Collagen: quantification, biomechanics, and role of minor subtypes in cartilage

Exogenous Collagen Crosslinking is Highly Detrimental to Articular Cartilage Lubrication

Healthy articular cartilage is a remarkable bearing material optimized for near-frictionless joint articulation. Because its limited self-repair capacity renders it susceptible to osteoarthritis (OA), approaches to reinforce or rebuild degenerative cartilage are of significant interest. While exogenous collagen crosslinking (CXL) treatments improve cartilage's mechanical properties and increase its resistance to enzymatic degradation, their effects on cartilage lubrication remain less clear. Here, we examined how the collagen crosslinking agents genipin (GP) and glutaraldehyde (GTA) impact cartilage lubrication using the convergent stationary contact area (cSCA) configuration. Unlike classical configurations, the cSCA sustains biofidelic kinetic friction coefficients (μk) via superposition of interstitial and hydrodynamic pressurization (i.e., tribological rehydration). As expected, glutaraldehyde- and genipin-mediated CXL increased cartilage's tensile and compressive moduli. Although net tribological rehydration was retained after CXL, GP or GTA treatment drastically elevated μk. Both healthy and "OA-like" cartilage (generated via enzymatic digestion) sustained remarkably low μk in saline- (≤0.02) and synovial fluid-lubricated contacts (≤0.006). After CXL, μk increased up to 30-fold, reaching values associated with marked chondrocyte death in vitro. These results demonstrate that mechanical properties (i.e., stiffness) are necessary, but not sufficient, metrics of cartilage function. Furthermore, the marked impairment in lubrication suggests that CXL-mediated stiffening is ill-suited to cartilage preservation or joint resurfacing.

SOX9 functionalized scaffolds as a barrier to against cartilage fibrosis

Hyaline cartilage regeneration will bring evangel to millions of people suffered from cartilage diseases. However, uncontrollable cartilage fibrosis and matrix mineralization are the primary causes of cartilage regeneration failure in many tissue engineering scaffolds. This study presents a new attempt to avoid endochondral ossification or fibrosis in cartilage regeneration therapy by establishing biochemical regulatory area. Here, SOX9 expression plasmids are assembled in cellulose gels by chitosan gene vectors to fabricate SOX9+ functionalized scaffolds. RT-qPCR, western blot and biochemical analysis all show that the SOX9 reinforcement strategy can enhance chondrogenic specific proteins expression and promote GAG production. Notably, the interference from SOX9 has resisted osteogenic inducing significantly, showing an inhibition of COL1, OPN and OC production, and the inhibition efficiency was about 58.4 %, 22.8 % and 76.9 % respectively. In vivo study, implantation of these scaffolds with BMSCs can induce chondrogenic differentiation and resist endochondral ossification effectively. Moreover, specific SOX9+ functionalized area of the gel exhibited the resistance to matrix mineralization, indicating the special biochemical functional area for cartilage regeneration. These results indicate that this strategy is effective for promoting the hyaline cartilage regeneration and avoiding cartilage fibrosis, which provides a new insight to the future development of cartilage regeneration scaffolds.

Osteopontin stabilization and collagen containment slows amorphous calcium phosphate transformation during human aortic valve leaflet calcification

Calcification of aortic valve leaflets is a growing mortality threat for the 18 million human lives claimed globally each year by heart disease. Extensive research has focused on the cellular and molecular pathophysiology associated with calcification, yet the detailed composition, structure, distribution and etiological history of mineral deposition remains unknown. Here transdisciplinary geology, biology and medicine (GeoBioMed) approaches prove that leaflet calcification is driven by amorphous calcium phosphate (ACP), ACP at the threshold of transformation toward hydroxyapatite (HAP) and cholesterol biomineralization. A paragenetic sequence of events is observed that includes: (1) original formation of unaltered leaflet tissues: (2) individual and coalescing 100's nm- to 1 μm-scale ACP spherules and cholesterol crystals biomineralizing collagen fibers and smooth muscle cell myofilaments; (3) osteopontin coatings that stabilize ACP and collagen containment of nodules preventing exposure to the solution chemistry and water content of pumping blood, which combine to slow transformation to HAP; (4) mm-scale nodule growth via ACP spherule coalescence, diagenetic incorporation of altered collagen and aggregation with other ACP nodules; and (5) leaflet diastole and systole flexure causing nodules to twist, fold their encasing collagen fibers and increase stiffness. These in vivo mechanisms combine to slow leaflet calcification and establish previously unexplored hypotheses for testing novel drug therapies and clinical interventions as viable alternatives to current reliance on surgical/percutaneous valve implants.

Simultaneous usage of sulforaphane nanoemulsion and tannic acid in ternary chitosan/gelatin/PEG hydrogel for knee cartilage tissue engineering: In vitro and in vivo study

The therapeutic potential of tissue engineering in addressing articular cartilage defects has been a focal point of research for numerous years. Despite its promising outlook, a persistent challenge within this domain is the lack of sufficient functional integration between engineered and natural tissues. This study introduces a novel approach that employs a combination of sulforaphane (SFN) nanoemulsion and tannic acid to enhance cartilage tissue engineering and promote tissue integration in a rat knee cartilage defect model. To substantiate our hypothesis, we conducted a series of in vitro and in vivo experiments. The SFN nanoemulsion was characterized using DLS, zeta potential, and TEM analyses. Subsequently, it was incorporated into a ternary polymer hydrogel composed of chitosan, gelatin, and polyethylene glycol. We evaluated the hydrogel with (H-SFN) and without (H) the SFN nanoemulsion through a comprehensive set of physicochemical, mechanical, and biological analyses. For the in vivo study, nine male Wistar rats were divided into three groups: no implant (Ctrl), H, and H-SFN. After inducing a cartilage defect, the affected area was treated with tannic acid and subsequently implanted with the hydrogels. Four weeks post-implantation, the harvested cartilage underwent histological examination employing H&E, safranin O/fast green, alcian blue, and immunohistochemistry staining techniques. Our results revealed that the SFN nanodroplets had an average diameter of 75 nm and a surface charge of -11.58 mV. Moreover, degradation, swelling rates, hydrophilicity, and elasticity features of the hydrogel incorporating SFN were improved. Histopathological analysis indicated a higher production of GAGs and collagen in the H-SFN group. Furthermore, the H-SFN group exhibited superior cartilage regeneration and tissue integration compared to the Ctrl and H groups. In conclusion, the findings of this study suggest the importance of considering cell protective properties in the fabrication of scaffolds for knee cartilage defects, emphasizing the potential significance of the proposed SFN nanoemulsion and tannic acid approach in advancing the field of cartilage tissue engineering.

Compositional, Structural, and Biomechanical Properties of Three Different Soft Tissue-Hard Tissue Insertions: A Comparative Review

Connective tissue attaches to bone across an insertion with spatial gradients in components, microstructure, and biomechanics. Due to regional stress concentrations between two mechanically dissimilar materials, the insertion is vulnerable to mechanical damage during joint movements and difficult to repair completely, which remains a significant clinical challenge. Despite interface stress concentrations, the native insertion physiologically functions as the effective load-transfer device between soft tissue and bone. This review summarizes tendon, ligament, and meniscus insertions cross-sectionally, which is novel in this field. Herein, the similarities and differences between the three kinds of insertions in terms of components, microstructure, and biomechanics are compared in great detail. This review begins with describing the basic components existing in the four zones (original soft tissue, uncalcified fibrocartilage, calcified fibrocartilage, and bone) of each kind of insertion, respectively. It then discusses the microstructure constructed from collagen, glycosaminoglycans (GAGs), minerals and others, which provides key support for the biomechanical properties and affects its physiological functions. Finally, the review continues by describing variations in mechanical properties at the millimeter, micrometer, and nanometer scale, which minimize stress concentrations and control stretch at the insertion. In summary, investigating the contrasts between the three has enlightening significance for future directions of repair strategies of insertion diseases and for bioinspired approaches to effective soft-hard interfaces and other tough and robust materials in medicine and engineering.

