# The Immunological Properties of Nanomaterials for Repairing Knee Ligament Sports Injuries

Authors: Xueliang Li
Journal: Journal of Nanomaterials
 (2022)

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## Abstract

With the development of science and the advancement of medicine, there are more and more treatment methods for repairing knee ligament sports injuries. At present, the common method of ligament repair is to implant artificial synthetic materials or natural biological materials into the body to form artificial ligaments to repair and reconstruct damaged ligaments. Existing ligament repair techniques are often accompanied by sequelae, and the implants are not well adapted. The purpose of this article is to compare the degree of repair of damaged ligaments after implantation of artificial ligaments made of different nanomaterials and to study the mechanical properties, biomechanical properties, and immunological properties of artificial ligaments implanted in the body, in order to explore the role of different artificial ligaments on knee ligament repair. According to the different synthetic materials of artificial ligaments, the experimental subjects were divided into three groups: silk fibroin polycaprolactone nanofiber membrane group (SF/PCL), polycaprolactone nanofiber membrane group (PCL), and control group. By comparing the biocompatibility, cell adhesion, cell proliferation rate, and repair ability of collagen fiber formation of the experimental scaffold after implantation in the body, as well as its immunological performance, the results of the study showed that compared with PCL, SF/PCL increased its biocompatibility by 25%, increased its cell proliferation by 57%, increased its somatic cell adhesion by 35%, and increased its collagen fiber formation by 12%, the porosity is about 60%, and the load is as high as907±132N. The data shows that the silk fibroin polycaprolactone nanofiber membrane scaffold has good biocompatibility, degradability, and mechanical properties.


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## Body

## 1. Introduction

Ligament injury is one of the common sports system injuries in clinical practice, which usually leads to a decline in work and sports ability. After ligament injury, there are usually small blood vessels rupture and hemorrhage, local pain, swelling, intraorganism hemorrhage, hematoma, joint swelling, movement disorder, and tenderness. On physical examination, the traction ligaments were found to be significantly painful, and if completely ruptured, the stability of the joint was reduced. With the increase in sports activities and the aging of the population, this number is still rising. Traditional treatment methods include conservative treatment, sutures, autologous and allogeneic transplants, and artificial prostheses. As a result, the tissue structure cannot be restored to its mechanical strength and movement angle before injury. Therefore, exploring methods that can effectively promote ligament regeneration and repair has extremely important clinical significance and application value.With the development of science and technology, materials science and biomedicine are more and more closely integrated, and nanomaterials have made great achievements in biological applications. The knee ligament is the main static and stable structure for knee flexion and rotation activities, and it plays an extremely important role in maintaining the stability of the knee joint [1]. Knee ligament injury is a high-energy injury, often accompanied by serious injury to other parts [2]. For damaged ligament tissues, we need scaffold materials to promote the regeneration of damaged tissues in the body, the application of surface modification and separation, and culture of cytokines, and seed cells are specific methods for constructing and selecting scaffold materials; a large number of scholars have done a lot of research in this direction [3]. By modifying the surface of artificial ligaments with biologically active materials, the surface biological properties of the graft are improved, and the formation of the new bone at the interface is promoted. Therefore, in order to achieve compactness, therefore, nanomaterials with surface modification through nanotechnology are widely used. It is very necessary to apply nanomaterials in the repair of artificial ligaments to bring good news to human health.This article discusses the immunological performance of nanomaterials for repairing knee ligament sports injuries and sets high standards for the selection of tissue engineering scaffolds. The mechanism of the stent in the process of repairing damaged ligaments and the problems discovered and resolved during the research process are also studied. Read et al. first proposed the application of engineered histology in the medical field and proposed a feasible treatment plan for repairing ligaments using nanomaterial scaffolds [4, 5]. Zult et al. first proposed the use of electrospinning technology to fuse silk fibroin and polycaprolactone nanofibers to improve the compatibility of materials and further improve the repair ability of damaged ligaments [6]. Kim et al. used to change the voltage value to explore the relationship between material and fiber diameter and find the best value between voltage and fiber diameter [7]. Evangelopoulos et al. first discovered the effect of SF concentration on fiber diameter during the experiment. When the optimal concentration is reached, the fiber diameter is uniform and neatly arranged, and the compatibility is best at this time [8]. Although their research has introduced various applications of nanomaterials, there is not much research on the repair of artificial ligaments. Therefore, this study is necessary.This article summarizes and analyzes the research experience and results of many predecessors. In addition, this article has made some innovations in research content and research methods. The specific innovations are as follows: first, this paper constructs the SF/PCL composite nanomaterial for the first time and studies its formation mechanism. The effect of SF content on the repair properties of artificial ligaments in SF/PCL blends is proposed. Secondly, this article uses electrospinning technology to construct a SF and PCL hybrid scaffold for the first time and studied the interaction mechanism of PCL and SF/PCL. Third, this article is the first to use scanning electron microscope observation, infrared spectroscopy, and thermal analysis to study the compatibility of silk fibroin and gelatin in hybrid nanofibers. The combination method is used to analyze statistical data, and the normal analysis of variance and multivariate analysis is used for formal combination verification. The use of electron microscope observation not only effectively increases the observation multiple and improves the clarity of the electron microscope but also can analyze the degree of healing of the artificial ligament.


