A combinatorial approach: Cryo-printing and electrospinning hybrid scaffolds for cartilage tissue engineering

Cryo-Electrospinning Generates Highly Porous Fiber Scaffolds Which Improves Trabecular Meshwork Cell Infiltration

Human trabecular meshwork is a sieve-like tissue with large pores, which plays a vital role in aqueous humor outflow. Dysfunction of this tissue can occur, which leads to glaucoma and permanent vision loss. Replacement of trabecular meshwork with a tissue-engineered device is the ultimate objective. This study aimed to create a biomimetic structure of trabecular meshwork using electrospinning. Conventional electrospinning was compared to cryogenic electrospinning, the latter being an adaptation of conventional electrospinning whereby dry ice is incorporated in the fiber collector system. The dry ice causes ice crystals to form in-between the fibers, increasing the inter-fiber spacing, which is retained following sublimation. Structural characterization demonstrated cryo-scaffolds to have closer recapitulation of the trabecular meshwork, in terms of pore size, porosity, and thickness. The attachment of a healthy, human trabecular meshwork cell line (NTM5) to the scaffold was not influenced by the fabrication method. The main objective was to assess cell infiltration. Cryo-scaffolds supported cell penetration deep within their structure after seven days, whereas cells remained on the outer surface for conventional scaffolds. This study demonstrates the suitability of cryogenic electrospinning for the close recapitulation of trabecular meshwork and its potential as a 3D in vitro model and, in time, a tissue-engineered device.

Recent Advances in "Functional Engineering of Articular Cartilage Zones by Polymeric Biomaterials Mediated with Physical, Mechanical, and Biological/Chemical Cues"

Articular cartilage (AC) plays an unquestionable role in joint movements but unfortunately the healing capacity is restricted due to its avascular and acellular nature. While cartilage tissue engineering has been lifesaving, it is very challenging to remodel the complex cartilage composition and architecture with gradient physio-mechanical properties vital to proper tissue functions. To address these issues, a better understanding of the intrinsic AC properties and how cells respond to stimuli from the external microenvironment must be better understood. This is essential in order to take one step closer to producing functional cartilaginous constructs for clinical use. Recently, biopolymers have aroused much attention due to their versatility, processability, and flexibility because the properties can be tailored to match the requirements of AC. This review highlights polymeric scaffolds developed in the past decade for reconstruction of zonal AC layers including the superficial zone, middle zone, and deep zone by means of exogenous stimuli such as physical, mechanical, and biological/chemical signals. The mimicked properties are reviewed in terms of the biochemical composition and organization, cell fate (morphology, orientation, and differentiation), as well as mechanical properties and finally, the challenges and potential ways to tackle them are discussed.

PVP/CS/Phyllanthus emblica Nanofiber Membranes for Dry Facial Masks: Manufacturing Process and Evaluations

In the wake of increasing demands on skin health, we propose simple, natural, and safe dry facial masks that restrict melanin synthesis. Phyllanthus emblica (P. emblica) is made into powders via a low-temperature extraction and freeze-drying process to serve as a natural agent. Next, it is added to mixtures containing Polyvinylpyrrolidone (PVP) and Chitosan (CS), after which the blends are electrospun into PVP/CS/P. emblica nanofiber membrane dry facial masks using the electrospinning technique. The dry facial masks are evaluated using the calibration analysis method, extraction rate test, scanning electron microscopy (SEM), release rate test, tyrosinase inhibition assay, biocompatibility test, and anti-inflammatory capacity test. Test results indicate that when the electrospinning mixture contains 29.0% P. emblica, the nanofibers have a diameter of ≤214.27 ± 74.51 nm and a water contact angle of 77.25 ± 2.21. P. emblica is completely released in twenty minutes, and the tyrosinase inhibition rate reaches 99.53 ± 0.45% and the cell activity ≥82.60 ± 1.30%. Moreover, the anti-inflammatory capacity test results suggest that dry facial masks confine inflammatory factors. PVP/CS/P. emblica nanofiber dry facial masks demonstrate excellent tyrosinase inhibition and are hydrophilic, biocompatible, and inflammation-free. The dry facial masks are a suitable material that is worthwhile exploring and applying to the cosmetic field.

Articulation inspired by nature: A review of biomimetic and biologically active 3D printed scaffolds for cartilage tissue engineering

In the human body, articular cartilage facilitates the frictionless movement of synovial joints. However, due to its avascular and aneural nature, it has a limited ability to self-repair when damaged due to injury or wear and tear over time. Current surgical treatment options for cartilage defects often lead to the formation of fibrous, non-durable tissue and thus a new solution is required. Nature is the best innovator and so recent advances in the field of tissue engineering have aimed to recreate the microenvironment of native articular cartilage using biomaterial scaffolds. However, the inability to mirror the complexity of native tissue has hindered the clinical translation of many products thus far. Fortunately, the advent of 3D printing has provided a potential solution. 3D printed scaffolds, fabricated using biomimetic biomaterials, can be designed to mimic the complex zonal architecture and composition of articular cartilage. The bioinks used to fabricate these scaffolds can also be further functionalised with cells and/or bioactive factors or gene therapeutics to mirror the cellular composition of the native tissue. Thus, this review investigates how the architecture and composition of native articular cartilage is inspiring the design of biomimetic bioinks for 3D printing of scaffolds for cartilage repair. Subsequently, we discuss how these 3D printed scaffolds can be further functionalised with cells and bioactive factors, as well as looking at future prospects in this field.

