The Combination of Light and Stem Cell
Therapies: A Novel Approach in Regenerative Medicine
Juanita Andersa, Helina Mogesa, Xingjia Wua, Ilko Ilevb,
Ronald Waynantb, and Leonardo Longoc
a
Department of Anatomy, Physiology and Genetics, Uniformed Services University of the Health Sciences,
Bethesda, MD 20814 USA
b
Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD
20993 USA
c
Institute of Laser Medicine, University of Siena, Siena 53100, Italy and University of San Marino 47890,
San Marino Republic
Abstract. Light therapy commonly referred to as low level laser therapy can alter cellular functions and clinical
conditions. Some of the commonly reported in vitro and in vivo effects of light therapy include cellular
proliferation, alterations in the inflammatory response to injury, and increases in mitochondrial respiration and
adenosine triphosphate synthesis. Based on the known effects of light on cells and tissues in general and on
reports in the last 5 years on the interaction of light with stem cells, evidence is mounting indicating that light
therapy could greatly benefit stem cell regenerative medicine. Experiments on a variety of harvested adult stem
cells demonstrate that light therapy enhances differentiation and proliferation of the cells and alters the
expression of growth factors in a number of different types of adult stem cells and progenitors in vitro. It also
has the potential to attenuate cytotoxic effects of drugs used to purge harvested autologous stem cells and to
increase survival of transplanted cells.
Keywords: Adult Stem Cells, Embryonic Stem Cells, Light Therapy, Progenitors, Proliferation,
Differentiation, Transplantation
PACS: 42.62.Be, 87.17.Uv, 87.19.L, 87.59.yt
INTRODUCTION TO STEM CELLS AND LIGHT THERAPY
A stem cell has the capacity for long term self-renewal and its daughter cells have the ability to
differentiate into many different types of specialized cells [1]. Embryonic stem cells, as the name implies,
are derived from the embryo. They are pluripotent and can give rise to all cell types of the body. Embryonic
stem cells are capable of long term self-renewal and can proliferate for long periods of time in vitro
producing millions of cells [2]. Embryonic stem cells are isolated from the inner cell mass of the embryo
and harvesting of these cells leads to the death of the embryo. This fact has resulted in political, religious
and ethical concerns [3].
It is now known that in the adult, most tissues have stem cells [2]. Adult stem cells can self-renew, are
multipotent and can produce differentiated cell types of their tissue of origin [1]. Adult stem cells can be
harvested from birth to adulthood and can be manipulated ex vivo to produce new cells and tissues for
transplantation [3]. There are reports that some adult stem cells can differentiate into cell types not related
to their tissue of origin. For example, adipose tissue which is derived from mesenchyme has adipose
derived stem cells that can differentiate along mesenchymal lineages [4], as well as, trans-differentiate into
many cell types including neurons, bone, cartilage, cardiac tissue, liver and smooth muscle [4, 5]. However,
reports that adult stem cells can differentiate into cell types that are not related to their tissue of origin are
controversial [6]. Most adult tissues contain low numbers of stem cells which can be difficult to identify
and isolate [2]. Also, improved methods to expand isolated adult stem cells and control their differentiation
in vitro are needed. Cell number expansion is critical since many cells are needed for stem cell replacement
CREDIT LINE (BELOW) TO BE INSERTED ON THE FIRST PAGE OF EACH PAPER
CP1226, Laser Florence 2009: A Gallery through the Laser Medicine World, edited by L. Longo
© 2010 American Institute of Physics 978-0-7354-0770-1/09/$30.00
3
therapies such as tissue grafting and transplantation [6, 3]. One concern with the use of embryonic and
adult stem cells in tissue replacement therapies is rejection by the immune response. However, autologous
stem cell therapy in which a patient’s somatic stem cells could be harvested, expanded in vitro,
differentiated and transplanted back into the patient would be less likely to initiate rejection [7].