## 2. Pathological Study on the Indexes of Off-Pump Transplantation

### 2.1. The Role of Knee Ligaments and the Impact on the Body after Injury

Ligament injury should be treated early and fully repaired. If it is not treated in time, the joint will be repeatedly sprained, which will inevitably cause damage to articular cartilage, meniscus, and other important structures, resulting in premature aging of the joint and severe secondary traumatic arthritis. The key to its treatment lies in the repair of damaged ligaments. Partial tears can be directly sutured and repaired, while complete ruptures require surgery to transfer and reconstruct adjacent tendons, fascia, and other tissues. Ligaments are dense connective tissue, mainly composed of collagen fibers. The main ligaments of the knee joint are the anterior cruciate ligament, the posterior cruciate ligament, the medial collateral ligament, and the lateral main ligament. They cross each other and are covered by the synovial membrane, located outside the synovial cavity, and are considered to be the central movement hub of the knee joint [9]. The role of the anterior cruciate ligament is as follows: during the extension and bending of the knee joint, the two bundles cross and twist, thereby increasing the stability of the knee joint. It has the functions of preventing forward displacement of the tibia, over extension of the knee, over bending of the knee, and prevention of knee virus and valgus [10]. The role of the posterior cruciate ligament is as follows: in order to limit the posterior movement of the tibia, ensure the stability of the posterior knee joint and limit the hyperextension of the tibia, and to a certain extent, limit the internal rotation, adduction, and abduction of the tibia tendon [11]. Each bremsstrahlung cooperates with other major belts and organizations to perform certain functions. Each major ligament of the knee joint contributes to the spontaneous tension interlocking inside and outside the joint, which not only becomes a powerful stabilizing device but also completes the function of the knee joint together [12]. Ligament injury has the ability to repair itself, but after the injury, the overall stability of the knee joint will change, and the load stress shared by different structures will also change from the normal situation [13]. After the injury of the posterior cruciate ligament, the function of the posterior cruciate ligament is good in the short and medium-term injuries, but in the later stage, it will lead to poor knee function, joint disease, and advanced osteoarthritis [14]. Anterior cruciate ligament injury can lead to knee osteoarthritis. The degeneration of articular cartilage in the later stage of the posterior cruciate ligament injury is related to the long-term abnormal mechanical environment after the posterior cruciate ligament injury, which makes the anterior cruciate ligament degeneration. Further exacerbated the instability of the knee joint [15, 16]. However, the rupture of the posterior cruciate ligament will also affect the function and structure of the anterior cruciate belt. The mechanical environment is responsible for the development of ligament tissue, and changes in the stress on the tissue will cause changes in the structure and function of tissues and organs. This process is called organizational remodeling [17]. The mechanical properties of the front crossbelt are changed under reduced tensile stress, and the tensile strength is reduced. When the ligament structure is exposed to a reduced stress environment, the longer the time, the greater the damage to the mechanical properties of the ligament and tissue structure. Even for short-term stress relief, it takes a long time to restore the mechanical properties of the ligament [18]. When the stress on the ligament decreases, we also find that the strength and stiffness of the ligament decrease. Ligament rupture can damage the stability of the knee joint and cause abnormal knee joint mechanics, which may be caused by damage to other tissues inside and outside the joint. Without timely treatment and intervention, knee pain and dysfunction will eventually occur [19]. After the back-crossbelt is injured, cartilage degeneration will occur, leading to osteoarthritis. In general, ligament injuries are accompanied by some complications. The complications of different ligament injuries are not necessarily the same, but all of them will cause inconvenience to the movement of the human body, and even lead to disability in severe cases.


### 2.2. Mechanism of Repairing Damaged Ligaments by Implanting Artificial Ligaments of Nanomaterials into the Body

The material of the artificial ligament is a nondegradable fiber with good chemical stability, but its hydrophobicity is strong, and the cell compatibility is poor. In order to improve the hydrophilicity and biocompatibility of materials used for surface treatment and modification, the development of nanotechnology and nanomaterials provides new methods to improve the biocompatibility of materials [20]. The surface area of nanomaterials increases, and the hydrophilicity increases, which can absorb more cells and extracellular matrix proteins. The nanostructures and patterns on the material surface can significantly improve the biocompatibility of orthopedic implants [21]. Researchers believe that the formation of nanopatterns and structures on the surface of the implant can promote the erection and proliferation of osteoblasts in vitro and promote bone formation and bone remodeling on the surface of endophytic bacteria in the body. In the torsion test, the internal fracture of the mineralized bone tissue and the interface between the bone tissue and the implant were intact [22]. Nanocomposites are commonly used as surface modification materials for prosthetic implants, which can greatly improve the affinity between the implant and the surrounding bone tissue. Nanocomposites overcome the shortcomings of common materials in performance. The surface of the artificial ligament implant is coated. Nano and nanocomposite materials have better advantages and excellent functions. Nano enhances the proliferation of osteoblasts and the synthesis of cell proteins and improves alkaline phosphatase (activity and mass deposition), thereby enhancing the tight integration of bones and internal plants and thereby increasing the use rate of prostheses [23]. Like cells adhere and grow better on the nanocomposite coating group, and the cell density will increase over time [24]. The thermal method after spraying is used to apply a nanocrystalline coating on the surface of the implant, which can maintain the structural integrity of the coating, increase the crystallinity, and improve the long-term stability of the implant coating in the body [25]. The nanocoating layer has good cell compatibility, and the nanocoating has excellent biocompatibility and biological activity, increasing the biological activity of the graft and increasing the adhesion of osteoblasts [26]. The composite material is composed of synthetic materials. In the normal coating group, the experimental group showed higher cell growth and proliferation rates and better effects, thereby improving the hydrophilicity of the implant. In vitro cell tests showed that the coating group greatly promoted the adhesion of osteoblasts and enhanced cell proliferation. Relevant studies have shown that, compared with the uncoated group, the cell expression level was higher, and as the expression amount increased, the expression became more active [27, 28]. Nanocomposite coatings have been successfully used in ligament tissue engineering implant materials. Nanostructure is a new system constructed or constructed according to certain rules on the basis of nanoscale material units. Applying the nanostructured artificial ligament to ligament injury will greatly improve its structural strength.As the content of nanofibers increases, the microstructure of the formed scaffold changes from a layered structure to a porous structure, indicating that its formability has been significantly improved [3]. More importantly, the content of nanofibers in the silk fibroin solution also affects the mechanical properties and stability of the scaffold in water. Without any posttreatment, a porous scaffold that can maintain the original overall structure and porous microstructure in water can be obtained, and its retention rate in water exceeds 85% [29]. Compared with traditional silk fibroin scaffold materials, the scaffold material has lower crystallinity and faster degradation performance; so, it shows good hydrophilicity and better biocompatibility. The application in the tissue field provides a richer matrix material [1]. The relationship between cell proliferation rate and nanofiber content is shown in formulas (1) and (2).
(1)Ts=∑j=1vMfD∗log2d+JV,(2)V=L∗snb∑i=1nlyin−fyiyl+yln+∑im+1nl+nRyin−fyiyR+yRn,whereV is the cell proliferation rate, and TS is the content of nanofibers.


