This is a collaborative research program that brings together an optical technology group (Dr. Xu) and an in vivo imaging group (Dr. Lin). The two groups share a common goal to develop imaging technology for solving biomedical problems and addressing clinical needs. Here we focus on the need to improve hematopoietic stem cell (HSC) homing and engraftment after HSC transplantation (HSCT). This life-saving procedure is often the last hope of cure for patients with cancers of the blood system such as leukemia or lymphoma, but successful transplantation can be achieved only if a sufficient number of transplanted HSCs are able to reach and engraft the patient's bone marrow (BM). To help improve stem cell homing and engraftment, the Lin group has developed intravital imaging methods to track individual HSCs in the BM of live animals after transplantation. However, the current view of the BM microenvironment is severely limited due to the inadequacies of the available imaging technology. To gain a more comprehensive view of the BM microenvironment, where multiple cell types interact and form a supportive niche for HSC engraftment, the Xu group will develop a novel fiber-based source for nonlinear microscopy, which will enable simultaneous imaging of multiple fluorescent indicators as well as enabling label-free harmonic generation and vibrational imaging. Integration of the new source with the intravital microscope will enable the Lin group to proceed with experiments that had been envisioned but were held back due to lack of a suitable technology. The proposed source is based on the following innovations: (1) Soliton self-frequency shift (SSFS) in a large mode area (LMA) fiber enables the generation of energetic, widely wavelength tunable soliton pulses seeded from a fiber laser at the telecom wavelength, and the subsequent second harmonic generation (SHG) of the fundamental wavelength enables a single turn-key, low-cost, fiber-based source to generate three independent wavelength tunable sources to excite multiple fluorophores. 2) All-fiber, high-speed intensity modulation to electronically control the wavelength, repetition rate, and pulse delay. 3) A single light source will enable experiments that currently require two synchronized Ti:sapphire lasers plus an optical parametric oscillator (OPO) and a regenerative amplifier. Leveraging the highly mature and integrated techniques that have been developed for the telecommunications industry, we aim to create a """"""""telecom grade"""""""" femtosecond source that is truly robust and versatile. The versatility is important for tailoring the source to meet specific imaging needs while the robustness is essential for the biological studies that require longitudinal imaging of large cohorts of animals. The successful completion of this program will not only advance imaging technology but also advance stem cell research. In addition, the technology will be broadly applicable and will significantly increase the accessibility of femtosecond sources to other biomedical researchers.
The proposed program, if successfully completed, will lead to a novel, fiber-based 3-color femtosecond source that will have a broad impact on biomedical applications of ultrafast technologies. It opens the opportunity for simultaneous excitation of multiphoton fluorescent markers for in vivo tissue imaging. By applying this novel laser source to address critical biomedical imaging needs, our program will not only mark a significant advancement in ultrafast technology but also provide new insight on ways to improve hematopoietic stem cell transplants.
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