Collagen scaffold for cartilage tissue engineering: the benefit of fibrin glue and the proper culture time in an infant cartilage model

Tomographic Assessment of Bone Regeneration in Osteochondral Lesion Treated with Various Biomaterials in a Sheep Model Study

Osteochondral defects, involving both articular cartilage and subchondral bone, pose significant challenges to joint function and health due to the lack of spontaneous healing and the risk of long-term degenerative diseases like osteoarthritis. Biomaterials have emerged as important components in the development of scaffolds, providing structural support that facilitates tissue growth, integration, and regeneration. This study aims to demonstrate the effectiveness of a tomographic assessment method for optimizing the evaluation of osteochondral regeneration, particularly using Hounsfield units, to enable the evaluation of scaffold integration and tissue regeneration. The sheep model was selected as a model study. Two distinct configurations of biomaterials were utilized in this study: Honey (HMG-Mg doped hydroxyapatite; HWS-wollastonite-hydroxyapatite) and Bi-layer (BWS-wollastonite-hydroxyapatite). The HMG scaffold demonstrated superior integration, reparative tissue quality, and regeneration potential compared to the HWS, BWS, and CTRL groups. The findings underscore the significance of CT assessment as a preliminary method for evaluating hard tissue, such as bone, employing Hounsfield units. Statistical evaluations validated the significant differences in performance, particularly favoring the HMG group. The results of this study underscore the importance of tomographic assessment in evaluation of osteochondral regeneration.

Endostatin in 3D Fibrin Hydrogel Scaffolds Promotes Chondrogenic Differentiation in Swine Neonatal Meniscal Cells

The success of cell-based approaches for the treatment of cartilage or fibro-cartilaginous tissue defects requires an optimal cell source with chondrogenic differentiation ability that maintains its differentiated properties and stability following implantation. For this purpose, the aim of this study was to evaluate the use of endostatin (COL18A1), an anti-angiogenic factor, which is physiologically involved in cell differentiation during meniscus development. Swine neonatal meniscal cells not yet subjected to mechanical stimuli were extracted, cultured in fibrin hydrogel scaffolds, and treated at two different time points (T1 = 9 days and T2 = 21 days) with different concentrations of COL18A1 (10 ng/mL; 100 ng/mL; 200 ng/mL). At the end of the treatments, the scaffolds were examined through biochemical, molecular, and histochemical analyses. The results showed that the higher concentration of COL18A1 promotes a fibro-chondrogenic phenotype and improves cellularity index (DNA content, p < 0.001) and cell efficiency (GAGs/DNA ratio, p < 0.01) after 21 days. These data are supported by the molecular analysis of collagen type I (COL1A1, a marker of fibrous-like tissue, p < 0.001), collagen type II (COL2A1, a marker of cartilaginous-like tissue, p < 0.001) and SRY-Box Transcription Factor 9 (SOX9, an early marker of chondrogenicity, p < 0.001), as well as by histological analysis (Safranin-O staining), laying the foundations for future studies evaluating the involvement of 3D endostatin hydrogel scaffolds in the differentiation of avascular tissues.

Physical, Mechanical, and Biological Properties of Fibrin Scaffolds for Cartilage Repair

Articular cartilage is a highly organized tissue that provides remarkable load-bearing and low friction properties, allowing for smooth movement of diarthrodial joints; however, due to the avascular, aneural, and non-lymphatic characteristics of cartilage, joint cartilage has self-regeneration and repair limitations. Cartilage tissue engineering is a promising alternative for chondral defect repair. It proposes models that mimic natural tissue structure through the use of cells, scaffolds, and signaling factors to repair, replace, maintain, or improve the specific function of the tissue. In chondral tissue engineering, fibrin is a biocompatible biomaterial suitable for cell growth and differentiation with adequate properties to regenerate damaged cartilage. Additionally, its mechanical, biological, and physical properties can be enhanced by combining it with other materials or biological components. This review addresses the biological, physical, and mechanical properties of fibrin as a biomaterial for cartilage tissue engineering and as an element to enhance the regeneration or repair of chondral lesions.

Waste-derived biomaterials as building blocks in the biomedical field

Recent developments in the biomedical arena have led to the fabrication of innovative biomaterials by utilizing bioactive molecules obtained from biological wastes released from fruit and beverage processing industries, and fish, meat, and poultry industries. These biological wastes that end up in water bodies as well as in landfills are an affluent source of animal- and plant-derived proteins, bio ceramics and polysaccharides such as collagens, gelatins, chitins, chitosans, eggshell membrane proteins, hydroxyapatites, celluloses, and pectins. These bioactive molecules have been intricately designed into scaffolds and dressing materials by utilizing advanced technologies for drug delivery, tissue engineering, and wound healing relevance. These biomaterials are environment-friendly, biodegradable, and biocompatible, and show excellent tissue regeneration attributes. Additionally, being cost-effective they can reduce the burden on the healthcare system as well as provide a sustainable solution to waste management. In this review, the current trends in the utilization of plant and animal waste-derived biomaterials in various biomedical fields are considered along with a separate section on their applications as xenografts.

Human-engineered auricular reconstruction (hEAR) by 3D-printed molding with human-derived auricular and costal chondrocytes and adipose-derived mesenchymal stem cells

Microtia is a small, malformed external ear, which occurs at an incidence of 1-10 per 10 000 births. Autologous reconstruction using costal cartilage is the most widely accepted surgical microtia repair technique. Yet, the method involves donor-site pain and discomfort and relies on the artistic skill of the surgeon to create an aesthetic ear. This study employed novel tissue engineering techniques to overcome these limitations by developing a clinical-grade, 3D-printed biodegradable auricle scaffold that formed stable, custom-made neocartilage implants. The unique scaffold design combined strategically reinforced areas to maintain the complex topography of the outer ear and micropores to allow cell adhesion for the effective production of stable cartilage. The auricle construct was computed tomography (CT) scan-based composed of a 3D-printed clinical-grade polycaprolactone scaffold loaded with patient-derived chondrocytes produced from either auricular cartilage or costal cartilage biopsies combined with adipose-derived mesenchymal stem cells. Cartilage formation was measured within the constructin vitro, and cartilage maturation and stabilization were observed 12 weeks after its subcutaneous implantation into a murine model. The proposed technology is simple and effective and is expected to improve aesthetic outcomes and reduce patient discomfort.

