the fast - acting insulin analog aspart ( novorapid ; novo nordisk a / s , baegsvard , denmark ) was administered with a flexpen with an 8-mm pen needle ( novofine 30 g ; novo nordisk ) ex vivo and in vivo by a trained study nurse . insulin was administered either as a single bolus of 18 iu or as nine boluses of 2 iu each in a predefined 10-mm grid pattern ( fig . to assess the dosing accuracy of each insulin pen used in the study , two insulin doses were injected into vials with both application strategies ( 1  18 iu and 9  2 iu ) , and then each dose was weighed with a microbalance ( sartorius , gttingen , germany ) . in total , 36 insulin pens were used ( 3 per subject to allow insulin injection within 1 min for the dispersed injection strategy ) . injected insulin weights were the same for the two injection strategies ( 18.3  0.4 g for 1  18 iu vs. 18.3  0.3 g for 9  2 iu ) . a : individual injection sites for the dispersed injection strategy ( 9  2 iu ) were separated by 10 mm . c : mean surface - to - volume ratios comparing two injection strategies ( 1  18 iu vs. 9  2 iu ) . * * p < 0.01 . the ex vivo micro - ct experiment was performed to compare the surface - to - volume ratio of the two injection strategies before their use in the in vivo clamp study . the two injection strategies were applied to explanted abdominal skin flaps ; surface and volume of each resulting subcutaneous liquid depot were measured with micro - ct . to enhance the contrast between the liquid depots and the surrounding adipose tissue , 10% ( by weight ) of the insulin aspart solution in the flexpen was replaced with a contrast agent ( iopamiro , iodine 200 mg / ml ; bracco s.p.a . , the contrast agent was selected for its high iodine content and low viscosity , providing good contrast enhancement at minimal viscosity changes of the insulin solution . twelve abdominal skin flaps with a minimal size of 50  50 mm and at least 20 mm of subcutaneous adipose tissue were collected from biobank ( medical university of graz , austria ) . the time span between explantation and injection of the insulin / contrast agent solution never exceeded 5 h. during this time , skin flaps were kept at room temperature . immediately after injection of the insulin and contrast agent solution , skin flaps were scanned with a micro - ct scanner ( inveon multimodality system , siemens , germany ) with siemens inveon acquisition workplace software ( version 1.2.2.2 ) . to optimize contrast , acquisition time , and resolution , the scanning sequence was set to a voltage of 50 kv , a current of 300 a , and an exposure time of 500 ms . a rotation of 210 in 180 rotation steps led to a resolution with an effective pixel size of 53 m . for three - dimensional ( 3d ) image reconstruction , the system supports a 3d reconstruction of an acquired data set of two - dimensional projections by using back projection of a filtered projection algorithm . the volume of interest was selected by a region - growing algorithm , with a spot of high intensity selected manually as a starting point . regions with decreasing levels of intensity were added to the volume of interest until the predefined injection volume ( 180  1.8 l ) was reached . the surface of the selected volume of interest was calculated for both injection strategies ( 1  18 iu and 9  2 iu ) ( fig . a monocentric , randomized , controlled , two - period crossover euglycemic clamp study was performed in 12 type 1 diabetic patients at the clinical research centre at the medical university of graz between april and june 2011 . the study was approved by the local ethics committee and performed in accordance with the declaration of helsinki and the principles of good clinical practice . participants gave written , informed consent after the purpose , nature , and potential risks of the study had been explained and before any study - related activities were started . participants had to fulfill all inclusion criteria ( fasting c - peptide < 0.3 nmol / l ; bmi 20.028.0 kg / m ; hemoglobin a1c < 10% ) and none of the exclusion criteria ( i.e. , insulin aspart use , lipodystrophy , smoking ) . the study consisted of four visits : one screening visit , two clamp visits separated by a washout phase of 521 days , and one follow - up visit . to avoid any residual action of their regular insulin regimens , participants were instructed to follow a specific regimen : participants on multiple daily injections administered their last dose of short - acting insulin at least 5 h before the clamp visit . participants