Dovepress INTERNATIONAL JOURNAL OF NANOMEDICINE OPEN ACCESS International Journal of Nanomedicine Growth Factor and Its Polymer Scaffold-Based Delivery System for Cartilage Tissue Engineering a ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/dijn20 Li Chen, Jiaxin Liu, Ming Guan, Tongqing Zhou, Xin Duan & Zhou Xiang To cite this article: Li Chen, Jiaxin Liu, Ming Guan, Tongqing Zhou, Xin Duan & Zhou Xiang (2020) Growth Factor and Its Polymer Scaffold-Based Delivery System for Cartilage Tissue Engineering, International Journal of Nanomedicine,, 6097-6111, DOI: 10.2147/IJN.S249829 To link to this article: https://doi.org/10.2147/IJN.S249829 CrossMark © 2020 Chen et al. Published online: 14 Aug 2020. bmit your article to this journal Article views: 433 QView related articles View Crossmark data Citing articles: 61 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=dijn20 Taylor & Francis Taylor & Francis Group International Journal of Nanomedicine Open Access Full Text Article Growth Factor and Its Polymer Scaffold-Based Delivery System for Cartilage Tissue Engineering 1,2,* Li Chen Jiaxin Liu¹›* Ming Guan 2,3 Tongqing Zhou² Xin Duan' I Zhou Xiang 'Department of Orthopedics, National Clinical Research Center for Geriatrics, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, People's Republic of China; 2School of Dentistry, University of Michigan, Ann Arbor, MI, 48109, USA; ³Department of Orthopedics, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, People's Republic of China *These authors contributed equally to this work Correspondence: Xin Duan Tel +86-28-85422426 Email dxbaal@hotmail.com Zhou Xiang Tel +86-28-85422605 Email xiangzhou15@hotmail.com submit your manuscript | www.dovepress.com DovePress in http://doi.org/10.2147/1JN.S249829 This article was published in the following Dove Press journal: International Journal of Nanomedicine Dovepress open access to scientific and medical research REVIEW Abstract: The development of biomaterials, stem cells and bioactive factors has led to cartilage tissue engineering becoming a promising tactic to repair cartilage defects. Various polymer three-dimensional scaffolds that provide an extracellular matrix (ECM) mimicking environment play an important role in promoting cartilage regeneration. In addition, numer- ous growth factors have been found in the regenerative process. However, it has been elucidated that the uncontrolled delivery of these factors cannot fully exert regenerative potential and can also elicit undesired side effects. Considering the complexity of the ECM, neither scaffolds nor growth factors can independently obtain successful outcomes in carti- lage tissue engineering. Therefore, collectively, an appropriate combination of growth factors and scaffolds have great potential to promote cartilage repair effectively; this approach has become an area of considerable interest in recent investigations. Of late, an increasing trend was observed in cartilage tissue engineering towards this combination to develop a controlled delivery system that provides adequate physical support for neo-cartilage formation and also enables spatiotemporally delivery of growth factors to precisely and fully exert their chon- drogenic potential. This review will discuss the role of polymer scaffolds and various growth factors involved in cartilage tissue engineering. Several growth factor delivery strategies based on the polymer scaffolds will also be discussed, with examples from recent studies highlighting the importance of spatiotemporal strategies for the controlled delivery of single or multiple growth factors in cartilage tissue engineering applications. Keywords: polymer scaffold, growth factor, delivery, cartilage repair Introduction Articular cartilage is a specific type of connective tissue that covers the articular surfaces of the bone; it is mainly composed of a dense extracellular matrix (ECM) and a sparse cell population. It plays an essential role in the biomechanical functions of the joints, including shock absorption, sheer resistance and load bearing.² Once articular cartilage is damaged, it has a limited potential for sponta- neous repair due to the lack of vascularity, nerves and lymphatics. This can result in joint pain, swelling, dysfunction, and eventually lead to osteoarthritis (OA).