Hypoxia as a Stimulus for the Maturation of Meniscal Cells: Highway to Novel Tissue Engineering Strategies?

The meniscus possesses low self-healing properties. A perfect regenerative technique for this tissue has not yet been developed. This work aims to evaluate the role of hypoxia in meniscal development in vitro. Menisci from neonatal pigs (day 0) were harvested and cultured under two different atmospheric conditions: hypoxia (1% O₂) and normoxia (21% O₂) for up to 14 days. Samples were analysed at 0, 7 and 14 days by histochemical (Safranin-O staining), immunofluorescence and RT-PCR (in both methods for SOX-9, HIF-1α, collagen I and II), and biochemical (DNA, GAGs, DNA/GAGs ratio) techniques to record any possible differences in the maturation of meniscal cells. Safranin-O staining showed increments in matrix deposition and round-shape “fibro-chondrocytic” cells in hypoxia-cultured menisci compared with controls under normal atmospheric conditions. The same maturation shifting was observed by immunofluorescence and RT-PCR analysis: SOX-9 and collagen II increased from day zero up to 14 days under a hypoxic environment. An increment of DNA/GAGs ratio typical of mature meniscal tissue (characterized by fewer cells and more GAGs) was observed by biochemical analysis. This study shows that hypoxia can be considered as a booster to achieve meniscal cell maturation, and opens new opportunities in the field of meniscus tissue engineering.

Human Chondrocytes from Human Adipose Tissue-Derived Mesenchymal Stem Cells Seeded on a Dermal-Derived Collagen Matrix Sheet: Our Preliminary Results for a Ready to Go Biotechnological Cartilage Graft in Clinical Practice

Background

The articular cartilage is unique in that it contains only a single type of cell and shows poor ability for spontaneous healing. Cartilage tissue engineering which uses mesenchymal stem cells (MSCs) and adipose tissue-derived mesenchymal stem cells (AT-MSCs) is considered an attractive treatment for cartilage lesions and osteoarthritis. The establishment of cartilage regenerative medicine is an important clinical issue, but the search for cell sources able to restore cartilage integrity proves to be challenging. The aim of this study was to create cartilage grafts from the combination of AT-MSCs and collagen substrates.

Methods

Mesenchymal stem cells were obtained from human donors' adipose tissue, and collagen scaffold, obtained from human skin and cleaned from blood vessels, adipose tissues, and debris, which only preserve dermis and epidermis, were seeded and cultured on collagen substrates and differentiated to chondrocytes. The obtained chondrocyte extracellular matrix of cartilage was then evaluated for the expression of chondrocyte-/cartilage-specific markers, the Cartilage Oligomeric Matrix Protein (COMP), collagen X, alpha-1 polypeptide (COL10A1), and the Collagen II, Human Tagged ORF Clone (COL2A1) by using the reverse transcription polymerase chain reaction (RT-PCR).

Results

Our findings have shown that the dermal collagen may exert important effects on the quality of in vitro expanded chondrocytes, leading in this way that the influence of collagen skin matrix helps to produce highly active and functional chondrocytes for long-term cartilage tissue regeneration.

Conclusion

This research opens up the possibility of generating cartilage grafts with the precise purpose of improving the existing limitation in current clinical procedures.

Biofunctional Extracellular Matrix-Polycaprolactone-Hydroxyapatite Scaffold and Synovium Mesenchymal Stem Cells/Chondrocytes for Repairing Cartilage Defects

Articular cartilage defects and degeneration can be caused by multiple factors, and the current clinical treatment schemes for pathological changes are relatively limited. Engineered cartilage tissue represents an alternative therapy for repairing cartilage defects in regenerative medicine. The scaffold material is considered the framework of tissue engineering; thus, scaffold material selection plays a crucial role in the therapy outcome. Polycaprolactone (PCL)-hydroxyapatite (HA) has been applied as a scaffold material for bone and cartilage tissue engineering with nontoxic, harmless metabolites and proper physical properties. The extracellular matrix (ECM) is mainly composed of collagen and proteoglycan, as well as a large number of growth factors and cytokines, which provide a tissue-specific microenvironment for host cells. Adipose-derived stem cells are pluripotent stem cells, and transforming growth factor-β3 (TGF-β3) enables mesenchymal stem cells to promote ECM production. This study, via in vitro and in vivo experiments, elucidated that the synovium mesenchymal stem cells (SMSCs) + chondrocytes + ECM-PCL-HA repair system, which is constructed upon the ECM-PCL-HA scaffold material, exhibits an adequate chondrogenic ability and reparatory effect. Overall, ECM-PCL-HA can be defined as a biofunctional scaffold material. The SMSCs + chondrocytes + ECM-PCL-HA repair system showed good confluency between the new cartilage and the surface, as well as the interface of the adjacent host cartilage. Furthermore, the structure of new cartilage tissue is consistent with adjacency. Thus, it can be used as a preferred plan for articular cartilage defect repair.