on long - acting insulin analogs were transferred to nph insulin 2 days before the clamp visit and received the last injection of nph insulin 20 h before the clamp visit . participants on continuous subcutaneous insulin infusion stopped their insulin infusion at least 5 h before the clamp visit . participants attended the research facility under fasting conditions and remained fasting throughout each clamp visit . one 18-gauge venous catheter was inserted in each arm : one was used for insulin and glucose infusion ; the other was used for blood sampling . the arm used for blood sampling was put under a heating blanket at 55c to obtain arterialized venous blood . the euglycemic clamp procedure was started by using a variable intravenous human insulin infusion ( actrapid ; novo nordisk ) or glucose infusion to obtain a stable plasma glucose ( target 5.5  1.1 mmol / l ) during the run - in period ( 37 h ) . during the last hour of the run - in period , the insulin infusion was tapered and finally switched off . at time 0 ( between 11 a.m. and 2 p.m. ) , a dose of 18 iu insulin aspart was injected into the subcutaneous adipose tissue of the abdominal wall . the insulin dose was administered either as 1  18 iu or as 9  2 iu . on arrival , the participant number was entered into the computer program randomizer , which assigned the participant randomly to one of the injection strategies . the dosing sequence was also randomly assigned by using randomizer according to parameters provided by the institute for medical informatics , statistics and documentation ( medical university of graz ) . for the 9  2 iu injection strategy , where administration took < 1 min , a transparent grid was used that separated the individual injection sites from each other by exactly 10 mm ( fig . mmol / l for 8 h after the insulin bolus administration or until plasma glucose rose above 200 mg / dl . euglycemia was maintained by variable glucose infusion ( glucose 10% ; fresenius kabi , bad homburg , germany ) , which was administered with a perfusion pump ( b. braun , melsungen , germany ) . arterialized venous blood samples were drawn in 5- to 10-min intervals throughout the euglycemic clamp . plasma glucose was measured in duplicate on site with a super gl 2 glucose analyzer ( mller gertebau , freital , germany ) . plasma samples for insulin determination were taken at baseline ( 0 min ) , every 5 min up to 120 min , every 15 min from 120 to 180 min , every 30 min from 180 to 240 min , and then at 60-min intervals until study end ( 480 min ) . plasma samples for insulin determination were deep frozen on site , and insulin measurements were subsequently performed at the laboratories of novo nordisk a / s ( maaloev , denmark ) by means of a homogenous immunoassay with analog - specific antibody for aspart determination . primary pharmacokinetic and secondary pharmacodynamic study end points were derived from insulin concentration profile and exogenous glucose infusion rate ( gir ) . pharmacokinetic data included time to maximum insulin concentration , times to 10% and 50% of maximum insulin concentration , and maximum insulin concentration . pharmacodynamic data included time to maximum gir , times to 10% and 50% of maximum gir , and maximum gir . area under the curve ( auc ) was calculated for insulin concentration and gir up to 480 min after insulin administration and for the time to reach maximum insulin concentration and maximum gir . the paired measurements were analyzed with paired t tests or wilcoxon signed rank tests , depending on whether the paired differences were normally distributed . the unpaired measurements from the micro - ct experiment were analyzed with mann - whitney u tests . bonferroni corrections were used to correct for multiple testing of the pharmacokinetic and pharmacodynamic results . unless otherwise specified , data are reported as mean  sd . the fast - acting insulin analog aspart ( novorapid ; novo nordisk a / s , baegsvard , denmark ) was administered with a flexpen with an 8-mm pen needle ( novofine 30 g ; novo nordisk ) ex vivo and in vivo by a trained study nurse . insulin was administered either as a single bolus of 18 iu or as nine boluses of 2 iu each in a predefined 10-mm grid pattern ( fig . to assess the dosing accuracy of each insulin pen used in the study , two insulin doses were injected into vials with both application strategies ( 1  18 iu and 9  2 iu ) , and then each dose was weighed with a microbalance ( sartorius , gttingen , germany ) . in total , 36 insulin pens were