diff --git a/biosimulators.json b/biosimulators.json
index b19f649..6d64c8b 100644
--- a/biosimulators.json
+++ b/biosimulators.json
@@ -122,8 +122,8 @@
         "title": "BioNetGen 2.2: advances in rule-based modeling",
         "authors": "Leonard A. Harris, Justin S. Hogg, José-Juan Tapia, John A. P. Sekar, Sanjana Gupta, Ilya Korsunsky, Arshi Arora, Dipak Barua, Robert P. Sheehan & James R. Faeder",
         "journal": "Bioinformatics",
-        "volume": 32,
-        "issue": 21,
+        "volume": "32",
+        "issue": "21",
         "pages": "3366-3368",
         "year": 2016,
         "identifiers": [{
@@ -136,7 +136,7 @@
         "title": "Rule-based modeling of biochemical systems with BioNetGen",
         "authors": "James R. Faeder, Michael L. Blinov & William S. Hlavacek",
         "journal": "Methods in Molecular Biology",
-        "volume": 500,
+        "volume": "500",
         "pages": "113-167",
         "year": 2009,
         "identifiers": [{
@@ -149,8 +149,8 @@
         "title": "BioNetGen: software for rule-based modeling of signal transduction based on the interactions of molecular domains",
         "authors": "Michael L. Blinov, James R. Faeder, Byron Goldstein & William S. Hlavacek",
         "journal": "Bioinformatics",
-        "volume": 20,
-        "issue": 17,
+        "volume": "20",
+        "issue": "17",
         "pages": "3289-3291",
         "year": 2004,
         "identifiers": [{
@@ -233,8 +233,8 @@
         "title": "CVODE, a stiff/nonstiff ODE solver in C",
         "authors": "Scott D. Cohen, Alan C. Hindmarsh & Paul F. Dubois",
         "journal": "Computers in Physics",
-        "volume": 10,
-        "issue": 2,
+        "volume": "10",
+        "issue": "2",
         "pages": "138-143",
         "year": 1996,
         "identifiers": [{
@@ -408,8 +408,8 @@
         "title": "Exact stochastic simulation of coupled chemical reactions",
         "authors": "Daniel T. Gillespie",
         "journal": "Journal of Physical Chemistry",
-        "volume": 81,
-        "issue": 25,
+        "volume": "81",
+        "issue": "25",
         "pages": "2340-2361",
         "year": 1977,
         "identifiers": [{
@@ -565,8 +565,8 @@
         "title": "A \"partitioned leaping\" approach for multiscale modeling of chemical reaction dynamics",
         "authors": "Leonard A. Harris & Paulette Clancy",
         "journal": "Journal of Chemical Physics",
-        "volume": 125,
-        "issue": 14,
+        "volume": "125",
+        "issue": "14",
         "pages": "144107",
         "year": 2006,
         "identifiers": [{
@@ -721,8 +721,8 @@
         "title": "Efficient modeling, simulation and coarse-graining of biological complexity with NFsim",
         "authors": "Michael W. Sneddon, James R. Faeder & Thierry Emonet",
         "journal": "Nature Methods",
-        "volume": 8,
-        "issue": 2,
+        "volume": "8",
+        "issue": "2",
         "pages": "177",
         "year": 2011,
         "identifiers": [{