Raman Spectroscopy Reveals New Insights into the Zonal Organization of Native and Tissue-Engineered Articular Cartilage

Pregnancy and age differentially affect stiffness, injury susceptibility, and composition of murine uterosacral ligaments

Pelvic organ prolapse is a debilitating condition that diminishes quality of life, and it has been linked to pregnancy and aging. Injury of the uterosacral ligaments (USLs), which provide apical support to the pelvic organs, is a major cause of uterine prolapse. In this study, we examined the effect of pregnancy and age on the apparent elastic modulus, susceptibility to collagen damage, and extracellular matrix (ECM) composition of the murine USL. USLs from mice at three different stages of pregnancy and across two age groups were mechanically tested and evaluated for collagen microdamage. Raman spectroscopy was used to evaluate changes in ECM composition. Our findings reveal that (1) all USLs subjected to mechanical stretch sustained collagen microdamage, (2) both pregnancy and age significantly affected USL stiffness and injury susceptibility, and (3) pregnancy, but not age, altered ECM composition. Overall, this work represents a major step toward understanding the role of tissue microstructure and mechanical function in USL injury, which should guide novel ECM-targeted treatment and prevention strategies for uterine prolapse.

Raman spectroscopic probe provides optical biomarkers of cartilage composition predictive of tissue function

OBJECTIVE

The diagnosis of early osteoarthritis when therapeutic interventions may be most effective at reversing cartilage degeneration presents a clinical challenge. We describe a Raman arthroscopic probe and spectral analysis that measures biomarkers reflective of the content of predominant cartilage extracellular matrix (ECM) constituents-glycosaminoglycans (GAG), collagen, water-essential to cartilage function. We compare the capability of Raman-probe-derived biomarkers to predict functional properties of cartilage to quantitative MRI and histopathology assessments.

DESIGN

Osteochondral blocks were sectioned from 6 bovine femoral condyles with no macroscopic injury (n=62 blocks) and 6 condyles with a focal chondral lesion (n=32 blocks), but no macroscopic degeneration of surrounding cartilage (n=34 blocks). Blocks from 10 human knees were further analyzed (age 27-75; n=235 blocks). Using a custom arthroscopic Raman spectroscopy probe, spectra of chondral layers were measured and subjected to multivariate linear decomposition to extract ECM biomarker scores, reflecting the contribution of each ECM constituent to the spectra. Blocks were further analyzed for elastic modulus, T2/T2* MRI relaxation times, and OARSI scores.

RESULTS

For bovine tissues, Raman biomarkers revealed depleted GAG and cartilage softening peripheral to the lesion despite no macroscopic degeneration. Raman biomarkers accounted for 78% of GAG content variation and 71% of modulus variation. For human tissues, Raman biomarkers accounted for 71% of modulus variation. Raman biomarkers accounted for a greater variation of modulus (71%-72%) than OARSI (12-54%), T2* (15%-27%), or T2 (25%-30%).

CONCLUSIONS

These data support the application of Raman-probe-derived biomarkers for molecular assessment of key ECM constituents that define cartilage properties in health and disease.

Harnessing Raman spectroscopy and multimodal imaging of cartilage for osteoarthritis diagnosis

Osteoarthritis (OA) is a complex disease of cartilage characterised by joint pain, functional limitation, and reduced quality of life with affected joint movement leading to pain and limited mobility. Current methods to diagnose OA are predominantly limited to X-ray, MRI and invasive joint fluid analysis, all of which lack chemical or molecular specificity and are limited to detection of the disease at later stages. A rapid minimally invasive and non-destructive approach to disease diagnosis is a critical unmet need. Label-free techniques such as Raman Spectroscopy (RS), Coherent anti-Stokes Raman scattering (CARS), Second Harmonic Generation (SHG) and Two Photon Fluorescence (TPF) are increasingly being used to characterise cartilage tissue. However, current studies are based on whole tissue analysis and do not consider the different and structurally distinct layers in cartilage. In this work, we use Raman spectroscopy to obtain signatures from the superficial (top) and deep (bottom) layer of healthy and osteoarthritic cartilage samples from 64 patients (19 control and 45 OA). Spectra were acquired both in the 'fingerprint' region from 700 to 1720 cm- 1 and high-frequency stretching region from 2500 to 3300 cm- 1. Principal component and linear discriminant analysis was used to identify the peaks that contributed significantly to classification accuracy of the different samples. The most pronounced differences were observed at the proline (855 cm- 1 and 921 cm- 1) and hydroxyproline (877 cm- 1 and 938 cm- 1), sulphated glycosaminoglycan (sGAG) (1064 cm- 1 and 1380 cm- 1) frequencies for both control and OA as well as the 1245 cm- 1 and 1272 cm- 1, 1320 cm- 1 and 1345 cm- 1, 1451 cm- 1 collagen modes were altered in OA samples, consistent with expected collagen structural changes. Classification accuracy based on Raman fingerprint spectral analysis of superficial and deep layer cartilage for controls was found to be 97% and 93% on using individual/all spectra and, 100% and 95% on using mean spectra per patient, respectively. OA diseased cartilage was classified with an accuracy of 88% and 84% for individual/all spectra, and 96% and 95% for mean spectra per patient based on analysis of the superficial and the deep layers, respectively. Raman spectra from the C-H stretching region (2500-3300 cm- 1) resulted in high classification accuracy for identification of different layers and OA diseased cartilage but low accuracy for controls. Differential changes in superficial and deep layer cartilage signatures were observed with age (under 60 and over 60 years), in contrast, less significant differences were observed with gender. Prominent chemical changes in the different layers of cartilage were preliminarily imaged using CARS, SHG and TPF. Cell clustering was observed in OA together with differences in pericellular matrix and collagen structure in the superficial and the deep layers correlating with the Raman spectral analysis. The current study demonstrates the potential of Raman Spectroscopy and multimodal imaging to interrogate cartilage tissue and provides insight into the chemical and structural composition of its different layers with significant implications for OA diagnosis for an increasing aging demographic.