used ( 3 per subject to allow insulin injection within 1 min for the dispersed injection strategy ) . injected insulin weights were the same for the two injection strategies ( 18.3  0.4 g for 1  18 iu vs. 18.3  0.3 g for 9  2 iu ) . a : individual injection sites for the dispersed injection strategy ( 9  2 iu ) were separated by 10 mm . c : mean surface - to - volume ratios comparing two injection strategies ( 1  18 iu vs. 9  2 iu ) . * * p < 0.01 . the ex vivo micro - ct experiment was performed to compare the surface - to - volume ratio of the two injection strategies before their use in the in vivo clamp study . the two injection strategies were applied to explanted abdominal skin flaps ; surface and volume of each resulting subcutaneous liquid depot were measured with micro - ct . to enhance the contrast between the liquid depots and the surrounding adipose tissue , 10% ( by weight ) of the insulin aspart solution in the flexpen was replaced with a contrast agent ( iopamiro , iodine 200 mg / ml ; bracco s.p.a . , the contrast agent was selected for its high iodine content and low viscosity , providing good contrast enhancement at minimal viscosity changes of the insulin solution . twelve abdominal skin flaps with a minimal size of 50  50 mm and at least 20 mm of subcutaneous adipose tissue were collected from biobank ( medical university of graz , austria ) . the time span between explantation and injection of the insulin / contrast agent solution never exceeded 5 h. during this time , skin flaps were kept at room temperature . immediately after injection of the insulin and contrast agent solution , skin flaps were scanned with a micro - ct scanner ( inveon multimodality system , siemens , germany ) with siemens inveon acquisition workplace software ( version 1.2.2.2 ) . to optimize contrast , acquisition time , and resolution , the scanning sequence was set to a voltage of 50 kv , a current of 300 a , and an exposure time of 500 ms . a rotation of 210 in 180 rotation steps led to a resolution with an effective pixel size of 53 m . for three - dimensional ( 3d ) image reconstruction , a downsample factor of 1 the system supports a 3d reconstruction of an acquired data set of two - dimensional projections by using back projection of a filtered projection algorithm . the volume of interest was selected by a region - growing algorithm , with a spot of high intensity selected manually as a starting point . regions with decreasing levels of intensity were added to the volume of interest until the predefined injection volume ( 180  1.8 l ) was reached . the surface of the selected volume of interest was calculated for both injection strategies ( 1  18 iu and 9  2 iu ) ( fig . a monocentric , randomized , controlled , two - period crossover euglycemic clamp study was performed in 12 type 1 diabetic patients at the clinical research centre at the medical university of graz between april and june 2011 . the study was approved by the local ethics committee and performed in accordance with the declaration of helsinki and the principles of good clinical practice . participants gave written , informed consent after the purpose , nature , and potential risks of the study had been explained and before any study - related activities were started . participants had to fulfill all inclusion criteria ( fasting c - peptide < 0.3 nmol / l ; bmi 20.028.0 kg / m ; hemoglobin a1c < 10% ) and none of the exclusion criteria ( i.e. , insulin aspart use , lipodystrophy , smoking ) . the study consisted of four visits : one screening visit , two clamp visits separated by a washout phase of 521 days , and one follow - up visit . to avoid any residual action of their regular insulin regimens , participants were instructed to follow a specific regimen : participants on multiple daily injections administered their last dose of short - acting insulin at least 5 h before the clamp visit . participants on long - acting insulin analogs were transferred to nph insulin 2 days before the clamp visit and received the last injection of nph insulin 20 h before the clamp visit . participants on continuous subcutaneous insulin infusion stopped their insulin infusion at least 5 h before the clamp visit . participants attended the research facility under fasting conditions and remained fasting throughout each clamp visit . one 18-gauge venous catheter was inserted in each arm : one was used for insulin and glucose infusion ; the other was used for blood sampling . the arm used for blood sampling was put under a heating blanket at 