³,4 In the past two decades, OA has been the most common form of arthritis accounting for approximately 300 million patients worldwide and undoubtedly has been considered as one of the most significant health problems that also pose a substantial financial burden on the public health system, and the patients themselves. Currently, conservative treatments, including pharmacological and non-pharmacological therapies, are commonly applied to improve joint pain, reduce stiffness and improve physical function in patients with OA. However, the therapies сс International Journal of Nanomedicine 2020:15 6097-6111 02 Ⓒ2020 Chen et al. This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms.php NC and incorporate the Creative Commons Attribution - Non Commercial (unported, v3.0) License (http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms (https://www.dovepress.com/terms.php). 6097 Chen et al 7-10 cannot prevent further joint degeneration. Surgical strate- gies are also designed to treat cartilage defects, including autologous chondrocyte implantation (ACI), microfrac- ture, osteochondral grafts and total joint arthroplasty. However, they have some inherent shortcomings such as the requirement of secondary surgery, immunogenic responses, shortage of donor tissues and pathogen trans- mission risks. Alternatively, cartilage tissue engineer- ing, which involves combining cells, scaffolds and growth factors, has emerged as a promising strategy for cartilage repair.¹¹ Meanwhile, the methods of minimally invasive surgery, including the implantation and injection, are an important component of clinical translation of tissue engi- neering techniques which have been verified in vitro. ¹2 In general, scaffolds as biologically active ECM provide mechanical support for cell growth and chondrogenic dif- ferentiation, which could be beneficial for stimulating and accelerating the cartilage regeneration process. With the development of chemistry and processing, numerous synthesized and natural materials have been applied to fabricate scaffolds that successfully promote the cartilage regeneration without noticeable signs of immune response and rejection. ¹3-15 12 16,17 While biomimetic three-dimensional scaffolds have been made, they cannot create high-quality cartilage tissue independently. Stem cells, pluripotent cells and native progenitor cells are commonly used in combination with scaffolds to accelerate and improve the regeneration process. Moreover, cell-based therapies are influenced by the cellular microenvironment to some extent. Growth factors are of high importance as they have the potency to induce and enhance cellular responses, which is beneficial for the cells as they need to differentiate into desired lineages.¹8 Although scaffolds can obtain sufficient growth factors from the culture medium under in vitro conditions, the incorporated growth factors can spread out of the scaffolds and degrade in a short time in vivo. Besides, different dosages and delivery rates are required for dif- ferent growth factors to induce the cells in in vitro or in vivo conditions. Today, a plethora of studies have been conducted to investigate the delivery of single or multiple growth factors from the scaffolds in a defined 18 19,20 manner. This review examined the delivery of growth factors for cartilage tissue engineering, with an emphasis on the polymer scaffold-based approaches. First, the aim is to enable an understanding of current applications of polymer scaffolds, following with the descriptions of different 6098 submit your manuscript | www.dovepress.com DovePress Dovepress growth factors involved in cartilage tissue engineering. A latter section will place a particular emphasis on the growth factor delivery strategies associated with polymer scaffolds. Finally, the current challenges and suggestions of polymer scaffold-based growth factor delivery for car- tilage tissue engineering are explained. Polymer Scaffolds Articular cartilage, with its unique mechanical properties pro- vides the contact surfaces for load transfer between bones, which enables the joint to withstand weight-bearing. The ability to do so is attributed to its complex structure comprised of a fluid phase and a solid matrix that is composed mainly of a depth-dependent collagen fibrous network and proteogly- cans, as well as other types of proteins, lipids, and cells. Therefore, the scaffold suitable for cartilage tissue engineering should have good biocompatibility for cell adhesion, migra- tion and proliferation, and also provide appropriate mechanical and structural support. In addition, biodegradability and being free of adverse reactions are basic properties required for a three-dimensional scaffold mimicking