## 2.1. The Role of Knee Ligaments and the Impact on the Body after Injury

Ligament injury should be treated early and fully repaired. If it is not treated in time, the joint will be repeatedly sprained, which will inevitably cause damage to articular cartilage, meniscus, and other important structures, resulting in premature aging of the joint and severe secondary traumatic arthritis. The key to its treatment lies in the repair of damaged ligaments. Partial tears can be directly sutured and repaired, while complete ruptures require surgery to transfer and reconstruct adjacent tendons, fascia, and other tissues. Ligaments are dense connective tissue, mainly composed of collagen fibers. The main ligaments of the knee joint are the anterior cruciate ligament, the posterior cruciate ligament, the medial collateral ligament, and the lateral main ligament. They cross each other and are covered by the synovial membrane, located outside the synovial cavity, and are considered to be the central movement hub of the knee joint [9]. The role of the anterior cruciate ligament is as follows: during the extension and bending of the knee joint, the two bundles cross and twist, thereby increasing the stability of the knee joint. It has the functions of preventing forward displacement of the tibia, over extension of the knee, over bending of the knee, and prevention of knee virus and valgus [10]. The role of the posterior cruciate ligament is as follows: in order to limit the posterior movement of the tibia, ensure the stability of the posterior knee joint and limit the hyperextension of the tibia, and to a certain extent, limit the internal rotation, adduction, and abduction of the tibia tendon [11]. Each bremsstrahlung cooperates with other major belts and organizations to perform certain functions. Each major ligament of the knee joint contributes to the spontaneous tension interlocking inside and outside the joint, which not only becomes a powerful stabilizing device but also completes the function of the knee joint together [12]. Ligament injury has the ability to repair itself, but after the injury, the overall stability of the knee joint will change, and the load stress shared by different structures will also change from the normal situation [13]. After the injury of the posterior cruciate ligament, the function of the posterior cruciate ligament is good in the short and medium-term injuries, but in the later stage, it will lead to poor knee function, joint disease, and advanced osteoarthritis [14]. Anterior cruciate ligament injury can lead to knee osteoarthritis. The degeneration of articular cartilage in the later stage of the posterior cruciate ligament injury is related to the long-term abnormal mechanical environment after the posterior cruciate ligament injury, which makes the anterior cruciate ligament degeneration. Further exacerbated the instability of the knee joint [15, 16]. However, the rupture of the posterior cruciate ligament will also affect the function and structure of the anterior cruciate belt. The mechanical environment is responsible for the development of ligament tissue, and changes in the stress on the tissue will cause changes in the structure and function of tissues and organs. This process is called organizational remodeling [17]. The mechanical properties of the front crossbelt are changed under reduced tensile stress, and the tensile strength is reduced. When the ligament structure is exposed to a reduced stress environment, the longer the time, the greater the damage to the mechanical properties of the ligament and tissue structure. Even for short-term stress relief, it takes a long time to restore the mechanical properties of the ligament [18]. When the stress on the ligament decreases, we also find that the strength and stiffness of the ligament decrease. Ligament rupture can damage the stability of the knee joint and cause abnormal knee joint mechanics, which may be caused by damage to other tissues inside and outside the joint. Without timely treatment and intervention, knee pain and dysfunction will eventually occur [19]. After the back-crossbelt is injured, cartilage degeneration will occur, leading to osteoarthritis. In general, ligament injuries are accompanied by some complications. The complications of different ligament injuries are not necessarily the same, but all of them will cause inconvenience to the movement of the human body, and even lead to disability in severe cases.


## 2.2. Mechanism of Repairing Damaged Ligaments by Implanting Artificial Ligaments of Nanomaterials into the Body

The material of the artificial ligament is a nondegradable fiber with good chemical stability, but its hydrophobicity is strong, and the cell compatibility is poor. In order to improve the hydrophilicity and biocompatibility of materials used for surface treatment and modification, the development of nanotechnology and nanomaterials provides new methods to improve the biocompatibility of materials [20]. The surface area of nanomaterials increases, and the hydrophilicity increases, which can absorb more cells and extracellular matrix proteins. The nanostructures and patterns on the material surface can significantly improve the biocompatibility of orthopedic implants [21]. Researchers believe that the formation of nanopatterns and structures on the surface of the implant can promote the erection and proliferation of osteoblasts in vitro and promote bone formation and bone remodeling on the surface of endophytic bacteria in the body. In the torsion test, the internal fracture of the mineralized bone tissue and the interface between the bone tissue and the implant were intact [22]. Nanocomposites are commonly used as surface modification materials for prosthetic implants, which can greatly improve the affinity between the implant and the surrounding bone tissue. Nanocomposites overcome the shortcomings of common materials in performance. The surface of the artificial ligament implant is coated. Nano and nanocomposite materials have better advantages and excellent functions. Nano enhances the proliferation of osteoblasts and the synthesis of cell proteins and improves alkaline phosphatase (activity and mass deposition), thereby enhancing the tight integration of bones and internal plants and thereby increasing the use rate of prostheses [23]. Like cells adhere and grow better on the nanocomposite coating group, and the cell density will increase over time [24]. The thermal method after spraying is used to apply a nanocrystalline coating on the surface of the implant, which can maintain the structural integrity of the coating, increase the crystallinity, and improve the long-term stability of the implant coating in the body [25]. The nanocoating layer has good cell compatibility, and the nanocoating has excellent biocompatibility and biological activity, increasing the biological activity of the graft and increasing the adhesion of osteoblasts [26]. The composite material is composed of synthetic materials. In the normal coating group, the experimental group showed higher cell growth and proliferation rates and better effects, thereby improving the hydrophilicity of the implant. In vitro cell tests showed that the coating group greatly promoted the adhesion of osteoblasts and enhanced cell proliferation. Relevant studies have shown that, compared with the uncoated group, the cell expression level was higher, and as the expression amount increased, the expression became more active [27, 28]. Nanocomposite coatings have been successfully used in ligament tissue engineering implant materials. Nanostructure is a new system constructed or constructed according to certain rules on the basis of nanoscale material units. Applying the nanostructured artificial ligament to ligament injury will greatly improve its structural strength.As the content of nanofibers increases, the microstructure of the formed scaffold changes from a layered structure to a porous structure, indicating that its formability has been significantly improved [3]. More importantly, the content of nanofibers in the silk fibroin solution also affects the mechanical properties and stability of the scaffold in water. Without any posttreatment, a porous scaffold that can maintain the original overall structure and porous microstructure in water can be obtained, and its retention rate in water exceeds 85% [29]. Compared with traditional silk fibroin scaffold materials, the scaffold material has lower crystallinity and faster degradation performance; so, it shows good hydrophilicity and better biocompatibility. The application in the tissue field provides a richer matrix material [1]. The relationship between cell proliferation rate and nanofiber content is shown in formulas (1) and (2).
(1)Ts=∑j=1vMfD∗log2d+JV,(2)V=L∗snb∑i=1nlyin−fyiyl+yln+∑im+1nl+nRyin−fyiyR+yRn,whereV is the cell proliferation rate, and TS is the content of nanofibers.


## 3. Experimental Detection of the Experimental Group and Normal Group

### 3.1. Experimental Sample Preparation and Experimental Methods

First weigh the silk fibroin powder of the corresponding mass, add it to the mixed solvent, seal it with plastic wrap, then sonicate it for 1 h until the silk fibroin powder is evenly dispersed in the mixed solvent, and then add 4.0 g PCL. The membrane is sealed and heated in an oil bath at 40°C for 24 h until the PCL is completely dissolved, and the spinning solution is uniform and stable. SF/PCL spinning parameters are different, used for electrospinning: receiving distance 10 cm, bolus speed 2 mL/h, receiving speed 140 r/min, and voltage 15 kV. SF/PCL spinning parameters under the same composition were as follows: receiving distance 10 cm, bolus injection speed 2 mL/h, receiving speed 140 r/min, and voltage 12-25 kV. The blended fiber membrane obtained by electrospinning is vacuum dried and stored. A certain amount of collagen is dissolved in an acetic acid solution to prepare a collagen solution with a concentration of 10%. After mixing, centrifuge to remove air bubbles, then remove the wire mesh holder, cut it to the width of the hole, and start making. Spread a layer of collagen and freeze at 20 degrees for about half an hour. Spread the thread and stretch it under certain tension. Then, spread a denser layer of collagen and freeze it at 15 degrees. Wrap them in tin foil, freeze them at 10°C for 4 hours, drain them in a vacuum dryer, and cut them into various lengths for in vivo repair. Divide 20 white rabbits into three groups and implant SF/on the PCL of the injury group. The PCL implantation injury group and control group were as follows. Chloral hydrate was injected intraperitoneally, the ear vein was anesthetized with a catheter, fixed in the supine position, the upper and lower legs in front of the left and right knee joints were shaved, and the left or right knee was randomly selected as the experimental group or the control group and disinfected with compound iodine. Put a sterile small hole towel on the skin and make an incision on the inside of the knee joint. The upper end starts from the upper part of the femur, and the lower end reaches the inside of the tibia, approximately the length. Cut the skin and fascia in turn to expose the medial collateral ligament of the knee joint, separate it, and then remove the ligament from it. The knee joint moved several times, and the tension of the reconstructed ligament was satisfactory. The wound was closed layer by layer, and the ear vein was placed with sterile gauze. After the operation, the medial collateral ligament specimen was fixed with formalin for several hours, and the ligament was cut. Embed the fractured tissue and scar in paraffin, slice, stain, and observe the arrangement and density of scar collagen under light. Use a microscope to understand its healing.