BMP signaling maintains auricular chondrocyte identity and prevents microtia development by inhibiting protein kinase A

Elastic cartilage constitutes a major component of the external ear, which functions to guide sound to the middle and inner ears. Defects in auricle development cause congenital microtia, which affects hearing and appearance in patients. Mutations in several genes have been implicated in microtia development, yet, the pathogenesis of this disorder remains incompletely understood. Here, we show that Prrx1 genetically marks auricular chondrocytes in adult mice. Interestingly, BMP-Smad1/5/9 signaling in chondrocytes is increasingly activated from the proximal to distal segments of the ear, which is associated with a decrease in chondrocyte regenerative activity. Ablation of Bmpr1a in auricular chondrocytes led to chondrocyte atrophy and microtia development at the distal part. Transcriptome analysis revealed that Bmpr1a deficiency caused a switch from the chondrogenic program to the osteogenic program, accompanied by enhanced protein kinase A activation, likely through increased expression of Adcy5/8. Inhibition of PKA blocked chondrocyte-to-osteoblast transformation and microtia development. Moreover, analysis of single-cell RNA-seq of human microtia samples uncovered enriched gene expression in the PKA pathway and chondrocyte-to-osteoblast transformation process. These findings suggest that auricle cartilage is actively maintained by BMP signaling, which maintains chondrocyte identity by suppressing osteogenic differentiation.

Investigation of Liquid Collagen Ink for Three-Dimensional Printing

Three-dimensional printing provides more versatility in the fabrication of scaffold materials for hard and soft tissue replacement, but a critical component is the ink. The ink solution should be biocompatible, stable, and able to maintain scaffold shape, size, and function once printed. This paper describes the development of a collagen ink that remains in a liquid pre-fibrillized state prior to printing. The liquid stability occurs due to the incorporation of ethylenediaminetetraacetic acid (EDTA) during dialysis of the collagen. Collagen inks were 3D-printed using two different printers. The resulting scaffolds were further processed using two different chemical crosslinkers, 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride)/N-hydroxysuccinimide (EDC/NHS) and genipin; gold nanoparticles were conjugated to the scaffolds. The 3D-printed scaffolds were characterized to determine their extrudability, stability, amount of AuNP conjugated, and overall biocompatibility via cell culture studies using fibroblast cells and stroma cells. The results demonstrated that the liquid collagen ink was amendable to 3D printing and was able to maintain its 3D shape. The scaffolds could be conjugated with gold nanoparticles and demonstrated enhanced biocompatibility. It was concluded that the liquid collagen ink is a good candidate material for the 3D printing of tissue scaffolds.

Plasma-Activated Polydimethylsiloxane Microstructured Pattern with Collagen for Improved Myoblast Cell Guidance

We focused on polydimethylsiloxane (PDMS) as a substrate for replication, micropatterning, and construction of biologically active surfaces. The novelty of this study is based on the combination of the argon plasma exposure of a micropatterned PDMS scaffold, where the plasma served as a strong tool for subsequent grafting of collagen coatings and their application as cell growth scaffolds, where the standard was significantly exceeded. As part of the scaffold design, templates with a patterned microstructure of different dimensions (50 × 50, 50 × 20, and 30 × 30 μm2) were created by photolithography followed by pattern replication on a PDMS polymer substrate. Subsequently, the prepared microstructured PDMS replicas were coated with a type I collagen layer. The sample preparation was followed by the characterization of material surface properties using various analytical techniques, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). To evaluate the biocompatibility of the produced samples, we conducted studies on the interactions between selected polymer replicas and micro- and nanostructures and mammalian cells. Specifically, we utilized mouse myoblasts (C2C12), and our results demonstrate that we achieved excellent cell alignment in conjunction with the development of a cytocompatible surface. Consequently, the outcomes of this research contribute to an enhanced comprehension of surface properties and interactions between structured polymers and mammalian cells. The use of periodic microstructures has the potential to advance the creation of novel materials and scaffolds in tissue engineering. These materials exhibit exceptional biocompatibility and possess the capacity to promote cell adhesion and growth.

Successive Protein Extraction Using Hydroxylamine to Increase the Depth of Proteome Coverage in Fresh, Forensic, and Archaeological Bones

Proteomics is continually being applied to a wider range of applications, now including the analysis of archaeological samples and anatomical specimens, particularly collagen-containing tissues such as bones and teeth. Here, we present the application of a chemical digestion-based proteomics sample preparation protocol to the analysis of fresh, anatomical, and archaeological samples. We describe and discuss two protocols: one that uses hydroxylamine as an additional step of the proteomic workflow, applied to the insoluble fraction, and another that applies hydroxylamine directly on demineralized bones and teeth. We demonstrate the additional information that can be extracted using both protocols, including an increase in the sequence coverage and number of peptides detected in modern and archaeological samples and an increase in the number of proteins identified in archaeological samples. By targeting research related to collagens or extracellular matrix proteins, the use of this protocol will open new insights, considering both fresh and ancient mineralized samples.

A review of advanced hydrogels for cartilage tissue engineering

With the increase in weight and age of the population, the consumption of tobacco, inappropriate foods, and the reduction of sports activities in recent years, bone and joint diseases such as osteoarthritis (OA) have become more common in the world. From the past until now, various treatment strategies (e.g., microfracture treatment, Autologous Chondrocyte Implantation (ACI), and Mosaicplasty) have been investigated and studied for the prevention and treatment of this disease. However, these methods face problems such as being invasive, not fully repairing the tissue, and damaging the surrounding tissues. Tissue engineering, including cartilage tissue engineering, is one of the minimally invasive, innovative, and effective methods for the treatment and regeneration of damaged cartilage, which has attracted the attention of scientists in the fields of medicine and biomaterials engineering in the past several years. Hydrogels of different types with diverse properties have become desirable candidates for engineering and treating cartilage tissue. They can cover most of the shortcomings of other treatment methods and cause the least secondary damage to the patient. Besides using hydrogels as an ideal strategy, new drug delivery and treatment methods, such as targeted drug delivery and treatment through mechanical signaling, have been studied as interesting strategies. In this study, we review and discuss various types of hydrogels, biomaterials used for hydrogel manufacturing, cartilage-targeting drug delivery, and mechanosignaling as modern strategies for cartilage treatment.

Establishment of a targeted proteomics method for the quantification of collagen chain: Revealing the chain stoichiometry of heterotypic collagen fibrils in sea cucumber

Collagen is the most abundant and important structural biomacromolecule in sea cucumbers. The sea cucumber collagen fibrils were previously confirmed to be heterotypic, nevertheless, the stoichiometry of collagen α-chains governing the complexity of collagen fibrils is still poorly understood. Herein, four representative collagen α-chains in sea cucumber including two clade A fibrillar collagens, one clade B fibrillar collagen, and one fibril-associated collagen with interrupted triple helices were selected. After the screening of signature peptides and optimization of multiple reaction monitoring (MRM) acquisition parameters including fragmentation, collision energy, and ion transition, a feasible MRM-based method was established. Consequently, the stoichiometry of the four collagen chains was determined to be approximately 100:54:3:4 based on the method. The assembly forms of sea cucumber collagen fibrils were further hypothesized according to the chain stoichiometry. This study facilitated the quantification of collagen and understanding of the collagen constituents in sea cucumber.

Exploring Tumor-Promoting Qualities of Cancer-Associated Fibroblasts and Innovative Drug Discovery Strategies With Emphasis on Thymoquinone

Tumor epithelial development and chemoresistance are highly promoted by the tumor microenvironment (TME), which is mostly made up of the cancer stroma. This is due to several causes. Cancer-associated fibroblasts (CAFs) stand out among them as being essential for the promotion of tumors. Understanding the fibroblastic population within a single tumor is made more challenging by the undeniable heterogeneity within it, even though particular stromal alterations are still up for debate. Numerous chemical signals released by tumors improve the connections between heterotypic fibroblasts and CAFs, promoting the spread of cancer. It becomes essential to have a thorough understanding of this complex microenvironment to effectively prevent solid tumor growth. Important new insights into the role of CAFs in the TME have been revealed by recent studies. The objective of this review is to carefully investigate the relationship between CAFs in tumors and plant secondary metabolites, with a focus on thymoquinone (TQ). The literature published between 2010 and 2023 was searched in PubMed and Google Scholar with keywords such as TQ, TME, cancer-associated fibroblasts, mechanism of action, and flavonoids. The results showed a wealth of data substantiating the activity of plant secondary metabolites, particularly TQ's involvement in blocking CAF operations. Scrutinized research also clarified the wider effect of flavonoids on pathways related to cancer. The present study highlights the complex dynamics of the TME and emphasizes the critical role of CAFs. It also examines the possible interventions provided by secondary metabolites found in plants, with TQ playing a vital role in regulating CAF function based on recent literature.