Unveiling the Molecular Secrets: A Comprehensive Review of Raman Spectroscopy in Biological Research

Raman spectroscopy has been proven to be a fast, convenient, and nondestructive technique for advancing our understanding of biological systems. The Raman effect originates from the inelastic scattering of light which directly probe vibration/rotational states in biological molecules and materials. Despite numerous advantages over infrared spectroscopy and continuous technical as well as operational improvement in Raman spectroscopy, an advanced development of the device and more applications have become possible. In this review, we explore the principles, techniques, and myriad applications of Raman spectroscopy in the realm of biology. We begin by providing an overview of Raman spectroscopy, highlighting its significance in unraveling the complexities of biological research. The focus of this review is on Raman spectroscopy concepts and methods, clarifying the fundamentals of Raman scattering and spectral interpretation. The review also highlights the key experimental considerations for productive biological applications. We explore the broad range of Raman applications including molecular structure, biomolecular composition, disease detection, and medication discovery. The Raman imaging and mapping can also be used to visualize biological samples at the molecular level. Raman spectroscopy is still developing, giving fresh insights and remedies, from biosensing to its use in tissue engineering and regenerative medicine. This review sheds light on the past, present, and future of Raman spectroscopy; it also highlights promising directions of future research developments and serves as a thorough resource for all researchers.

Strategies to engineer articular cartilage with biomimetic zonal features: a review

Articular cartilage (AC) is a highly specialized tissue with restricted ability for self-regeneration, given its avascular and acellular nature. Although a considerable number of surgical treatments is available for the repair, reconstruction, and regeneration of AC defects, most of them do not prioritize the development of engineered cartilage with zonal stratification derived from biomimetic biochemical, biomechanical and topographic cues. In the absence of these zonal elements, engineered cartilage will exhibit increased susceptibility to failure and will neither be able to withstand the mechanical loading to which AC is subjected nor will it integrate well with the surrounding tissue. In this regard, new breakthroughs in the development of hierarchical stratified engineered cartilage are highly sought after. Initially, this review provides a comprehensive analysis of the composition and zonal organization of AC, aiming to enhance our understanding of the significance of the structure of AC for its function. Next, we direct our attention towards the existing in vitro and in vivo studies that introduce zonal elements in engineered cartilage to elicit appropriate AC regeneration by employing tissue engineering strategies. Finally, the advantages, challenges, and future perspectives of these approaches are presented.

Sulfur-species in Zinc-specific Condylar Zones of a Rat Temporomandibular Joint

In this study, we performed synchrotron-based micro-X-ray fluorescence (μ-XRF) imaging of elements Zn and S, and X-ray absorption near edge spectroscopy (XANES) coupled with μ-XRF for identification of Zn and S species in the condylar zones of a rat temporomandibular joint (TMJ). Histologic localization of Zn and hypoxia-inducible factor-1α (HIF-1α) were mapped using an optical microscope. These data were visually correlated with μ-XRF and XANES data to provide insights into plausible biological S-species in Z-enriched condylar zones of a rat TMJ. Furthermore, μ-XRF coupled with micro-X-ray diffraction (μ-XRD) was used to underline Z-incorporated biological apatite in the subchondral bone and bone of the rat TMJ. Results illustrated the potential dependence between biometal Zn and nonmetal S and their collective governance of cell and tissue functions in a zone-specific manner. Elemental Zn with organic and inorganic S-species at the cartilage-bone interface and transformation of plausible Zn-enriched mineralization kinetics of biological apatite from subchondral bone to condylar bone were ascertained using μ-XRF-XANES and μ-XRD. The coupled μ-XRF-XANES complementing with μ-XRD and immunohistology provided an informative view of S and Zn and their association with zone-specific biological pathways in situ. Understanding the spatial distributions of the main S-species with redox-inert Zn in regions of cartilage, bone, and the interface is essential for further unlocking questions surrounding formation and resorption-related biomineralization pathways as related to osteoarthritis or genetically inherited diseases. Using these complementary techniques with microspectroscopic spatial information provided insights into the associations between biometal Zn and nonmetal S and a window into detecting the plausible early-stage diagnostic biomarkers for humans with TMJ osteoarthritis.