physiological characteristics.2¹ Currently, a wide range of natural and syn- thetic polymers play an important role in the development of scaffolds for cartilage tissue engineering. Due to superior biocompatibility and biodegradation, natural polymers like collagen, chitosan, silk fibroin, alginate, hyaluronic acid and chondroitin sulfate are suitable for initiating a fast regeneration process. However, potential pathogen transmission, immuno- genicity and poor mechanical properties limit their clinical application. On the other hand; synthesized polymers can artificially regulate the degree of polymerization, thereby con- trolling its mechanical properties, internal structure and degra- dation, which can effectively promote the regeneration process. Poly (lactic acid) (PLA), poly glycolic acid (PGA), poly lactide-co-glycolic acid (PLGA) and poly caprolactone (PCL) are the most commonly synthesized polymers in the application of three-dimensional scaffolds for cartilage tissue engineering.23 When comparing these to natural polymers, the properties of synthetic polymer-based scaffolds are consider- ably different in terms of their tunable properties, such as molecular weight, transition temperatures and crystallinity.24 Polymer nanofibers have been extensively studied due to their ability to encapsulate and deliver growth factors for different tissue regeneration purposes. Nanofiber scaf- folds with high surface to volume ratio and interconnected porous structure, seem to hold the lead position as the ideal candidate for cartilage tissue engineering. They play a role in stimulating the ECM environment, allowing 21 International Journal of Nanomedicine 2020:15 Dovepress cells to populate empty spaces and organize themselves, and mechanical stimulation can be applied to this porous structure to orient the cells and maintain a chondrocyte phenotype. As a result, scaffolds will be degraded and replaced by newly formed ECM, without producing adverse effects due to the degradation products. To date, various technologies such as electrospinning, phase separation, self-assembly, drawing and template synthesis have been applied in attempts to optimize nanofiber scaf- folds to make them more consistently bioactive and mechanically stable for effective tissue regeneration application. For example; a nanofibrous scaffold was developed that was highly porous, interconnected and degradable. It was developed using phase separation of poly l-lactic acid (PLLA) solutions combined with poro- gen leaching techniques. Through a series of characteristic tests, chondrogenic evaluations in vitro and in vivo demonstrated that this nanofibrous PLLA scaffold is an excellent candidate providing an advantageous three- dimensional microenvironment for a wide variety of car- tilage repair strategies (Figure 1).² 27-29 Growth Factors 30 Growth factors are a group of peptides that mediate cel- lular proliferation, migration and differentiation by bind- ing to transmembrane receptors located on target cells. When a sufficient number of receptors are activated, the signaling transduction process may trigger a series of specific cellular activities.³0 Concerning cartilage develop- ment, growth factors play an essential role in regulating the processes of chondrogenesis and hypertrophy, such as the members of transforming growth factor-ß (TGF-B) superfamily, insulin-like growth factor-1 (IGF-1), fibro- blast growth factor (FGF) family and platelet-derived growth factor (PDGF). In order to provide a better under- standing of their potential, descriptions of their roles involved in the regeneration and maintenance of articular cartilage will now be described (Table 1). Transforming Growth Factor-B Superfamily The TGF-ß superfamily is comprised of more than 30 closely related polypeptides, mainly including typical TGF-ßs, bone morphogenetic proteins (BMPs), growth and differentiation factors (GDFs) and activin/inhibin, which regulate multiple cell functions from early develop- ment to regulating homeostasis throughout adult life.