Angiostatin-functionalized collagen scaffolds suppress angiogenesis but do not induce chondrogenesis by mesenchymal stromal cells in vivo

Tissue engineering for fibrocartilage regeneration using mesenchymal stromal cells (MSC) and biomaterial scaffolds is emerging as a promising strategy, but inhibiting vascularization to prevent endochondral ossification is important to develop stable implants. The objective of this study was to investigate the effect of angiostatin on inhibition of angiogenesis and promotion of chondrogenesis by collagen scaffolds with or without MSC implanted subcutaneously in rats. One scaffold from the following groups was implanted in each animal: Collagen scaffolds only, scaffolds functionalized with angiostatin, scaffolds loaded with MSC and scaffolds functionalized with angiostatin and loaded with MSC. The various scaffolds were harvested after 2 and 8 weeks for histological analysis, Real-time quantitative polymerase chain reaction (RT-qPCR) and immunofluorescence quantification. Results demonstrated significantly decreased expression of inflammatory (interleukin 1 alpha and beta) and angiogenic genes (platelet and endothelial cell adhesion molecule 1) in scaffolds functionalized with angiostatin after 2 weeks in vivo. Histologically, after 8 weeks, the scaffolds with angiostatin had less inflammatory cells and more collagen matrix formation, but no fibrocartilage formation was detected. Thus, although angiostatin suppressed angiogenesis, it did not stimulate ectopic chondrogenesis in tissue engineered constructs in vivo.

Atelocollagen promotes chondrogenic differentiation of human adipose-derived mesenchymal stem cells

Effective engineering approaches for cartilage regeneration involve a combination of cells and biomaterial scaffolds. Multipotent mesenchymal stem cells (MSCs) are important sources for cartilage regeneration. Atelocollagen provides a suitable substrate for MSC attachment and enhancing chondrogenic differentiation. Here, we assessed the chondrogenic potential of adipose tissue derived human MSCs (hMSCs) mixed with atelocollagen gel. We observed cell attachment, viability, and microstructures by electron microscopy over 21 days. The levels of Sox9, type II collagen, aggrecan, type I collagen, Runx2, type X collagen, ALP, Osterix, and MMP13 were measured by RT-qPCR. Cartilage matrix-related proteins were assessed by enzyme-linked immunosorbent assay (ELISA), histology, and immunohistochemistry. hMSCs of all groups exhibited well-maintained cell survival, distribution and morphology. Abundant type II collagen fibers developed on day 21; while Sox9, type II collagen, and aggrecan expression increased over time in the atelocollagen group. However, type I collagen, RUNX2, type X collagen (CoL10A1), Osterix, and ALP were not expressed. These results corroborated the protein expression detected by ELISA. Further, histological analysis revealed lacunae-like structures, while staining demonstrated glycosaminoglycan accumulation. Cumulatively, these results indicate that atelocollagen scaffolds improve hMSC chondrogenic differentiation and are a potential approach for cartilage regeneration.

Tissue Engineering: An Alternative to Repair Cartilage

Herein we review the state-of-the-art in tissue engineering for repair of articular cartilage. First, we describe the molecular, cellular, and histologic structure and function of endogenous cartilage, focusing on chondrocytes, collagens, extracellular matrix, and proteoglycans. We then explore in vitro cell culture on scaffolds, discussing the difficulties involved in maintaining or obtaining a chondrocytic phenotype. Next, we discuss the diverse compounds and designs used for these scaffolds, including natural and synthetic biomaterials and porous, fibrous, and multilayer architectures. We then report on the mechanical properties of different cell-loaded scaffolds, and the success of these scaffolds following in vivo implantation in small animals, in terms of generating tissue that structurally and functionally resembles native tissue. Last, we highlight future trends in this field. We conclude that despite major technical advances made over the past 15 years, and continually improving results in cartilage repair experiments in animals, the development of clinically useful implants for regeneration of articular cartilage remains a challenge

Evaluation of a Cell-Free Collagen Type I-Based Scaffold for Articular Cartilage Regeneration in an Orthotopic Rat Model

The management of chondral defects represents a big challenge because of the limited self-healing capacity of cartilage. Many approaches in this field obtained partial satisfactory results. Cartilage tissue engineering, combining innovative scaffolds and stem cells from different sources, emerges as a promising strategy for cartilage regeneration. The aim of this study was to evaluate the capability of a cell-free collagen I-based scaffold to promote cartilaginous repair after orthotopic implantation in vivo. Articular cartilage lesions (ACL) were created at the femoropatellar groove in rat knees and cell free collagen I-based scaffolds (S) were then implanted into right knee defect for the ACL-S group. No scaffold was implanted for the ACL group. At 4-, 8- and 16-weeks post-transplantation, degrees of cartilage repair were evaluated by morphological, histochemical and gene expression analyses. Histological analysis shows the formation of fibrous tissue, at 4-weeks replaced by a tissue resembling the calcified one at 16-weeks in the ACL group. In the ACL-S group, progressive replacement of the scaffold with the newly formed cartilage-like tissue is shown, as confirmed by Alcian Blue staining. Immunohistochemical and quantitative real-time PCR (qRT-PCR) analyses display the expression of typical cartilage markers, such as collagen type I and II (ColI and ColII), Aggrecan and Sox9. The results of this study display that the collagen I-based scaffold is highly biocompatible and able to recruit host cells from the surrounding joint tissues to promote cartilaginous repair of articular defects, suggesting its use as a potential approach for cartilage tissue regeneration.

Studies of proliferation and chondrogenic differentiation of rat adipose stem cells using an anti-oxidative polyurethane scaffold combined with cyclic compression culture

The adipose stem cell is a potential candidate for the autologous chondrocytes repairing approach because of the abundance of fat in the animal body and its versatile differentiation capability. In this study, rat adipose stem cells (rASCs) were seeded into anti-oxidative N-acetylcysteine (NAC) grafted polyurethane (PU) scaffold and then combined with short dynamic compressive stimulation (24 h) to induce rASCs chondrogenesis differentiation in vitro. The inner pore surface of the PU scaffold was first modified via alginate and type I collagen to promote rASCs adherence. The modified layers crosslinked by genipin showed outstanding stability after ultrasonic treatment, indicating the modified layers were stable and can keep the cells adhesion well during dynamic compressive stimulation. After inner pore surface modification and 10 mM NAC grafting, the PU scaffold-A-C-G (graft 10 mM NAC) has shown the best proliferation efficiency with homogeneous cell distribution after 72hr static culture. After short term dynamic compressive stimulation, significant gene expression in chondrogenic markers, Sox-9, and Aggrecan, were noted in both PU scaffold-A-C-G and PU scaffold-A-C-G (graft 10 mM NAC). Considering the cell proliferation efficiency and gene expression, the anti-oxidative NAC grafted PU scaffold combined with short term dynamic compressive stimulation could be useful for cell culturing in stem cell therapy.