Light therapy (LT) commonly referred to as low level laser therapy (LLLT) can alter cellular functions
and clinical conditions [8, 9]. Some of the commonly reported in vitro and in vivo effects of LT include
cellular proliferation [10-12], alterations in the inflammatory response to injury [13], and increases in
mitochondrial respiration and adenosine triphosphate (ATP) synthesis [14-16]. Based on the reported
effects of LT on cells and tissues, LT could benefit stem cell regenerative medicine in several ways. It has
the potential to increase the number of adult stem cells in vitro by increasing cell division or shortening cell
cycle phases and may affect the differentiation of stem cells along different cell lineages. LT would also be
a useful adjunct to stem cell transplantation and tissue grafting by decreasing the immune response of the
host and increasing survival of the cells or tissue post-transplantation.
EFFECTS OF LIGHT THERAPY ON ADULT STEM CELLS
Mesenchymal Stem Cells In Vitro and In Vivo
Adult mesenchymal stem cells (MSCs) are multipotent cells that can be isolated from bone marrow,
proliferate as undifferentiated cells in vitro, and differentiate into a number of mesenchymal lineages
including bone, cartilage, muscle, fat, and other connective tissues [17]. Several studies have examined the
potential of LT to increase the number of MSCs in vitro, affect their differentiation, and improve cell
survival following transplantation.
The effect of 647 nm wavelength light (+10nm) from a light-emitting diode (LED) on osteogenic
differentiation was examined using mouse MSCs [18]. The cells were cultured for three days in the
presence of osteogenic differentiation medium and then treated with light (9.29 mW/cm2, cells irradiated
once for 10 s, 30 s, or 90 s at radiation energies of 0.093 J, 0.279 J and 0.836 J). Alterations in the MSCs
were analyzed at 48 hours post-irradiation by several bioassays. All three LED settings enhanced
differentiation of the MSCs into osteoblasts compared to the control, non-irradiated MSCs. This enhanced
differentiation was confirmed by increased Alizarin Red-S staining for calcification deposits, higher
alkaline phosphatase (ALP) activity (ALP is expressed at the initial stages of osteoblast maturation), higher
mRNA expression of markers of osteoblast differentiation including osteocalcin, collagen type I,
osteopontin, and Runt-related transcription factor2 and increased CD44 expression. CD44 is an adhesion
molecule that is a positive marker for human and rat MSCs and plays a role in the differentiation of MSCs.
For the treatment of many malignancies, harvesting of MSCs from a patient for later regenerative
treatment requires in vitro purging of the cells with cytotoxic agents. However, exposure to cytotoxic drugs
can result in dysfunction of the MSCs. In a recent study, murine MSCs were used to investigate the effects
of light on preventing deterioration of stem cells subjected to purging with high dose chemotherapy [19]. A
diode laser with 660 nm wavelength light, output power of 60 mW, and laser beam diameter of 10mm was
used. Various energy densities were used (1.9 J/cm2 to 11.7 J/cm2 ). Power density varied from 76 mW/cm2
for 1.9 J/cm2 to 156 mW/cm2 for 11.7 J/cm2. The low energy density LT increased MSC proliferation
(based on a DNA assay) while the high energy density LT decreased MSC proliferation. LT was able to
prevent or attenuate some of the effects of the various cytotoxic drugs tested and amplified others. LT at
1.9 J/cm2 eliminated the effects of high concentration Carboplatin on the cells but when it was combined
with ineffective concentrations of Paclitaxel inhibition of stem cell proliferation occurred. The results
depended not only on the laser parameters used but also on the type and concentration of the cytotoxic drug
tested. This report has important clinical implications in the field of high dose chemotherapy coupled with
autologous stem cell rescue, purging and preservation for later use in autologous stem cell grafts.