Revealing chemistry-structure-function relationships in shark vertebrae across length scales

Shark cartilage presents a complex material composed of collagen, proteoglycans, and bioapatite. In the present study, we explored the link between microstructure, chemical composition, and biomechanical function of shark vertebral cartilage using Polarized Light Microscopy (PLM), Atomic Force Microscopy (AFM), Confocal Raman Microspectroscopy, and Nanoindentation. Our investigation focused on vertebrae from Blacktip and Shortfin Mako sharks. As typical representatives of the orders Carcharhiniformes and Lamniformes, these species differ in preferred habitat, ecological role, and swimming style. We observed structural variations in mineral organization and collagen fiber arrangement using PLM and AFM. In both sharks, the highly calcified corpus calcarea shows a ridged morphology, while a chain-like network is present in the less mineralized intermedialia. Raman spectromicroscopy demonstrates a relative increase of glucosaminocycans (GAGs) with respect to collagen and a decrease in mineral-rich zones, underlining the role of GAGs in modulating bioapatite mineralization. Region-specific testing confirmed that intravertebral variations in mineral content and arrangement result in distinct nanomechanical properties. Local Young's moduli from mineralized regions exceeded bulk values by a factor of 10. Overall, this work provides profound insights into a flexible yet strong biocomposite, which is crucial for the extraordinary speed of cartilaginous fish in the worlds' oceans. STATEMENT OF SIGNIFICANCE: Shark cartilage is a morphologically complex material composed of collagen, sulfated proteoglycans, and calcium phosphate minerals. This study explores the link between microstructure, chemical composition, and biological mechanical function of shark vertebral cartilage at the micro- and nanometer scale in typical Carcharhiniform and Lamniform shark species, which represent different vertebral mineralization morphologies, swimming styles and speeds. By studying the intricacies of shark vertebrae, we hope to lay the foundation for biomimetic composite materials that harness lamellar reinforcement and tailored stiffness gradients, capable of dynamic and localized adjustments during movement.

Fundamentals and Applications of Raman-Based Techniques for the Design and Development of Active Biomedical Materials

Raman spectroscopy is an analytical method based on light-matter interactions that can interrogate the vibrational modes of matter and provide representative molecular fingerprints. Mediated by its label-free, non-invasive nature, and high molecular specificity, Raman-based techniques have become ubiquitous tools for in situ characterization of materials. This review comprehensively describes the theoretical and practical background of Raman spectroscopy and its advanced variants. The numerous facets of material characterization that Raman scattering can reveal, including biomolecular identification, solid-to-solid phase transitions, and spatial mapping of biomolecular species in bioactive materials, are highlighted. The review illustrates the potential of these techniques in the context of active biomedical material design and development by highlighting representative studies from the literature. These studies cover the use of Raman spectroscopy for the characterization of both natural and synthetic biomaterials, including engineered tissue constructs, biopolymer systems, ceramics, and nanoparticle formulations, among others. To increase the accessibility and adoption of these techniques, the present review also provides the reader with practical recommendations on the integration of Raman techniques into the experimental laboratory toolbox. Finally, perspectives on how recent developments in plasmon- and coherently-enhanced Raman spectroscopy can propel Raman from underutilized to critical for biomaterial development are provided.

Integrative cartilage repair using acellular allografts for engineered structure and surface lubrication in vivo

The repair of articular cartilage after damage is challenging, and decellularized tissue offers a possible treatment option to promote regeneration. Here, we show that acellular osteochondral allografts improve integrative cartilage repair compared to untreated defects after 6 months in an ovine model. Functional measures of intratissue strain/structure assessed by MRI demonstrate similar biomechanics of implants and native cartilage. Compared to native tissue and defects, the structure, composition, and tribology of acellular allografts preserve surface roughness and lubrication, material properties under compression and relaxation, compositional ratios of collagen:glycosaminoglycan and collagen:phosphate, and relative composition of types I/II collagen. While high cellularity was observed in bone regions and integration zones between cartilage-allografts, recellularization of chondral implants was inconsistent, with cell migration typically less than ~750 µm into the dense decellularized tissue, possibly limiting long-term cellular maintenance. Our results demonstrate the structural and biomechanical efficacy of acellular allografts for at least six months in vivo.

Shining Light on Osteoarthritis: Spatially Offset Raman Spectroscopy as a Window into Cartilage Health

Articular cartilage is a complex tissue, and early detection of osteoarthritis (OA) is crucial for effective treatment. However, current imaging modalities lack molecular specificity and primarily detect late-stage changes. In this study, we propose the use of spatially offset Raman spectroscopy (SORS) for noninvasive, depth-dependent, and molecular-specific diagnostics of articular cartilage. We demonstrate the potential of SORS to penetrate deep layers of cartilage, providing a comprehensive understanding of disease progression. Our SORS measurements were characterized and validated through mechanical and histological techniques, revealing strong correlations between spectroscopic measurements and both Young's modulus and depth of cartilage damage. By longitudinally monitoring enzymatically degraded condyles, we further developed a depth-dependent damage-tracking method. Our analysis revealed distinct components related to sample depth and glycosaminoglycan (GAG) changes, offering a comprehensive picture of cartilage health. Collectively, these findings highlight the potential of SORS as a valuable tool for enhancing OA management and improving patient outcomes.