Evaluation of in Vivo Response of Three Biphasic Scaffolds for Osteochondral Tissue Regeneration in a Sheep Model

Osteochondral defects are a common problem in both human medicine and veterinary practice although with important limits concerning the cartilaginous tissue regeneration. Interest in the subchondral bone has grown, as it is now considered a key element in the osteochondral defect healing. The aim of this work was to generate and to evaluate the architecture of three cell-free scaffolds made of collagen, magnesium/hydroxyapatite and collagen hydroxyapatite/wollastonite to be implanted in a sheep animal model. Scaffolds were designed in a bilayer configuration and a novel “Honey” configuration, where columns of hydroxyapatite were inserted within the collagen matrix. The use of different types of scaffolds allowed us to identify the best scaffold in terms of integration and tissue regeneration. The animals included were divided into four groups: three were treated using different types of scaffold while one was left untreated and represented the control group. Evaluations were made at 3 months through CT analysis. The novel “Honey” configuration of the scaffold with hydroxyapatite seems to allow for a better reparative process, although we are still far from obtaining a complete restoration of the defect at this time point of follow-up.

Repair of Osteochondral Defects in Rabbit Knee Using Menstrual Blood Stem Cells Encapsulated in Fibrin Glue: A Good Stem Cell Candidate for the Treatment of Osteochondral Defects

Background

In recent years, researchers discovered that menstrual blood-derived stem cells (MenSCs) have the potential to differentiate into a wide range of tissues including the chondrogenic lineage. In this study, we aimed to investigate the effect of MenSCs encapsulated in fibrin glue (FG) on healing of osteochondral defect in rabbit model.

Methods

We examined the effectiveness of MenSCs encapsulated in FG in comparison with FG alone in the repair of osteochondral defect (OCD) lesions of rabbit knees after 12 and 24 weeks.

Results

Macroscopical evaluation revealed that the effectiveness of MenSCs incorporation with FG is much higher than FG alone in repair of OCD defects. Indeed, histopathological evaluation of FG + MenSCs group at 12 weeks post-transplantation demonstrated that defects were filled with hyaline cartilage-like tissue with proper integration, high content of glycosaminoglycan and the existence of collagen fibers especially collagen type II, as well as by passing time (24 weeks post-transplantation), the most regenerated tissue in FG + MenSCs group was similar to hyaline cartilage with relatively good infill and integration. As the same with the result of 12 weeks post-implantation, the total point of microscopical examination in FG + MenSCs group was higher than other experimental groups, however, no significant difference was detected between groups at 24 weeks (p > 0.05).

Conclusion

In summary, MenSCs as unique stem cell population, is suitable for in vivo repair of OCD defects and promising for the future clinical application.

Collagen Scaffolds in Cartilage Tissue Engineering and Relevant Approaches for Future Development

BACKGROUND

Cartilage tissue engineering (CTE) aims to obtain a structure mimicking native cartilage tissue through the combination of relevant cells, three-dimensional scaffolds, and extraneous signals. Implantation of 'matured' constructs is thus expected to provide solution for treating large injury of articular cartilage. Type I collagen is widely used as scaffolds for CTE products undergoing clinical trial, owing to its ubiquitous biocompatibility and vast clinical approval. However, the long-term performance of pure type I collagen scaffolds would suffer from its limited chondrogenic capacity and inferior mechanical properties. This paper aims to provide insights necessary for advancing type I collagen scaffolds in the CTE applications.

METHODS

Initially, the interactions of type I/II collagen with CTE-relevant cells [i.e., articular chondrocytes (ACs) and mesenchymal stem cells (MSCs)] are discussed. Next, the physical features and chemical composition of the scaffolds crucial to support chondrogenic activities of AC and MSC are highlighted. Attempts to optimize the collagen scaffolds by blending with natural/synthetic polymers are described. Hybrid strategy in which collagen and structural polymers are combined in non-blending manner is detailed.

RESULTS

Type I collagen is sufficient to support cellular activities of ACs and MSCs; however it shows limited chondrogenic performance than type II collagen. Nonetheless, type I collagen is the clinically feasible option since type II collagen shows arthritogenic potency. Physical features of scaffolds such as internal structure, pore size, stiffness, etc. are shown to be crucial in influencing the differentiation fate and secreting extracellular matrixes from ACs and MSCs. Collagen can be blended with native or synthetic polymer to improve the mechanical and bioactivities of final composites. However, the versatility of blending strategy is limited due to denaturation of type I collagen at harsh processing condition. Hybrid strategy is successful in maximizing bioactivity of collagen scaffolds and mechanical robustness of structural polymer.

CONCLUSION

Considering the previous improvements of physical and compositional properties of collagen scaffolds and recent manufacturing developments of structural polymer, it is concluded that hybrid strategy is a promising approach to advance further collagen-based scaffolds in CTE.