In another set of experiments, the effects of LT on MSCs prior to implantation were assessed. Laser
irradiated MSCs isolated from rat bone marrow were implanted into the infarcted rat heart [20]. The in
vitro MSCs were irradiated with 804 nm wavelength laser light (power density of 50mW/cm2, 20 s, 1J/cm2,
a 1.5 mm diameter metal backed optical fiber) when the cells reached a confluence of 90%. At 24 hours
post-irradiation, MSCs were harvested, labeled with 5-bromo-2’-deoxyuridine (BrdU), and implanted into
the heart at thirty minutes post-infarction. The investigators waited for 24 hours post-irradiation before
4
injection of the cells to allow time for the cells to up regulate expression of cytoprotective factors prior to
implantation. The MSCs were injected into two sites, one near the infarction area and one in the lower part
of the left ventricle. The hearts were removed three weeks post-implantation. The irradiated MSCs caused a
significant reduction in the infarct size (53%) compared to the hearts implanted with non-irradiated MSCs.
There was a significant increase in the cell density of the irradiated MSCs in the infracted area of the heart
compared to the non-irradiated cells and there was increased angiogenesis and expression of vascular
endothelial growth factor in the hearts implanted with the laser treated MSCs. Another intriguing finding in
this study was that there was an eight-fold increase in the light treated transplanted MSCs in the infarcted
area compared to the number in the entire left ventricle. The authors suggest that the transplanted cells
migrated toward the infarct zone. However, migration and differentiation studies were not done. This study
demonstrates that LT of stem cells prior to implantation can significantly increase their survival and/or
proliferation and may increase the migration of the cells to the injury site. As was reported in a number of
studies reviewed here, LT of stem cells can alter their expression of growth factors.
Human Osteoblasts In Vitro
Several studies reported that LT affected osteogenesis and bone repair in animal injury models [21]. The
cellular and molecular mechanisms involved in this effect are still unclear but bone cell proliferation and
differentiation have been proposed. Based on these reports, the effect of LT on proliferation and
differentiation of a human osteoblast cell line was examined [22]. A laser emitting 632 nm wavelength light
(output power of 10 mW, a 1.8 mm beam diameter, 180 mW/cm2 ) was used. Various times were tested
with the best results at 3 sec exposure and 0.43 J/cm2. The osteoblasts were irradiated on the second and
third days post-seeding. LT resulted in a 25% increase in the number of cells based on cell counts and a
40% increase in mitochondrial enzyme activity based on the colorimetric dimethylthiazol diphenyl
terrazolium bromide (MTT) assay. Also, 40% to 60% of the cells expressed ALP activity compared to 20%
in the non-light treated cells. These results indicate that LT can promote proliferation and maturation of
osteoblasts in vitro.
The effect of superpulsed laser irradiation on osteogenic activity of human osteoblast-like MG-63 cells
has been examined [23]. In this study, cells were exposed to superpulsed laser irradiation using a dental
device with 904-910nm wavelength light (pulse width 200 nanoseconds, minimum peak power 33 W,
frequency 30 kHz, average output power 200 mW, total energy 60 J, exposure time 5 minutes). The
following parameters were evaluated: cell growth and viability (light microscopy, lactate dehydrogenase
release), calcium deposits (Alizarin Red S staining), and expression of bone morphogenetic factors (realtime PCR). The laser irradiation decreased cell growth, induced expression of molecules that are mediators
of bone formation including TGF-β2, BMP-4, and BMP-7, type I collagen, ALP, and osteocalcin, and
increased the size and the number of calcium deposits. These studies support the hypothesis that LT can
promote proliferation and differentiation of osteoblasts in vitro.