Holistic vibrational spectromics assessment of human cartilage for osteoarthritis diagnosis

Osteoarthritis (OA) is the most common degenerative joint disease, presented as wearing down of articular cartilage and resulting in pain and limited mobility for 1 in 10 adults in the UK [Osteoarthr. Cartil.28(6), 792 (2020)10.1016/j.joca.2020.03.004]. There is an unmet need for patient friendly paradigms for clinical assessment that do not use ionizing radiation (CT), exogenous contrast enhancing dyes (MRI), and biopsy. Hence, techniques that use non-destructive, near- and shortwave infrared light (NIR, SWIR) may be ideal for providing label-free, deep tissue interrogation. This study demonstrates multimodal "spectromics", low-level abstraction data fusion of non-destructive NIR Raman scattering spectroscopy and NIR-SWIR absorption spectroscopy, providing an enhanced, interpretable "fingerprint" for diagnosis of OA in human cartilage. This is proposed as method level innovation applicable to both arthro- or endoscopic (minimally invasive) or potential exoscopic (non-invasive) optical approaches. Samples were excised from femoral heads post hip arthroplasty from OA patients (n = 13) and age-matched control (osteoporosis) patients (n = 14). Under multivariate statistical analysis and supervised machine learning, tissue was classified to high precision: 100% segregation of tissue classes (using 10 principal components), and a classification accuracy of 95% (control) and 80% (OA), using the combined vibrational data. There was a marked performance improvement (5 to 6-fold for multivariate analysis) using the spectromics fingerprint compared to results obtained from solely Raman or NIR-SWIR data. Furthermore, clinically relevant tissue components were identified through discriminatory spectral features - spectromics biomarkers - allowing interpretable feedback from the enhanced fingerprint. In summary, spectromics provides comprehensive information for early OA detection and disease stratification, imperative for effective intervention in treating the degenerative onset disease for an aging demographic. This novel and elegant approach for data fusion is compatible with various NIR-SWIR optical devices that will allow deep non-destructive penetration.

RamanSPy: An Open-Source Python Package for Integrative Raman Spectroscopy Data Analysis

Raman spectroscopy is a nondestructive and label-free chemical analysis technique, which plays a key role in the analysis and discovery cycle of various branches of science. Nonetheless, progress in Raman spectroscopic analysis is still impeded by the lack of software, methodological and data standardization, and the ensuing fragmentation and lack of reproducibility of analysis workflows thereof. To address these issues, we introduce RamanSPy, an open-source Python package for Raman spectroscopic research and analysis. RamanSPy provides a comprehensive library of tools for spectroscopic analysis that supports day-to-day tasks, integrative analyses, the development of methods and protocols, and the integration of advanced data analytics. RamanSPy is modular and open source, not tied to a particular technology or data format, and can be readily interfaced with the burgeoning ecosystem for data science, statistical analysis, and machine learning in Python. RamanSPy is hosted at https://github.com/barahona-research-group/RamanSPy, supplemented with extended online documentation, available at https://ramanspy.readthedocs.io, that includes tutorials, example applications, and details about the real-world research applications presented in this paper.

Analysis of the mechanism of curcumin against osteoarthritis using metabolomics and transcriptomics

Curcumin, a polyphenolic compound derived from the turmeric plant (Curcuma longa), has been extensively studied for its anti-inflammatory and anti-proliferative properties. The safety and efficacy of curcumin have been thoroughly validated. Nevertheless, the underlying mechanism for treating osteoarthritis remains ambiguous. This study aims to reveal the potential mechanism of curcumin in treating osteoarthritis by using metabolomics and transcriptomics. Firstly, we validated the effect of curcumin on inflammatory factors in human articular chondrocytes. Secondly, we explored the cellular metabolism mechanism of curcumin against osteoarthritis using cell metabolomics. Thirdly, we assessed the differences in gene expression of human articular chondrocytes through transcriptomics. Lastly, to evaluate the essential targets and elucidate the potential mechanism underlying the therapeutic effects of curcumin in osteoarthritis, we conducted a screening of the proteins within the shared pathway of metabolomics and transcriptomics. Our results demonstrated that curcumin significantly decreased the levels of inflammatory markers, such as IL-β, IL-6, and TNF-α, in human articular chondrocytes. Cell metabolomics identified 106 differential metabolites, including beta-aminopropionitrile, 3-amino-2-piperidone, pyrrole-2-carboxaldehyde, and various other components. The transcriptomic analysis yielded 1050 differential mRNAs. Enrichment analysis showed that the differential metabolites and mRNAs were significantly enriched in seven pathways, including glycine, serine, and threonine metabolism; pentose and glucuronate interconversions; glycerolipid metabolism; histidine metabolism; mucin-type o-glycan biosynthesis; inositol phosphate metabolism; and cysteine and methionine metabolism. A total of 23 key targets were identified to be involved in these pathways. We speculate that curcumin may alleviate osteoarthritis by targeting key proteins involved in glycine, serine, and threonine metabolism; inhibiting pyruvate production; and modulating glycolysis.