55c to obtain arterialized venous blood . the euglycemic clamp procedure was started by using a variable intravenous human insulin infusion ( actrapid ; novo nordisk ) or glucose infusion to obtain a stable plasma glucose ( target 5.5  1.1 mmol / l ) during the run - in period ( 37 h ) . during the last hour of the run - in period , the insulin infusion was tapered and finally switched off . at time 0 ( between 11 a.m. and 2 p.m. ) , a dose of 18 iu insulin aspart was injected into the subcutaneous adipose tissue of the abdominal wall . the insulin dose was administered either as 1  18 iu or as 9  2 iu . on arrival , the participant number was entered into the computer program randomizer , which assigned the participant randomly to one of the injection strategies . the dosing sequence was also randomly assigned by using randomizer according to parameters provided by the institute for medical informatics , statistics and documentation ( medical university of graz ) . for the 9  2 iu injection strategy , where administration took < 1 min , a transparent grid was used that separated the individual injection sites from each other by exactly 10 mm ( fig . mmol / l for 8 h after the insulin bolus administration or until plasma glucose rose above 200 mg / dl . euglycemia was maintained by variable glucose infusion ( glucose 10% ; fresenius kabi , bad homburg , germany ) , which was administered with a perfusion pump ( b. braun , melsungen , germany ) . arterialized venous blood samples were drawn in 5- to 10-min intervals throughout the euglycemic clamp . plasma glucose was measured in duplicate on site with a super gl 2 glucose analyzer ( mller gertebau , freital , germany ) . plasma samples for insulin determination were taken at baseline ( 0 min ) , every 5 min up to 120 min , every 15 min from 120 to 180 min , every 30 min from 180 to 240 min , and then at 60-min intervals until study end ( 480 min ) . plasma samples for insulin determination were deep frozen on site , and insulin measurements were subsequently performed at the laboratories of novo nordisk a / s ( maaloev , denmark ) by means of a homogenous immunoassay with analog - specific antibody for aspart determination . primary pharmacokinetic and secondary pharmacodynamic study end points were derived from insulin concentration profile and exogenous glucose infusion rate ( gir ) . pharmacokinetic data included time to maximum insulin concentration , times to 10% and 50% of maximum insulin concentration , and maximum insulin concentration . pharmacodynamic data included time to maximum gir , times to 10% and 50% of maximum gir , and maximum gir . area under the curve ( auc ) was calculated for insulin concentration and gir up to 480 min after insulin administration and for the time to reach maximum insulin concentration and maximum gir . the paired measurements were analyzed with paired t tests or wilcoxon signed rank tests , depending on whether the paired differences were normally distributed . the unpaired measurements from the micro - ct experiment were analyzed with mann - whitney u tests . bonferroni corrections were used to correct for multiple testing of the pharmacokinetic and pharmacodynamic results . unless otherwise specified , data are reported as mean  sd . to directly compare the calculated surface - to - volume ratios of the subcutaneous insulin depots with each other , the two injection strategies ( 1  18 iu and 9  2 iu ) were applied with the same total volume . although the measured mean volume of the dispersed injection strategy was thus similar to that of the single injection strategy ( 179.6  0.96 mm vs. 180.6  0.70 mm ) , the mean surface of the dispersed injection strategy was significantly larger than the single injection surface ( 703.6  83.8 mm vs. 396.6  101.1 mm ; p < 0.01 ) . the dispersed injection strategy thus enhanced the surface - to - volume ratio by a factor of 1.8 ( 3.9  0.48 vs. 2.2  0.57 ; p < 0.01 ) , which is in line with the expected increase in surface calculated from geometric analysis according to the assumption of spherical liquid depots ( fig . 