence used for deposition. The cell activity increases with increasing fluence. This pattern was repeated for alkaline phosphatase production by the cells. Differences in cell spreading were apparent which were correlated with the fluence used to deposit the HA. The optimum surface for initial attachment and spreading of osteoblasts was one of the HA films deposited using 9 J cm(-2) laser fluence and subsequently annealed at 575 degrees C.

In vitro bioactive behavior of hydroxylapatite-coated porous Al(2)O(3)

To produce bioactive materials for bone substitutes, two major deposition methods, suspension method and thermal deposition method, were employed to develop bioactive, mechanically strong, and porous ceramics. Hydroxylapatite (HA) has been uniformly coated onto inner pore surfaces of reticulated alumina substrates. It has been found that the in vitro bioactivity of HA coatings was affected by both structural crystallinity and specific surface area. Well-crystallized HA heat-treated at high temperatures has resulted in reduced bioactivity. The bio-reaction rate was found to increase with the surface area of HA. We have found that the stability of the well-crystallized HA is associated with the high driving force required for the formation of hydroxy-carbonate apatite (HCA) phase.

Flow cytometry analysis of the effects of pre-immersion on the biocompatibility of glass-reinforced hydroxyapatite plasma-sprayed coatings

Multilayered coatings composed of mixtures of HA and P2O5-based bioactive glasses are of potential clinical benefit in orthopaedic and dental surgery. Pre-immersion of these materials has been reported to further enhance their efficacy in vivo, although the precise biological effects of this treatment are not yet known. In this study we have therefore prepared double-layer plasma-sprayed coatings and evaluated the effects of pre-immersion on the growth and function of human osteosarcoma cells in vitro, using the MTT assay and flow cytometry analysis, respectively. The results showed that the increase in numbers of viable cells was the same or elevated following incubation on the pre-immersed HA and glass-reinforced HA coatings compared with the non-immersed materials. In addition, the expression of bone sialoprotein and fibronectin, two key connective tissue antigens, was up-regulated in cultures grown on the pre-immersed surfaces compared with the non-treated materials. Moreover, cell numbers and antigen expression both improved as the proportion of glass increased, particularly in the pre-immersed samples. Our findings thus suggest that the immersion treatment of these materials appeared to improve the response of these bone-like cells.

Flow cytometry analysis of effects of glass on response of osteosarcoma cells to plasma-sprayed hydroxyapatite/CaO-P(2)O(5) coatings

Multilayered coatings composed of mixtures of hydroxyapatite (HA) and P(2)O(5)-based bioactive glasses offer potential clinical benefits in orthopedic and dental surgery. In this study double-layer plasma-sprayed coatings were prepared and the biological response evaluated in tissue culture using two human osteosarcoma cell lines, MG63 and HOS TE85 (HOS). The cells were cultured on the materials and the effects on cell growth were determined using a spectrophometric assay of a mitochondrial enzyme that is active in viable cells. While none of the materials influenced the growth of the MG63 cells, the HOS cells appeared to undergo less proliferation on all the HA materials. Flow cytometry analysis was carried out using rabbit antibodies against osteonectin, osteopontin, bone sialoprotein, fibronectin, and collagen type I to measure the effects of the materials on key cellular functions. The results showed that the materials downregulated the expression of these extracellular matrix antigens by MG63 cells whereas they had less effect on the HOS cells compared to the same cells incubated on a plastic surface. Notably, with both cell lines the composite with the higher percentage of glass restored the production of connective tissue proteins to levels that were more similar to those present in the control cells.

A histological and histomorphometrical evaluation of the application of screw-designed calciumphosphate (Ca-P)-coated implants in the cancellous maxillary bone of the goat

Various studies already have shown that the occurrence of oral implant failure is higher in the maxilla than in the mandible. To learn whether Ca-P coatings can improve the success rate of oral implants in the maxilla, three different plasma-sprayed, Ca-P-coated, self-tapping Brånemark implants were inserted in the trabecular bone of the maxilla. Before the insertion of the implants, the two first upper premolars of 16 goats were bilaterally extracted. Four months later, each animal received four types of implants: three different Ca-P-coated types and one uncoated. After an endosseous period of 6 months, the implants were provided with permucosal abutments. Four months later the animals were killed. At the end of the experiment, it appeared that 10 of the 16 installed noncoated implants had failed while of the 48 Ca-P-coated implants, only 6 had failed. All successful implants were retrieved and prepared for histomorphometrical evaluation of the bone and gingiva response. The Ca-P-coated implants showed a significantly greater percentage of bone in contact with the implant surface compared with the uncoated implants. The length of the epithelium was not significantly different for the coated compared to the uncoated implants, but the connective tissue was significantly thicker for the noncoated implants than for the Ca-P-coated implants. Also, measurements revealed that all coatings showed reduction in thickness. On the basis of these findings, we concluded that the application of Ca-P coatings (1) improves the bone-implant reaction, although all coatings reduced in thickness, and (2) is of benefit during the healing period in less mineralized trabecular bone.

In vitro growth of human adult bone-derived cells on hydroxyapatite plasma-sprayed coatings

The growth of adult human bone-derived cells on hydroxyapatite (HA) plasma-sprayed coatings was investigated. Such cells were difficult to grow on original plasma-sprayed coatings, even following rinsing and rubbing down. We obtained cell growth only on samples previously immersed 15 or 22 days in complete culture medium. We describe a dissolution/precipitation phenomenon on the HA coating surface assessed by modifications of Ca and P concentrations in the culture medium, by the transformation of the HA coating into carbonated HA (X-ray diffraction and infrared spectrometry and by the presence demonstrated by scanning electron microscopy of spherocrystallites on the HA after 15 days of immersion. Our results show that adult human bone-derived cells are apparently particularly sensitive to the changes in the coating surface induced by liquid immersion. We raise the question of the limits of in vitro investigations on bioactive ceramics such as HA plasma-sprayed coatings susceptible to modification by simple immersion in aqueous solutions such as cell culture medium or physiologic saline.