Robot-Aided Electrospinning Toward Intelligent Biomedical Engineering

Tan et al. Robot. Biomim. (2017) 4:17 DOI 10.1186/s40638-017-0075-1 REVIEW Open Access Robot‑aided electrospinning toward intelligent biomedical engineering Rong Tan1, Xiong Yang1 and Yajing Shen1,2* Abstract The rapid development of robotics ofers new opportunities for the traditional biofabrication in higher accuracy and controllability, which provides great potentials for the intelligent biomedical engineering. This paper reviews the state of the art of robotics in a widely used biomaterial fabrication process, i.e., electrospinning, including its working principle, main applications, challenges, and prospects. First, the principle and technique of electrospinning are introduced by categorizing it to melt electrospinning, solution electrospinning, and near-feld electrospinning. Then, the applications of electrospinning in biomedical engineering are introduced briefy from the aspects of drug delivery, tissue engineering, and wound dressing. After that, we conclude the existing problems in traditional electrospinning such as low production, rough nanofbers, and uncontrolled morphology, and then discuss how those problems are addressed by robotics via four case studies. Lastly, the challenges and outlooks of robotics in electrospinning are discussed and prospected. Keywords: Robotics, Electrospinning, Biomedical engineering Introduction electrospinning have high surface area and highly porous Te basic idea of electrospinning originated in the period structure, and furthermore, design fexibility is an impor- from 1934 to 1944, when researchers describes the use of tant advantage of electrospun nanofbers [3]. electrostatic force to produce polymer flament device. Electrospinning has widely been used in biomedi- Te main principle is using high-voltage electrostatic cal engineering, including wound dressings, fltration, feld to stimulate the polymer charged jet and then to and drug delivery systems, as well as tissue engineering obtain the polymer nanofbers by charged jet curing. scafolds [4]. Electrospinning process depends on sev- From the middle of the twentieth century to present, eral parameters, including [5] the properties of solution electrospinning technology ended up more than 60 years (viscosity, elasticity, electrical conductivity, and surface of silence, and fnally in the last decade of twentieth cen- tension), applied voltage, nozzle–collector distance, ejec- tury ushered in its glorious era. In 1994, “electrospinning” tion speed, surrounding temperature, humidity, air fow became a professional term, instead of “electrostatic spin- rate, etc. Terefore, the precise control of each param- ning,” ofcially declared electrospinning as an independ- eter directly afects the morphology of the nanofbers [6]. ent academic feld, began its research and development In vivo, tissue engineering scafolds must be not only a in the feld of nanotechnology and related bioengineer- three-dimensional structure which is required to mimic ing. At present, electrospinning is rapidly emerging as extracellular matrix but also a high porosity, large surface a unique and versatile technique for the preparation of area, suitable pore size, and highly interconnected pore smooth nanofbers with controllable morphology from structure [7]. Terefore, it is challenging for the tradi- various polymers [1, 2]. Te nanofbers produced by tional electrospinning method to obtain such biocom- patibility, biodegradability, non-toxicity, and structural integrity scafolds precisely due to the randomly inter- *Correspondence: [email protected] twined nanofbers [8, 9]. Hence, the urgent requirement 1 City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, SAR on electrospinning is how to precisely control the mor- Full list of author information is available at the end of the article phology and diameter of electrospinning so that it can © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Tan et al. Robot. Biomim. (2017) 4:17 Page 2 of 13 produce thinner nanofbers with the structure of three- surface tension of the liquid when it increases to a critical dimensional in biomedical engineering. value [14]. Te polymer jet occurs under the infuence of As an emerging technology, robotics has involved in high electric feld, resulting in extremely high-frequency and benefts many biofabrication process to ensure and irregular spiral motion [13]. Ultimately, a fber of nanom- improve the accuracy, fexibility, and controllability, such eter diameter is formed and scattered on the collector in as 3D printing, 3D plotting, nanoimprinting. Robot- a random manner to form a non-woven fabric [15]. aided electrospinning is integrating robot to general electrospinning process to improve the control of param- Melt electrospinning and solution electrospinning eters, the diameter of nanofbers, the rate of producing Te solution electrospinning is a method for the prepa- nanofbers, and so on. In this review, we summarize the ration of nanofbers by solvent evaporation and polymer state of the art of electrospinning in biomedical engineer- curing under the action of high-voltage electric feld, and ing and discuss how the robotics beneft the electrospin- the melt solution refers to the polymer heating and melt- ning process, i.e., including its working principle, main ing, by the electric feld force to be drawn to obtain poly- applications, challenges, and prospects. mer fber material process [16]. Structurally, both of them have a nearly identical composition, except that the melt Basic principle and technique of electrospinning electrospinning has an extra heater and that the solu- Basic principle tion electrospinning has an infusion pump (Fig. 1a, b). In As the one of the most straightforward and cost-efective addition, the low cost makes them a common advantage, method, electrospinning technique with unique physio- but these two methods diferentiate themselves by their chemical property has gained an extensive application in typical properties. biomedical feld [10–12]. An integrated electrospinning Solution electrospinning is well known for its simplic- device consists of a DC high-voltage supply, a syringe is ity of operation and suitability for many polymers. Te jet flled with polymer solution, a needle, and a collector. To of solution electrospinning has the virtue of low viscosity fabricate nanofbers, one electrode of DC high-voltage and is easy to obtain nanofbers with diameter less than supply is connected to the needle of the syringe, and the 100 nm. Besides, the surface of fber presents the porous polymer is ejected to the target collector from the top of structure due to solvent evaporation [17]. Te advantage the needle. During the process, the polymer droplets are of melt electrospinning is that there is no need to fnd held by the surface tension at the needle, which collects the solvent for dissolving polymer, and the end-product the charge on the surface induced by the electric feld, is suitable for the application of biomedical engineering while it receives an electric feld force which is oppo- such as tissue engineering and drug release. In a sense, it site to the surface tension [13]. Te droplets are pulled is easy to realize the mass production due to not require from spherical to cone-shaped structure named Taylor- the use of volatile solvents [18, 19]. While comparing cone. However, the electric feld force will overcome the these two approaches, solution electrospinning is facing Fig. 1 Diference in structure between melt electrospinning, solution electrospinning, and near-feld electrospinning. a Melt electrospinning [20]. b Solution electrospinning [20]. c Near-feld electrospinning [22] Tan et al. Robot. Biomim. (2017) 4:17 Page 3 of 13 the challenges of signifcant solvent evaporation, dif- distance is regarded as the most efective way, and then cult direct-writing, and low output. In these and several adding additional conditions (e.g., magnetic feld force) respects, as a kind of raw materials with wide applica- to decrease the electric fled also was reported by Yang bility, favorable direct-writing capability, non-toxic pol- et al. [29]. lution, and high conversion rate of product technology, Although near-feld electrospinning is termed a best the melt electrospinning handles better than the solution tool to deposit solid nanofbers in using direct-write, it electrospinning, but it requires severe external conditions is not capable enough to fabricate mass production with like higher spinning temperature, more time to build, and its single nozzle; moreover, it is easy to cause fber diam- heat-resistant polymers [20]. eters become thicker because of shortening spinneret-to- Nevertheless, these two techniques are difcult to substrate distance [14]. Facing this a series of questions, achieve the requirement of high-precision pattern and researchers are using robot-aided for realizing large-scale structure when the polymer steps into the instability production of electrospinning, and thinner nanofbers motion and splitting process [21] since the high volt- will be applied in much more felds. age (≤ 10 kV) limits softness of nanofbers and choice of polymer materials. Finally, this could lead to

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