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Mesenchymal stem cell therapies show great promise in regenerative medicine. However, to generate clinically relevant numbers of these stem cells, significant in vitro expansion of the cells is required before transplantation into the affected wound or defect. The current gold standard protocol for recovering in vitro cultured cells involves treatment with enzymes such as trypsin which can affect the cell phenotype and ability to interact with the environment. Alternative enzyme free methods of adherent cell recovery have been investigated, but none match the convenience and performance of enzymatic detachment. In this work we have developed a synthetically simple, low cost cell culture substrate functionalized with gold nanorods that can support cell proliferation and detachment. When these nanorods are irradiated with biocompatible low intensity near infrared radiation (785 nm, 560 mWcm-2) they generate localized surface plasmon resonance induced nanoscale heating effects which trigger detachment of adherent mesenchymal stem cells. Through simulations and thermometry experiments we show that this localized heating is concentrated at the cell-nanorod interface, and that the stem cells detached using this technique show either similar or improved multipotency, viability and ability to differentiate into clinically desirable osteo and adipocytes, compared to enzymatically harvested cells. This proof-of-principle work shows that photothermally mediated cell detachment is a promising method for recovering mesenchymal stem cells from in vitro culture substrates, and paves the way for further studies to scale up this process and facilitate its clinical translation. STATEMENT OF SIGNIFICANCE: New non-enzymatic methods of harvesting adherent cells without damaging or killing them are highly desirable in fields such as regenerative medicine. Here, we present a synthetically simple, non-toxic, infra-red induced method of harvesting mesenchymal stem cells from gold nanorod functionalized substrates. The detached cells retain their ability to differentiate into therapeutically valuable osteo and adipocytes. This work represents a significant improvement on similar cell harvesting studies due to: its simplicity; the use of clinically valuable stem cells as oppose to immortalized cell lines; and the extensive cellular characterization performed. Understanding, not just if cells live or die but how they proliferate and differentiate after photothermal detachment will be essential for the translation of this and similar techniques into commercial devices.

The use of biomaterials to direct osteogenic differentiation of human mesenchymal stem cells (hMSCs) in the absence of osteogenic supplements is thought to be part of the next generation of orthopedic implants. We previously engineered surface-roughness gradients of average roughness (Ra) varying from the sub-micron to the micrometer range ( 0.5–4.7 lm), and mean distance between peaks (RSm) gradually varying from 214 lm to 33 lm. Here we have screened the ability of such surface-gradients of polycaprolactone to influence the expression of alkaline phosphatase (ALP), collagen type 1 (COL1) and mineralization by hMSCs cultured in dexamethasone (Dex)-deprived osteogenic induction medium (OIM) and in basal growth medium (BGM). Ra 1.53 lm/RSm 79 lm in Dex-deprived OI medium, and Ra 0.93 lm/RSm 135 lm in BGM consistently showed higher effectiveness at supporting the expression of the osteogenic markers ALP, COL1 and mineralization, compared to the tissue culture polystyrene (TCP) control in complete OIM. The superior effectiveness of specific surface-roughness revealed that this strategy may be used as a compelling alternative to soluble osteogenic inducers in orthopedic applications featuring the clinically relevant biodegradable polymer polycaprolactone., This work was supported by the Foundation for Science and Technology for the PhD Grant of A.B. Faia-Torres (SFRH/BD/36476/2007). We are also grateful to the Swiss National Science Foundation (SNSF) Grant P300P3_154664 for providing funds to MC.