1c ) . we included 12 c - peptide  negative type 1 diabetic patients ( age 32  9 years ; 6 females ; bmi 23.9  2.5 kg / m ; hemoglobin a1c 7.3  0.6% ; diabetes duration 19  10 years ) . all participants completed both clamp visits , no clinically relevant adverse events were observed , and all collected data were used for subsequent statistical analysis . time to reach maximum insulin concentration was shorter for 9  2 iu , although the differences were only significant for the time to reach 10% ( p < 0.03 ) and 50% ( p < 0.001 ) of the maximum insulin concentrations ( fig . pharmacokinetic and pharmacodynamic parameters for the two injection strategies a : mean insulin curve for 9  2 iu (  ) and 1  18 iu (  ) injections of insulin aspart . b : mean glucose infusion rate curve for 9  2 iu ( solid line ) and 1  18 iu ( dashed line ) injections of insulin aspart . the time to reach maximum gir was almost 50% shorter for 9  2 iu than for 1  18 iu ( table 1 ) . the times taken to reach 10% and 50% of maximum gir were still significantly lower for the dispersed injection strategy ( fig . 2b ) , whereas the concentrations at maximum insulin action were similar for both injection strategies . individual gir data for times to reach 10% of maximum gir , 50% of maximum gir , and maximum gir are indicated in fig . the auc for glucose was significantly larger for 9  2 iu during the first 60 min , whereas the auc until time of maximum gir was smaller for 9  2 iu ( table 1 ) . individual gir profile data showing time to 10% of maximum gir ( a ) , time to 50% of maximum gir ( b ) , time to maximum gir ( c ) . horizontal bars indicate means for the 1  18 iu and 9  2 iu injection strategies . to directly compare the calculated surface - to - volume ratios of the subcutaneous insulin depots with each other , the two injection strategies ( 1  18 iu and 9  2 iu ) were applied with the same total volume . although the measured mean volume of the dispersed injection strategy was thus similar to that of the single injection strategy ( 179.6  0.96 mm vs. 180.6  0.70 mm ) , the mean surface of the dispersed injection strategy was significantly larger than the single injection surface ( 703.6  83.8 mm vs. 396.6  101.1 mm ; p < 0.01 ) . the dispersed injection strategy thus enhanced the surface - to - volume ratio by a factor of 1.8 ( 3.9  0.48 vs. 2.2  0.57 ; p < 0.01 ) , which is in line with the expected increase in surface calculated from geometric analysis according to the assumption of spherical liquid depots ( fig . 1c ) . we included 12 c - peptide  negative type 1 diabetic patients ( age 32  9 years ; 6 females ; bmi 23.9  2.5 kg / m ; hemoglobin a1c 7.3  0.6% ; diabetes duration 19  10 years ) . all participants completed both clamp visits , no clinically relevant adverse events were observed , and all collected data were used for subsequent statistical analysis . time to reach maximum insulin concentration was shorter for 9  2 iu , although the differences were only significant for the time to reach 10% ( p < 0.03 ) and 50% ( p < 0.001 ) of the maximum insulin concentrations ( fig . pharmacokinetic and pharmacodynamic parameters for the two injection strategies a : mean insulin curve for 9  2 iu (  ) and 1  18 iu (  ) injections of insulin aspart . b : mean glucose infusion rate curve for 9  2 iu ( solid line ) and 1  18 iu ( dashed line ) injections of insulin aspart . the time to reach maximum gir was almost 50% shorter for 9  2 iu than for 1  18 iu ( table 1 ) . the times taken to reach 10% and 50% of maximum gir were still significantly lower for the dispersed injection strategy ( fig . 2b ) , whereas the concentrations at maximum insulin action were similar for both injection strategies . individual gir data for times to reach 10% of maximum gir , 50% of maximum gir , and maximum gir are indicated in fig . the auc for glucose was significantly larger for 9  2 iu during the first 60 min , whereas the auc until time of maximum gir was smaller for 9  2 iu ( table 1 ) . individual gir profile data showing time to 10% of maximum gir ( a ) , time to 50% of maximum gir ( b ) , time to maximum gir ( c ) . horizontal bars indicate means for the 1  18 iu and 9  2 iu injection strategies . although fast - acting insulin analogs are designed for a more rapid absorption into the vascular system , it is still difficult to achieve a physiological insulin profile . to accelerate insulin absorption of the fast - acting insulin aspart , we tested whether a dispersed injection strategy would affect insulin absorption in comparison with a regular single - bolus insulin injection by using ex vivo micro - ct in explanted abdominal skin flaps and by assessing pharmacokinetic and pharmacodynamic parameters in vivo in a euglycemic clamp study in type 1 diabetic patients . liquid depots with a higher surface - to - volume ratio can be absorbed faster , because a larger depot surface involves more capillaries and enhances absorption into the vascular system . enhanced drug