Extracellular matrix-derived materials for tissue engineering and regenerative medicine: A journey from isolation to characterization and application

Biomaterial choice is an essential step during the development tissue engineering and regenerative medicine (TERM) applications. The selected biomaterial must present properties allowing the physiological-like recapitulation of several processes that lead to the reestablishment of homeostatic tissue or organ function. Biomaterials derived from the extracellular matrix (ECM) present many such properties and their use in the field has been steadily increasing. Considering this growing importance, it becomes imperative to provide a comprehensive overview of ECM biomaterials, encompassing their sourcing, processing, and integration into TERM applications. This review compiles the main strategies used to isolate and process ECM-derived biomaterials as well as different techniques used for its characterization, namely biochemical and chemical, physical, morphological, and biological. Lastly, some of their applications in the TERM field are explored and discussed.

A Traumatic Impact Immediately Changes the Mechanical Properties of Articular Cartilage

OBJECTIVE

To investigate whether and how a single traumatic impact changes the mechanical properties of talar articular cartilage.

DESIGN

A marble was placed on the joint surface and a weight was dropped on both medial and lateral caprine talus to create a well-defined single focal impact. The mechanical properties of intact and impacted talar cartilage were measured with a micro-indenter. Elastic (storage) and viscous (loss) moduli were determined by oscillatory ramp and dynamic mechanical analysis protocols.

RESULTS

We found significant differences between ankles and within the same ankle joint, with the medial talus having significantly higher storage- and loss moduli than the lateral talus. The storage- and loss moduli of intact articular cartilage increased with greater indentation depths. However, postimpact the storage- and loss moduli were significantly and consistently lower in all specimens indicating immediate posttraumatic damage. The deeper regions of talar cartilage were less affected by the impact than the more superficial regions.

CONCLUSIONS

A single traumatic impact results in an immediate and significant decrease of storage- and loss moduli. Further research must focus on the development of non- or minimally invasive diagnostic tools to address the exact microdamage caused by the impact. We speculate that the traumatic impact damaged the collagen fibers that confine the water-binding proteoglycans and thereby decreasing the hydrostatic pressure of cartilage. As part of the treatment directly after a trauma, one could imagine a reduction or restriction of peak loads to prevent the progression of the cascade towards PTOA of the ankle joint.

Cholesterol-Bearing Polysaccharide-Based Nanogels for Development of Novel Immunotherapy and Regenerative Medicine

Novel functional biomaterials are expected to bring about breakthroughs in developing immunotherapy and regenerative medicine through their application as drug delivery systems and scaffolds. Nanogels are defined as nanoparticles with a particle size of 100 nm or less and as having a gel structure. Nanogels have a three-dimensional network structure of cross-linked polymer chains, which have a high water content, a volume phase transition much faster than that of a macrogel, and a quick response to external stimuli. As it is possible to transmit substances according to the three-dimensional mesh size of the gel, a major feature is that relatively large substances, such as proteins and nucleic acids, can be taken into the gel. Furthermore, by organizing nanogels as a building block, they can be applied as a scaffold material for tissue regeneration. This review provides a brief overview of the current developments in nanogels in general, especially drug delivery, therapeutic applications, and tissue engineering. In particular, polysaccharide-based nanogels are interesting because they have excellent complexation properties and are highly biocompatible.

Synthesis and characterization of a bovine collagen: GAG scaffold with Uruguayan raw material for tissue engineering

Tissue engineering (TE) and regenerative medicine offer strategies to improve damaged tissues by using scaffolds and cells. The use of collagen-based biomaterials in the field of TE has been intensively growing over the past decades. Mesenchymal stromal cells (MSCs) and dental pulp stem cells (DPSCs) are promising cell candidates for development of clinical composites. In this study, we proposed the development of a bovine collagen type I: chondroitin-6-sulphate (CG) scaffold, obtained from Uruguayan raw material (certified as free bovine spongiform encephalopathy), with CG crosslinking enhancement using different gamma radiation doses. Structural, biomechanical and chemical characteristics of the scaffolds were assessed by Scanning Electron Microscopy, axial tensile tests, FT-IR and Raman Spectroscopy, respectively. Once we selected the most appropriate scaffold for future use as a TE product, we studied the behavior of MSCs and DPSCs cultured on the scaffold by cytotoxicity, proliferation and differentiation assays. Among the diverse porous scaffolds obtained, the one with the most adequate properties was the one exposed to 15 kGy of gamma radiation. This radiation dose contributed to the crosslinking of molecules, to the formation of new bonds and/or to the reorganization of the collagen fibers. The selected scaffold was non-cytotoxic for the tested cells and a suitable substrate for cell proliferation. Furthermore, the scaffold allowed MSCs differentiation to osteogenic, chondrogenic, and adipogenic lineages. Thus, this work shows a promising approach to the synthesis of a collagen-scaffold suitable for TE.