Poroelastic Modeling of Highly Hydrated Collagen Hydrogels: Experimental Results vs. Numerical Simulation With Custom and Commercial Finite Element Solvers

This study presents a comparison between the performances of two Finite Element (FE) solvers for the modeling of the poroelastic behavior of highly hydrated collagen hydrogels. Characterization of collagen hydrogels has been a widespread challenge since this is one of the most used natural biomaterials for Tissue Engineering (TE) applications. V-Biomech® is a free custom FE solver oriented to soft tissue modeling, while Abaqus® is a general-purpose commercial FE package which is widely used for biomechanics computational modeling. Poroelastic simulations with both solvers were compared to two experimental protocols performed by Busby et al. (2013) and Chandran and Barocas (2004), also using different implementations of the frequently used Neo-Hookean hyperelastic model. The average differences between solvers outputs were under 5% throughout the different tests and hydrogel properties. Thus, differences were small enough to be considered negligible and within the variability found experimentally from one sample to another. This work demonstrates that constitutive modeling of soft tissues, such as collagen hydrogels can be achieved with either V-Biomech or Abaqus standard options (without user-subroutine), which is important for the biomechanics and biomaterials research community. V-Biomech has shown its potential for the validation of biomechanical characterization of soft tissues, while Abaqus' versatility is useful for the modeling and analysis of TE applications where other complex phenomena may also need to be captured.

Autologous liquid platelet rich fibrin: A novel drug delivery system

There is currently widespread interest within the biomaterial field to locally deliver biomolecules for bone and cartilage regeneration. Substantial work to date has focused on the potential role of these biomolecules during the healing process, and the carrier system utilized is a key factor in their effectiveness. Platelet rich fibrin (PRF) is a naturally derived fibrin scaffold that is easily obtained from peripheral blood following centrifugation. Slower centrifugation speeds have led to the commercialization of a liquid formulation (liquid-PRF) resulting in an upper plasma layer composed of liquid fibrinogen/thrombin prior to clot formation that remains in its liquid phase for approximately 15 min until injected into bodily tissues. Herein, we introduce the use of liquid PRF as an advanced local delivery system for small and large biomolecules. Potential target molecules including large (growth factors/cytokines and morphogenetic/angiogenic factors), as well as small (antibiotics, peptides, gene therapy and anti-osteoporotic) molecules are considered potential candidates for enhanced bone/cartilage tissue regeneration. Furthermore, liquid-PRF is introduced as a potential carrier system for various cell types and nano-sized particles that are capable of limiting/by-passing the immune system and minimizing potential foreign body reactions within host tissues following injection.

STATEMENT OF SIGNIFICANCE

There is currently widespread interest within the biomaterial field to locally deliver biomolecules for bone and cartilage regeneration. This review article focuses on the use of a liquid version of platelet rich fibrin (PRF) composed of liquid fibrinogen/thrombin as a drug delivery system. Herein, we introduce the use of liquid PRF as an advanced local delivery system for small and large biomolecules including growth factors, cytokines and morphogenetic/angiogenic factors, as well as antibiotics, peptides, gene therapy and anti-osteoporotic molecules as potential candidates for enhanced bone/cartilage tissue regeneration.

Development and biological validation of a cyclic stretch culture system for the ex vivo engineering of tendons

INTRODUCTION

An innovative approach to the treatment of tendon injury or degeneration is given by engineered grafts, made available through the development of bioreactors that generate tendon tissue in vitro, by replicating in vivo conditions. This work aims at the design of a bioreactor capable of applying a stimulation of cyclic strain on cell constructs to promote the production of bioartificial tissue with mechanical and biochemical properties resembling those of the native tissue.

METHODS

The system was actuated by an electromagnet and design specifications were imposed as follows. The stimulation protocol provides to scaffolds a 3% preload, a 10% deformation, and a stimulation frequency rate set at 0.5, 1, and 2 Hz, which alternates stimulation/resting phases. Porcine tenocytes were seeded on collagen scaffolds and cultured in static or dynamic conditions for 7 and 14 days.

RESULTS

The culture medium temperature did not exceed 37°C during prolonged culture experiments. The applied force oscillates between 1.5 and 4.5 N. The cyclic stimulation of the engineered constructs let both the cells and the scaffold fibers align along the strain direction in response to the mechanical stimulus.

CONCLUSION

We designed a pulsatile strain bioreactor for tendon tissue engineering. The in vitro characterization shows a preferential cell alignment at short time points. Prolonged culture time, however, seems to influence negatively on the survival of the cells indicating the need of further optimization concerning the culture conditions and the mechanical stimulation.

Micromechanical study of the load transfer in a polycaprolactone-collagen hybrid scaffold when subjected to unconfined and confined compression

Scaffolds are used in diverse tissue engineering applications as hosts for cell proliferation and extracellular matrix formation. One of the most used tissue engineering materials is collagen, which is well known to be a natural biomaterial, also frequently used as cell substrate, given its natural abundance and intrinsic biocompatibility. This study aims to evaluate how the macroscopic biomechanical stimuli applied on a construct made of polycaprolactone scaffold embedded in a collagen substrate translate into microscopic stimuli at the cell level. Eight poro-hyperelastic finite element models of 3D printed hybrid scaffolds from the same batch were created, along with an equivalent model of the idealized geometry of that scaffold. When applying an 8% confined compression at the macroscopic level, local fluid flow of up to 20 [Formula: see text]m/s and octahedral strain levels mostly under 20% were calculated in the collagen substrate. Conversely unconfined compression induced fluid flow of up to 10 [Formula: see text]m/s and octahedral strain from 10 to 35%. No relevant differences were found amongst the scaffold-specific models. Following the mechanoregulation theory based on Prendergast et al. (J Biomech 30:539-548, 1997. https://doi.org/10.1016/S0021-9290(96)00140-6 ), those results suggest that mainly cartilage or fibrous tissue formation would be expected to occur under unconfined or confined compression, respectively. This in silico study helps to quantify the microscopic stimuli that are present within the collagen substrate and that will affect cell response under in vitro bioreactor mechanical stimulation or even after implantation.

