diff --git a/src/scgenerator/physics/materials.py b/src/scgenerator/physics/materials.py
index 1def4c7..322fbd1 100644
--- a/src/scgenerator/physics/materials.py
+++ b/src/scgenerator/physics/materials.py
@@ -7,7 +7,7 @@ from typing import Any, TypeVar
 import numpy as np
 
 import scgenerator.math as math
-from scgenerator import utils
+from scgenerator import io
 from scgenerator.logger import get_logger
 from scgenerator.physics import units
 from scgenerator.physics.units import NA, c, epsilon0, kB
@@ -27,7 +27,7 @@ class Sellmeier:
     @classmethod
     @cache
     def load(cls, name: str) -> Sellmeier:
-        mat_dico = utils.load_material_dico(name)
+        mat_dico = io.load_material_dico(name)
         s = mat_dico.get("sellmeier", {})
         return cls(
             **{
@@ -109,7 +109,7 @@ class Gas:
 
     def __init__(self, gas_name: str):
         self.name = gas_name
-        self._raw_sellmeier = utils.load_material_dico(gas_name)
+        self._raw_sellmeier = io.load_material_dico(gas_name)
         self.atomic_mass = self._raw_sellmeier["atomic_mass"]
         self.atomic_number = self._raw_sellmeier["atomic_number"]
         self.ionization_energy = self._raw_sellmeier.get("ionization_energy")