In vitro evaluation of ultrafast laser drilling large-size holes on sheepshank bone

Real-Time Monitoring of Thermal Phenomena during Femtosecond Ablation of Bone Tissue for Process Control

Femtosecond (fs) laser technology is currently being considered in innovative fields such as osteotomy and treatment of hard tissue thanks to the achievable high resolution and ability to prevent tissue damage. In a previous study, suitable process parameters were obtained to achieve competitive ablation rates on pork femur processing. Nevertheless, a better control of thermal accumulation in the tissue during laser ablation could further improve the postoperative regeneration of the treated bone compared with conventional procedures and push forward the exploitation of such technology. This study presents methods for real time analyses of bone tissue temperature and composition during fs laser ablation and highlights the importance of implementing an efficient cooling method of bone tissue in order to achieve optimized results. Results show that it is possible to achieve a larger process window for bone tissue ablation where bone tissue temperature remains within the protein denaturation temperature in water-based processing environment. This is a key outcome towards a clinical exploitation of the presented technology, where higher process throughputs are necessary. The effects of process parameters and environments on bone tissue were confirmed by LIBS technique, which proved to be an efficient method by which to record real-time variation of bone tissue composition during laser irradiation.

Evolution between bright and dark pulses in a MoxW1-xTe2 based fiber laser

We proposed an erbium-doped fiber laser mode-locked with a MoxW1-xTe2-based nonlinear optical modulator for the first time to our best knowledge. This fiber laser can deliver bright pulses, bright-dark pulse pairs, dark pulses, bright-dark-bright pulses, and dark-dark-bright pulses. The modulation depth and saturation intensity of the MoxW1-xTe2-based saturable absorber were about 7.8% and 8.6 MW/cm2, respectively. When 10% of the laser in the cavity was output, conventional soliton pulses with central wavelength of 1560.1 nm can be obtained in the cavity. When 70% of the laser was output, dual-wavelength domain-wall dark pulses appeared in the laser cavity. This experiment revealed that an appropriate increase in the ratio of output energy can improve the chance of dark pulses in fiber lasers. The mode-locking states in this fiber laser can evolve with each other between bright pulses, bright-dark pulse pairs and dark pulses by adjusting the polarization controller. The results indicated that the MoxW1-xTe2 can be used to make modulators for generating dark pulses. Furthermore, our work will be of great help to improve the chance of the generation of dark pulse in fiber lasers.

Bone Laser Patterning to Decipher Cell Organization

The laser patterning of implant materials for bone tissue engineering purposes has proven to be a promising technique for controlling cell properties such as adhesion or differentiation, resulting in enhanced osteointegration. However, the possibility of patterning the bone tissue side interface to generate microstructure effects has never been investigated. In the present study, three different laser-generated patterns were machined on the bone surface with the aim of identifying the best surface morphology compatible with osteogenic-related cell recolonization. The laser-patterned bone tissue was characterized by scanning electron microscopy and confocal microscopy in order to obtain a comprehensive picture of the bone surface morphology. The cortical bone patterning impact on cell compatibility and cytoskeleton rearrangement on the patterned surfaces was assessed using Stromal Cells from the Apical Papilla (SCAPs). The results indicated that laser machining had no detrimental effect on consecutively seeded cell metabolism. Orientation assays revealed that patterns with larger hatch distances were correlated with higher cell cytoskeletal conformation to the laser-machined patterns. To the best of our knowledge, this study is the first to consider and evaluate bone as a biological interface that can be engineered for improvement. Further investigations should focus on the in vivo implications of this direct patterning.

Orthopedics-Related Applications of Ultrafast Laser and Its Recent Advances

The potential of ultrafast lasers (pico- to femtosecond) in orthopedics-related procedures has been studied extensively for clinical adoption. As compared to conventional laser systems with continuous wave or longer wave pulse, ultrafast lasers provide advantages such as higher precision and minimal collateral thermal damages. Translation to surgical applications in the clinic has been restrained by limitations of material removal rate and pulse average power, whereas the use in surface texturing of implants has become more refined to greatly improve bioactivation and osteointegration within bone matrices. With recent advances, we review the advantages and limitations of ultrafast lasers, specifically in orthopedic bone ablation as well as bone implant laser texturing, and consider the difficulties encountered within orthopedic surgical applications where ultrafast lasers could provide a benefit. We conclude by proposing our perspectives on applications where ultrafast lasers could be of advantage, specifically due to the non-thermal nature of ablation and control of cutting.

Preliminary study on the osseointegration effects of contactless automated implant cavity preparation via femtosecond laser ablation

Microrobots were used to control the femtosecond laser ablation of bone tissues to prepare implant cavities for dental implant surgery. The method was optimized through depth-of-cut experiments of ex vivo rabbit femurs, and the optimized method was used to prepare implant cavities on the left femurs of eight live rabbits. A power of 10 W and a scanning rate of 4000 mm/s were found to be optimal. After seven days of osteoinduction, the expression of collagen type I was significantly higher in the experimental group than in the control group (manually drilled implant cavities). The bone-implant contacts of the experimental group at 4 and 8 weeks were 9.65% and 23.08%, respectively.

Ablation of Bone Tissue by Femtosecond Laser: A Path to High-Resolution Bone Surgery

Femtosecond lasers allow for high-precision, high-quality ablation of biological tissues thanks to their capability of minimizing the thermal loads into the irradiated material. Nevertheless, reported ablation rates remain still too limited to enable their exploitation on a clinical level. This study demonstrates the possibility to upscale the process of fs laser ablation of bone tissue by employing industrially available fs laser sources. A comprehensive parametric study is presented in order to optimize the bone tissue ablation rate while maintaining the tissue health by avoiding excessive thermal loads. Three different absorption regimes are investigated by employing fs laser sources at 1030 nm, 515 nm and 343 nm. The main differences in the three different wavelength regimes are discussed by comparing the evolution of the ablation rate and the calcination degree of the laser ablated tissue. The maximum of the ablation rate is obtained in the visible regime of absorption where a maximum value of 0.66 mm³/s is obtained on a non-calcined tissue for the lowest laser repetition rate and the lowest spatial overlap between successive laser pulses. In this regime, the hemoglobin present in the fresh bone tissue is the main chromophore involved in the absorption process. To the best of our knowledge, this is the highest ablation rate obtained on porcine femur upon fs laser ablation.