In Vivo Evaluation of Biocompatibility and Chondrogenic Potential of a Cell-Free Collagen-Based Scaffold

Injured articular cartilage has a limited innate regenerative capacity, due to the avascular nature and low cellularity of the tissue itself. Although several approaches have been proposed to repair the joint cartilage, none of them has proven to be effective. The absence of suitable therapeutic options has encouraged tissue-engineering approaches combining specific cell types and biomaterials. In the present work, we have evaluated the potential of a cell-free Collagen I-based scaffold to promote the augmentation of cartilage-like phenotype after subcutaneous implantation in the mouse. Forty female mice were grafted subcutaneously with scaffolds, while four additional mice without scaffold were used as negative controls. The effects of scaffold were evaluated at 1, 2, 4, 8, or 16 weeks after implantation. Immunohistochemical analysis shows the expression of typical cartilage markers, including type-II Collagen, Aggrecan, Matrilin-1 and Sox 9. These data are also confirmed by qRT-PCR that further show that both COL2A1 and COL1A1 increase over time, but the first one increases more rapidly, thus suggesting a typical cartilage-like address. Histological analysis shows the presence of some pericellular lacunae, after 8 and 16 weeks. Results suggest that this scaffold (i) is biocompatible in vivo, (ii) is able to recruit host cells (iii) induce chondrogenic differentiation of host cells. Such evidences suggest that this cell-free scaffold is promising and represents a potential approach for cartilage regeneration.

In situ handheld three-dimensional bioprinting for cartilage regeneration

Articular cartilage injuries experienced at an early age can lead to the development of osteoarthritis later in life. In situ three-dimensional (3D) printing is an exciting and innovative biofabrication technology that enables the surgeon to deliver tissue-engineering techniques at the time and location of need. We have created a hand-held 3D printing device (biopen) that allows the simultaneous coaxial extrusion of bioscaffold and cultured cells directly into the cartilage defect in vivo in a single-session surgery. This pilot study assessed the ability of the biopen to repair a full-thickness chondral defect and the early outcomes in cartilage regeneration, and compared these results with other treatments in a large animal model. A standardized critical-sized full-thickness chondral defect was created in the weight-bearing surface of the lateral and medial condyles of both femurs of six sheep. Each defect was treated with one of the following treatments: (i) hand-held in situ 3D printed bioscaffold using the biopen (HH group), (ii) preconstructed bench-based printed bioscaffolds (BB group), (iii) microfractures (MF group) or (iv) untreated (control, C group). At 8 weeks after surgery, macroscopic, microscopic and biomechanical tests were performed. Surgical 3D bioprinting was performed in all animals without any intra- or postoperative complication. The HH biopen allowed early cartilage regeneration. The results of this study show that real-time, in vivo bioprinting with cells and scaffold is a feasible means of delivering a regenerative medicine strategy in a large animal model to regenerate articular cartilage.

The Good the Bad and the Ugly of Glycosaminoglycans in Tissue Engineering Applications

High sulfation, low cost, and the status of heparin as an already FDA- and EMA- approved product, mean that its inclusion in tissue engineering (TE) strategies is becoming increasingly popular. However, the use of heparin may represent a naïve approach. This is because tissue formation is a highly orchestrated process, involving the temporal expression of numerous growth factors and complex signaling networks. While heparin may enhance the retention and activity of certain growth factors under particular conditions, its binding 'promiscuity' means that it may also inhibit other factors that, for example, play an important role in tissue maintenance and repair. Within this review we focus on articular cartilage, highlighting the complexities and highly regulated processes that are involved in its formation, and the challenges that exist in trying to effectively engineer this tissue. Here we discuss the opportunities that glycosaminoglycans (GAGs) may provide in advancing this important area of regenerative medicine, placing emphasis on the need to move away from the common use of heparin, and instead focus research towards the utility of specific GAG preparations that are able to modulate the activity of growth factors in a more controlled and defined manner, with less off-target effects.

Concise Review: Mesenchymal Stem Cells for Functional Cartilage Tissue Engineering: Taking Cues from Chondrocyte-Based Constructs

Osteoarthritis, the most prevalent form of joint disease, afflicts 9% of the U.S. population over the age of 30 and costs the economy nearly $100 billion annually in healthcare and socioeconomic costs. It is characterized by joint pain and dysfunction, though the pathophysiology remains largely unknown. Due to its avascular nature and limited cellularity, articular cartilage exhibits a poor intrinsic healing response following injury. As such, significant research efforts are aimed at producing engineered cartilage as a cell-based approach for articular cartilage repair. However, the knee joint is mechanically demanding, and during injury, also a milieu of harsh inflammatory agents. The unforgiving mechano-chemical environment requires tissue replacements that are capable of bearing such burdens. The use of mesenchymal stem cells (MSCs) for cartilage tissue engineering has emerged as a promising cell source due to their ease of isolation, capacity to readily expand in culture, and ability to undergo lineage-specific differentiation into chondrocytes. However, to date, very few studies utilizing MSCs have successfully recapitulated the structural and functional properties of native cartilage, exposing the difficult process of uniformly differentiating stem cells into desired cell fates and maintaining the phenotype during in vitro culture and after in vivo implantation. To address these shortcomings, here, we present a concise review on modulating stem cell behavior, tissue development and function using well-developed techniques from chondrocyte-based cartilage tissue engineering. Stem Cells Translational Medicine 2017;6:1295-1303.