Characterization of the Age-Related Differences in Porcine Acetabulum and Femoral Head Articular Cartilage

OBJECTIVE

The use of porcine animal models for cartilage injury has increased recently due to their similarity with humans with regard to cartilage thickness, limited intrinsic healing of chondral defects, and joint loading biomechanics. However, variations in the mechanical and biochemical properties of porcine hip articular cartilage among various tissue ages and weightbearing (WB) regions are still unknown. This study's aim was to characterize the mechanical and biochemical properties of porcine hip articular cartilage across various ages and WB regions.

METHODS

Articular cartilage explants were harvested from WB and non-weightbearing (NWB) surfaces of the femoral head and acetabulum of domesticated pigs (Sus scrofa domesticus) at fetal (gestational age: 80 days), juvenile (6 months), and adult (2 years) ages. Explants underwent compressive stress-relaxation mechanical testing, biochemical analysis for total collagen and glycosaminoglycan (GAG) content, and histological staining.

RESULTS

Juvenile animals consistently had the highest mechanical properties, with 2.2- to 7.6-time increases in relaxation modulus, 1.3- to 2.3-time increases in instantaneous modulus, and 4.1- to 14.2-time increases in viscosity compared with fetal cartilage. Mechanical properties did not significantly differ between the WB and NWB regions. Collagen content was highest in the NWB regions of the juvenile acetabulum (65.3%/dry weight [DW]) and femoral head (75.4%/DW) cartilages. GAG content was highest in the WB region of the juvenile acetabulum (23.7%/DW) and the WB region of the fetal femoral head (27.5%/DW) cartilages. Histological staining for GAG and total collagen content followed the trends from the quantitative biochemical assays.

CONCLUSION

This study provides a benchmark for the development and validation of preclinical porcine models for hip cartilage pathologies.

Proton Transport Across Collagen Fibrils and Scaffolds: The Role of Hydroxyproline

Collagen is one of the most studied proteins due to its fundamental role in creating fibrillar structures and supporting tissues in our bodies. Accordingly, collagen is also one of the most used proteins for making tissue-engineered scaffolds for various types of tissues. To date, the high abundance of hydroxyproline (Hyp) within collagen is commonly ascribed to the structure and stability of collagen. Here, we hypothesize a new role for the presence of Hyp within collagen, which is to support proton transport (PT) across collagen fibrils. For this purpose, we explore here three different collagen-based hydrogels: the first is prepared by the self-assembly of natural collagen fibrils, and the second and third are based on covalently linking between collagen via either a self-coupling method or with an additional cross-linker. Following the formation of the hydrogel, we introduce here a two-step reaction, involving (1) attaching methanesulfonyl to the -OH group of Hyp, followed by (2) removing the methanesulfonyl, thus reverting Hyp to proline (Pro). We explore the PT efficiency at each step of the reaction using electrical measurements and show that adding the methanesulfonyl group vastly enhances PT, while reverting Hyp to Pro significantly reduces PT efficiency (compared with the initial point) with different efficiencies for the various collagen-based hydrogels. The role of Hyp in supporting the PT can assist in our understanding of the physiological roles of collagen. Furthermore, the capacity to modulate conductivity across collagen is very important to the use of collagen in regenerative medicine.

Strategies for Anisotropic Fibrillar Hydrogels: Design, Cell Alignment, and Applications in Tissue Engineering

Efficient cellular alignment in biomaterials presents a considerable challenge, demanding the refinement of appropriate material morphologies, while ensuring effective cell-surface interactions. To address this, biomaterials are continuously researched with diverse coatings, hydrogels, and polymeric surfaces. In this context, we investigate the influence of physicochemical parameters on the architecture of fibrillar hydrogels that significantly orient the topography of flexible hydrogel substrates, thereby fostering cellular adhesion and spatial organization. Our Review comprehensively assesses various techniques for aligning polymer fibrils within hydrogels, specifically interventions applied during and after the cross-linking process. These methodologies include mechanical strains, precise temperature modulation, controlled fluidic dynamics, and chemical modulators, as well as the use of magnetic and electric fields. We highlight the intrinsic appeal of these methodologies in fabricating cell-aligning interfaces and discuss their potential implications within the fields of biomaterials and tissue engineering, particularly concerning the pursuit of optimal cellular alignment.

An upright life, the postural stability of birds: a tensegrity system

Birds are so stable that they can rest and even sleep standing up. We propose that stable static balance is achieved by tensegrity. The rigid bones can be held together by tension in the tendons, allowing the system to stabilize under the action of gravity. We used the proportions of the bird's osteomuscular system to create a mathematical model. First, the extensor muscles and tendons of the leg are replaced by a single cable that follows the leg and is guided by joint pulleys. Analysis of the model shows that it can achieve balance. However, it does not match the biomechanical characteristics of the bird's body and is not stable. We then replaced the single cable with four cables, roughly corresponding to the extensor groups, and added a ligament loop at the knee. The model is then able to reach a stable equilibrium and the biomechanical characteristics are satisfied. Some of the anatomical features used in our model correspond to innovations unique to the avian lineage. We propose that tensegrity, which allows light and stable mechanical systems, is fundamental to the evolution of the avian body plan. It can also be used as an alternative model for bipedal robots.

Immunohistochemical Analysis of Knee Chondral Defect Repair after Autologous Particulated Cartilage and Platelet-Rich Plasma Treatment in Sheep

This study performs an analysis that will enable the evaluation of the quality, durability, and structure of repaired cartilaginous extracellular matrix tissue using an autologous-based particulated autograft cartilage and platelet-rich plasma treatment (PACI + PRP). A single-blind controlled experiment was conducted on 28 sheep to evaluate the efficacy of the PACI + PRP treatment for cartilage defects. Full-thickness 8 mm diameter defects were created in the weight-bearing area of both knees. The right knees received PACI + PRP. The left knees were treated with Ringer's lactate solution (RLS) or hyaluronic acid (HA) injections. Sheep were euthanized at 9- or 18-months post-surgery. An extensive immunohistochemical analysis was performed to assess collagen types (I, II, III, V, VI, IX, X, XI) and aggrecan positivity. A semiquantitative scoring system provided a detailed evaluation of immunostaining. Collagens and aggrecan scores in the PACI + PRP groups were similar to healthy cartilage. Significant differences were found in collagens associated with matrix maturity (II and V), degradation (IX), structure and mechanics (VI), and hypertrophy (X) between healthy cartilage and RLS- or HA-repaired cartilage. The PACI + PRP treatment advanced the repair cartilage process in chondral defects with mature hyaline cartilage and enhanced the structural and mechanical qualities with better consistent cartilage, less susceptible to degradation and without hypertrophic formation over time.

Combining bioengineered human skin with bioprinted cartilage for ear reconstruction

Microtia is a congenital disorder that manifests as a malformation of the external ear leading to psychosocial problems in affected children. Here, we present a tissue-engineered treatment approach based on a bioprinted autologous auricular cartilage construct (EarCartilage) combined with a bioengineered human pigmented and prevascularized dermo-epidermal skin substitute (EarSkin) tested in immunocompromised rats. We confirmed that human-engineered blood capillaries of EarSkin connected to the recipient's vasculature within 1 week, enabling rapid blood perfusion and epidermal maturation. Bioengineered EarSkin displayed a stratified epidermis containing mature keratinocytes and melanocytes. The latter resided within the basal layer of the epidermis and efficiently restored the skin color. Further, in vivo tests demonstrated favorable mechanical stability of EarCartilage along with enhanced extracellular matrix deposition. In conclusion, EarCartilage combined with EarSkin represents a novel approach for the treatment of microtia with the potential to circumvent existing limitations and improve the aesthetic outcome of microtia reconstruction.