The tissue engineering triad of biomaterials, cells and therapeutics as it applies to the formulation of biomimetic bioinks for cartilage repair. These bioinks can be functionalised with cells or cellular therapeutics to promote cartilage repair.

Conductive Polymeric-Based Electroactive Scaffolds for Tissue Engineering Applications: Current Progress and Challenges from Biomaterials and Manufacturing Perspectives

The practice of combining external stimulation therapy alongside stimuli-responsive bio-scaffolds has shown massive potential for tissue engineering applications. One promising example is the combination of electrical stimulation (ES) and electroactive scaffolds because ES could enhance cell adhesion and proliferation as well as modulating cellular specialization. Even though electroactive scaffolds have the potential to revolutionize the field of tissue engineering due to their ability to distribute ES directly to the target tissues, the development of effective electroactive scaffolds with specific properties remains a major issue in their practical uses. Conductive polymers (CPs) offer ease of modification that allows for tailoring the scaffold's various properties, making them an attractive option for conductive component in electroactive scaffolds. This review provides an up-to-date narrative of the progress of CPs-based electroactive scaffolds and the challenge of their use in various tissue engineering applications from biomaterials perspectives. The general issues with CP-based scaffolds relevant to its application as electroactive scaffolds were discussed, followed by a more specific discussion in their applications for specific tissues, including bone, nerve, skin, skeletal muscle and cardiac muscle scaffolds. Furthermore, this review also highlighted the importance of the manufacturing process relative to the scaffold's performance, with particular emphasis on additive manufacturing, and various strategies to overcome the CPs' limitations in the development of electroactive scaffolds.

Influence of surface topography on PCL electrospun scaffolds for liver tissue engineering

Severe liver disease is one of the most common causes of death globally. Currently, whole organ transplantation is the only therapeutic method for end-stage liver disease treatment, however, the need for donor organs far outweighs demand. Recently liver tissue engineering is starting to show promise for alleviating part of this problem. Electrospinning is a well-known method to fabricate a nanofibre scaffold which mimics the natural extracellular matrix that can support cell growth. This study aims to investigate liver cell responses to topographical features on electrospun fibres. Scaffolds with large surface depression (2 μm) (LSD), small surface depression (0.37 μm) (SSD), and no surface depression (NSD) were fabricated by using a solvent-nonsolvent system. A liver cell line (HepG2) was seeded onto the scaffolds for up to 14 days. The SSD group exhibited higher levels of cell viability and DNA content compared to the other groups. Additionally, the scaffolds promoted gene expression of albumin, with all cases having similar levels, while the cell growth rate was altered. Furthermore, the scaffold with depressions showed 0.8 MPa higher ultimate tensile strength compared to the other groups. These results suggest that small depressions might be preferred by HepG2 cells over smooth and large depression fibres and highlight the potential for tailoring liver cell responses.

Architected fibrous scaffolds for engineering anisotropic tissues

Mimicking the native three-dimensional microenvironment is of crucial importance when biofabricating a new healthcare material. One aspect of the native tissue that is often omitted when designing a suitable scaffold is its anisotropy. Not only is matching native mechanical properties important when designing implantable scaffolds or healthcare materials, but matching physiological structure is also important as many cell populations respond differently to fiber orientation. Therefore, novel aligned electrospun scaffolds with varying fiber angles and spacing of bundles were created and mechanically characterized. Through controlling the angle between the fibers in each layer of the scaffold, a range of different physiological anisotropic mechanical properties were achieved that encompasses values found in native tissues. Extrapolation of this mechanical data allowed for any native tissue's anisotropic Young's modulus to be mimicked by electrospinning fibers at a particular angle. These electrospun scaffolds were then incorporated with cell-laden hydrogels to create hybrid structures that contain the benefits of both scaffolding techniques with the ability to encapsulate cells in the hydrogel. To conclude, this study develops a novel bundled fiber scaffold that was architected to yield anisotropic properties matching native tissues.

Response differences of HepG2 and Primary Mouse Hepatocytes to morphological changes in electrospun PCL scaffolds

Liver disease cases are rapidly expanding across the globe and the only effective cure for end-stage disease is a transplant. Transplant procedures are costly and current supply of donor livers does not satisfy demand. Potential drug treatments and regenerative therapies that are being developed to tackle these pressing issues require effective in-vitro culture platforms. Electrospun scaffolds provide bio-mimetic structures upon which cells are cultured to regulate function in-vitro. This study aims to shed light on the effects of electrospun PCL morphology on the culture of an immortalised hepatic cell line and mouse primary hepatocytes. Each cell type was cultured on large 4-5 µm fibres and small 1-2 µm fibres with random, aligned and highly porous cryogenically spun configurations. Cell attachment, proliferation, morphology and functional protein and gene expression was analysed. Results show that fibre morphology has a measurable influence on cellular morphology and function, with the alteration of key functional markers such as CYP1A2 expression.