### 3.2. Experimental Results

In the first week after implantation, the number of human-derived cells in the injured area gradually decreased over time. Two weeks after implantation, these genes were detected in the damaged part of the ligament. The secretory ligament matrix promotes ligament repair. SF/PCL scaffold can only help ligament repair and secrete ligament extracellular matrix and can also secrete growth factors to affect ligament regeneration. Most growth factors accelerate cell proliferation, and FS/PCL may also synthesize various factors that can induce musculoskeletal tissue. The expression of chemokines and growth factors is involved in tissue repair and regeneration before and after stent implantation. The cells express chemokines one week after implantation and still express two weeks after implantation, indicating that SF/PCL can secrete chemokines to attract host cells to participate in the formation of new ligaments. The overall observation results four weeks after implantation showed that all the damaged areas of the abdominal cavity window were repaired by connective tissue, and the muscle and spinal cord tissue was significantly proliferated. There was no significant difference between the two groups. There was no significant difference in the muscle health collagen content of each group every week. Thirty days after implantation, a dense tissue was formed, which was mainly composed of spindle-shaped lyocells and collagen fiber bundles. After being implanted in the body, the engineered ligament will undergo a maturation process. Although collagen fibers are still relatively scarce and small and uniform in diameter, collaborative mechanical stimulation can still promote the maturation of collagen fibers. The diameter of collagen fibers increased by about 25%, and the expression of ligament-specific transcription genes and extracellular matrix genes increased during ligament repair. At 12 weeks, the maximum tensile force of the experimental group was significantly higher than that of the control group.


### 3.3. Material Selection and Physiological Characteristics of Tissue Engineering Scaffold for Knee Ligament Repair

The repair of damaged ligaments is completed by the tissue engineering scaffold implanted in the body; so, the selection of the scaffold is more demanding. The extracellular matrix (ECM) is not only the supporting structure of cells but also functional. It creates a dynamic three-dimensional microenvironment for cells, realizes the signal transmission between the cell nucleus and the extracellular matrix, and promotes cell adhesion, proliferation, migration, and differentiation. Therefore, it is particularly important to imitate the composition and structure of ECM in tissue engineering. It has been found that cell-collagen interaction affects cell growth and differentiation. The biggest advantage of electrospun nanofibers as a tissue engineering scaffold is that it can simulate the composition and structure of the extracellular matrix (ECM). The ideal tissue engineering material should have the following characteristics: nontoxic; that is, the material itself and its degradation products will not produce inflammation and toxic reactions; it has good biocompatibility, biodegradability, and degradation adaptability and will not cause inflammatory and toxic reactions. In short, as a matrix material for different seed cells, the inoculated cells can be positioned, attached, and positioned to grow and proliferate. At the same time, the material can arrange cells orderly in the scaffold space, differentiate with specific functions, and synthesize appropriate extracellular matrix (ECM). In addition, when transplanting functional tissue engineering into the body, the scaffold material should also have mechanical support functions, blood pressure resistance, blood compatibility, thermal stability, and dimensional stability. This material was selected as the primary problem medical treatment for electrospun nanofiber biomaterials. Anterior cruciate ligament (ACL) cells and NIH3T3 cells can adhere, proliferate, and secrete the extracellular matrix on the scaffold material. The scaffold material has excellent biocompatibility and certain mechanical properties, and the maximum tensile force of the experimental group is significantly higher than that of the control group. The grafts coated with SF can greatly induce new bone formation, and the average width of the graft bone interface is significantly lower than the control group. In addition, the surface of the ligament graft also stimulates the high expression of bone morphogenetic protein and vascular endothelial growth factor at the local interface. SF/PCL infiltrated many megakaryocytes, the inflammatory response was mild, and there were many fibroblasts and new blood vessels around. The absorbable material placed in the anterior cruciate ligament (ACL) reconstruction graft gradually degrades and absorbs with the growth of new tissue after surgery and is finally completely replaced by collagen fibrous tissue. Histological examination confirmed that there was no obvious lymphocyte infiltration, the cells were spindle-shaped, the fibrous tissue was arranged neatly and evenly, and capillary hyperplasia was visible. And the discovery of nonself-tissue alleles indicates that the implanted cells remain viable. The mixed form of nanofibers can promote the proliferation of ACL fibroblasts. Cell morphology analysis shows that the mixed nanofiber material scaffold has better biocompatibility than PCL nanofiber. SF/PCL nanofibers are biomaterials with application potential, suitable for ligament tissue engineering repair. Fibroblasts have been successfully planted on the scaffold material and adhere to and grow well on the material. The results show that the constructed scaffold material has good three-dimensional configuration and biocompatibility, and it is expected to provide a new type of scaffold material for repairing anterior cruciate ligament injury. The data analysis showing the influence of fiber diameter on tensile strength and elongation is shown in Table1.Table 1
The effect of fiber diameter on tensile strength and elongation.
GroupFiber diameterTensile strength (MP)Elongation (%)The first2923.5538.9Second4384.562.8Third2504.250.4It can be seen from the above chart 1 that when the concentration of SF/PCL is 45%, the fiber diameter is the largest, the arrangement is uniform, and the stability is good. Its tensile strength increases by 30%, and the elongation rate increases to 62.5%. Affected by the SF concentration, it increases with the increase of the concentration at the initial stage, and when it is 45% higher, it decreases with the increase of the concentration. The material concentration directly affects the performance of the material.