Spatial analysis of the osteoarthritis microenvironment: techniques, insights, and applications

Osteoarthritis (OA) is a debilitating degenerative disease affecting multiple joint tissues, including cartilage, bone, synovium, and adipose tissues. OA presents diverse clinical phenotypes and distinct molecular endotypes, including inflammatory, metabolic, mechanical, genetic, and synovial variants. Consequently, innovative technologies are needed to support the development of effective diagnostic and precision therapeutic approaches. Traditional analysis of bulk OA tissue extracts has limitations due to technical constraints, causing challenges in the differentiation between various physiological and pathological phenotypes in joint tissues. This issue has led to standardization difficulties and hindered the success of clinical trials. Gaining insights into the spatial variations of the cellular and molecular structures in OA tissues, encompassing DNA, RNA, metabolites, and proteins, as well as their chemical properties, elemental composition, and mechanical attributes, can contribute to a more comprehensive understanding of the disease subtypes. Spatially resolved biology enables biologists to investigate cells within the context of their tissue microenvironment, providing a more holistic view of cellular function. Recent advances in innovative spatial biology techniques now allow intact tissue sections to be examined using various -omics lenses, such as genomics, transcriptomics, proteomics, and metabolomics, with spatial data. This fusion of approaches provides researchers with critical insights into the molecular composition and functions of the cells and tissues at precise spatial coordinates. Furthermore, advanced imaging techniques, including high-resolution microscopy, hyperspectral imaging, and mass spectrometry imaging, enable the visualization and analysis of the spatial distribution of biomolecules, cells, and tissues. Linking these molecular imaging outputs to conventional tissue histology can facilitate a more comprehensive characterization of disease phenotypes. This review summarizes the recent advancements in the molecular imaging modalities and methodologies for in-depth spatial analysis. It explores their applications, challenges, and potential opportunities in the field of OA. Additionally, this review provides a perspective on the potential research directions for these contemporary approaches that can meet the requirements of clinical diagnoses and the establishment of therapeutic targets for OA.

Depth-Dependent Strain Model (1D) for Anisotropic Fibrils in Articular Cartilage

The mechanical response of articular cartilage (AC) under compression is anisotropic and depth-dependent. AC is osmotically active, and its intrinsic osmotic swelling pressure is balanced by its collagen fibril network. This mechanism requires the collagen fibers to be under a state of tensile pre-strain. A simple mathematical model is used to explain the depth-dependent strain calculations observed in articular cartilage under 1D axial compression (perpendicular to the articular surface). The collagen fibers are under pre-strain, influenced by proteoglycan concentration (fixed charged density, FCD) and collagen stiffness against swelling stress. The stiffness is introduced in our model as an anisotropic modulus that varies with fibril orientation through tissue depth. The collagen fibers are stiffer to stretching parallel to their length than perpendicular to it; when combined with depth-varying FCD, the model successfully predicts how tissue strains decrease with depth during compression. In summary, this model highlights that the mechanical properties of cartilage depend not only on proteoglycan concentration but also on the intrinsic properties of the pre-strained collagen network. These properties are essential for the proper functioning of articular cartilage.

Unraveling Molecular Composition in Biological Samples-Systematic Evaluation of Statistical Methods for the Analysis of Hyperspectral Raman Data

Recently, confocal Raman microscopy has gained popularity in biomedical research for studying tissues in healthy and diseased state due to its ability to acquire chemically selective data in a noninvasive approach. However, biological samples, such as brain tissue, are inherently difficult to analyze due to the superposition of molecules in the Raman spectra and low variation of spectral features within the sample. The analysis is further impeded by pathological hallmarks, for example beta-amyloid (Aβ) plaques in Alzheimer's disease, which are often solely characterized by subtle shifts in the respective Raman peaks. To unravel the underlying molecular information, convoluted statistical procedures are inevitable. Unfortunately, such statistical methods are often inadequately described, and most natural scientists lack knowledge of their appropriate use, causing unreproducible results and stagnation in the application of hyperspectral Raman imaging. Therefore, we have set out to provide a comprehensive guide to address these challenges with the example of a complex hyperspectral data set of brain tissue samples with Aβ plaques. Our study encompasses established as well as novel statistical methods, including univariate analysis, principal component analysis, cluster analysis, spectral unmixing, and 2D correlation spectroscopy, and critically compares the outcomes of each analysis. Moreover, we transparently demonstrate the effect of preprocessing decisions like denoising and scaling techniques, providing valuable insights into implications of spectral quality for data evaluation. Thereby, this study provides a comprehensive evaluation of analysis approaches for complex hyperspectral Raman data, laying out a blueprint for elucidating meaningful information from biological samples in chemical imaging.

Quantitative Raman chemical imaging of intracellular drug-membrane aggregates and small molecule drug precipitates in cytoplasmic organelles

Raman confocal microscopes have been used to visualize the distribution of small molecule drugs within different subcellular compartments. This visualization allows the discovery, characterization, and detailed analysis of the molecular transport phenomena underpinning the Volume of Distribution - a key parameter governing the systemic pharmacokinetics of small molecule drugs. In the specific case of lipophilic small molecules with large Volumes of Distribution, chemical imaging studies using Raman confocal microscopes have revealed how weakly basic, poorly soluble drug molecules can accumulate inside cells by forming stable, supramolecular complexes in association with cytoplasmic membranes or by precipitating out within organelles. To study the self-assembly and function of the resulting intracellular drug inclusions, Raman chemical imaging methods have been developed to measure and map the mass, concentration, and ionization state of drug molecules at a microscopic, subcellular level. Beyond the field of drug delivery, Raman chemical imaging techniques relevant to the study of microscopic drug precipitates and drug-lipid complexes which form inside cells are also being developed by researchers with seemingly unrelated scientific interests. Highlighting advances in data acquisition, calibration methods, and computational data management and analysis tools, this review will cover a decade of technological developments that enable the conversion of spectral signals obtained from Raman confocal microscopes into new discoveries and information about previously unknown, concentrative drug transport pathways driven by soluble-to-insoluble phase transitions occurring within the cytoplasmic organelles of eukaryotic cells.