absorption with increased surface - to - volume ratio has been demonstrated in a canine model ( 14 ) , and in humans an increased volume slowed the speed of pharmacokinetics in large versus small skin blisters ( 15 ) . by using micro - ct , a nondestructive 3d imaging technique , we were able to compare quantitatively the surface - to - volume ratio of subcutaneous insulin depots of a dispersed injection strategy ( 9  2 iu ) with that of a single insulin injection ( 1  18 iu ) . for the dispersed injection strategy , we found a 1.8-fold higher surface - to - volume ratio , which is in line with theoretical calculations from spherical liquid depots . a recently developed technology for morphometric tissue analysis , micro - ct is mainly used in bone and dental structure analysis ( 1618 ) . in combination with a ct contrast agent , micro - ct provided excellent resolution , fast analysis , and exact semiautomated volume and surface calculations for each individual insulin depot . because micro - ct measurements require no tissue fixation and only minimal tissue manipulation , we were able to assess unaltered samples that closely matched in vivo conditions immediately after insulin injection . insulin pharmacokinetic and pharmacodynamic data collected during the clinical trial in type 1 diabetic patients supported the micro - ct findings . the lag time between insulin injection and insulin appearance in blood plasma was significantly reduced when the fast - acting insulin aspart was administered with a dispersed injection strategy . other approaches to accelerate insulin absorption , such as the use of hyaluronidase to facilitate the dissociation of insulin hexamers into more easily absorbed monomers and dimers , have also been associated with faster insulin absorption and an earlier onset of insulin action ( 12,19 ) . adding hyaluronidase to a fast - acting insulin analog reduced time to reach maximum insulin concentration by 51% ( 19 ) and resulted in an even more pronounced effect in comparison with our dispersed injection strategy ( 15% ) . the decrease in the time to reach 50% of maximum insulin concentrations with the dispersed injection strategy ( 29% ) was comparable with the hastening of the onset of insulin action by adding hyaluronidase ( 34% ) . application of local heating to the injection site , which locally increases the blood flow , has also been demonstrated to result in an accelerated insulin absorption and more rapid onset of insulin action ( 9 ) . heating the injection site reduced time to maximum insulin concentration by 42% and time to 50% of maximum insulin concentration by 29% . the very similar twice as fast onset of insulin action of a dispersed insulin bolus is most likely caused by an increase in the number of capillaries involved in the absorption of insulin into the vascular system , comparable with the effect of intradermal injections with microneedles that access a more dense capillary network ( 20 ) . in a study that compared insulin injection of a fast - acting insulin analog using a jet injector , time to maximum insulin concentration and insulin action this was attributed to a cone - like dispersion pattern with a large surface area caused by the jet injector , as described earlier by mitragotri et al . use of the dispersed injection strategy not only reduced the lag time but also improved all other pharmacokinetic parameters during the first 60 min after insulin injection . the shorter duration of insulin action can contribute to reduced late postprandial hypoglycemia , which occurs when the carbohydrate content of a meal is already consumed but insulin action is still present . although pharmacokinetic data are important for the development of new insulin analogs , pharmacodynamic results from glucose infusion rates provide relevant data for more efficient glycemic control . in our in vivo clamp study in type 1 diabetic patients , the time to reach maximum gir was almost halved when the insulin bolus was evenly dispersed among nine injection sites compared with a single injection site , indicating a much faster onset of insulin action . in combination with fast - acting insulin analogs , the effect of a dispersed injection strategy can lead to a clinically relevant improvement of glycemic control . although we have shown that multiple injection sites significantly accelerate the absorption of a fast - acting insulin analog , the simultaneous injection of multiple small boluses is not feasible for routine diabetes care . the use of a sprinkler needle concept