### 3.4. Factors Affecting the Repair Performance of Nanomaterial Scaffolds and Immunological Performance

When silk fibroin material is added to PCL, the diameter of the fiber is relatively small, about 290 nanometers, and a bead-shaped fiber is formed. This is because the spinning solution is relatively thin, the surface tension is small, and the electric field force is large to obtain traction. The lower surface tension is not conducive to the complete volatilization of water. Beads appear very easily; after adding silk powder, fine particles will adhere to the PCL fiber. With the addition of silk powder, the composition continues to increase, from 4.8% to 45%. The diameter of the composite fiber also increased from 320 nm to 440 nm. After adding silk fibroin powder, the bead fiber gradually disappeared, and the diameter of the composite fiber increased without being fully extended. When the SF/PCL concentration is 45%, the composite fiber has the largest diameter, and the fiber distribution is more uniform. At this time, the compatibility between silk fibroin powder and polycaprolactone is the best. If the content of silk fibroin powder continues to increase, if the viscosity of the solution is too high, the silk fibroin powder seems to agglomerate obviously, and the diameter of the composite fiber is reduced to 350 nm. The compatibility of silk fibroin powder with polycaprolactone deteriorates, the spinnability of the spinning solution decreases, and the fiber thickness is uneven. The gaps between the fibers are large, and the fibers are bent and deformed. Because the concentration is too large, the electric field force is not enough to overcome the surface tension of the liquid and reduce the relative amount of solvent. The volatilization of the solvent causes the fiber to coagulate and deform the fiber. When the SF/PCL concentration is 45%, the silk fibroin powder in the composite fiber does not appear lumpy, indicating that the concentration at this time is moderate. During the experiment, when the voltage was increased from 15 kV to 25 kV, the fiber diameter increased from 440 nm to 465 nm, and the fiber diameter did not change significantly, but at 20 kV, the fiber diameter was uniform, and the gap between the fibers was large. At 25 kV, the fiber diameter changes again. The size is different, because the applied voltage is too large, the large amount of charge in the solution will make the spinneret spin faster and faster, and the traction will pull out a large amount of solution, resulting in uneven fiber thickness. When the concentration is 45%, the voltage difference affects the uniformity of the fiber diameter. When the voltage is 18 kV and 21 kV, the fiber diameter is 480 nm and 524 nm, the fiber diameter is the same thickness, and the fiber arrangement is uniform and compact. The electric field force overcomes the surface tension of the solution during the stretching process, so that after the fibers are completely solidified, the arrangement is more uniform. The graft has varying degrees of inflammation in the early postoperative period, and there is inflammatory cell infiltration around the artificial ligament. Considering that inflammation affects the regeneration of tissue collagen, leading to the formation of fibrous blisters, controlling inflammation can help improve the transplanted ligament. Hyaluronic acid can be greatly reduced, and hyaluronic acid has been shown to have the ability to inhibit the activity of inflammatory cytokines.


## 3.1. Experimental Sample Preparation and Experimental Methods

First weigh the silk fibroin powder of the corresponding mass, add it to the mixed solvent, seal it with plastic wrap, then sonicate it for 1 h until the silk fibroin powder is evenly dispersed in the mixed solvent, and then add 4.0 g PCL. The membrane is sealed and heated in an oil bath at 40°C for 24 h until the PCL is completely dissolved, and the spinning solution is uniform and stable. SF/PCL spinning parameters are different, used for electrospinning: receiving distance 10 cm, bolus speed 2 mL/h, receiving speed 140 r/min, and voltage 15 kV. SF/PCL spinning parameters under the same composition were as follows: receiving distance 10 cm, bolus injection speed 2 mL/h, receiving speed 140 r/min, and voltage 12-25 kV. The blended fiber membrane obtained by electrospinning is vacuum dried and stored. A certain amount of collagen is dissolved in an acetic acid solution to prepare a collagen solution with a concentration of 10%. After mixing, centrifuge to remove air bubbles, then remove the wire mesh holder, cut it to the width of the hole, and start making. Spread a layer of collagen and freeze at 20 degrees for about half an hour. Spread the thread and stretch it under certain tension. Then, spread a denser layer of collagen and freeze it at 15 degrees. Wrap them in tin foil, freeze them at 10°C for 4 hours, drain them in a vacuum dryer, and cut them into various lengths for in vivo repair. Divide 20 white rabbits into three groups and implant SF/on the PCL of the injury group. The PCL implantation injury group and control group were as follows. Chloral hydrate was injected intraperitoneally, the ear vein was anesthetized with a catheter, fixed in the supine position, the upper and lower legs in front of the left and right knee joints were shaved, and the left or right knee was randomly selected as the experimental group or the control group and disinfected with compound iodine. Put a sterile small hole towel on the skin and make an incision on the inside of the knee joint. The upper end starts from the upper part of the femur, and the lower end reaches the inside of the tibia, approximately the length. Cut the skin and fascia in turn to expose the medial collateral ligament of the knee joint, separate it, and then remove the ligament from it. The knee joint moved several times, and the tension of the reconstructed ligament was satisfactory. The wound was closed layer by layer, and the ear vein was placed with sterile gauze. After the operation, the medial collateral ligament specimen was fixed with formalin for several hours, and the ligament was cut. Embed the fractured tissue and scar in paraffin, slice, stain, and observe the arrangement and density of scar collagen under light. Use a microscope to understand its healing.


## 3.2. Experimental Results

In the first week after implantation, the number of human-derived cells in the injured area gradually decreased over time. Two weeks after implantation, these genes were detected in the damaged part of the ligament. The secretory ligament matrix promotes ligament repair. SF/PCL scaffold can only help ligament repair and secrete ligament extracellular matrix and can also secrete growth factors to affect ligament regeneration. Most growth factors accelerate cell proliferation, and FS/PCL may also synthesize various factors that can induce musculoskeletal tissue. The expression of chemokines and growth factors is involved in tissue repair and regeneration before and after stent implantation. The cells express chemokines one week after implantation and still express two weeks after implantation, indicating that SF/PCL can secrete chemokines to attract host cells to participate in the formation of new ligaments. The overall observation results four weeks after implantation showed that all the damaged areas of the abdominal cavity window were repaired by connective tissue, and the muscle and spinal cord tissue was significantly proliferated. There was no significant difference between the two groups. There was no significant difference in the muscle health collagen content of each group every week. Thirty days after implantation, a dense tissue was formed, which was mainly composed of spindle-shaped lyocells and collagen fiber bundles. After being implanted in the body, the engineered ligament will undergo a maturation process. Although collagen fibers are still relatively scarce and small and uniform in diameter, collaborative mechanical stimulation can still promote the maturation of collagen fibers. The diameter of collagen fibers increased by about 25%, and the expression of ligament-specific transcription genes and extracellular matrix genes increased during ligament repair. At 12 weeks, the maximum tensile force of the experimental group was significantly higher than that of the control group.


