*4.1. Materials*

Bovine collagen electrospun (BCE) was prepared by Department of Textile Materials College, Donghua University, Shanghai, China, and its biocompatibility and cytotoxicity were confirmed. Bovine collagen sponge (BCS) prepared with polyethylene oxide (PEO) (BCE I) and PEO with chitosan (BCE II) were compared with tilapia collagens. The weight ratio of bovine collagen, PEO and chitosan was 150:17:2. Tilapia skin collagens were prepared by Shanghai Ocean University, Shanghai, China. Briefly, Pepsin soluble collagen sponge (PCS) and acid soluble collagen sponge (ACS) from Tilapia skin were prepared as per our previous method [22]. Both collagens were composed of two α-chains and a β-chain and characterized as type-I collagen [22]. BCS was kindly provided by HaoHai Biological Technology, Shanghai, China, which was characterized as type-I collagen. Woundplast was purchased from Johnson & Johnson (Shanghai, China) and medical gauze was procured from Shanghai Health Materials Factory Co. Ltd., Shanghai, China.

SD rats were purchased from Shanghai Slac Laboratory Animal Co. Ltd., Shanghai, China. Animal study protocols and procedures were approved by the Shanghai Ocean University institutional animal care and use committee (Permit Number: SHOU-DW-2018-054). All methods were employed in accordance with the relevant guidelines and regulations of Scientific and Ethical Care and Use of Laboratory Animals of Shanghai Ocean University.

### *4.2. Skin Wound Healing in SD Rats*

The wound healing experiment was performed as follows: female rats (body weight 200–250 g) were maintained in a pathogen free environment and fed a standard diet. 63 rats were injected intraperitoneal with sodium pentobarbital. Two full-thickness wounds of size 1 cm in diameter were created on the dorsum of SD rats which were 1.5 cm apart from the spine. These wounds were covered with medical gauze, woundplast, BCS, PCS, ACS, BCE I, and BCE II (*n* = 6) to avoid infections. Control group was served without any treatment (only medical gauze). Medical adhesive tape was used to attach the dressings in the wounds. Dressing change was done every two days and rats were kept in individual cages. On days 3, 7, and 14 after surgery, the morphology of the wounds was examined. The skin wounds of animals were photographed and subsequently, the rats were euthanized. Wound tissues were removed by sacrificing three rats each from all groups periodically on the 3rd, 7th, and 14th days of post wound creation and the granulation tissues formed were collected.

#### *4.3. Determination of Total Protein and Hydroxyproline Content*

Skin tissue (~90 ± 10 mg) was taken from the wound for determination of total protein and hydroxyproline content. The harvested skin samples collected on days 3, 7, and 14 were washed with ice-cold saline and dried by filter paper. They were then used to determine hydroxyproline and total protein level in specimen [37]. The HYP content in tissue samples was determined using a Tissue hydroxyproline kit, as per the manufacturer's instruction (JianChen Gene Company, Nanjing, China). The healed skin tissues (*n* = 6) were harvested and cut into pieces and then incubated with tissue lysis buffer for 20 min at 95 ◦C and homogenized. The tubes were centrifuged (13,000 rpm) at 4 ◦C and supernatant was collected. Total protein concentration was evaluated using a total protein kit (JianChen Gene Company, Nanjing, China) according to the manufacturer's instructions. The average value was taken from the triplicate readings.
