Animal studies for the evaluation of in situ tissue-engineered vascular grafts — a systematic review, evidence map, and meta-analysis

Vascular in situ tissue engineering (TE) is an approach that uses bioresorbable grafts to induce endogenous regeneration of damaged blood vessels. The evaluation of newly developed in situ TE vascular grafts heavily relies on animal experiments. However, no standard for in vivo models or study design has been defined, hampering inter-study comparisons and translational efficiency. To provide input for formulating such standard, the goal of this study was to map all animal experiments for vascular in situ TE using off-the-shelf available, resorbable synthetic vascular grafts. A literature search (PubMed, Embase) yielded 15,896 studies, of which 182 studies met the inclusion criteria (n = 5,101 animals). The reports displayed a wide variety of study designs, animal models, and biomaterials. Meta-analysis on graft patency with subgroup analysis for species, age, sex, implantation site, and follow-up time demonstrated model-specific variations. This study identifies possibilities for improved design and reporting of animal experiments to increase translational value.

Yes when it was stated that the outcome assessor was blinded, or when the order of analysis of the samples was random. Unclear: when it was not stated if the samples were randomly assessed. NA when there was only 1 included animal.

Reporting of Animal Information
Q6 Is the animal species described?
Yes: animal species described Q7 Is the animal strain described?
Unclear: when it was only described for some experimental groups Q8 Is the sex of animals described?
Unclear: when it was only described for some experimental groups Q9 Is the age of animals described?
Unclear when only "young" or "adult" "juvenile" was given Q10 Is the weight of animals described? Q11 Is the ethical review board described?
Yes: when board was given, but also when referred to NIH guidelines Unclear: when only stated : "approved by a local ethic committee" Q12 Is the number of animals allocated to each experimental group described?
Unclear: when not described in material and methods, and only mentioned in 1 figure legend Q13 Is the allocated follow-up time described?
Unclear: when not described for all experimental groups Reporting of Procedure: Q14 Is the synthetic material of the vascular graft described?
Yes: this was an inclusion criterium Q15 Are the dimensions of the vascular graft described? (length, diameter, wall thickness) Yes: when all 3 values were given: length, inner diameter and wall thickness Unclear: when only 1/3 or 2/3 dimensions were given No: when none of these were given Q16 Is sterilization/disinfection of the vascular grafts described? Unclear: when not described for all experimental groups / or when only mentioned "worked sterile"/ "sterilized" but no method given Q17 Is the vascular graft storage prior to implantation described?
Unclear: when only stated "packed" Q18 If applicable, is the procedure for functionalization of the vascular graft described?
Unclear: when it is described, but no clear method is given and no references to other papers in which it is described Q19 If applicable, is the procedure for on-the-fly cell seeding of the vascular graft described?
Yes: described or referred to a source describing the seeding process.
Q20 Is the location of implantation of the vascular graft described?
Yes: all answered yes, because one of the inclusion criteria Q21 Is the surgical procedure of implantation of the vascular graft described (including references to other papers)?
No: when no explanation is given and no references to other papers Unclear when no reference is given and when the surgical procedure is hardly described Q23 Is the use and period of anti-coagulation described?
Unclear: when only the use is given during operation or only post implantation, but not both No: not at all stated if and when anticoagulation was used. Could also be the case for when authors refer to other source for the implantation procedure, but then not "briefly" describe the most important details like eg use of anticoagulation. Q23 Is the use and period of anaesthesia, analgesia described?
Unclear when only was stated "animals were anesthetized" No: when not reported. Could also be the case for when authors refer to other source for the implantation procedure, but then not "briefly" describe the most important details like eg anesthesia. Reporting of general outcome: Q24 Are adverse events described?
Unclear: only based on occlusion rates, but not really described that they looked for eg thrombosis / stenosis / aneurysm / other complications Q25 Is the final number of animals analyzed in each experimental group per timepoint described?
Yes: when the initial number of included animals was clear and the drop outs per group. No: when the initial number of included animals were not clear Unclear: when the drop outs per timepoint were not clear, but for the overall group were clear Q26 Are numbers of drop-outs described?
Unclear: when not given for all experimental groups. Or when not clearly stated, but only when calculating by the reader the drop outs can be known. NA: when only 1 animal was included and it survived Q26a If applicable: Are the reasons for drop-outs described?
Yes: when cause was given, NB: also when stated "death due to unknown cause" No: when not given, only mentioned death. NA when all animals survived and no animals dropped out Unclear when animals dropped out, and you know the number, but not the reason why Q26b If applicable: Is the timepoint of drop-outs described?
Yes: timepoint is mentioned (perioperative or the timeframe in which the animals died prior to planned explant-time) No: when not given, only mentioned deaths per experimental groups. NA when all animals survived and no animals dropped out Unclear when animals dropped out, and you know the amount, but not the timepoint Supplementary Figure 1 Forest plot of overall patency rate of all included experimental groups illustrated as event rate with 95% conficence interval. *for sheep studies: method description mentioning "juvenile" or "lamb" was sufficient to make the categorization Supplementary Figure 2: Sensitivity analysis on subcategorization of age and follow-up time. A) Adjusted cut-off values for subcategorization for sensitivity analysis. B) Sensitivity analysis on age, including period of puberty with young age group, showed no differences compared to previous categorization. C) Sensitivity analysis on follow-up time showed similar trends with previous categorization. Numbers in bar represent number of experimental groups. Black dotted line and grey shades representing grouped ER with 95% CI respectively. Red dotted line: overall ER patency. Significance * p<0.05.