is one way to translate our findings into a technology acceptable for patients . enhanced absorption of human insulin with flatter blood glucose profiles and less pronounced blood glucose peaks has been found with the sprinkler needle relative to a regular injection needle ( 13 ) . although the lag time between insulin injection and insulin appearance is already reduced in fast - acting insulin analogs , an earlier onset of insulin action would enable diabetic patients to inject insulin regularly after meals without having to take into account the delayed action of currently available insulins . this would be of considerable benefit for glycemic control in pediatric diabetic patients , in whom the consumed carbohydrates and the resulting blood glucose are difficult to predict because of highly variable eating habits and activity levels ( 23 ) and in geriatric patients with varying levels of appetite depending on their health status . these patient populations always bear an increased risk of postprandial hypoglycemic events when applying premeal insulin boluses without complete consumption of the planned meal . maintenance of good glucose control in diabetic pregnancy is also essential to avoid adverse fetal outcomes , such as fetal growth acceleration ( 24,25 ) . glucose uptake , endogenous glucose production , and insulin requirements strongly vary throughout pregnancy . especially in late gestation of type 1 diabetic pregnancies , postprandial glucose control is difficult to manage because of slower glucose disposal ( 26 ) . faster insulin absorption can also promote the development of closed - loop artificial pancreas systems that use subcutaneous insulin administration and continuous glucose measurement . the substantial lag time between insulin administration and the onset of insulin action is a major obstacle for the development of algorithms that control closed - loop systems ( 27 ) . a shortened absorption time of fast - acting insulin analogs can lead to faster control algorithms , and a clinically feasible dispersed injection strategy would be a major step toward the successful implementation of fully closed - loop systems , which do not require a meal announcement followed by a priming bolus . in summary , this study confirmed acceleration of insulin absorption of a fast - acting insulin analog by using a dispersed insulin bolus . a clinically feasible dispersed injection strategy might better mimic physiological insulin profiles and contribute to improvements in glycemic control . to evaluate the implications for clinical outcomes , such as a reduction of late postprandial hypoglycemia , both reduction of glucose fluctuations and improvement in glycemic control need to be addressed in further clinical trials .
objectivewe investigated the impact of two different injection strategies on the pharmacokinetics and pharmacodynamics of insulin aspart in vivo in an open - label , two - period crossover study and verified changes in the surface - to - volume ratio ex vivo.research design and methodsbefore the clinical trial , insulin aspart was injected ex vivo into explanted human abdominal skin flaps . 
 the surface - to - volume ratio of the subcutaneous insulin depot was assessed by microfocus computed tomography that compared 1 bolus of 18 iu with 9 dispersed boluses of 2 iu . 
 these two injection strategies were then tested in vivo , in 12 c - peptide  negative type 1 diabetic patients in a euglycemic glucose clamp ( glucose target 5.5  1.1 mmol / l ) for 8 h after the first insulin administration.resultsthe ex vivo experiment showed a 1.8-fold higher mean surface - to - volume ratio for the dispersed injection strategy . 
 the maximum glucose infusion rates ( gir ) were similar for the two strategies ( 10  4 vs. 9  4 ; p = 0.5 ) ; however , times to reach maximum gir and 50% and 10% of the maximum gir were significantly reduced by using the 9  2 iu strategy ( 68  33 vs. 127  93 min ; p = 0.01 ; 38  9 vs. 49  16 min ; p < 0.01 ; 23  6 vs. 30  10 min ; p < 0.05 ) . for 9  2 iu , 
 the area under the gir curve was greater during the first 60 min ( 219  89 vs. 137  75 ; p < 0.01 ) and halved until maximum gir ( 242  183 vs. 501  396 ; p < 0.01 ) ; however , it was similar across the whole study period ( 1,361  469 vs. 1,565  527 ; p = 0.08).conclusionsa dispersed insulin injection strategy enhanced the effect of a fast - acting insulin analog . 
 the increased surface - to - volume ratio of the subcutaneous insulin depot can facilitate insulin absorption into the vascular system .