## 3.3. Material Selection and Physiological Characteristics of Tissue Engineering Scaffold for Knee Ligament Repair

The repair of damaged ligaments is completed by the tissue engineering scaffold implanted in the body; so, the selection of the scaffold is more demanding. The extracellular matrix (ECM) is not only the supporting structure of cells but also functional. It creates a dynamic three-dimensional microenvironment for cells, realizes the signal transmission between the cell nucleus and the extracellular matrix, and promotes cell adhesion, proliferation, migration, and differentiation. Therefore, it is particularly important to imitate the composition and structure of ECM in tissue engineering. It has been found that cell-collagen interaction affects cell growth and differentiation. The biggest advantage of electrospun nanofibers as a tissue engineering scaffold is that it can simulate the composition and structure of the extracellular matrix (ECM). The ideal tissue engineering material should have the following characteristics: nontoxic; that is, the material itself and its degradation products will not produce inflammation and toxic reactions; it has good biocompatibility, biodegradability, and degradation adaptability and will not cause inflammatory and toxic reactions. In short, as a matrix material for different seed cells, the inoculated cells can be positioned, attached, and positioned to grow and proliferate. At the same time, the material can arrange cells orderly in the scaffold space, differentiate with specific functions, and synthesize appropriate extracellular matrix (ECM). In addition, when transplanting functional tissue engineering into the body, the scaffold material should also have mechanical support functions, blood pressure resistance, blood compatibility, thermal stability, and dimensional stability. This material was selected as the primary problem medical treatment for electrospun nanofiber biomaterials. Anterior cruciate ligament (ACL) cells and NIH3T3 cells can adhere, proliferate, and secrete the extracellular matrix on the scaffold material. The scaffold material has excellent biocompatibility and certain mechanical properties, and the maximum tensile force of the experimental group is significantly higher than that of the control group. The grafts coated with SF can greatly induce new bone formation, and the average width of the graft bone interface is significantly lower than the control group. In addition, the surface of the ligament graft also stimulates the high expression of bone morphogenetic protein and vascular endothelial growth factor at the local interface. SF/PCL infiltrated many megakaryocytes, the inflammatory response was mild, and there were many fibroblasts and new blood vessels around. The absorbable material placed in the anterior cruciate ligament (ACL) reconstruction graft gradually degrades and absorbs with the growth of new tissue after surgery and is finally completely replaced by collagen fibrous tissue. Histological examination confirmed that there was no obvious lymphocyte infiltration, the cells were spindle-shaped, the fibrous tissue was arranged neatly and evenly, and capillary hyperplasia was visible. And the discovery of nonself-tissue alleles indicates that the implanted cells remain viable. The mixed form of nanofibers can promote the proliferation of ACL fibroblasts. Cell morphology analysis shows that the mixed nanofiber material scaffold has better biocompatibility than PCL nanofiber. SF/PCL nanofibers are biomaterials with application potential, suitable for ligament tissue engineering repair. Fibroblasts have been successfully planted on the scaffold material and adhere to and grow well on the material. The results show that the constructed scaffold material has good three-dimensional configuration and biocompatibility, and it is expected to provide a new type of scaffold material for repairing anterior cruciate ligament injury. The data analysis showing the influence of fiber diameter on tensile strength and elongation is shown in Table1.Table 1
The effect of fiber diameter on tensile strength and elongation.
GroupFiber diameterTensile strength (MP)Elongation (%)The first2923.5538.9Second4384.562.8Third2504.250.4It can be seen from the above chart 1 that when the concentration of SF/PCL is 45%, the fiber diameter is the largest, the arrangement is uniform, and the stability is good. Its tensile strength increases by 30%, and the elongation rate increases to 62.5%. Affected by the SF concentration, it increases with the increase of the concentration at the initial stage, and when it is 45% higher, it decreases with the increase of the concentration. The material concentration directly affects the performance of the material.


## 3.4. Factors Affecting the Repair Performance of Nanomaterial Scaffolds and Immunological Performance

When silk fibroin material is added to PCL, the diameter of the fiber is relatively small, about 290 nanometers, and a bead-shaped fiber is formed. This is because the spinning solution is relatively thin, the surface tension is small, and the electric field force is large to obtain traction. The lower surface tension is not conducive to the complete volatilization of water. Beads appear very easily; after adding silk powder, fine particles will adhere to the PCL fiber. With the addition of silk powder, the composition continues to increase, from 4.8% to 45%. The diameter of the composite fiber also increased from 320 nm to 440 nm. After adding silk fibroin powder, the bead fiber gradually disappeared, and the diameter of the composite fiber increased without being fully extended. When the SF/PCL concentration is 45%, the composite fiber has the largest diameter, and the fiber distribution is more uniform. At this time, the compatibility between silk fibroin powder and polycaprolactone is the best. If the content of silk fibroin powder continues to increase, if the viscosity of the solution is too high, the silk fibroin powder seems to agglomerate obviously, and the diameter of the composite fiber is reduced to 350 nm. The compatibility of silk fibroin powder with polycaprolactone deteriorates, the spinnability of the spinning solution decreases, and the fiber thickness is uneven. The gaps between the fibers are large, and the fibers are bent and deformed. Because the concentration is too large, the electric field force is not enough to overcome the surface tension of the liquid and reduce the relative amount of solvent. The volatilization of the solvent causes the fiber to coagulate and deform the fiber. When the SF/PCL concentration is 45%, the silk fibroin powder in the composite fiber does not appear lumpy, indicating that the concentration at this time is moderate. During the experiment, when the voltage was increased from 15 kV to 25 kV, the fiber diameter increased from 440 nm to 465 nm, and the fiber diameter did not change significantly, but at 20 kV, the fiber diameter was uniform, and the gap between the fibers was large. At 25 kV, the fiber diameter changes again. The size is different, because the applied voltage is too large, the large amount of charge in the solution will make the spinneret spin faster and faster, and the traction will pull out a large amount of solution, resulting in uneven fiber thickness. When the concentration is 45%, the voltage difference affects the uniformity of the fiber diameter. When the voltage is 18 kV and 21 kV, the fiber diameter is 480 nm and 524 nm, the fiber diameter is the same thickness, and the fiber arrangement is uniform and compact. The electric field force overcomes the surface tension of the solution during the stretching process, so that after the fibers are completely solidified, the arrangement is more uniform. The graft has varying degrees of inflammation in the early postoperative period, and there is inflammatory cell infiltration around the artificial ligament. Considering that inflammation affects the regeneration of tissue collagen, leading to the formation of fibrous blisters, controlling inflammation can help improve the transplanted ligament. Hyaluronic acid can be greatly reduced, and hyaluronic acid has been shown to have the ability to inhibit the activity of inflammatory cytokines.