Raman Spectroscopy and Machine Learning Enables Estimation of Articular Cartilage Structural, Compositional, and Functional Properties

OBJECTIVE

To differentiate healthy from artificially degraded articular cartilage and estimate its structural, compositional, and functional properties using Raman spectroscopy (RS).

DESIGN

Visually normal bovine patellae (n = 12) were used in this study. Osteochondral plugs (n = 60) were prepared and artificially degraded either enzymatically (via Collagenase D or Trypsin) or mechanically (via impact loading or surface abrasion) to induce mild to severe cartilage damage; additionally, control plugs were prepared (n = 12). Raman spectra were acquired from the samples before and after artificial degradation. Afterwards, reference biomechanical properties, proteoglycan (PG) content, collagen orientation, and zonal (%) thickness of the samples were measured. Machine learning models (classifiers and regressors) were then developed to discriminate healthy from degraded cartilage based on their Raman spectra and to predict the aforementioned reference properties.

RESULTS

The classifiers accurately categorized healthy and degraded samples (accuracy = 86%), and successfully discerned moderate from severely degraded samples (accuracy = 90%). On the other hand, the regression models estimated cartilage biomechanical properties with reasonable error (≤ 24%), with the lowest error observed in the prediction of instantaneous modulus (12%). With zonal properties, the lowest prediction errors were observed in the deep zone, i.e., PG content (14%), collagen orientation (29%), and zonal thickness (9%).

CONCLUSION

RS is capable of discriminating between healthy and damaged cartilage, and can estimate tissue properties with reasonable errors. These findings demonstrate the clinical potential of RS.

Characterization of Distinct Chondrogenic Cell Populations of Patients Suffering from Microtia Using Single-Cell Micro-Raman Spectroscopy

Microtia is a congenital condition of abnormal development of the outer ear. Tissue engineering of the ear is an alternative treatment option for microtia patients. However, for this approach, the identification of high regenerative cartilage progenitor cells is of vital importance. Raman analysis provides a novel, non-invasive, label-free diagnostic tool to detect distinctive biochemical features of single cells or tissues. Using micro-Raman spectroscopy, we were able to distinguish and characterize the particular molecular fingerprints of differentiated chondrocytes and perichondrocytes and their respective progenitors isolated from healthy individuals and microtia patients. We found that microtia chondrocytes exhibited lower lipid concentrations in comparison to healthy cells, thus indicating the importance of fat storage. Moreover, we suggest that collagen is a useful biomarker for distinguishing between populations obtained from the cartilage and perichondrium because of the higher spectral contributions of collagen in the chondrocytes compared to perichondrocytes from healthy individuals and microtia patients. Our results represent a contribution to the identification of cell markers that may allow the selection of specific cell populations for cartilage tissue engineering. Moreover, the observed differences between microtia and healthy cells are essential for gaining better knowledge of the cause of microtia. It can be useful for designing novel treatment options based on further investigations of the discovered biochemical substrate alterations.

Shining Light on Osteoarthritis: Spatially Offset Raman Spectroscopy as a Window into Cartilage Health

Articular cartilage is a complex tissue, and early detection of osteoarthritis (OA) is crucial for effective treatment. However, current imaging modalities lack molecular specificity and primarily detect late-stage changes. In this study, we propose the use of Spatially Offset Raman Spectroscopy (SORS) for non-invasive, depth-dependent, and molecular-specific diagnostics of articular cartilage. We demonstrate the potential of SORS to penetrate deep layers of cartilage, providing a comprehensive understanding of disease progression. Our SORS measurements were characterized and validated through mechanical and histological techniques, revealing strong correlations between spectroscopic measurements and both Young's modulus and depth of cartilage damage. By longitudinally monitoring enzymatically degraded condyles, we further developed a depth-dependent damage-tracking method. Our analysis revealed distinct components related to sample depth and glycosaminoglycan (GAG) changes, offering a comprehensive picture of cartilage health. Collectively, these findings highlight the potential of SORS as a valuable tool for enhancing OA management and improving patient outcomes.

