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276 14. USING 3-D PRINTING AND BIOPRINTING TECHNOLOGIES FOR PERSONALIZED IMPLANTS

Besides the ventilation, the larynx is responsible for two other essential functions: swallowing and phonation. It is
located at the intersection between the digestive and aerial ways. Any injury to the integrity of this part can quickly put
the patient’s life at risk. If the diameter of this single respiratory tract is reduced, the consequence on respiratory func-
tion can be dramatic and even lethal. Moreover, in this area, patient can also suffer from swallowing disorders that can
cause the passage of the food bolus directly in the airways, which cause inhalation pneumopathies. If not treated cor-
rectly, these inhalation pneumopathies can be fatal.

14.4.2.1 Different Types of Stenosis of the Respiratory Tract
a. Laryngeal stenosis
Laryngeal stenosis corresponds to a narrowing of the diameter of the larynx. They are most often acquired in adults
and congenital in children [63]. A laryngeal dyspnea is a difficulty in inspiration that can quickly affect patient respi-
ratory capacity leading to respiratory distress. Moreover, depending on the cause of the stenosis, the mobility of the
larynx may be impaired, preventing it from performing its role of protective sphincter for the lower respiratory tract. It
is therefore quickly necessary to perform a tracheotomy (establishment of an alternative route for airflow by introduc-
ing an incision in the trachea secured with a cannula) to shunt the obstacle and allow normal breathing and protection
of the lungs. Despite the progress of anesthesia and intensive care equipment, the vast majority of laryngeal stenosis is
related to translaryngeal tracheal intubation at any age [64].
Many other causes may be responsible for laryngeal stenosis:

- Posttracheostomy injuries are rare and the consequence of an incorrect technique [65]
- External laryngeal trauma [66]
- Laryngotracheal burns by inhalation of smoke
- Not only sequelae of benign or malignant laryngeal tumors but also surgical treatment of these tumors by partial
laryngectomies
- Radiotherapy, which can lead to major laryngeal stenosis on larynx [67]
- Inflammatory systemic diseases responsible for obstructive laryngeal granulations

b. Tracheobronchial stenosis
We can distinguish benign stenosis from malignant stenosis.
Benign stenosis due to postintubation represents more than 90% of the cases, Fig. 14.4B–E. There are tracheal lesions
that lead to stenosis [68] Lesions can remain microscopic without sequelae. In the most unfavorable cases, these lesions
can lead to severe stenosis within a few hours. Causes increasing the development of these lesions are multifactorial
and will not be detailed here. Malignant stenosis is rare. The most common histologies are cystic adenoid carcinomas,
squamous cell carcinomas, sarcomas, and lymphomas, Fig. 14.4F–G.
Finally, bronchial stenosis is in majority in connection with bronchopulmonary malignant tumors like bronchocel-
lular carcinomas. Benign tumoral etiologies such as papillomatosis or inflammatory granulomatous type are also
found.
c. The contrast tomodensitometry (CT)

CT is considered as the gold standard in the characterization of stenosis: its caliber, its location, its length, but also
for research purposes and its etiological assessment [69]. It also allows the realization of 3-D reconstructions that allow
excellent visual representation of the stenosis (Fig. 14.5). This “virtual endoscopy” technique makes it possible to
explore stenosis that is too tight to allow an endoscope to proceed, in particular, to ensure the examination of structures
(whether they are healthy or not) below the stenosis [70].
14.4.2.2 Management of Stenosis: Development of Silicone Soft Implants
The management of these diseases is extremely complex and to this day poorly standardized. The only way to defin-
itively cure the patient is to respect the stenotic area and perform an end-to-end anastomosis of the extremities. Nev-
ertheless, these procedures, such as tracheal resection/anastomosis, remain difficult surgeries, which are performed
only in the context of a limited stenosis, in young, otherwise healthy patients. Whether at the laryngeal, tracheal, or
bronchial level, the majority of the treatments are done endoscopically, either in a palliative context for tracheobron-
chial cancers or because of the too large extent of the stenosis at the tracheal level (greater than 50% of the tracheal
length). To avoid resection, several implants that can be used to ensure the continuity of the airways have been devel-
oped in form of stents or plugs. In this section, we will present some silicone implants that have been developed to treat

II. MECHANOBIOLOGY AND TISSUE REGENERATION