## 4. Analysis and Discussion of Influencing Factors in Repairing Injured Ligaments with Stents

### 4.1. Analysis of the Results of Repairing Damaged Ligaments with Nanomaterial Scaffolds

The test results show that the crystallinity of polycaprolactone is not the main factor affecting the difference in mechanical properties, but the increase in the crystallinity of the stent through heat treatment should further enhance the mechanical properties of the stent. PCL provides space to repair cell adhesion and growth, while SF/PCL provides sufficient mechanical strength. The research results show that, compared with PCL scaffold, SF/PC scaffold has more collagen deposition and rougher collagen production, and its mechanical properties are closer to normal tissues. After adding silk fibroin, the morphology of nanofibers is improved, the diameter of nanofibers is reduced, and the hydrophilicity of the material is increased. The mixed form of nanofibers can promote the proliferation of ACL fibroblasts. Cell morphology analysis shows that the mixed nanofiber material scaffold has better biocompatibility than PCL nanofiber. This proves that SF/PCL nanofibers are biomaterials with application potential and are suitable for ligament tissue engineering repair. At the same time, protein drugs embedded in silk fibroin can maintain its activity for a long time.The maximum load of SF/PCL artificial ligament is 2.73 times that of human ACL, and it is resistant to repetition. The strength of twisting and bending can prevent damage caused by excessive traction; SF/PCL ligament fibers line up the normal physiological structure of people, and the gap between the fibers is moderate, which is conducive to the normal growth of human tissues, increases the viscoelasticity of ligaments, and avoids wear and tear. Peeling is as follows: LARS ligament has stable performance and is not affected by the human body’s biological reaction process; 6 months after surgery, it was found that there are collagen fibers and vascular endothelial cells in the artificial ligament. The patient does not have acute synovitis and feels good; the patient who reconstructed ACL with SF/PCL ligament has no synovial inflammation and serious complications. The biomechanical test data of different experimental groups are shown in Table2.Table 2
Experimental group biomechanics test data.
GroupMaximum loadStiffnessEnergyDisplacementThe first36.1±22.721.8±8.540.6±35.42.3±0.5Second47.0±7.424.3±3.178.1±32.93.3±1.0Three88.2±18.346.21±1.8171.2±90.53.3±1.1The results of the study showed that the biomechanics of the body was changed. Compared with the PCL group, the maximum load of SF/PCL increased by 28%, the stiffness decreased by 10%, and the energy increased by 75%, indicating that the addition of SF material affects the biomechanics and improves the ligament.The SF/PCL artificial ligament is made of high-strength polyester fiber: its design combines the principles of bionics, the internal structure is similar to normal human ligaments, and the longitudinal fibers in the joints are elastic but not elongated and the external mesh of the joint. The fibrous fibers provide strength without being stretched, and there is no transverse fiber structure inside. The fiber structure promotes the growth of tissue cells and achieves the purpose of repair and reconstruction. It can prevent the friction between the fibers from generating debris particles, thereby avoiding the occurrence of synovitis. In addition, the material has good plasticity and can mimic the movement of normal human ligaments according to the rotation of the ligaments, and the fatigue strength depends on the number of fibers, as shown in Figure1.Figure 1
The effect of stent implantation time on fiber diameter and tensile strength.The data analysis results shown in Figure1 clearly show that the extensibility of bone marrow stromal stem cells increased by 38% after SF treatment, and the ability to adhere to cells was greatly enhanced, which was twice that of the PCL group, and the morphology was significantly better than that of the untreated group. The proliferation rate of artificial ligament cells after SF treatment increased significantly. The quantitative phosphatase activity was 12% higher than that of the untreated group.The SF/PCL scaffold has similar compressive modulus and mechanical strength to human trabecular bone. By culturing human osteoblasts, it was found that the cells can maintain the phenotype and show higher levels of alkaline phosphatase and mineral deposits. SF and PCL are raw materials, and SF/PCL stents are made by free surface electrospinning. The scaffold can improve the osteogenic differentiation of bone marrow mesenchymal stem cells derived from human cord blood, promote alkaline phosphatase activity and the expression of bone cell-specific transcription factors, osteocalcin, and type I collagen, and is an ideal bone tissue engineering supporting materials, as shown in Figure2.Figure 2
The relationship between SF concentration and fiber diameter and elongation.From the data in Figure2, it can be seen that the artificial ligament scaffold increased the cell proliferation rate, the number of cells increased with time, the extracellular genes of the control group decreased, and a large number of cells adhered to the SF/PCL patch, which was higher than the control 67% of the group and was 30% higher than that of the PCL group, inflammation-related genes were 40% lower than the blank group, and adhesion-related genes were 25% higher than the blank group.


### 4.2. Analysis of Biological Characteristics of Silk Fibroin Polycaprolactone Nanofibers

In the spinning process, the fiber diameter distribution is uneven, the dispersion is large, the mass fraction is 15%, and the effect on the spinning solution is more obvious. When the mass fraction of the spinning solution is 13%, the obtained nanofibers have a regular morphology, a small diameter, and a relatively uniform diameter distribution. When the mass fraction is 11%, the diameter of the fiber is the smallest, the average diameter is close to 100 nm, the diameter distribution is relatively concentrated, and the dispersion is small. Therefore, the mass fraction of the spinning solution can be 11% and 13%, as shown in Figure3.Figure 3
The fiber diameter changes with the voltage affect the artificial ligament load.It can be seen from the data in Figure3 that the voltage also has a certain effect on the engineering tissue scaffold. When the voltage reaches 20 kV, the fiber diameter is uniform, and the gap between the fibers is larger. At this time, the diameter increases by 8%. When the voltage continues to increase, the concentration slowly increases, the fiber diameter varies, and the gap becomes smaller, which affects the infiltration of cells. Such a scaffold will hinder the repair of the damaged ligament.Polycaprolactone (PCL) and SF are used to manufacture three-dimensional porous scaffolds through electrospinning technology. The addition of sericin enhances the adhesion and proliferation of human skin fibroblasts on the material. The hybrid nanofiber scaffold prepared by this technology is more conducive to the proliferation of ligament keratinocytes and fibroblasts. The scaffold material with SF as the matrix can well promote the growth of fibroblasts and can help wound healing and reconstruct the function of damaged ligaments, as shown in Figure4.Figure 4
The effect of stent implantation time on adhesion rate.It can be seen from Figure4 that the stent implantation time affects the repair of various ligament functions. After one week of implantation, the human source in the injured area is reduced by 30%, and the stromal cells increase by 13% at the second week. After 30 days of implantation, the collagen fiber diameter increases by 25%, 12 weeks, and the maximum pulling force is higher than the control group.