Combination of Collagen-Based Scaffold and Bioactive Factors Induces Adipose-Derived Mesenchymal Stem Cells Chondrogenic Differentiation In vitro

Recently, multipotent mesenchymal stem cells (MSCs) have attracted much attention in the field of regenerative medicine due to their ability to give rise to different cell types, including chondrocytes. Damaged articular cartilage repair is one of the most challenging issues for regenerative medicine, due to the intrinsic limited capability of cartilage to heal because of its avascular nature. While surgical approaches like chondral autografts and allografts provide symptoms and function improvement only for a short period, MSC based stimulation therapies, like microfracture surgery or autologous matrix-induced chondrogenesis demonstrate to be more effective. The use of adult chondrocytes, which are the main cellular constituent of cartilage, in medical practice, is indeed limited due to their instability in monolayer culture and difficulty to collect donor tissue (articular and nasal cartilage). The most recent cartilage engineering approaches combine cells, biomaterial scaffold and bioactive factors to promote functional tissue replacements. Many recent evidences demonstrate that scaffolds providing specific microenvironmental conditions can promote MSCs differentiation toward a functional phenotype. In the present work, the chondrogenic potential of a new Collagen I based 3D scaffold has been assessed in vitro, in combination with human adipose-derived MSCs which possess a higher chondrogenic potential compared to MSCs isolated from other tissues. Our data indicate that the scaffold was able to promote the early stages of chondrogenic commitment and that supplementation of specific soluble factors was able to induce the complete differentiation of MSCs in chondrocytes as demonstrated by the appearance of cartilage distinctive markers (Sox 9, Aggrecan, Matrilin-1, and Collagen II), as well as by the cartilage-specific Alcian Blue staining and by the acquisition of typical cellular morphology. Such evidences suggest that the investigated scaffold formulation could be suitable for the production of medical devices that can be beneficial in the field of articular cartilage engineering, thus improving the efficacy and durability of the current therapeutic options.

Smart Polymeric Hydrogels for Cartilage Tissue Engineering: A Review on the Chemistry and Biological Functions

Stimuli responsive hydrogels (SRHs) are attractive bioscaffolds for tissue engineering. The structural similarity of SRHs to the extracellular matrix (ECM) of many tissues offers great advantages for a minimally invasive tissue repair. Among various potential applications of SRHs, cartilage regeneration has attracted significant attention. The repair of cartilage damage is challenging in orthopedics owing to its low repair capacity. Recent advances include development of injectable hydrogels to minimize invasive surgery with nanostructured features and rapid stimuli-responsive characteristics. Nanostructured SRHs with more structural similarity to natural ECM up-regulate cell-material interactions for faster tissue repair and more controlled stimuli-response to environmental changes. This review highlights most recent advances in the development of nanostructured or smart hydrogels for cartilage tissue engineering. Different types of stimuli-responsive hydrogels are introduced and their fabrication processes through physicochemical procedures are reported. The applications and characteristics of natural and synthetic polymers used in SRHs are also reviewed with an outline on clinical considerations and challenges.

Design and characterization of microcapsules-integrated collagen matrixes as multifunctional three-dimensional scaffolds for soft tissue engineering

Three-dimensional (3D) porous scaffolds based on collagen are promising candidates for soft tissue engineering applications. The addition of stimuli-responsive carriers (nano- and microparticles) in the current approaches to tissue reconstruction and repair brings about novel challenges in the design and conception of carrier-integrated polymer scaffolds. In this study, a facile method was developed to functionalize 3D collagen porous scaffolds with biodegradable multilayer microcapsules. The effects of the capsule charge as well as the influence of the functionalization methods on the binding efficiency to the scaffolds were studied. It was found that the binding of cationic microcapsules was higher than that of anionic ones, and application of vacuum during scaffolds functionalization significantly hindered the attachment of the microcapsules to the collagen matrix. The physical properties of microcapsules-integrated scaffolds were compared to pristine scaffolds. The modified scaffolds showed swelling ratios, weight losses and mechanical properties similar to those of unmodified scaffolds. Finally, in vitro diffusional tests proved that the collagen scaffolds could stably retain the microcapsules over long incubation time in Tris-HCl buffer at 37°C without undergoing morphological changes, thus confirming their suitability for tissue engineering applications. The obtained results indicate that by tuning the charge of the microcapsules and by varying the fabrication conditions, collagen scaffolds patterned with high or low number of microcapsules can be obtained, and that the microcapsules-integrated scaffolds fully retain their original physical properties.

Combined numerical and experimental biomechanical characterization of soft collagen hydrogel substrate

This work presents a combined experimental-numerical framework for the biomechanical characterization of highly hydrated collagen hydrogels, namely with 0.20, 0.30 and 0.40% (by weight) of collagen concentration. Collagen is the most abundant protein in the extracellular matrix of animals and humans. Its intrinsic biocompatibility makes collagen a promising substrate for embedding cells within a highly hydrated environment mimicking natural soft tissues. Cell behaviour is greatly influenced by the mechanical properties of the surrounding matrix, but the biomechanical characterization of collagen hydrogels has been challenging up to now, since they present non-linear poro-viscoelastic properties. Combining the stiffness outcomes from rheological experiments with relevant literature data on collagen permeability, poroelastic finite element (FE) models were developed. Comparison between experimental confined compression tests available in the literature and analogous FE stress relaxation curves showed a close agreement throughout the tests. This framework allowed establishing that the dynamic shear modulus of the collagen hydrogels is between 0.0097 ± 0.018 kPa for the 0.20% concentration and 0.0601 ± 0.044 kPa for the 0.40% concentration. The Poisson's ratio values for such conditions lie within the range of 0.495-0.485 for 0.20% and 0.480-0.470 for 0.40%, respectively, showing that rheology is sensitive enough to detect these small changes in collagen concentration and thus allowing to link rheology results with the confined compression tests. In conclusion, this integrated approach allows for accurate constitutive modelling of collagen hydrogels. This framework sets the grounds for the characterization of related hydrogels and to the use of this collagen parameterization in more complex multiscale models.

Unraveling the swine genome: implications for human health

The pig was first used in biomedical research in ancient Greece and over the past few decades has quickly grown into an important biomedical research tool. Pigs have genetic and physiological traits similar to humans, which make them one of the most useful and versatile animal models. Owing to these similarities, data generated from porcine models are more likely to lead to viable human treatments than those from murine work. In addition, the similarity in size and physiology to humans allows pigs to be used for many experimental approaches not feasible in mice. Research areas that employ pigs range from neonatal development to translational models for cancer therapy. Increasing numbers of porcine models are being developed since the release of the swine genome sequence, and the development of additional porcine genomic and epigenetic resources will further their use in biomedical research.