Tissue anisotropy and collagenomics in porcine penile tunica albuginea: Implications for penile structure-function relationships and tissue engineering

The tunica albuginea (TA) of the penis is an elastic layer that serves a structural role in penile erection. Disorders affecting the TA cause pain, deformity, and erectile dysfunction. There is a substantial clinical need for engineered replacements of TA, but data are scarce on the material properties and biochemical composition of healthy TA. The objective of this study was to assess tissue organization, protein content, and mechanical properties of porcine TA to establish structure-function relationships and design criteria for tissue engineering efforts. TA was isolated from six pigs and subjected to histomorphometry, quantification of collagen content and pyridinoline crosslinks, bottom-up proteomics, and tensile mechanical testing. Collagen was 20 ± 2%/wet weight (WW) and 53 ± 4%/dry weight (DW). Pyridinoline content was 426 ±131 ng/mg WW, 1011 ± 190 ng/mg DW, and 45 ± 8 mmol/mol hydroxyproline. Bottom-up proteomics identified 14 proteins with an abundance of >0.1% of total protein. The most abundant collagen subtype was type I, representing 95.5 ± 1.5% of the total protein in the samples. Collagen types III, XII, and VI were quantified at 1.7 ± 1.0%, 0.8 ± 0.2%, and 0.4 ± 0.2%, respectively. Tensile testing revealed anisotropy: Young's modulus was significantly higher longitudinally than circumferentially (60 ± 18 MPa vs. 8 ± 5 MPa, p < 0.01), as was ultimate tensile strength (16 ± 4 MPa vs. 3 ± 3 MPa, p < 0.01). Taken together, the tissue mechanical and compositional data obtained in this study provide important benchmarks for the development of TA biomaterials. STATEMENT OF SIGNIFICANCE: The tunica albuginea of the penis serves an important structural role in physiologic penile erection. This tissue can become damaged by disease or trauma, leading to pain and deformity. Treatment options are limited. Little is known about the precise biochemical composition and biomechanical properties of healthy tunica albuginea. In this study, we characterize the tissue using proteomic analysis and tensile testing to establish design parameters for future tissue engineering efforts. To our knowledge, this is the first study to quantify tissue anisotropy and to use bottom-up proteomics to characterize the composition of penile tunica albuginea.

Cartilage Tissue Engineering in Practice: Preclinical Trials, Clinical Applications, and Prospects

Articular cartilage defects significantly compromise the quality of life in the global population. Although many strategies are needed to repair articular cartilage, including microfracture, autologous osteochondral transplantation, and osteochondral allograft, the therapeutic effects remain suboptimal. In recent years, with the development of cartilage tissue engineering, scientists have continuously improved the formulations of therapeutic cells, biomaterial-based scaffolds, and biological factors, which have opened new avenues for better therapeutics of cartilage lesions. This review focuses on advances in cartilage tissue engineering, particularly in preclinical trials and clinical applications, prospects, and challenges.

Effect of matrix properties on transmission and reflectance mode division-of-focal-plane Stokes polarimetry

Significance

Division-of-focal-plane Stokes polarimetry is emerging as a powerful tool for the microstructural characterization of soft tissues. How individual extracellular matrix (ECM) properties influence polarimetric signals in reflectance or transmission modes of quantitative polarized light imaging (QPLI) is not well understood.

Aim

We aimed to investigate how ECM properties affect outcomes obtained from division-of-focal-plane polarimetric imaging in reflectance or transmission modes.

Approach

Tunable collagen gel phantoms were used to modulate ECM properties of anisotropy, collagen density, crosslinking, and absorber density; the effects of degree of linear polarization (DoLP) and angle of polarization (AoP) on polarimetry outcomes were assessed. A model biological tissue (i.e., bovine tendon) was similarly imaged and evaluated using both reflectance and transmission modes.

Results

Reflectance QPLI resulted in decreased DoLP compared with transmission mode. A 90 deg shift in AoP was observed between modes but yielded similar spatial patterns. Collagen density had the largest effect on outcomes besides anisotropy in both imaging modes.

Conclusions

Both imaging modes were sufficiently sensitive to detect structural anisotropy differences in gels of varying fiber alignment. Conclusions drawn from phantom experiments should carry over when interpreting data from more complex tissues and can help provide context for interpretation of other Stokes polarimetry data.

Physiologic Doses of TGF-β Improve the Composition of Engineered Articular Cartilage

For cartilage regeneration applications, transforming growth factor beta (TGF-β) is conventionally administered at highly supraphysiologic doses (10-10,000 ng/mL) in an attempt to cue cells to fabricate neocartilage that matches the composition, structure, and functional properties of native hyaline cartilage. While supraphysiologic doses enhance ECM biosynthesis, they are also associated with inducing detrimental tissue features, such as fibrocartilage matrix deposition, pathologic-like chondrocyte clustering, and tissue swelling. Here we investigate the hypothesis that moderated TGF-β doses (0.1-1 ng/mL), akin to those present during physiological cartilage development, can improve neocartilage composition. Variable doses of media-supplemented TGF-β were administered to a model system of reduced-size cylindrical constructs (Ø2-Ø3 mm), which mitigate the TGF-β spatial gradients observed in conventional-size constructs (Ø4-Ø6 mm), allowing for a novel assessment of the intrinsic effect of TGF-β doses on macroscale neocartilage properties and composition. The administration of physiologic TGF-β to reduced-size constructs yields neocartilage with native-matched sGAG content and mechanical properties while providing a more hyaline cartilage-like composition, marked by: 1) reduced fibrocartilage-associated type I collagen, 2) 77% reduction in the fraction of cells present in a clustered morphology, and 3) 45% reduction in the degree of tissue swelling. Physiologic TGF-β appears to achieve an important balance of promoting requisite ECM biosynthesis, while mitigating hyaline cartilage compositional deficits. These results can guide the development of novel physiologic TGF-β-delivering scaffolds to improve the regeneration clinical-sized neocartilage tissues.

Regulatory T-cell deficiency leads to features of autoimmune liver disease overlap syndrome in scurfy mice

Introduction

Scurfy mice have a complete deficiency of functional regulatory T cells (Treg) due to a frameshift mutation in the Foxp3 gene. The impaired immune homeostasis results in a lethal lymphoproliferative disorder affecting multiple organs, including the liver. The autoimmune pathology in scurfy mice is in part accompanied by autoantibodies such as antinuclear antibodies (ANA). ANA are serological hallmarks of several autoimmune disorders including autoimmune liver diseases (AILD). However, the underlying pathogenesis and the role of Treg in AILD remain to be elucidated. The present study therefore aimed to characterize the liver disease in scurfy mice.

Methods

Sera from scurfy mice were screened for ANA by indirect immunofluorescence assay (IFA) and tested for a wide range of AILD-associated autoantibodies by enzyme-linked immunosorbent assay, line immunoassay, and addressable laser bead immunoassay. CD4+ T cells of scurfy mice were transferred into T cell-deficient B6/nude mice. Monoclonal autoantibodies from scurfy mice and recipient B6/nude mice were tested for ANA by IFA. Liver tissue of scurfy mice was analyzed by conventional histology. Collagen deposition in scurfy liver was quantified via hepatic hydroxyproline content. Real-time quantitative PCR was used to determine fibrosis-related hepatic gene expression. Hepatic immune cells were differentiated by flow cytometry.

Results

All scurfy mice produced ANA. AILD-associated autoantibodies, predominantly antimitochondrial antibodies, were detected at significantly higher levels in scurfy sera. CD4+ T cells from scurfy mice were sufficient to induce anti-dsDNA autoantibodies and ANA with an AILD-related nuclear envelope staining pattern. Liver histology revealed portal inflammation with bile duct damage and proliferation, as in primary biliary cholangitis (PBC), and interface hepatitis with portal-parenchymal necroinflammation, as found in autoimmune hepatitis (AIH). In scurfy liver, TNFα and fibrosis-related transcripts including Col1a1, Timp1, Acta2, Mmp2, and Mmp9 were upregulated. The level of proinflammatory monocytic macrophages (Ly-6Chi) was increased, while M2-type macrophages (CD206+) were downregulated compared to wildtype controls. Despite severe hepatic inflammation, fibrosis did not develop within 25 days, which is close to the lifespan of scurfy mice.