## 4.1. Analysis of the Results of Repairing Damaged Ligaments with Nanomaterial Scaffolds

The test results show that the crystallinity of polycaprolactone is not the main factor affecting the difference in mechanical properties, but the increase in the crystallinity of the stent through heat treatment should further enhance the mechanical properties of the stent. PCL provides space to repair cell adhesion and growth, while SF/PCL provides sufficient mechanical strength. The research results show that, compared with PCL scaffold, SF/PC scaffold has more collagen deposition and rougher collagen production, and its mechanical properties are closer to normal tissues. After adding silk fibroin, the morphology of nanofibers is improved, the diameter of nanofibers is reduced, and the hydrophilicity of the material is increased. The mixed form of nanofibers can promote the proliferation of ACL fibroblasts. Cell morphology analysis shows that the mixed nanofiber material scaffold has better biocompatibility than PCL nanofiber. This proves that SF/PCL nanofibers are biomaterials with application potential and are suitable for ligament tissue engineering repair. At the same time, protein drugs embedded in silk fibroin can maintain its activity for a long time.The maximum load of SF/PCL artificial ligament is 2.73 times that of human ACL, and it is resistant to repetition. The strength of twisting and bending can prevent damage caused by excessive traction; SF/PCL ligament fibers line up the normal physiological structure of people, and the gap between the fibers is moderate, which is conducive to the normal growth of human tissues, increases the viscoelasticity of ligaments, and avoids wear and tear. Peeling is as follows: LARS ligament has stable performance and is not affected by the human body’s biological reaction process; 6 months after surgery, it was found that there are collagen fibers and vascular endothelial cells in the artificial ligament. The patient does not have acute synovitis and feels good; the patient who reconstructed ACL with SF/PCL ligament has no synovial inflammation and serious complications. The biomechanical test data of different experimental groups are shown in Table2.Table 2
Experimental group biomechanics test data.
GroupMaximum loadStiffnessEnergyDisplacementThe first36.1±22.721.8±8.540.6±35.42.3±0.5Second47.0±7.424.3±3.178.1±32.93.3±1.0Three88.2±18.346.21±1.8171.2±90.53.3±1.1The results of the study showed that the biomechanics of the body was changed. Compared with the PCL group, the maximum load of SF/PCL increased by 28%, the stiffness decreased by 10%, and the energy increased by 75%, indicating that the addition of SF material affects the biomechanics and improves the ligament.The SF/PCL artificial ligament is made of high-strength polyester fiber: its design combines the principles of bionics, the internal structure is similar to normal human ligaments, and the longitudinal fibers in the joints are elastic but not elongated and the external mesh of the joint. The fibrous fibers provide strength without being stretched, and there is no transverse fiber structure inside. The fiber structure promotes the growth of tissue cells and achieves the purpose of repair and reconstruction. It can prevent the friction between the fibers from generating debris particles, thereby avoiding the occurrence of synovitis. In addition, the material has good plasticity and can mimic the movement of normal human ligaments according to the rotation of the ligaments, and the fatigue strength depends on the number of fibers, as shown in Figure1.Figure 1
The effect of stent implantation time on fiber diameter and tensile strength.The data analysis results shown in Figure1 clearly show that the extensibility of bone marrow stromal stem cells increased by 38% after SF treatment, and the ability to adhere to cells was greatly enhanced, which was twice that of the PCL group, and the morphology was significantly better than that of the untreated group. The proliferation rate of artificial ligament cells after SF treatment increased significantly. The quantitative phosphatase activity was 12% higher than that of the untreated group.The SF/PCL scaffold has similar compressive modulus and mechanical strength to human trabecular bone. By culturing human osteoblasts, it was found that the cells can maintain the phenotype and show higher levels of alkaline phosphatase and mineral deposits. SF and PCL are raw materials, and SF/PCL stents are made by free surface electrospinning. The scaffold can improve the osteogenic differentiation of bone marrow mesenchymal stem cells derived from human cord blood, promote alkaline phosphatase activity and the expression of bone cell-specific transcription factors, osteocalcin, and type I collagen, and is an ideal bone tissue engineering supporting materials, as shown in Figure2.Figure 2
The relationship between SF concentration and fiber diameter and elongation.From the data in Figure2, it can be seen that the artificial ligament scaffold increased the cell proliferation rate, the number of cells increased with time, the extracellular genes of the control group decreased, and a large number of cells adhered to the SF/PCL patch, which was higher than the control 67% of the group and was 30% higher than that of the PCL group, inflammation-related genes were 40% lower than the blank group, and adhesion-related genes were 25% higher than the blank group.


## 4.2. Analysis of Biological Characteristics of Silk Fibroin Polycaprolactone Nanofibers

In the spinning process, the fiber diameter distribution is uneven, the dispersion is large, the mass fraction is 15%, and the effect on the spinning solution is more obvious. When the mass fraction of the spinning solution is 13%, the obtained nanofibers have a regular morphology, a small diameter, and a relatively uniform diameter distribution. When the mass fraction is 11%, the diameter of the fiber is the smallest, the average diameter is close to 100 nm, the diameter distribution is relatively concentrated, and the dispersion is small. Therefore, the mass fraction of the spinning solution can be 11% and 13%, as shown in Figure3.Figure 3
The fiber diameter changes with the voltage affect the artificial ligament load.It can be seen from the data in Figure3 that the voltage also has a certain effect on the engineering tissue scaffold. When the voltage reaches 20 kV, the fiber diameter is uniform, and the gap between the fibers is larger. At this time, the diameter increases by 8%. When the voltage continues to increase, the concentration slowly increases, the fiber diameter varies, and the gap becomes smaller, which affects the infiltration of cells. Such a scaffold will hinder the repair of the damaged ligament.Polycaprolactone (PCL) and SF are used to manufacture three-dimensional porous scaffolds through electrospinning technology. The addition of sericin enhances the adhesion and proliferation of human skin fibroblasts on the material. The hybrid nanofiber scaffold prepared by this technology is more conducive to the proliferation of ligament keratinocytes and fibroblasts. The scaffold material with SF as the matrix can well promote the growth of fibroblasts and can help wound healing and reconstruct the function of damaged ligaments, as shown in Figure4.Figure 4
The effect of stent implantation time on adhesion rate.It can be seen from Figure4 that the stent implantation time affects the repair of various ligament functions. After one week of implantation, the human source in the injured area is reduced by 30%, and the stromal cells increase by 13% at the second week. After 30 days of implantation, the collagen fiber diameter increases by 25%, 12 weeks, and the maximum pulling force is higher than the control group.


## 5. Conclusions

(1)
In the process of tissue engineering scaffold repairing damaged ligaments, the concentration of SF increases, the fiber diameter increases, the traction force increases, the tensile strength increases by 30%, the stretching rate increases to 62.5%, and the maximum load ratio of SF/PCL is as follows. The PCL group increased by 28%, stiffness decreased by 10%, and energy increased by 75%. When increased to a certain extent, the fiber diameter is uniform, the pores are large, and the arrangement is neat, which is conducive to cell infiltration, generating new cells, and rebuilding damaged ligaments(2)
The research in this paper shows that the SF/PCL scaffold can make more use of damaged ligaments to recover, increase biocompatibility by 25%, increase cell proliferation rate by 57%, increase somatic cell adhesion rate by 35%, and increase collagen fiber formation by 12%, the porosity is about 60%, and the load is as high as907±132N. However, a large number of cells adhere to the SF/PCL membrane, which is higher than 67% in the control group and 30% higher than in the PCL group. Inflammation-related genes are lower than 40% in the blank group, and adhesion-related genes are 25% higher than those in the blank group. The data shows that the performance of the artificial ligament has been greatly changed by adding SF(3)
The study found that when the mass ratio of nanofibers to ordinary silk fibroin is 1 : 7, the mechanical properties of the scaffold are the best. The crystallinity of the scaffold material is reduced by 23%, the degradation performance is increased by 31%, and the hydrophilicity is increased by 60%. The compatibility is improved by 58%. These factors meet the conditions of the ideal scaffold required by tissue engineering and become the first choice for repairing knee ligament injuries. This result has given scientists a new understanding of the selection of scaffolds and laid a new foundation for the development of medicine



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*Source: 1760783-2022-05-19.xml*