Incorporation of fibrin into a collagen-glycosaminoglycan matrix results in a scaffold with improved mechanical properties and enhanced capacity to resist cell-mediated contraction

Fibrin has many uses as a tissue engineering scaffold, however many in vivo studies have shown a reduction in function resulting from the susceptibility of fibrin to cell-mediated contraction. The overall aim of the present study was to develop and characterise a reinforced natural scaffold using fibrin, collagen and glycosaminoglycan (FCG), and to examine the cell-mediated contraction of this scaffold in comparison to fibrin gels. Through the use of an injection loading technique, a homogenous FCG scaffold was developed. Mechanical testing showed a sixfold increase in compressive modulus and a thirtyfold increase in tensile modulus of fibrin when reinforced with a collagen-glycosaminoglycan backbone structure. Human vascular smooth muscle cells (vSMCs) were successfully incorporated into the FCG scaffold and demonstrated excellent viability over 7 days, while proliferation of these cells also increased significantly. VSMCs were seeded into both FCG and fibrin-only gels at the same seeding density for 7 days and while FCG scaffolds did not demonstrate a reduction in size, fibrin-only gels contracted to 10% of their original diameter. The FCG scaffold, which is composed of natural biomaterials, shows potential for use in applications where dimensional stability is crucial to the functionality of the tissue.

STATEMENT OF SIGNIFICANCE

Fibrin is a versatile scaffold for tissue engineering applications, but its weak mechanical properties leave it susceptible to cell-mediated contraction, meaning the dimensions of the fibrin construct will change over time. We have reinforced fibrin with a collagen glycosaminoglycan matrix and characterised the mechanical properties and bioactivity of the reinforced fibrin (FCG). This is the first scaffold manufactured from all naturally derived materials that resists cell-mediated contraction. In fact, over 7 days, the FCG scaffold fully resisted cell-mediated contraction of vascular smooth muscle cells. This FCG scaffold has many potential applications where natural scaffold materials can encourage regeneration.

Efficacy of the porcine species in biomedical research

Since domestication, pigs have been used extensively in agriculture and kept as companion animals. More recently they have been used in biomedical research, given they share many physiological and anatomical similarities with humans. Recent technological advances in assisted reproduction, somatic cell cloning, stem cell culture, genome editing, and transgenesis now enable the creation of unique porcine models of human diseases. Here, we highlight the potential applications and advantages of using pigs, particularly minipigs, as indispensable large animal models in fundamental and clinical research, including the development of therapeutics for inherited and chronic disorders, and cancers.

The vascularized periosteum flap as novel tissue engineering model for repair of cartilage defects

Periosteum is a promising tissue engineering scaffold in research of cartilage repair; so far however, periosteum transfers have not been realized successfully because of insufficient nourishment of the graft. In a translational approach we, for the first time, designed a vascularized periosteum flap as ‘independent’ biomaterial with its own blood supply to address this problem and to reconstruct circumscript cartilage defects. In six 3-month-old New Zealand rabbits, a critical size cartilage defect of the medial femur condyle was created and covered by a vascularized periosteum flap pedicled on the saphenous vessels. After 28 days, formation of newly built cartilage was assessed macroscopically, histologically and qualitatively via biomechanical compression testing, as well as on molecular biological level via immunohistochemistry. All wounds healed completely, all joints were stable and had full range of motion. All flaps survived and were perfused through their pulsating pedicles. They showed a stable attachment to the bone, although partially incomplete adherence. Hyaline cartilage with typical columnar cell distribution and positive Collagen II staining was formed in the transferred flaps. Biomechanical testing revealed a significantly higher maximum load than the positive control, but a low elasticity. This study proved that vascularization of the periosteum flap is the essential step for flap survival and enables the flap to transform into cartilage. Reconstruction of circumscript cartilage defects seems to be possible. Although these are the first results out of a pilot project, this technique, we believe, can have a wide range of potential applications and high relevance in the clinical field.

Osteochondral repair by a novel interconnecting collagen-hydroxyapatite substitute: a large-animal study

A novel three-dimensional bicomponent substitute made of collagen type I and hydroxyapatite was tested for the repair of osteochondral lesions in a swine model. This scaffold was assembled by a newly developed method that guarantees the strict integration between the organic and the inorganic parts, mimicking the biological tissue between the chondral and the osseous phase. Thirty-six osteochondral lesions were created in the trochlea of six pigs; in each pig, two lesions were treated with scaffolds seeded with autologous chondrocytes (cell+group), two lesions were treated with unseeded scaffolds (cell- group), and the two remaining lesions were left untreated (untreated group). After 3 months, the animals were sacrificed and the newly formed tissue was analyzed to evaluate the degree of maturation. The International Cartilage Repair Society (ICRS) macroscopic assessment showed significantly higher scores in the cell- and untreated groups when compared with the cell+ group. Histological evaluation showed the presence of repaired tissue, with fibroblast-like and hyaline-like areas in all groups; however, with respect to the other groups, the cell- group showed significantly higher values in the ICRS II histological scores for "cell morphology" and for the "surface/superficial assessment." While the scaffold seeded with autologous chondrocytes promoted the formation of a reparative tissue with high cellularity but low glycosaminoglycans (GAG) production, on the contrary, the reparative tissue observed with the unseeded scaffold presented lower cellularity but higher and uniform GAG distribution. Finally, in the lesions treated with scaffolds, the immunohistochemical analysis showed the presence of collagen type II in the peripheral part of the defect, indicating tissue maturation due to the migration of local cells from the surroundings. This study showed that the novel osteochondral scaffold was easy to handle for surgical implantation and was stable within the site of lesion; at the end of the experimental time, all implants were well integrated with the surrounding tissue and no signs of synovitis were observed. The quality of the reparative tissue seemed to be superior for the lesions treated with the unseeded scaffolds, indicating the promising potential of this novel biomaterial for use in a one-stage procedure for osteochondral repair.