Study of functional shape memory composites based on biocompatible electrospun nanofibers

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Study of functional shape memory composites based on biocompatible electrospun nanofibers


Author: Tan, Lin
Title: Study of functional shape memory composites based on biocompatible electrospun nanofibers
Degree: Ph.D.
Year: 2016
Subject: Shape memory polymers.
Composite materials.
Hong Kong Polytechnic University -- Dissertations
Department: Institute of Textiles and Clothing
Pages: xxv, 221 pages : color illustrations
Language: English
Abstract: Both shape memory polymers and nanofibers are fascinating materials which have been intensively studied in recent years, and the exploration of novel and smart constructs based on electrospun nanofibers is of great significance in both academic and industrial fields. In this project, several novel shape memory composites (SMCs) with multi-functions based on electrospun nanofibers/nanofibrous mats are successfully fabricated. The design concept, preparation process, structure characterization, function evaluation and mechanism analysis for each type of SMCs are presented in this thesis. Briefly, three types of SMCs, including polymer-polymers, polymer-inorganic sheets and polymer-inorganic particles, and five composites of shape memory polyurethane (SMPU)/chitosan/gelatin, bilayered SMPU/gelatin, thermoplastic polyurethane (TPU)/cellulose, SMPU/graphene oxide (GO), and SMPU/hydroxyapatite (HA) were fabricated using electrospinning method. Afterwards, various types of instrumental analysis were employed to comprehensively characterize the SMCs. Additionally, biological properties and functions were also investigated and evaluated. The first composite was derived from the blends of SMPU/chitosan/gelatin (denoted as CNMs) by electrospinning and subsequent post-treatment with a silver nitrate solution for wound dressing application. The obtained CNMs have thermal sensitive shape memory effect (SME) and show desirable water vapor transmission ratio, surface wettability and satisfactory biological properties. In addition, such CNMs can possibly benefit the wound healing through shape fixation-assisted easy processing and shape recovery-assisted closure of cracked wounds, which can be fine-tuned by pre-programming. Inspired by the multi-layered wound dressing for practical use, the second composite, bilayered SMPU/gelatin (denoted as BNFs), was fabricated through sequential electrospinning. Due to the bilayered construction and individual performance of each layer, the obtained BNFs show different surface wettability in double layers. Meanwhile, BNFs have desirable thermally regulated water vapor transmission rate, water-absorption ratio and adhesive force between the two layers. Additionally, satisfactory antibacterial activity and hemostatic property were also easily incorporated into the BNFs. More importantly, the needful characteristics of each layer are highly adjustable based on this concept.
The third composite, a quick response water-sensitive SMC, was prepared by introducing cellulose nanofibrous mats as the filler in TPU matrix. The composites (denoted as CPs) presented desirable shape fixity and recovery behavior, and the elastic modulus (E') was showntobe responsive promptly and reversibly against drying and wetting cycles. The mechanism experienced in the CPs was also proposed. This work brings the development of SMCs by introducing nanomaterials with large specific surface area. The above three composites belong to polymer-polymers type, the fourth composite was based on SMPU and GO. A series of graphene oxide (GO) filled SMPU nanofibrous mats (denoted as SGNs) were prepared and systematically investigated on the morphological, thermal and mechanical properties, surface wettability, and SME followed by the proposed programming model. Results showed that GO could be well dispersed within the SMPU matrix, and the SGNs showed improved SME, mechanical strength, surface wettability and thermal stability compared with pristine SMPU. Aiming to fabricate the biomimic scaffolds, the last SMC was composed of SMPU and HA with different mass ratios (denoted as SHs).The optimal composites showed desirable SME and mechanicalproperties.What's more,the in vitro bone-bonding ability of the nanofibrous shape memory scaffolds increased significantly when the ratio of HA was around 8wt% (SH8), while no obvious apatite-forming happened among the scaffolds derived from the pristine SMPU and the composites of SH2 and SH4. Furthermore, the shape memory nanofibrous scaffolds with desirable apatite-forming ability have good cytocompatibility and can promote the proliferation of MC 3T3 E1 efficiently, indicating that they are promising scaffolds for human bone repair. In general, three types of SMCs with unique properties and functions were successfully fabricated based on electrospun nanofibers. The findings from the fabricated SMCs in the project can shed a reference on designing of other novel composites through polymer-polymers, polymer-inorganic sheets and polymer-inorganic particles. Specifically, the completion of this project significantly contributes to the development of shape memory nano-composites and benefits the expansion of their potential applications. Moreover, multiple disciplines involved in this study are beneficial for the application and development of polymer chemistry, nanotechnology and biological evaluation in material fields.

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