A New Strategy for the Preparation of Porous Silk Fibroin Scaffolds

Research Article

Ann Materials Sci Eng. 2021; 5(1): 1037.

A New Strategy for the Preparation of Porous Silk Fibroin Scaffolds

Zhang T1,2, Xiong Q2, Shan Y1* and Zhang F3

¹Department of Urology, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China

²Department of Urology, Children’s Hospital of Soochow University, Suzhou, Jiangsu, China

³College of Textile and Clothing Engineering, National Engineering Laboratory for Modern Silk, China

*Corresponding author: Yuxi Shan, Department of Urology, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China

Received: May 29, 2021; Accepted: June 19, 2021; Published: June 26, 2021


In order to prepare Silk Fibroin (SF) scaffolds with excellent pore structure, the fresh SF solution was concentrated at relative humidity 55% and 25°C for 3 days. During the above process, SF micelles, existed in the fresh SF solution, aggregated into nanofilaments as concentration increased, and the nanofilament feature of SF were similar to that observed in silk gland. SF nanofilaments were easy to form SF scaffolds with porous and silk I structure, in contrary, SF micelles were liable for formation of SF scaffolds with lamellar and random coil structure. It suggested that the formation of SF nanofilaments is a critical step for pore and secondary structure control of lyophilized SF scaffolds.

Keywords: Silk fibroin; Porous materials; Microstructure; Nanofilaments


Silk is a unique material, which has historically been regarded as high-grade raw materials of textile for its strength and luster [1]. Silkbased materials have been transformed from the commodity textile to a growing web of applications in high-technology areas, especially as a biomaterial because of several desirable properties [2]. In particular, these properties include its biocompatibility, biodegradation, and versatility in processing into multiple materials formats [1]. The porous SF scaffolds have attracted considerable attention because it can provide a versatile 3D porous structure which is known to play a critical role for cell attachment, proliferation, migration, and tissue growth, as well as for nutrient and waste transport [3].

Porous SF scaffolds can be fabricated by a variety of methods, including lyophilization, porogens, gas foaming, etc. [1]. However, the scaffolds from pure SF solution undergo lyophilization easily form separate layers or lamellar structures rather than porous structures, and this lamellar structure will cause the loss of compressive properties and affect its application as a biomaterial [4,5]. Recently, it is reported that the porous structure of lyophilized SF scaffolds was closely related to SF assembly nanostructure. SF scaffolds with excellent pore structure could be prepared from nanofilament solution which derived from concentrated SF solution [6]. However, the way used to control drying rate of SF solution by a series of lids with hole is unstable due to the change of temperature and relative humidity around [7]. In our previous research, it was found that temperature and relative humidity played an important role in controlling SF selfassembly and the secondary structure of regenerated SF films [7,8].

In this paper, we firstly prepared SF solution with nanofilaments through controlling concentrating conditions of temperature and relative humidity. Subsequently, the effect of SF nanostructure on morphology, structure and thermal property of porous SF scaffolds was investigated in detail.

Material and Methods

Preparation of B. mori SF nanofilaments solution

SF aqueous solution was prepared as described previously [9]. The aqueous SF solution was concentrated in Binder Temperature & Humidity Chamber (Binder, German) at relative humidity 55% and temperature 25°C for 3 days. The final concentration was ~25 wt%, determined by weighing the remaining solid after drying.

Preparation of SF scaffold

The fresh and concentrated SF solution were diluted to 2%, and then were placed at -20°C for 24 h to freeze and then lyophilized for 72 h.


The morphology of SF in water was observed by AFM (Veeco, Nanoscope V) in air. A 225μm long silicon cantilever with a spring constant of 3 Nm-1 was used in tapping mode at 0.5-1 Hz scan rate.

The morphology of SF scaffolds was observed using SEM (Hitachi S-520, Japan) at 20°C, 60 RH. Samples were mounted on a copper plate and sputter-coated with gold layer 20-30 nm thick prior to imaging.

The structure of the scaffolds was analyzed by FTIR on a Magna spectrometer (NicoLET5700, America), X-ray diffractometer (X'Pert- Pro MPD, PANalytical B.V. Holland),

Thermogravimetry/differential thermal analysis (TG-DTA, PES', America), and TA instrument Q100 DSC (TA instruments, New Castle, DE).

Results and Discussion

It is well known that pore architecture in scaffolds plays a critical role in tissue engineering for the seeded cells to form goal tissue and organs [10]. The morphology of SF in solution and porous 3D scaffolds was examined by AFM and SEM. The fresh SF solution showed a micelle structure, as Figure 1a showed, and the scaffolds from this solution showed separate layer or lamellar structure rather than porous 3D structure as our previous report (Figure 2a,2b) [5]. SF nanofilaments were formed at relative humidity 55% and 30°C for 3 days as the concentration increased, as Figure 1b showed, and the nanofilament features of SF were similar to this observed in the silk gland [11]. The scaffolds derived from above solution containing SF nanofilament demonstrated excellent porous structure, as Figure 2c showed. It had been also reported that lyophilized SF scaffolds with excellent porous structure which were prepared from SF isolated from silk glands [10], indicating the important role of bionic nanofilament structure in the formation of porous structure. Furthermore, the micelle and nanofilament structure of SF observed in fresh and concentrating solution were also found in the crosssection of relevant SF scaffolds (Figure 2b,2c). The nanofilament, similar to ECM structure, in porous SF scaffolds would provide a favorable microenvironment for cells growth and proliferation [6].