Discussion

Our findings suggest that Treg-deficient scurfy mice spontaneously develop clinical, serological, and immunopathological characteristics of AILD with overlapping features of PBC and AIH.

Human nasal cartilage: Functional properties and structure-function relationships for the development of tissue engineering design criteria

Nose reconstruction often requires scarce cartilage grafts. Nasal cartilage properties must be determined to serve as design criteria for engineering grafts. Thus, mechanical and biochemical properties were obtained in multiple locations of human nasal septum, upper lateral cartilage (ULC), and lower lateral cartilage (LLC). Within each region, no statistical differences among locations were detected, but anisotropy at some septum locations was noted. In the LLC, the tensile modulus and ultimate tensile strength (UTS) in the inferior-superior direction were statistically greater than in the anterior-posterior direction. Cartilage from all regions exhibited hyperelasticity in tension, but regions varied in degree of hyalinicity (i.e., Col II:Col I ratio). The septum contained the most collagen II and least collagen I and III, making it more hyaline than the ULC and LLC. The septum had a greater aggregate modulus, UTS, and lower total collagen/wet weight (Col/WW) than the ULC and LLC. The ULC had greater tensile modulus, DNA/WW, and lower glycosaminoglycan/WW than the septum and LLC. The ULC had a greater pyridinoline/Col than the septum. Histological staining suggested the presence of chondrons in all regions. In the ULC and LLC, tensile modulus correlated with total collagen content, while aggregate modulus correlated with pyridinoline content and weakly with pentosidine content. However, future studies should be performed to validate these proposed structure-function relationships. This study of human nasal cartilage provides 1) crucial design criteria for nasal cartilage tissue engineering efforts, 2) quantification of major and minor collagen subtypes and crosslinks, and 3) structure-function relationships. Surprisingly, the large mechanical properties found, particularly in the septum, suggests that nasal cartilage may experience higher-than-expected mechanical loads. STATEMENT OF SIGNIFICANCE: While tissue engineering holds promise to generate much-needed cartilage grafts for nasal reconstruction, little is known about nasal cartilage from an engineering perspective. In this study, the mechanical and biochemical properties of the septum, upper lateral cartilage (ULC), and lower lateral cartilage (LLC) were evaluated using cartilage-specific methods. For the first time in this tissue, all major and minor collagens and collagen crosslinks were measured, demonstrating that the septum was more hyaline than the ULC and LLC. Additionally, new structure-function relationships in the ULC and LLC were identified. This study greatly expands upon the quantitative understanding of human nasal cartilage and provides crucial engineering design criteria for much-needed nasal cartilage tissue engineering efforts.

Proteomic Identification and Characterization of Collagen from Bactrian Camel (Camelus bactrianus) Hoof

With the development of camel-derived food and pharmaceutical cosmetics, camel hoof, as a unique by-product of the camel industry, has gradually attracted the attention of scientific researchers in the fields of nutrition, health care, and biomaterial development. In this study, the protein composition and collagen type of Bactrian camel hoof collagen extract (CHC) were analyzed by LC-MS/MS, and the functional properties of CHC were further investigated, including its rheological characteristics, emulsification and emulsion stability, and hygroscopicity and humectancy. Proteomic identification confirmed that CHC had 13 collagen subunits, dominated by type I collagen (α1, α2), with molecular weights mainly in the 100-200 KDa range and a pI of 7.48. An amino acid study of CHC revealed that it carried the standard amino acid profile of type I collagen and was abundant in Gly, Pro, Glu, Ala, and Arg. Additionally, studies using circular dichroism spectroscopy and Fourier transform infrared spectroscopy revealed that CHC contains a collagen-like triple helix structure that is stable and intact. Different concentrations of CHC solutions showed shear-thinning flow behavior. Its tan δ did not differ much with increasing concentration. The CHC has good emulsifying ability and stability, humectancy, and hygroscopicity. This study provides a basis for utilizing and developing Bactrian camel hoof collagen as a functional ingredient.

Validation of Fourier Transform Infrared Microspectroscopy for the Evaluation of Enzymatic Cross-Linking of Bone Collagen

Enzymatic cross-linking of the bone collagen is important to resist to crack growth and to increased flexural strength. In the present study, we proposed a new method for assessment of enzymatic cross-link based on Fourier transform infrared (FTIR) microspectroscopy that takes into account secondary structure of type I collagen. Briefly, femurs were collected from sham or ovariectomized mice and subjected either to high-performance liquid chromatography-mass spectrometry or embedded in polymethylmethacrylate, cut and analyzed by FTIR microspectroscopy. FTIR acquisition was recorded before and after ultraviolet (UV) exposure or acid treatment. In addition, femurs from a second animal study were used to compare gene expression of Plod2 and Lox enzymes and enzymatic cross-links determined by FTIR microspectroscopy. We evidenced here that intensities and areas of subbands located at ~1660, ~1680, and ~1690 cm-1 were positively and significantly associated with the concentration of pyridinoline (PYD), deoxypyridinoline, or immature dihydroxylysinonorleucine/hydroxylysinonorleucine cross-links. Seventy-two hours exposure to UV light significantly reduced by ~86% and ~89% the intensity and area of the ~1660 cm-1 subband. Similarly, 24 h of acid treatment significantly reduced by 78% and 76% the intensity and area of the ~1690 cm-1 subband. Plod2 and Lox expression were also positively associated to the signal of the ~1660 and ~1690 cm-1 subbands. In conclusion, our study provided a new method for decomposing the amide I envelope of bone section that positively correlates with PYD and immature collagen cross-links. This method allows for investigation of tissue distribution of enzymatic cross-links in bone section.

Recombinant Collagen-Templated Biomineralized Synthesis of Biocompatible pH-Responsive Porous Calcium Carbonate Nanospheres

The synthesis of calcium carbonate with controlled morphology is crucial for its biomedical applications. In this study, we synthesized well-ordered porous calcium carbonate nanospheres using recombinant collagen as a biomineralization template. Porous collagen-calcium carbonate was created by incubating calcium chloride and sodium carbonate with collagen biotemplates at room temperature. Our results show that the recombinant collagen-calcium carbonate nanomaterials underwent a morphological transition from solid nanospheres to more porous nanospheres and a phase transformation from vaterite to a mixture of calcite and vaterite. This study highlights the crucial role of recombinant collagen in modulating the morphology and crystallinity of calcium carbonate nanoparticles. Importantly, the highly porous recombinant collagen-calcium carbonate hybrid nanospheres demonstrated superior loading efficacy for the model drug cefoperazone. Furthermore, the drug loading and releasing results suggest that hybrid nanospheres have the potential to be robust and biocompatible pH-responsive drug carriers. Our findings suggest that recombinant collagen's unique amino acid content and rodlike structure make it a superior template for biomineralized synthesis. This study provides a promising avenue for the production of novel organic-inorganic nanostructures, with potential applications in biomedical fields such as drug delivery.

Low-oxygen tension augments chondrocyte sensitivity to biomimetic thermomechanical cues in cartilage-engineered constructs

Chondrocytes respond to various biophysical cues, including oxygen tension, transient thermal signals, and mechanical stimuli. However, understanding how these factors interact to establish a unique regulatory microenvironment for chondrocyte function remains unclear. Herein, we explore these interactions using a joint-simulating bioreactor that independently controls the culture's oxygen concentration, evolution of temperature, and mechanical loading. Our analysis revealed significant coupling between these signals, resulting in a remarkable ∼14-fold increase in collagen type II (COL2a) and aggrecan (ACAN) mRNA expression. Furthermore, dynamic thermomechanical stimulation enhanced glycosaminoglycan and COL2a protein synthesis, with the magnitude of the biosynthetic changes being oxygen dependent. Additionally, our mechanistic study highlighted the crucial role of SRY-box transcription factor 9 (SOX9) as a major regulator of chondrogenic response, specifically expressed in response to combined biophysical signals. These findings illuminate the integration of various mechanobiological cues by chondrocytes and provide valuable insights for improving the extracellular matrix content in cartilage-engineered constructs.

