**Core Concept**
Irradiation is a method of sterilization that uses ionizing radiation to inactivate or kill microbial organisms. This process is commonly used for medical devices, instruments, and equipment that are sensitive to heat or chemicals.

**Why the Correct Answer is Right**
The correct answer is **D. Bronchoscope** because irradiation is not suitable for sterilizing flexible endoscopes like bronchoscopes. This is due to the risk of radiation-induced damage to the delicate optics, electronics, and other components of these devices. Sterilization of bronchoscopes typically involves high-level disinfection with a combination of chemicals and physical cleaning.

**Why Each Wrong Option is Incorrect**
* **Option A:** Bone grafts can be sterilized using irradiation without compromising their structural integrity or biological activity.
* **Option B:** Sutures can be sterilized using irradiation, which is a common method for sterilizing medical textiles.
* **Option C:** Artificial tissue grafts, such as skin substitutes or vascular grafts, can be sterilized using irradiation without affecting their biological function.

**Clinical Pearl / High-Yield Fact**
When choosing a sterilization method, consider the type of material, its sensitivity to heat or chemicals, and the risk of radiation-induced damage to the device. Irradiation is a suitable option for sterilizing medical devices made of plastic, metal, or paper, but not for sensitive instruments like flexible endoscopes.

**✓ Correct Answer: D. Bronchoscope**