Polymeric piezoelectric actuator substrate for osteoblast mechanical stimulation
Introduction
Bone is a living structure in constant adaptation and remodeling. The processes of bone resorption and deposition are strongly related to mechanical stimuli (Bourrin et al., 1995; Forwood and Turner, 1995; Hillam and Skerry, 1995; Judex and Zernicke, 2000). Osteocytes and osteoblasts play a central role in mechanical stimuli sensing and transduction in living bone and thus, osteoclastic activity too. Mechanosensation implies that cells respond to an applied force and this mechanism is not necessarily dependent on a chemical stimulus. It has been suggested that forces capable of inducing cell deformation induce changes in membrane channels and on protein structure (Charras et al., 2004; Gudi et al., 1998) and that ultimately, cytoskeleton deformation exerts direct influence on cell nuclei (Bacabac et al., 2006; Burger and Klein-Nulend, 1999; Charras et al., 2004; Jessop et al., 2002). There are several substances produced by osteoblasts that work as messenger molecules, in response to mechanical stimuli, like prostaglandins (particularly PGE2) and nitric oxide (Bakker et al., 2001; Fan et al., 2006; Kanamaru et al., 2001; Smalt et al., 1997). A single osteocyte can disseminate a mechanical stimulus to its surrounding osteocytes via extracellular soluble signaling factors like nitric oxide (Vatsa et al., 2007). A wide variety of devices have been tested for mechanical stimulation of cells and tissues in vitro, namely of osteocytes and osteoblasts (Appleford et al., 2007; Brown, 2000; Lewandowska-Szumiel et al., 2007; McGarry et al., 2008; Tanaka, 1999), although many of these systems are difficult to adapt to an in vivo device. Cell responses depend upon the strain, load and frequency of the stimulus; dynamic, short loading exerts the strongest bone adaptation response, and bone cells tend to accommodate to a routine, so the stimulus must vary in order to elicit a same level of response; a stochastic bone cells response in vitro and in vivo has been reported (Bacabac et al., 2006; Bakker et al., 2001; Burr et al., 2002; Cullen et al., 2001; Hsieh and Turner, 2001; Robling et al., 2001; Tanaka et al., 2003a, Tanaka et al., 2003b; Turner et al., 1995). Some authors suggest that high frequency associated with a high enough number of cycles are needed to maximize osteoblast proliferation in vitro (Kaspar et al., 2002).
Tanaka reported the use for in vitro assays of a piezoelectric actuator in which the cells were seeded on a collagen gel block. This block was then submitted to uniaxial tension and/or compression by the displacement originated by two piezoelectric ceramic layers by the loading of voltage; both strain and frequency applied may vary (Tanaka, 1999).
The bone has piezoelectric properties, as Fukada and Yasuda (1957) described mechanical stress applied to dried bone produces polarization and submission of bone to an electric field originates strain. The development of biocompatible materials that could mimic this behavior could provide a powerful therapeutic tool. The in vitro studies here presented aim to prove the concept of use of piezoelectric materials as a mean to produce controlled and effective mechanical stimulation and to call upon the huge potential of such materials. The values for total protein and viability are similar for cells grown on the devices under the static and dynamic conditions but nitric oxide values are higher under dynamic conditions, suggesting that this increase is due to effective mechanical stimulation and not to cell death or decreased viability.
Section snippets
Physical phenomena of the piezoelectric substrate
The polymeric piezoelectric films used (polyvinylidene fluoride (PVDF)) were supplied by Measurement Specialties Inc. Company (USA). These 52-μm-thick films consist of a 12×13 mm2 active area, printed with silver ink electrodes on both surfaces in a 15×40 mm2 die-cut piezoelectric polymer substrate (see Fig. 1a and b). It is polarized along the thickness and has as piezoelectric strain constants dzy=23×10−12 and dzy=−33×10−12 ((m/m)/(V/m)).
Theoretically, based on the converse piezoelectricity
Deposition of thin films in the piezoelectric actuators
Fig. 3 shows the active area already coated. The coated device has a total thickness of 72 μm, with the coating thickness of 10–11 μm and the electrical isolation of the surface was guaranteed.
Numerical modeling
NM gave an estimation of strain and displacement distribution along the polymeric piezoelectric surface, at peak voltage. The values are in the range 6.4<y<77.3 nm. The higher displacement was observed in the piezoelectric free extremity. It is possible to observe a sinusoidal numerical perturbation in the
Discussion and conclusions
In this work the strain was constant because the applied peak voltage was constant. The frequency varied. According to the definition of piezoelectricity every time a voltage is applied a maximum peak strain is reached and then material recovers the initial shape.