Adult Human Adipose Derived Stem Cells In Vitro
Adipose tissue like bone marrow is derived from the mesenchyme and contains an easily isolated
supportive stroma containing stem cells. The ability of LT to support proliferation and differentiation of
primary cultures of adult human adipose derived stem cells was examined [24]. A 635 nm wavelength LED
with an output power of 50.2 mW, a 3.3 mm beam diameter (5.5 mW/cm2, 5 J/cm2) was used. The light
increased cellular viability based on ATP luminescence, increased proliferation based on an optical density
assay, and increased the expression of the stem cell marker, β1-integrin, which the authors interpreted as
indicating maintenance of stem cell properties. It is not clear if β1-integrin also plays a role in
differentiation of adult human adipose derived stem cells similar to the CD44 marker for MSCs (see section
on Mesenchymal Stem Cells In Vitro and In Vivo) and no differentiation markers were used in this series
of experiments. Therefore, it is not known if the LT caused differentiation of a sub-population of the stem
cells as reported in the mesenchymal stem cell and human osteoblast studies described above.
5
Adult Human Dental Pulp Stem Cells In Vitro
The effectiveness of LT to alter proliferation of adult human dental pulp stem cells (hDPSCs) in vitro
was evaluated [25]. A strain of hDPSCs was used. The cells were kept semi-confluent and were grown in
nutritionally deficient medium. A laser emitting 660 nm wavelength light was used (output powers of 40
and 20 mW were used at an energy density of 3 J/cm2, beam area was 3.6 mm2). The irradiation of the cells
was done through the bottom of the 96-well microtitration plates. The irradiation at 20 mW was more
effective in stimulating cell growth of the hDPSCs. Unfortunately, the authors chose to use the MTT assay.
for cell growth analysis. The MTT assay is a colorimetric assay that measures the activity of the reductase
enzymes to reduce MTT to formazan. These reductions take place only when the reductase enzymes are
active, and therefore the MTT assay is often used as a measure of cellular viability. However, many
different conditions can increase or decrease metabolic activity. Changes in metabolic activity can give
large changes in MTT while the number of viable cells remains constant. Several studies have examined
the effects of LT on cell proliferation using both the MTT test and a DNA-based assay and showed no
change in cellular proliferation with the DNA-based assay but large increases with the MTT assay
indicating that LT altered the cellular metabolic activity but not proliferation [26]. These results indicated
that for assessment of proliferation in LT research, cell counts, optical density assays or DNA-based assays
should be used. Therefore, in this study it is not possible to assess if LT altered proliferation of the
hDPSCs.
Muscle Satellite Cells In Vitro
As previously discussed (see Mesenchymal Stem Cells In Vivo and In Vitro), treatment of stem cells
prior to implantation can increase their survival and/or proliferation and alter their expression of growth
factors. In another study, the effects of LT on stem cells prior to and after transplantation were investigated
[27]. Regeneration of muscle depends on resident stem cells known as satellite cells. If there is a loss of
large amounts of muscle tissue, the resident satellite cells can not replace the tissue indicating a need for
myoblast transplantation. However, myoblast transplantation therapy attempts had failed due to the loss of
transplanted cells within hours of transplantation [27]. In this set of experiments, rat muscle satellite cells
were harvested from male rat skeletal muscle, irradiated, seeded on gel scaffolds and incubated for three
days. The scaffolds were then transplanted into partially excised muscle of female rats.A He-Ne laser
(632.8 nm wavelength, 4.5 mW, 1.8 mm beam diameter, 200 mW/cm2, and 0.6 J/cm2) was used to treat
the satellite cells prior to transplantation and the site of the transplantation. The male donor cells were
identified in the female muscle tissue with Y-chromosome in situ hybridization. Cells treated with LT prior
to and at the time of transplantation survived and fused with the host myoblasts to form a host-donor
syncytium. However, non-irradiated cells did not survive. This study illustrates that LT, a simple and
reproducible procedure, can be used to treat stem cells prior to and at the time of transplantation. The
benefits of LT on transplantation of stem cells post-transplantation have not been explored.
