Spinal dura mater tears are a common issue in surgical procedures, especially in intradural tumor resection [1] [2] . Spinal dura mater tears can result in some complications, such as cerebrospinal fluid leak, headache, infection, and fever [3] . Primary dural closure with sutures is the preferred method for spinal duraplasty, whenever possible, to minimize the risk of persistent cerebrospinal fluid leak, optimizing recovery and outcome. When direct repair with suture is not possible, the resort to indirect repair by fat or muscle patches, which lengthen the surgery length and secondary injury for patient because of the fat or muscle access, and a lot of implant grafts are approved to repair the defect cranial dura mater, but implant grafts approved to repair the spinal dura mater are not much, which perhaps it’s the spinal dura mater differs from the cranial dura mater [4] .

Nowadays, electrostatic spinning fibers have been used for various biomedical applications, including dural regeneration, due to their interesting properties, such as porosity, superior mechanical properties, and most importantly, similarity with the extracellular matrix (ECM) [5] .

Here, we retrospectively reviewed the earliest cases involving the use of electrostatic spinning synthetic dura substitute for repairing defects in the spinal dura mater 2017.

From June to September 2017, seven patients were treated in the Neurosurgery Department, Peking University Third Hospital, China. The pre-operative diagnosis for all the cases was established by magnetic resonance imaging (MRI) and computed tomography (CT), and the lesions were located in the thoracolumbar regions and were symptomatic as shown in Table 1 and Table 2 . The most common symptom, present in six cases, was increasing progressive paralysis and walking difficulty. One case was back pain and the patient couldn’t blend her back, and the symptom was progressive. ( Table 1 )

The laminotomy was performed for all the patients and the cancers were resected, then the electrostatic spinning synthetic dura substitute made of polylactic acid ReDura^TM, which has been approved by CFDA before 2017, was onlay on the

Abbreviation: F, female; M, male; T, thoracic; L, lumbar.

defect place without suturing. The follow-up period ranged from 1 month to 3 months, and no complication like CSF leak, cerebral contusion, hemorrhage, adhesion, or wound infection, as well as pseudomeningocele was found.

A 20-year-old woman complained of back pain and she couldn’t blend the back, which had begun 3 years ago. And the symptoms were increasing progressively one year ago. CT and MRI revealed a tumor in the thoracolumbar region, which was located between T12 and L4 ( Figure 1 ). After laminotomy and resection of the tumor, the margins of the dura were stitched together and were onlay with a well-fitting sheet of ReDura^TM ( Figure 2 and Figure 3 ). None of the complications

like CSF leak, cerebral contusion, hemorrhage, or wound infection, as well as pseudo meningocele were observed in the follow-up month.

The dura mater is the outermost meningeal membrane enclosing the brain and spinal cord. The cerebrospinal fluid steadily flows under the dura mater. When the dural defect occurs, the leakage of cerebrospinal fluid will result in several complications. In this study, seven cases of spinal duraplasty were repaired with the electrostatic spinning fibers synthetic dura substitute ReDura^TM did not find the cerebrospinal fluid leakage and the other related complications, which showed that the electrostatic spinning fibers synthetic dura substitute can effectively repair the defect spinal dura mater.

A. L. Miguel Angel Reina et al. study showed that at the spinal level, the dura mater is composed of collagen fibers and about 80 concentric dural laminas measuring approximately 250 - 400 μm. Each dural lamina has a thickness of 5 μm and is formed by thinner laminas. These collagen fibers are oriented in various directions and form each dural lamina, and these fibers measure 2 μm in diameter and have a rough surface [6] .

ReDura^TM is manufactured by electrostatic spinning, which is composed of a lot of fibers in microstructure, and Kunxue Deng reported [7] that each fiber’s average diameter of ReDura^TM is about 1 - 2 μm, with the structure and fiber diameter similar to the human spinal dura mater microstructure [6] . Besides, Bernhard Schick reported [8] cellular migration from the dura borders at the site of the defect during the wound healing process. Thus, the fiber graft is the ideal biomimetic dural cell matrix for cellular migration and could help the defective spine dura mater repair.

Except for the above biomimetic microstructure of ReDura^TM, its mechanical properties are also similar to those of the spinal dura mater. Runza et al. [9] reported Young’s moduli of 4 - 6 MPa, and Sacha Cavelier et al. reported similar results [3] . Kunxue Deng reported [7] that the tense strength of ReDura^TM 4.80 - 5.49 MPa, which is similar to that of the human spinal dura mater.

Therefore, the electrostatic spinning technology manufactured by the substitute can provide both a similar cell-matrix and mechanical properties, which make the substitute similar to native spine dura mater as far as possible.

However, these cases only have a follow-up duration of 1 - 3.5 months, but for spinal dural repair, long-term follow-up data will be more helpful in tracking the clinical performance of the material, and potential long-term complications are usually paid attention in the dura substitute.

We retrospectively reviewed the earliest cases involving electrostatic spinning synthetic dura substitute for repairing defects in the spinal dura mater in 2017, and no complication was found in these cases after surgery. Because of the technical characteristics of electrostatic spinning, electrostatic spinning synthetic dura substitute can provide cell-trix and mechanical properties similar to native spine dura mater.

Thus, the electrostatic spinning synthetic dura substitute might be the ideal promising alternative for repairing the spinal dura mater.

This work was supported by the Open Project of Sichuan Provincial Key Laboratory for Clinical Immunology Translational Medicine (grant number: LCMYZHYX-KFKT202202).

Limin Lin, Kunxue Deng and Hongji Yang performed and analyzed the data and drafted the manuscript. Zhenyu Wang and Chenxiao Dong collected the data and performed the data analysis. Bin Liu conceived of and designed the study and revised the paper. All authors reviewed the results and approved the final version of the manuscript.

These patients or family representatives in these cases were contacted by telephone to obtain verbal informed consent about the case reports to be published.

*These authors contributed equally to this work.

^#Corresponding author.