³1 31 International Journal of Nanomedicine 2020:15 Chen et al A large number of studies have shown that they have significant regulatory effects on the homeostasis and repair of articular cartilage. Transforming Growth Factor-B TGF-B is a dimer with a molecular weight of 25 kilo Daltons (kDa) that is composed of two identical or similar chains. There are three isoforms (1-3) that are generally considered to be potent stimulators in all stages of chon- drogenesis with a function of inducing proteoglycans and type II collagen synthesis. ³2 TGF-ß signaling transduction is based on the membrane-bound heteromeric receptors (type I and type II). Binding to type II receptors leads to the phosphorylation of type I receptors, causing the phos- phorylation of TGF-B specific Smad proteins, particularly Smad 2 and 3. In addition, some Smad-independent pathways, including p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (Erk) and stress-activated protein kinase/c-Jun NH(2)-terminal kinase (SAPK/JNK) can also be activated by TGF-B.³4 33 34 35 TGF-B is one of the main initiators of chondrogenesis of mesenchymal precursor cells, and the differentiation of mesenchymal stem cells (MSC) into chondrocytes also requires its stimulation. The expression of N-cadherin was induced by strong stimulation of TGF-ß to enhance cell adhesion and aggregation, and subsequently promote cell proliferation, differentiation and deposition of the cartilage- specific extracellular matrix.³5 Among these three isoforms, TGF-B1 was the first to be discovered, and TGF-ß1 and TGF- 33 have been used in a large number of studies to explore the effect of TGF-B on the repair of cartilage after it defects. Although some studies suggest that the ability of TGF-32 and TGF-33 to promote cartilage differentiation may be more superior to that of TGF-31, there is a consensus that there is no significant difference among the three TGF-B isoforms regarding their ability to promote cartilage differentiation. 36,37 In a Sprague-Dawley rat full-thickness cartilage defect model, Lentivirus-TGF-ß1-EGFP transduced BMSCs/calcium alginate gel significantly improved the amount of glycosaminoglycan (GAG) and type II collagen in the defect area in the early stage via activating the Smad pathway, when compared to a BMSCs/calcium alginate gel without TGF-31 transfection. Hypertrophy markers gene expression of chondrocytes were also inhibited by increasing Yes-associated protein-1 (YAP-1).38 Additionally, TGF- 31-incorporated collagen vitrigel had a better effect on mana- ging the early pain mitigation and osteochondral defect repair compared to collagen vitrigel alone.39 Moreover, BMSC submit your manuscript | www.dovepress.com DovePress 6099 Chen et al A Acc. V Magn 10.0kV 100x C 6100 E 200m were induced for the first 4 days with transient soluble TGF- B1, in which the accumulation of proteoglycans was 10-fold higher than TGF-B1-free culture after 3 weeks. These results suggest that TGF-ß promotes chondrogenic differentiation mainly depends on the extent of stimulation of the first week. 40 Nevertheless, there are still some studies that do not support the role of TGF-ß in cartilage repair in vivo. In a rabbit osteochondral defect model, oligo polyethene glycol B D submit your manuscript | www.dovepress.com DovePress F Figure I Nanofibrous PLLA scaffolds induce cartilage regeneration in vitro and in vivo. (A) SEM micrographs of nanofibrous PLLA scaffolds with macro-porous structures (Scale bar: 200 µm). (B) SEM micrographs of the nanofibrous microstructure of the pore walls at a higher magnification (Scale bar: 10 µm). (C) H&E staining showed that BMSCs grew throughout the whole scaffolds after 4 weeks in vitro chondrogenic culture on nanofibrous PLLA scaffold (Scale bar: 200um). (D) Alcian blue staining showed a dense GAG matrix deposition after 4 weeks in vitro chondrogenic culture on nanofibrous PLLA scaffold (Scale bar: 100 µm). (E) H&E staining revealed that BMSCs/ nanofibrous PLLA scaffold constructs had typical cartilage morphology after 8 weeks implanted in nude mice (Scale bar: 200 µm). (F) Safranin-O staining showed that BMSCs/nanofibrous PLLA scaffold constructs were positive for GAG-containing matrix in vivo (Scale bar: 200 µm). 10 mm. Notes: Reprinted from Gupte MJ, Swanson WB, Hu J, et al. Pore size directs bone marrow stromal cell fate and tissue regeneration in nanofibrous macroporous scaffolds by mediating vascularization. Acta Biomater. 2018;82:1-11. Copyright (2018), with permission from Elsevier.27 Dovepress (PEG) fumarate (OPF) hydrogel composites containing gela- tin microparticles (GMPs) loaded with MSCs with or without TGF-B1 did not improve cartilage morphology. Besides, undesirable side effects such as synovial fibrosis, endochon- dral ossification and hypertrophic scars were observed in vivo after a continuous stimulation by TGF-B1.4 Therefore, it is crucial to properly deliver and present TGF- ẞs in vivo for cartilage regeneration. 42-44 International Journal of Nanomedicine 2020:15