The use of antifreeze proteins to modify pore structure in directionally frozen alginate sponges for cartilage tissue engineering

It is thought that osteoarthritis is one of the world's leading causes of disability, with over 8.75 million people in the UK alone seeking medical treatment in 2013. Although a number of treatments are currently in use, a new wave of tissue engineered structures are being investigated as potential solutions for early intervention. One of the key challenges seen in cartilage tissue engineering is producing constructs that can support the formation of articular cartilage, rather than mechanically inferior fibrocartilage. Some research has suggested that mimicking structural properties of the natural cartilage can be used to enhance this response. Herein directional freezing was used to fabricate scaffolds with directionally aligned pores mimicking the mid-region of cartilage, anti-freeze proteins were used to modify the porous structure, which in turn effected the mechanical properties. Pore areas at the tops of the scaffolds were 180.46 ± 44.17 μm2 and 65.66 ± 36.20 μm² for the AFP free and the AFP scaffolds respectively, and for the bases of the scaffolds were 91.22 ± 19.05 μm² and 69.41 ± 21.94 μm² respectively. Scaffolds were seeded with primary bovine chondrocytes, with viability maintained over the course of the study, and regulation of key genes was observed.

Integrational Technologies for the Development of Three-Dimensional Scaffolds as Platforms in Cartilage Tissue Engineering

The prevalence of osteoarthritis is on the rise, and an effective treatment for cartilage defects is still being sought. Cartilage tissue in vivo encompasses complex structures and composition, both of which influence cells and many properties of the native cartilage. The extracellular matrix structure and components provides both morphological cues and the necessary signals to promote cell functions including metabolism, proliferation, and differentiation. In the present study, cryo-printing and electrospinning were combined to produce multizone scaffolds that consist of three distinctive zones. These scaffolds successfully mimic the collagen fiber orientation of the native cartilage. Moreover, in vitro analysis of chondrocyte-seeded scaffolds demonstrated the ability of multizone scaffolds to support long-term chondrocyte attachment and survival over a 5 week culture period. Moreover, multizone scaffolds were found to regulate the expression of key genes in comparison to the controls and allowed the detection of sulfated glycosaminoglycan. Evaluation of the compressive properties revealed that the multizone scaffolds possess more suitable mechanical properties, for the native cartilage, in comparison to the electrospun and phase-separated controls. Multizone scaffolds provide viable initial platforms that capture the complex structure and compressive properties of the native cartilage. They also maintain chondrocyte phenotype and function, highlighting their potential in cartilage tissue engineering applications.

Hybrid cardiovascular sourced extracellular matrix scaffolds as possible platforms for vascular tissue engineering

The aim when designing a scaffold is to provide a supportive microenvironment for the native cells, which is generally achieved by structurally and biochemically imitating the native tissue. Decellularized extracellular matrix (ECM) possesses the mechanical and biochemical cues designed to promote native cell survival. However, when decellularized and reprocessed, the ECM loses its cell supporting mechanical integrity and architecture. Herein, we propose dissolving the ECM into a polymer/solvent solution and electrospinning it into a fibrous sheet, thus harnessing the biochemical cues from the ECM and the mechanical integrity of the polymer. Bovine aorta and myocardium were selected as ECM sources. Decellularization was achieved using sodium dodecyl sulfate (SDS), and the ECM was combined with polycaprolactone and hexafluoro-2-propanol for electrospinning. The scaffolds were seeded with human umbilical vein endothelial cells (HUVECs). The study found that the inclusion of aorta ECM increased the scaffold's wettability and subsequently lead to increased HUVEC adherence and proliferation. Interestingly, the inclusion of myocardium ECM had no effect on wettability or cell viability. Furthermore, gene expression and mechanical changes were noted with the addition of ECM. The results from this study show the vast potential of electrospun ECM/polymer bioscaffolds and their use in tissue engineering.

Electrospun Polymers in Cartilage Engineering-State of Play

Articular cartilage defects remain a clinical challenge. Articular cartilage defects progress to osteoarthritis, which negatively (e.g., remarkable pain, decreased mobility, distress) affects millions of people worldwide and is associated with excessive healthcare costs. Surgical procedures and cell-based therapies have failed to deliver a functional therapy. To this end, tissue engineering therapies provide a promise to deliver a functional cartilage substitute. Among the various scaffold fabrication technologies available, electrospinning is continuously gaining pace, as it can produce nano- to micro- fibrous scaffolds that imitate architectural features of native extracellular matrix supramolecular assemblies and can deliver variable cell populations and bioactive molecules. Herein, we comprehensively review advancements and shortfalls of various electrospun scaffolds in cartilage engineering.