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Photobiomodulation (PBM) describes light-induced photochemical reactions achieved by the application of red or near infrared lasers/LED light with low energy densities. This noninvasive and painless method has been used in some clinical areas but controversial outcomes demand a skeptical look for its promising and potential effects. In this detailed in vitro study, the osteoblast cells were irradiated with 635 and 809 nm diode lasers at energy densities of 0.5, 1, and 2 J/cm. Cell viability, proliferation, bone formation, and osteoblast differentiation were evaluated by methylthiazole tetrazolium (MTT) assay, Alamar Blue assay, acridine orange/propidium iodide staining, alkaline phosphatase (ALP) activity, Alizarin red staining, and reverse-transcription polymerase chain reaction (RT-PCR) to test the expression of collagen type I, ALPL, and osteocalcin. The results indicate that studied energy doses have a transient effect (48 h after laser irradiation) on the osteoblast viability and proliferation. Similarly, laser irradiation did not appear to have any effect on ALP activity. These results were confirmed by RT-PCR analysis of osteoblast markers. This study suggests that several irradiation parameters and variations in the methods should be clearly established in the laboratory before laser treatment becomes a postulated application for bone tissue regeneration in clinical level.

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A one-step synthesis strategy based on aza-Michael reaction of poly(ethylene glycol) diacrylate (PEGDA) or PEGDA/1,6-hexanediol diacrylate (HDDA) mixture and cystamine was employed to fabricate injectable, biocompatible and degradable novel poly(-amino ester) (PBAE) hydrogels.The gelation was monitored by real-time dynamic rheological measurements in order to follow formation of the PBAE hydrogel networks. The obtained hydrogels were responsive to both pH and redox state which enabled the control of swelling, degradation and release properties by external triggers. Degradation products of the hydrogels were shown to have no significant cytotoxicity on A549 adenocarcinomic human alveolar basal epithelial cells and MCF-7 human breast cancer cells. The hydrogels were loaded with a photosensitizer, methylene blue (MB), as a model compound by simply adding the MB molecules into the precursor mixture. The activity of released MB was assessed by in vitro photodynamic therapy (PDT) studies conducted with A549 cells.