LIGHT INTERACTION WITH HUMAN NEURAL PROGENITOR CELLS
IN VITRO
We have previously reported on the effects of 810 nm wavelength light on the differentiation of normal
human neural progenitor cells (NHNPCs) in vitro compared to growth factors [28]. This report was the first
to demonstrate that light could be used as a replacement for growth factors for in vitro differentiation of
neural progenitor cells. NHNPCs were separated into three groups: Control Group (no light, no factors),
Factors Group (factors only, no light), and Light Treated Group (light only, no factors). Light treated
NHNPCs were exposed to continuous-wave 810 nm wavelength light, 150 mW power diode laser (at a
power density of 50 mW/cm2, an exposure time of 4 s, and a radiation dose of 0.2 J/cm2 or 100 mW/cm2, 2
s, and 0.2 J/cm2).
The light treatment parameters used in this study were based on a series of preliminary experiments. For
the initial preliminary experiments, NHNPCs were plated on slides and treated with light once a day for
three days and grown for a total of seven days using the following laser parameters: 1) wavelengths: 458.6,
477, 488.7, 515, 646, 660, 780, 807, 810, and 975 nm and an energy density of 0.2J/cm2. For this
6
experiment, beam diameter was 10 mm corresponding to an area of 0.785 cm2. A minimum of two slides
containing NHNPCs per experimental group was used. Control and Factors slides were included in the
analysis. A surface area analysis using a mm2 grid randomly placed over the chamber slide was used to
evaluate the growth of the NHNPCs. The results of the experiment on the effectiveness of the various
wavelengths showed that the 810 nm wavelength light was comparable to growth factors in the percentage
of surface area occupied by the NHNPCs clusters and processes (810 nm significantly greater than:646 nm
(p<0.01); 477 nm (p<0.05); and Control, 458.6 nm, 488.7 nm (p<0.001)). The 515 nm wavelength light
was inhibitory compared to the growth factors and 810 nm light (515 nm significantly less than: 660 nm,
780 nm (p<0.01); 807 nm (p<0.05); and 810 nm, 975 nm (p<0.001)). Statistics were based on One-Way
ANOVA with Tukey Post hoc test (Fig. 1).
Percentage of Area by Wavelength
50
Percent
40
***
***
30
20
***
10
0
Control Factors 458.6
477
488.7
515
646
660
780
807
810
975
FIGURE 1. The bar graph shows the percentage of area occupied by the NHNPCs clusters and processes. The area
occupied by the NHNPCs treated with the 810 nm wavelength light was comparable to the factors while the 515 nm
wavelength light was significantly less than the factors and 810 nm wavelength light groups. The photomicrographs
show the appearance of the NHNPCs under different conditions: A. control group with no light, B. the factors group, C.
515 nm wavelength light treated group and D. 810 nm wavelength light treated group. Key: *** (p<0.001).
Optimization of dosimetry and power density (intensity) is currently of great interest to scientists and
clinicians working in the area of light therapy. Various combinations of dosimetry and power density for
810 nm were evaluated using in vitro NHNPCs. NHNPC were placed into one of three treatment groups,
two slides per group: 1) Control (no factors, no light); 2) Factors (no light); and 3) 810 nm wavelength
Light Treated (spot size 0.78cm2). The 810 nm wavelength Light Treated group consisted of 4 subgroups:
1) 0.01 J/cm2 dose: 1, 5 and 19 mW/cm2; 2) 0.05 J/cm2 dose: 1, 5, 15, 19, 25, and 50 mW/cm2; 3) 0.2 J/cm2
dose: 1, 5, 15, 19, 25, and 50 mW/cm2; and 4) 1 J/cm2 dose: 1, 5, 15, 19, 25, and 50 mW/cm2 (Table 1).