Preparation and characterization of 3D hydroxyapatite/collagen scaffolds and its application in bone regeneration with bone morphogenetic protein-2

Desirable bone engineering materials should have a conducive three-dimensional (3D) structure and bioactive mediators for guided bone regeneration. In the present study, hydroxyapatite (HA)/collagen (Col) scaffolds were prepared by an optimized freeze-drying process. The porosity, moisture content, and mechanical properties of the composite have been investigated. The micro-morphology and structure were analyzed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM), confirmed that self-cross-linked HA/Col was evenly distributed and formed a 3D porous scaffold. The physicochemical/mechanical characterization was carried out by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Morphological observation and CCK-8 assay of co-culture cells indicated that HA/Col scaffolds were biocompatible. Then HA/Col scaffolds coupled with recombinant human bone morphogenetic proteins 2 (rhBMP-2) were implanted in the mandibular critical size defect in rats, and histological staining was used to evaluate the bone reconstruction. The result showed that HA/Col coupled with rhBMP-2 could significantly improve the formation of new bone and angiogenesis within the scaffolds as well as the proliferation and differentiation of osteoblasts. Thanks to the encouraging osteogenesis effects, the well-defined 3D scaffolds (HA/Col) cooperating with bioactive agents (rhBMP-2) are expected to be a promising candidate for bone tissue engineering applied to regenerative medicine.

Pd@Pt nanoparticle-linked immunosorbent assay for quantification of Collagen type II

The evaluation of specific protein content in engineered tissues provides a gateway for developing regenerative medicine treatments. Since collagen type II, the major component of articular cartilage, is critical for the blossoming field of articular cartilage tissue engineering, the interest in this protein is growing rapidly. Accordingly, the need for quantification of collagen type II is increasing as well. In this study, we provide recent results for a new quantifying nanoparticle sandwich immunoassay technique for collagen type II. Since mesoporous palladium@platinum (Pd@Pt) nanoparticles have peroxidase-like catalytic activities, these nanoparticles were utilized in an enzyme-linked immunosorbent assay (ELISA)-like format to circumvent the need for traditional enzymes. These nanoparticles were easily conjugated with anti-collagen type II antibodies by the natural affinity interaction and used to develop a direct sandwich ELISA-like format for nanoparticle-linked immunosorbent assays. Using this method, we obtained a limit of detection of 1 ng mL-1, a limit of quantification of 9 ng mL-1. and a broad linear range between 1 ng mL-1 and 50 μg mL-1 for collagen type II with an average relative standard deviation of 5.5%, useable over a pH range of 7 - 9 at least. The assay was successfully applied to quantify collagen type II in cartilage tissues and compared with the results of commercial ELISAs and gene expression by reverse transcription-quantitative polymerase chain reaction. This method provides a thermally stable and cost-efficient alternative to traditional ELISAs. It also extends the application of nanoparticle-linked immunosorbent assays, thereby providing the potential to quantify other proteins and apply the technology in the medical, environmental, and biotechnology industry fields.

In Vitro Effects of Triamcinolone and Methylprednisolone on the Viability and Mechanics of Native Articular Cartilage

BACKGROUND

The chondrotoxic effects of methylprednisolone acetate (MP) and triamcinolone acetonide (TA) have been well described. However, the mechanical effects of these commonly used steroids on native cartilage are largely unknown.

PURPOSE

To investigate the in vitro effects of a single 1-hour MP or TA exposure on the viability, mechanics, and biochemical content of native articular cartilage explants.

STUDY DESIGN

Controlled laboratory study.

METHODS

Articular cartilage explants (n = 6 per group) were harvested from the femoral condyles of bovine stifles. Explants were exposed to chondrogenic medium containing a clinical dose of MP or TA for 1 hour, followed by fresh medium wash and exchange. Explants in the control group underwent the same treatment with chondrogenic medium alone. At 24 hours after treatment, samples were assessed for viability (live/dead), mechanical properties (creep indentation and Instron tensile testing), biochemical (collagen and glycosaminoglycan) content, and pyridinoline crosslinking via mass spectrometry.

RESULTS

Mean cell viability was significantly decreased in native explants exposed to MP (35.5%) compared with the control (49.8%; P < .001) and TA (45.7%; P = .01) specimens. Significant decreases were seen in the mechanical properties of steroid-treated native explants when compared with controls, with decreases in aggregate modulus (646.3 vs 312.8 kPa [MP] and 257.0 kPa [TA]; P < .001), shear modulus (370.1 vs 191.2 kPa [MP] and 157.4 kPa [TA]; P < .001), and ultimate tensile strength (9.650 vs 5.648 MPa [MP; P = .021] and 6.065 MPa [TA; P = .0403]). No significant differences in collagen and glycosaminoglycan content were found in the steroid-treated groups. Pyridinoline crosslinking was significantly decreased in explants exposed to TA compared with controls (P = .027).

CONCLUSION

Exposure of MP to articular cartilage explants was chondrotoxic, and exposure of articular cartilage explants to MP or TA resulted in significant decreases in mechanical properties of articular cartilage explants compared with controls. Clinicians should be judicious regarding use of intra-articular steroids, particularly in patients with intact healthy articular cartilage.

Extracellular Matrix-Based and Electrospun Scaffolding Systems for Vaginal Reconstruction

Congenital vaginal anomalies and pelvic organ prolapse affect different age groups of women and both have significant negative impacts on patients' psychological well-being and quality of life. While surgical and non-surgical treatments are available for vaginal defects, their efficacy is limited, and they often result in long-term complications. Therefore, alternative treatment options are urgently needed. Fortunately, tissue-engineered scaffolds are promising new treatment modalities that provide an extracellular matrix (ECM)-like environment for vaginal cells to adhere, secrete ECM, and be remodeled by host cells. To this end, ECM-based scaffolds or the constructs that resemble ECM, generated by self-assembly, decellularization, or electrospinning techniques, have gained attention from both clinicians and researchers. These biomimetic scaffolds are highly similar to the native vaginal ECM and have great potential for clinical translation. This review article aims to discuss recent applications, challenges, and future perspectives of these scaffolds in vaginal reconstruction or repair strategies.

Strategic outline of interventions targeting extracellular matrix for promoting healthy longevity

The extracellular matrix (ECM), composed of interlinked proteins outside of cells, is an important component of the human body that helps maintain tissue architecture and cellular homeostasis. As people age, the ECM undergoes changes that can lead to age-related morbidity and mortality. Despite its importance, ECM aging remains understudied in the field of geroscience. In this review, we discuss the core concepts of ECM integrity, outline the age-related challenges and subsequent pathologies and diseases, summarize diagnostic methods detecting a faulty ECM, and provide strategies targeting ECM homeostasis. To conceptualize this, we built a technology research tree to hierarchically visualize possible research sequences for studying ECM aging. This strategic framework will hopefully facilitate the development of future research on interventions to restore ECM integrity, which could potentially lead to the development of new drugs or therapeutic interventions promoting health during aging.

Cartilage-Related Collagens in Osteoarthritis and Rheumatoid Arthritis: From Pathogenesis to Therapeutics

Collagens serve essential mechanical functions throughout the body, particularly in the connective tissues. In articular cartilage, collagens provide most of the biomechanical properties of the extracellular matrix essential for its function. Collagen plays a very important role in maintaining the mechanical properties of articular cartilage and the stability of the ECM. Noteworthily, many pathogenic factors in the course of osteoarthritis and rheumatoid arthritis, such as mechanical injury, inflammation, and senescence, are involved in the irreversible degradation of collagen, leading to the progressive destruction of cartilage. The degradation of collagen can generate new biochemical markers with the ability to monitor disease progression and facilitate drug development. In addition, collagen can also be used as a biomaterial with excellent properties such as low immunogenicity, biodegradability, biocompatibility, and hydrophilicity. This review not only provides a systematic description of collagen and analyzes the structural characteristics of articular cartilage and the mechanisms of cartilage damage in disease states but also provides a detailed characterization of the biomarkers of collagen production and the role of collagen in cartilage repair, providing ideas and techniques for clinical diagnosis and treatment.

