Table 1.

Overview of investigations carried out to assess the effects of various injection parameters on cell viability and functionality

Aim of study	Experimental design	Cell type	Syringe and needle	Flow rate(s) and other parameters	Brief description of results	Assays for assessment of cellular health				Refs.
						Viability	Apoptosis	Senescence	Others
Viability after cell transfusion: various needles and flow rates	In vitro	Bone marrow-derived mono-nuclear cells	Automatic injection pump and 16, 18, 22 G needles	1 and 0.5 mm/s	No difference detected in viability ratios	√	×	×	×	95
Changes in hMSCs by transcatheter injection	In vitro	hMSCs	1-mL syringe and 26 G (155 cm) Nitinol needle	400 or 1600 µL/min	Viability not affected by varying rate. Slightly altered gene expression, but effects not translated into significant differences in protein production	√	×	×	Clonogenicity, gene expression profile and cytokine secretion	29
Response after manipulation in narrow-bore syringe system	In vitro	Murine MSCs	10 μL syringes and 26, 25 or 22 G needles	Drawn up at 30 μL/min; ejected at 20, 5 and 1 μL/min; time within syringe	Needle bore size and time within the syringe affected viable cell density	√	√	×	Cell attachment and spreading	94
Effect of delivery via needles and catheters at multiple flow rates	In vitro	Rat and human MSCs	20, 25 and 30 G needles, and SL-10 microcatheter	60, 120, 240 and 500 mL/h	No significant effect on viability (>70%). Delayed drop in viability at 24 h. No change in cell surface markers or function	√	√	×	Immunophenotyping and multilineage differentiation	25
Small-bore size to deliver single/multiple cell injections	In vitro and in vivo (IV by tail vein injection)	hMSCs	24, 25 and 26 G needles and 1 mL syringe. Multiple injections (10×): 26 G needle and 1 mL syringe	2000 μL/min	26 G needles can be safely used. Multiple injections were non-detrimental to cells (kept functional characteristics)	√	×	√	Morphology, immunophenotyping, trilineage differentiation, in vivo migration	93
Impact of manual handling procedures	In vitro	Mouse ESC cell lines	20 mL syringes: one containing cell suspension, luer-locked to stainless steel capillary (500 µm D, 1 cm L)	Pass cells between syringes at 0.80 mL/s. Centrifugation: 300×g, 600×g and 1000×g.Inoculation cell density	Gentle cell handling and minimal variations in environmental conditions needed to maintain viability. Inoculation density and time exposed to ambient conditions impacted phenotype.	√	×	×	Phenotyping	73
Impact of injection parameters in automated delivery for the brain	In vitro	Neural progenitor cells and bone marrow stromal cells	Automated injection device; 250 µL syringes with 20 G and 27 G needles, 3.8 or 15.2 cm in length	Flow rate of 1 µL or 10 µL/s; initial acceleration rate of 42 or 208 µL/s2.Delay between loading and injection	Longer, thinner cannulas and greater cell concentrations were harmful for delivery	√	×	×	×	50
Effect of DMSO, cell density and needle size on viability in 3D hydrogels	In vitro	NIH-3T3 cells	27 G needle	—	Viability of cryopreserved cells was significantly lower than freshly collected cells. Needle significantly reduced cell survival rates. Higher DMSO concentration and cell density lowered survival	√	×	×	×	96
Effect of varying ejection rate, cell density and needle gauge on cell health	In vitro	NIH-3T3 cells	30 and 34 G needles attached to 100 µL syringes	Drawn up at 300 µL/min, and ejected at 20–300 µL/min controlled using a syringe pump	Ejections at 150 μL/min resulted in highest percentage of dose delivered. Difference in proportions of apoptotic cells 48 h post-ejection was higher at slower rates	√	√	√	Cytotoxicity	60
Investigation of cell suspensions in large injection cannulas oriented at various angles	In vitro	Primary rat embryonic cell suspensions of neural tissue	18, 21 and 25 G metal cannulas. Glass cannulaswith nominal ID of 0.8 mm. Cannulas attached via a short siliconetubing to a 100-µL Hamilton syringe	10 µL/min using a syringe pump. Delay of 20 mins between loading and injection	Cell behaviour was affected by cannula diameter, orientation (horizontal/vertical) and material	×	×	×	Mean cell counts	75
Effect of transcatheter injections on cell viability and cytokine release	In vitro	Mononuclear cells	Cell suspension was aspirated into a 5-mL syringe and then infused through a 25 G needle. Cells were passed through an Excelsior SL-10 catheter; Iodine and heparin exposure	0.5–5 mL/min	Flow rates from 0.5–2 mL/min did not alter viability, but 5 mL/min reduced viability by 19%. Catheter delivery at 2 mL/min did not affect VEGF, IL-10 or IGF-1 levels. Iodine and low-dose heparin did not affect viability, but high-dose heparin caused cell death	√	√	×	Cellular function was assessed by production and release of VEGF, IL-10 and IGF-1	118
Effect of ejection rate and needle gauge on cell health	In vitro	hMSCs	30 and 34 G needles attached to 100 µL syringes	Drawn up at 300 µL/min, and ejected at 10–300 µL/min using a syringe pump	300 μL/min resulted in highest viable cell recovery. Apoptosis levels at 10 µL/min were significantly higher than control. Downregulation of CD105 expression at 10 µL/min	√	√	√	Immunophenotyping, trilineage differentiation	74

CBF cerebral blood flow, G gauge, IV intravenous.