NHNPCs were treated for three consecutive days and fixed on day seven. Images of twenty random
neurospheres per group were captured digitally and assayed for differentiation by determining neurite
number and length. The total neurite length for all neurites per neurosphere was determined and averaged
per group. The data was analyzed using one way ANOVA with Tukey Post tests. Based on this data, total
7
TABLE 1. Light treated groups compared to Factors group: Average Summed Neurite Length
1 mW/cm2
5 mW/cm2
15 mW/cm2
19 mW/cm2
25 mW/cm2
50 mW/cm2
2
0.01 J/cm
NS
NS
-----
NS
-----
-----
0.05 J/cm2
NS
NS
NS
S**
S**
NS
0.2 J/cm
NS
NS
NS
S*
S*
S**
2
NS
NS
NS
NS
NS
S*
Parameters
2
1 J/cm
NS: No statistical difference. S: Groups significantly greater than Factors group. (One way ANOVA *p<0.01,
**p<0.001)
neurite length per neurosphere was increased as power density (19-50 mW/cm2) and dosage (0.05-1J/cm2)
was increased (Table 1). These data suggest that there is not one optimal combination of dose and power
density, but rather an island of effective combinations of dose and power density for a given wavelength.
NHNPCs were not only capable of being sustained by light in the absence of growth factors, they were
also able to differentiate normally as assessed by neurite formation and immunostaining for neuronal and
glial markers [28]. The NHNPCs had an up-regulation in the expression of endogenous FGF-2, BDNF and
NGF in response to the light. Suramin hexasodium salt, a nonselective P2 receptor antagonist, significantly
decreased neurite outgrowth in the light treated cells but did not have an effect on neurite extension in the
control or factor treated NHNPCs (Fig.2).
FIGURE 2. The graph shows the effects of the suramin hexasodium salt, a non-selective P2Y purinergic antagonist on
neurite extension. Suramin hexasodium salt was added to the cultures before light or factor treatment. Three different
concentrations of suramin hexasodium salt were used:10µM, 50µM and 100µM. Suramin hexasodium salt decreased
neurite extension in a dose dependent manner. Control NHNPCs treated with 10µM suramin (C-10sur), Control
NHNPCs treated with 50µM suramin (C-50sur), Control NHNPCs treated with 100µM suramin (C-100sur), Light
treated NHNPCs with 10µM suramin (L-10sur), Light treated NHNPCs with 50µM suramin (L-50sur), Light treated
NHNPCs with 100µM suramin (L-100sur), Factor treated NHNPCs with 10µM suramin (F-10sur), Factor treated
NHNPCs with 50µM suramin (F-50sur), Factor treated NHNPCs with 100µM suramin (F-100sur), # indicates that the
group had a statistically significant increase compared to the control group, * indicates that the groups had a
statistically significant decrease compared to the light group.
P2Y2 and P2Y11 receptors were found to be expressed by the NHNPCs (Fig. 3) by immunolabeling.
Based on these findings, the mechanism by which light supports NHNPC differentiation was hypothesized
to be due to increases in ATP leading to increased extracellular ATP activating the P2Y receptors [28].
Furthermore, it has been reported that ATP can stimulate neurite outgrowth independent of other
8
neurotrophic factors and the neurotrophic effect of ATP may be mediated through the mitogen-activated
protein kinase (MAPK) pathway [29]. MAPK pathways transduce a large variety of external signals,
resulting in many cellular responses, including growth, differentiation, inflammation and apoptosis [30].
FIGURE 3. Photomicrographs of NHNPCs labeled with fluorescence tagged primary antibodies against the P2Y2 and
P2Y11 receptors. The nuclei were visualized by DAPI staining.
CONCLUSIONS
Based on a series of reports in the last 5 years, evidence is mounting indicating that LT could greatly
benefit stem cell regenerative medicine. Experiments on a variety of harvested adult stem cells demonstrate
that LT enhances differentiation and proliferation of the cells in vitro. LT alters the expression of growth
factors in a number of different types of adult stem cells and progenitors in vitro. It also has the potential to
attenuate cytotoxic effects of drugs used to purge harvested stem cells for later use in autologous stem cell
grafts. Treatment of stem cells with light prior to transplantation and/or at the time of transplantation
increased survival of the transplanted cells. Based on the general LT literature, a number of cellular
functions could be altered by LT that would result in enhanced survival of the transplanted cells. For
example, LT can increase expression of anti-apoptotic proteins and reduce pro-apoptotic proteins [31].