Development of a rapid, efficient, and reusable magnetic bead-based immunocapture system for recombinant human procollagen type II isolation from yeast fermentation broth

Recombinant collagen production, especially using yeasts as expression systems, could represent a promising alternative over traditional extractive methods from animal sources, offering controllable, scalable, and high-quality products. Monitoring the efficiency and efficacy of procollagen/collagen expression, especially in the initial fermentation phases, can be difficult and time consuming, as biological matrices necessitate purification and commonly used analytical methods are only partially informative. We propose a straightforward, efficient, and reusable immunocapture system able to specifically isolate human procollagen type II from fermentation broths and to release it in few experimental steps. A recovered sample allows for a detailed characterization providing information on structural identity and integrity, which can strongly support the monitoring of fermentation processes. The immunocapture system relies on the use of protein A-coated magnetic beads which have been functionalized and cross-linked with a human anti-procollagen II antibody (average immobilization yield of 97.7%) to create a stable and reusable support for the specific procollagen fishing. We set up the binding and release conditions ensuring specific and reproducible binding with a synthetic procollagen antigen. The absence of non-specific interaction with the support and binding specificity was demonstrated, and the latter was also confirmed by a peptide mapping epitope study in reversed-phase liquid chromatography high-resolution mass spectrometry (RP-LC-HRMS). The bio-activated support proved to be reusable and stable over 21 days from the initial use. Finally, the system was successfully tested on a raw yeast fermentation sample to provide a proof of concept of the applicability within recombinant collagen production.

Integrative Analysis Reveals the Diverse Effects of 3D Stiffness upon Stem Cell Fate

The origin of life and native tissue development are dependent on the heterogeneity of pluripotent stem cells. Bone marrow mesenchymal stem cells (BMMSCs) are located in a complicated niche with variable matrix stiffnesses, resulting in divergent stem cell fates. However, how stiffness drives stem cell fate remains unknown. For this study, we performed whole-gene transcriptomics and precise untargeted metabolomics sequencing to elucidate the complex interaction network of stem cell transcriptional and metabolic signals in extracellular matrices (ECMs) with different stiffnesses, and we propose a potential mechanism involved in stem cell fate decision. In a stiff (39~45 kPa) ECM, biosynthesis of aminoacyl-tRNA was up-regulated, and increased osteogenesis was also observed. In a soft (7~10 kPa) ECM, biosynthesis of unsaturated fatty acids and deposition of glycosaminoglycans were increased, accompanied by enhanced adipogenic/chondrogenic differentiation of BMMSCs. In addition, a panel of genes responding to the stiffness of the ECM were validated in vitro, mapping out the key signaling network that regulates stem cells' fate decisions. This finding of "stiffness-dependent manipulation of stem cell fate" provides a novel molecular biological basis for development of potential therapeutic targets within tissue engineering, from both a cellular metabolic and a biomechanical perspective.

Pharmacological Functions, Synthesis, and Delivery Progress for Collagen as Biodrug and Biomaterial

Collagen has been widely applied as a functional biomaterial in regulating tissue regeneration and drug delivery by participating in cell proliferation, differentiation, migration, intercellular signal transmission, tissue formation, and blood coagulation. However, traditional extraction of collagen from animals potentially induces immunogenicity and requires complicated material treatment and purification steps. Although semi-synthesis strategies such as utilizing recombinant E. coli or yeast expression systems have been explored as alternative methods, the influence of unwanted by-products, foreign substances, and immature synthetic processes have limited its industrial production and clinical applications. Meanwhile, macromolecule collagen products encounter a bottleneck in delivery and absorption by conventional oral and injection vehicles, which promotes the studies of transdermal and topical delivery strategies and implant methods. This review illustrates the physiological and therapeutic effects, synthesis strategies, and delivery technologies of collagen to provide a reference and outlook for the research and development of collagen as a biodrug and biomaterial.

Photoacoustic remote sensing elastography

The mechanical properties of organisms are important indicators for clinical disputes and disease monitoring, yet most existing elastography techniques are based on contact measurements, which are limited in many application scenarios. Photoacoustic remote sensing elastography (PARSE) is the first, to the best of our knowledge, elastography modality based on acoustic pressure monitoring, where elastic contrast information is obtained by using an all-optical non-contact and non-coherent intensity monitoring method through the time-response properties of laser-induced photoacoustic pressure. To validate PARSE, sections of different elastic organs were measured and this modality was applied to differentiate between bronchial cartilage and soft tissue to confirm the validity of the elasticity evaluation. PARSE, through a mathematical derivation process, has a 9.5-times greater distinction detection capability than photoacoustic remote sensing (PARS) imaging in stained bronchial sections, expands the scope of conventional PARS imaging, and has potential to become an important complementary imaging modality.

High-resolution confocal and light-sheet imaging of collagen 3D network architecture in very large samples

Although notoriously difficult, imaging collagen network architecture, a key element affecting tissue mechanical properties, is of paramount importance in developmental and cancer biology. Here, we introduce a simple and robust method of whole-mount collagen staining with the 'Fast Green' dye that provides unmatched visualization of collagen 3D network architecture, via confocal or light-sheet microscopy, compatible with solvent-based tissue clearing and immunostaining.

The Matrix Reloaded—The Role of the Extracellular Matrix in Cancer

As the core component of all organs, the extracellular matrix (ECM) is an interlocking macromolecular meshwork of proteins, glycoproteins, and proteoglycans that provides mechanical support to cells and tissues. In cancer, the ECM can be remodelled in response to environmental cues, and it controls a plethora of cellular functions, including metabolism, cell polarity, migration, and proliferation, to sustain and support oncogenesis. The biophysical and biochemical properties of the ECM, such as its structural arrangement and being a reservoir for bioactive molecules, control several intra- and intercellular signalling pathways and induce cytoskeletal changes that alter cell shapes, behaviour, and viability. Desmoplasia is a major component of solid tumours. The abnormal deposition and composition of the tumour matrix lead to biochemical and biomechanical alterations that determine disease development and resistance to treatment. This review summarises the complex roles of ECM in cancer and highlights the possible therapeutic targets and how to potentially remodel the dysregulated ECM in the future. Furthering our understanding of the ECM in cancer is important as the modification of the ECM will probably become an important tool in the characterisation of individual tumours and personalised treatment options.

Seasonal Molecular Difference in Fibrillar Collagen Extracts Derived from the Marine Sponge Chondrosia reniformis (Nardo, 1847) and Their Impact on Its Derived Biomaterials

Chondrosia reniformis (Nardo, 1847) is a marine sponge of high biotechnological interest both for its natural compound content and for its peculiar collagen, which is suitable for the production of innovative biomaterials in the form, for instance, of 2D membranes and hydrogels, exploitable in the fields of tissue engineering and regenerative medicine. In this study, the molecular and chemical-physical properties of fibrillar collagen extracted from specimens collected in different seasons are studied to evaluate the possible impact of sea temperature on them. Collagen fibrils were extracted from sponges harvested by the Sdot Yam coast (Israel) during winter (sea temperature: 17 °C) and during summer (sea temperature: 27 °C). The total AA composition of the two different collagens was evaluated, together with their thermal stability and glycosylation level. The results showed a lower lysyl-hydroxylation level, lower thermal stability, and lower protein glycosylation level in fibrils extracted from 17 °C animals compared to those from 27 °C animals, while no differences were noticed in the GAGs content. Membranes obtained with fibrils deriving from 17 °C samples showed a higher stiffness if compared to the 27 °C ones. The lower mechanical properties shown by 27 °C fibrils are suggestive of some unknown molecular changes in collagen fibrils, perhaps related to the creeping behavior of C. reniformis during summer. Overall, the differences in collagen properties gain relevance as they can guide the intended use of the biomaterial.

Progress in biomechanical stimuli on the cell-encapsulated hydrogels for cartilage tissue regeneration

BACKGROUND

Worldwide, many people suffer from knee injuries and articular cartilage damage every year, which causes pain and reduces productivity, life quality, and daily routines. Medication is currently primarily used to relieve symptoms and not to ameliorate cartilage degeneration. As the natural healing capacity of cartilage damage is limited due to a lack of vascularization, common surgical methods are used to repair cartilage tissue, but they cannot prevent massive damage followed by injury.