The amount of strain distribution along the piezoelectric material was assumed as an acceptable value for cells to endure. ESPI results on observed displacement along the z-axis complement the FNM estimations on the displacement/strain
Conflict of interest statement
There are no conflicts of interest to declare by the authors.
Acknowledgements
The authors would like to thank the Portuguese Foundation for Science and Technology (FCT) for financial support under the Grant PTDC/EMEPME/70155/2006 Grants SFRH/BD/22856/2005 and SFRH/BD/31895/2006, to INESCPorto, INEB (OPorto) and ITN (Lisbon), especially to Prof. Doutora Luísa Botelho.
References (44)
- et al.
Ultrasound effect on osteoblast precursor cells in trabecular calcium phosphate scaffolds
Biomaterials
(2007) - et al.
The production of nitric oxide and prostaglandin E2 by primary bone cells is shear stress dependent
Journal of Biomechanics
(2001) Techniques for mechanical stimulation of cells in vitro: a review
Journal of Biomechanics
(2000)- et al.
Effects of biomechanical stress on bones in animals
Bone
(2002) - et al.
Estimating the sensitivity of mechanosensitive ion channels to membrane strain and tension
Biophysical Journal
(2004) - et al.
Serial passage of MC3T3-E1 cells alters osteoblastic function and responsiveness to transforming growth factor-β1 and bone morphogenetic protein-2
Biochemical and Biophysical Research Communications
(1999) - et al.
Skeletal adaptations to mechanical usage: results from tibial loading studies in rats
Bone
(1995) - et al.
The effect of chitosan and PVDF substrates on the behavior of embryonic rat cerebral cortical stem cells
Biomaterials
(2006) - et al.
Mechanical strain and fluid movement both activate extracellular regulated kinase (ERK) in osteoblast-like cells but via different signaling pathways
Bone
(2002) - et al.
Proliferation of human-derived osteoblast-like cells depends on the cycle number and frequency of uniaxial strain
Journal of Biomechanics
(2002)
Osteoblast response to the elastic strain of metallic support
Journal of Biomechanics
Activation of extracellular-signal regulated kinase (ERK1/2) by fluid shear is Ca2+- and ATP-dependent in MC3T3-E1 osteoblasts
Bone
Evaluation of Alamar Blue reduction for the in vitro assay of hepatocyte toxicity
Toxicology in Vitro
Functionalization of PVDF membranes with carbohydrate derivates for the controlled delivery of chlorhexidin
Biomolecular Engineering
A new mechanical stimulator for cultured bone cells using piezoelectric actuator
Journal of Biomechanics
Effects of broad frequency vibration on cultured osteoblasts
Journal of Biomechanics
Extracellular NO signalling from a mechanically stimulated osteocyte
Journal of Biomechanics
Discordant expression of osteoblast markers in MC3T3-E1 cells that synthesize a high turnover matrix
Journal of Biological Chemistry
A dye-based lymphocyte proliferation assay that permits multiple immunological analyses: mRNA, cytogenetic, apoptosis, and immunophenotyping studies
Journal of Immunological Methods
A new rapid and simple non-radioactive assay to monitor and determine the proliferation of lymphocytes: an alternative to [3H]thymidine incorporation assay
Journal of Immunological Methods
Bone cell responses to high-frequency vibration stress: does the nucleus oscillate within the cytoplasm?
The FASEB Journal
Effect of physical training on bone adaptation in three zones of the rat tibia
The Journal of Bone and Mineral Research
Cited by (46)
Alginate-based biomaterial-mediated regulation of macrophages in bone tissue engineering
2023, International Journal of Biological MacromoleculesMaterials for Biocompatible Piezoelectric Devices
2023, Encyclopedia of Materials: ElectronicsPiezoelectric nanomaterials for biomedical applications
2022, Food, Medical, and Environmental Applications of NanomaterialsRecent advances of polymer-based piezoelectric composites for biomedical applications
2021, Journal of the Mechanical Behavior of Biomedical MaterialsCitation Excerpt :This effect may be achieved by implanted batteries, external electrical stimulation devices, or varying physiological electrical environment (Tandon et al., 2018). To this purpose, Frias et al. (2010a) have used PVDF films to investigate the effect of mechanical stimulation of bone cells by converse piezoelectric effect. To achieve the mechanical stimulation, an alternating sinusoidal current (AC) of 5 V at 1 Hz and 3 Hz was applied on a substrate undergoing dynamic mechanical conditions.
- 1
Both authors contributed equally for this work.