Another area of potential use of LT that has not been explored to date is the manipulation of
endogenous adult stem cell populations. For example, LT could be used to target the self renewal capacity
of resident stem cells to increase the regenerative pool when needed, to induce resident adult stem cells to
differentiate along a specific lineage, and to mobilize cells to migrate to an area of injury/disease and
replenish the injured and dying cells.
REFERENCES
M. R. Allison, J. Path. 217, 141-143 (2009)
M. R. Allison and S. Islam, J. Path. 217, 144-160 (2009)
J. T. Moore, Med.Tech.SA 121, 3-6 (2007)
J. A. de Villiers, N. Houreld and H. Abrahamse, Stem Cell Rev. Rep. 5, 256-265 (2009)
A. Schaffler and C. Buchler, Stem Cells 25, 818-827 (2008)
http://stemcells.nin.gov
P. Bianco and P. G. Robey, Nature 414, 118-121(2001)
T. Karu, “Low-Power Laser Therapy” in Biomedical Photonics Handbook, edited by T. Vo-Dinh, Boca Raton: CRC
Press, 2003.
9. J. Tuner, The Laser Therapy Handbook, Grangesberg: Priman, 2004.
10. R. P. Abergel et. al., J. Dermatol. Surg. Oncol. 13, 127-133 (1987)
11. E. M. Vinck et. al., Photomed. Laser Surg. 23, 167-171 (2005)
12. P. Moore et. al., Lasers Surg. Med. 36, 8-12 (2005)
13. K. Byrnes et. al., Lasers Surg. Med. 36, 171-185 (2005)
1.
2.
3.
4.
5.
6.
7.
8.
9
14. Y. Morimoto et. al., Lasers Surg. Med. 15, 191-199 (1994)
15. W. Yu et. al., Photochem. Photobiol. 66, 866-871 (1997)
16. U. Oron et. al., Photomed. Laser Surg. 25, 180-182 (2007)
17. A. Caplan, J. Path. 217, 318-324 (2009)
18. H. K. Kim et. al., Laser Med. Sci. 24, 214-222 (2009)
19. K. H. Karajz et. al., Lasers Surg. Med. 41, 463-469 (2009)
20. H. Tuby, L. Maltz, and U. Oron, Photomed. Laser Surg. 27, 227-234 (2008)
21. O. Barushka, T. Yaakobi and U. Oron, Bone 16, 47-55 (1995)
22. A. Stein et. al., Photomed. Laser Surg. 23: 161-166 (2005)
23. S. Saracino et. al., Lasers Surg. Med. 41, 298-304 (2009)
24. B. Mulva et. al., Laser Med. Sci. 23, 277-282 (2008)
25. F. de P. Eduardo et. al., Lasers Surg. Med. 40, 433-438 (2008)
26. P. Brondon, I. Stadler and R. Lanzafame, Photomed. Laser Surg. 25, 144-149 (2007)
27. G. Shefer et. al., Lasers Surg. Med. 40, 38-45 (2008)
28. J. Anders et. al., IEEE J. Selected Topics Quantum Electronics 14, 118-125 (2008)
29. S. Lakshmi and P.G. Joshi, Neuroscience 141, 179-189 (2006)
30. H.J. Schaeffer and M.J. Weber, Mol. Cell. Biol. 19, 2435-2444 (1999)
31. G. Shefer et. al., J. Cell. Sci. 115, 1461-1469 (2002)
10
Copyright of AIP Conference Proceedings is the property of American Institute of Physics and its content may
not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written
permission. However, users may print, download, or email articles for individual use.