MAIN BODY

Functional tissue engineering has recently attracted attention for the repair of cartilage damage using a combination of cells, scaffolds (constructs), biochemical factors, and biomechanical stimuli. As cyclic biomechanical loading is the key factor in maintaining the chondrocyte phenotype, many studies have evaluated the effect of biomechanical stimulation on chondrogenesis. The characteristics of hydrogels, such as their mechanical properties, water content, and cell encapsulation, make them ideal for tissue-engineered scaffolds. Induced cell signaling (biochemical and biomechanical factors) and encapsulation of cells in hydrogels as a construct are discussed for biomechanical stimulation-based tissue regeneration, and several notable studies on the effect of biomechanical stimulation on encapsulated cells within hydrogels are discussed for cartilage regeneration.

CONCLUSION

Induction of biochemical and biomechanical signaling on the encapsulated cells in hydrogels are important factors for biomechanical stimulation-based cartilage regeneration.

Collagen constitutes about 12% in females and 17% in males of the total protein in mice

Collagen has been postulated to be the most abundant protein in our body, making up one-third of the total protein content in mammals. However, a direct assessment of the total collagen levels of an entire mammal to confirm this estimate is missing. Here we measured hydroxyproline levels as a proxy for collagen content together with total protein levels of entire mice or of individual tissues. Collagen content normalized to the total protein is approximately 0.1% in the brain and liver, 1% in the heart and kidney, 4% in the muscle and lung, 6% in the colon, 20-40% in the skin, 25-35% in bones, and 40-50% in tendons of wild-type (CD1 and CB57BL/6) mice, consistent with previous reports. To our surprise, we find that collagen is approximately 12% in females and 17% in males of the total protein content of entire wild-type (CD1 and CB57BL/6) mice. Although collagen type I is the most abundant collagen, the most abundant proteins are albumin, hemoglobulin, histones, actin, serpina, and then collagen type I. Analyzing amino acid compositions of mice revealed glycine as the most abundant amino acid. Thus, we provide reference points for collagen, matrisome, protein, and amino acid composition of healthy wild-type mice.

Unusual Suspects: Bone and Cartilage ECM Proteins as Carcinoma Facilitators

The extracellular matrix (ECM) is the complex three-dimensional network of fibrous proteins and proteoglycans that constitutes an essential part of every tissue to provide support for normal tissue homeostasis. Tissue specificity of the ECM in its topology and structure supports unique biochemical and mechanical properties of each organ. Cancers, like normal tissues, require the ECM to maintain multiple processes governing tumor development, progression and spread. A large body of experimental and clinical evidence has now accumulated to demonstrate essential roles of numerous ECM components in all cancer types. Latest findings also suggest that multiple tumor types express, and use to their advantage, atypical ECM components that are not found in the cancer tissue of origin. However, the understanding of cancer-specific expression patterns of these ECM proteins and their exact roles in selected tumor types is still sketchy. In this review, we summarize the latest data on the aberrant expression of bone and cartilage ECM proteins in epithelial cancers and their specific functions in the pathogenesis of carcinomas and discuss future directions in exploring the utility of this selective group of ECM components as future drug targets.

Progress of Microfluidic Hydrogel-Based Scaffolds and Organ-on-Chips for the Cartilage Tissue Engineering

Cartilage degeneration is among the fundamental reasons behind disability and pain across the globe. Numerous approaches have been employed to treat cartilage diseases. Nevertheless, none have shown acceptable outcomes in the long run. In this regard, the convergence of tissue engineering and microfabrication principles can allow developing more advanced microfluidic technologies, thus offering attractive alternatives to current treatments and traditional constructs used in tissue engineering applications. Herein, the current developments involving microfluidic hydrogel-based scaffolds, promising structures for cartilage regeneration, ranging from hydrogels with microfluidic channels to hydrogels prepared by the microfluidic devices, that enable therapeutic delivery of cells, drugs, and growth factors, as well as cartilage-related organ-on-chips are reviewed. Thereafter, cartilage anatomy and types of damages, and present treatment options are briefly overviewed. Various hydrogels are introduced, and the advantages of microfluidic hydrogel-based scaffolds over traditional hydrogels are thoroughly discussed. Furthermore, available technologies for fabricating microfluidic hydrogel-based scaffolds and microfluidic chips are presented. The preclinical and clinical applications of microfluidic hydrogel-based scaffolds in cartilage regeneration and the development of cartilage-related microfluidic chips over time are further explained. The current developments, recent key challenges, and attractive prospects that should be considered so as to develop microfluidic systems in cartilage repair are highlighted.

Comparative study of alginate and type I collagen as biomaterials for cartilage stem/progenitor cells to construct tissue-engineered cartilage in vivo

With the help of biomaterials, cartilage stem/progenitor cells (CSPCs) derived from cartilage tissue present a promising choice for cartilage regeneration. In our previous study, we investigated whether CSPCs could be ideal seeding cells for cartilage tissue regeneration. Biomaterials are fabricated to accelerate tissue regeneration, providing a suitable environment for cell attachment, proliferation, and differentiation. Among the biomaterials used in cartilage regeneration medicine, alginate and collagen are classified as natural biomaterials and are characterized by high biocompatibility, bioactivity, and non-toxic degradation products. However, it is unclear which material would have a competitive advantage in CSPC-based cartilage regeneration in vivo. In the present study, we employed alginate and type Ⅰ collagen as substrates for CSPCs and chondrocytes, which was made control group, to explore a more suitable biomaterials for CSPCs to fabricate tissue-engineered cartilage, in vivo. Hematoxylin and eosin (HE) staining, Safranin O, immunohistochemical assay, and quantitative real-time polymerase chain reaction (qRT-PCR) were used to evaluate the tissue-engineered cartilage in vivo. Compared with the alginate group, collagen enhanced the expression of cartilage-specific genes, such as ACAN, SOX9, and COLII, more markedly. Furthermore, the marker genes of expression, dedifferentiation, and hypertrophy, COLI and COLX, were downregulated in the collagen group. The results demonstrated that collagen as a substrate was superior to alginate in increasing the accumulation of cartilage-like ECM for CSPCs in vivo. In summary, compared with alginate, collagen hydrogel is an effective biomaterial for CSPC-based cartilage regeneration.

Application of decellularized vascular matrix in small-diameter vascular grafts

Coronary artery bypass grafting (CABG) remains the most common procedure used in cardiovascular surgery for the treatment of severe coronary atherosclerotic heart disease. In coronary artery bypass grafting, small-diameter vascular grafts can potentially replace the vessels of the patient. The complete retention of the extracellular matrix, superior biocompatibility, and non-immunogenicity of the decellularized vascular matrix are unique advantages of small-diameter tissue-engineered vascular grafts. However, after vascular implantation, the decellularized vascular matrix is also subject to thrombosis and neoplastic endothelial hyperplasia, the two major problems that hinder its clinical application. The keys to improving the long-term patency of the decellularized matrix as vascular grafts include facilitating early endothelialization and avoiding intravascular thrombosis. This review article sequentially introduces six aspects of the decellularized vascular matrix as follows: design criteria of vascular grafts, components of the decellularized vascular matrix, the changing sources of the decellularized vascular matrix, the advantages and shortcomings of decellularization technologies, modification methods and the commercialization progress as well as the application prospects in small-diameter vascular grafts.

Assessment of Collagen in Translational Models of Lung Research

The extracellular matrix (ECM) plays an important role in lung health and disease. Collagen is the main component of the lung ECM, widely used for the establishment of in vitro and organotypic models of lung disease, and as scaffold material of general interest for the field of lung bioengineering. Collagen also is the main readout for fibrotic lung disease, where collagen composition and molecular properties are drastically changed and ultimately result in dysfunctional "scarred" tissue. Because of the central role of collagen in lung disease, quantification, determination of molecular properties, and three-dimensional visualization of collagen is important for both development and characterization of translational models of lung research. In this chapter, we provide a comprehensive overview on the various methodologies currently available for quantification and characterization of collagen including their detection principles, advantages, and disadvantages.