Label-Free Quantification of Microscopic Alignment in Engineered Tissue Scaffolds by Polarized Raman Spectroscopy

Monitoring of extracellular matrix (ECM) microstructure is essential in studying structure-associated cellular processes, improving cellular function, and for ensuring sufficient mechanical integrity in engineered tissues. This paper describes a novel method to study the microscale alignment of the matrix in engineered tissue scaffolds (ETS) that are usually composed of a variety of biomacromolecules derived by cells. First, a trained loading function was derived from Raman spectra of highly aligned native tissue via principal component analysis (PCA), where prominent changes associated with specific Raman bands (e.g., 1444, 1465, 1605, 1627-1660, and 1665-1689 cm-1) were detected with respect to the polarization angle. These changes were mainly caused by the aligned matrix of many compounds within the tissue relative to the laser polarization, including proteins, lipids, and carbohydrates. Hence this trained function was applied to quantify the alignment within ETS of various matrix components derived by cells. Furthermore, a simple metric called Amplitude Alignment Metric (AAM) was derived to correlate the orientation dependence of polarized Raman spectra of ETS to the degree of matrix alignment. It was found that the AAM was significantly higher in anisotropic ETS than isotropic ones. The PRS method revealed a lower p-value for distinguishing the alignment between these two types of ETS as compared to the microscopic method for detecting fluorescent-labeled protein matrices at a similar microscopic scale. These results indicate that the anisotropy of a complex matrix in engineered tissue can be assessed at the microscopic scale using a PRS-based simple metric, which is superior to the traditional microscopic method. This PRS-based method can serve as a complementary tool for the design and assessment of engineered tissues that mimic the native matrix organizational microstructures.

Full Regional Creep Displacement Map of Articular Cartilage Based on Nanoindentation Array

The elucidation of the mechanisms underlying articular cartilage lesions poses a formidable challenge in the field of cartilage repair. Despite significant strides in cartilage mechanics research, the region-dependent creep properties of articular cartilage remain elusive. In this study, we employ depth-sensing indentation tests to experimentally determine the creep properties of four distinct regions of articular cartilage, thereby unveiling a region-dependent full map of creep parameters. The measured creep displacement-time response curves indicate that the creep properties of the articular cartilage exhibit a clear regional correlation. Accordingly, the full regional creep map of articular cartilage is experimentally constructed for the first time. The correlation between the microstructures and the creep properties of cartilage in different regions is revealed. A three-parameter model is established to describe the creep velocity-displacement response of cartilage. Raman spectra reveal that the proteoglycan content is positively correlated with creep properties. The Raman shift directly indicates diverse residual stresses in different microregions. The obtained data facilitate a deep understanding of the potential creep dependent damage mechanism of cartilage and the further development of artificial cartilage materials.

Quantitative chemometric phenotyping of three-dimensional liver organoids by Raman spectral imaging

Confocal Raman spectral imaging (RSI) enables high-content, label-free visualization of a wide range of molecules in biological specimens without sample preparation. However, reliable quantification of the deconvoluted spectra is needed. Here we develop an integrated bioanalytical methodology, qRamanomics, to qualify RSI as a tissue phantom calibrated tool for quantitative spatial chemotyping of major classes of biomolecules. Next, we apply qRamanomics to fixed 3D liver organoids generated from stem-cell-derived or primary hepatocytes to assess specimen variation and maturity. We then demonstrate the utility of qRamanomics for identifying biomolecular response signatures from a panel of liver-altering drugs, probing drug-induced compositional changes in 3D organoids followed by in situ monitoring of drug metabolism and accumulation. Quantitative chemometric phenotyping constitutes an important step in developing quantitative label-free interrogation of 3D biological specimens.

Electroporation-Assisted Surface-Enhanced Raman Detection for Long-Term, Label-Free, and Noninvasive Molecular Profiling of Live Single Cells

Molecule characterization of live single cells is greatly important in disease diagnoses and personalized treatments. Conventional molecule detection methods, such as mass spectrography, gene sequencing, or immunofluorescence, are usually destructive or labeled and unable to monitor the dynamic change of live cellular molecules. Herein, we propose an electroporation-assisted surface-enhanced Raman scattering (EP-SERS) method using a microchip to implement label-free, noninvasive, and continuous detections of the molecules of live single cells. The microchip containing microelectrodes with nanostructured EP-SERS probes has a multifunction of cell positioning, electroporation, and SERS detection. The EP-SERS method capably detects both the intracellular and extracellular molecules of live single cells without losing cell viability so as to enable long-term monitoring of the molecular pathological process in situ. We detect the molecules of single cells for two breast cancer cell lines with different malignancies (MCF-7 and MDA-MB-231), one liver cancer cell line (Huh-7), and one normal cell line (293T) using the EP-SERS method and classify these cell types to achieve high accuracies of 91.4-98.3% using their SERS spectra. Furthermore, 24 h continuous monitoring of the heterogeneous molecular responses of different cancer cell lines under doxorubicin treatment is successfully implemented using the EP-SERS method. This work provides a long-term, label-free, and biocompatible approach to simultaneously detect intracellular and extracellular molecules of live single cells on a chip, which would facilitate research and applications of cancer diagnoses and personalized treatments.

Modular stimuli-responsive hydrogel sealants for early gastrointestinal leak detection and containment

Millions of patients every year undergo gastrointestinal surgery. While often lifesaving, sutured and stapled reconnections leak in around 10% of cases. Currently, surgeons rely on the monitoring of surrogate markers and clinical symptoms, which often lack sensitivity and specificity, hence only offering late-stage detection of fully developed leaks. Here, we present a holistic solution in the form of a modular, intelligent suture support sealant patch capable of containing and detecting leaks early. The pH and/or enzyme-responsive triggerable sensing elements can be read out by point-of-need ultrasound imaging. We demonstrate reliable detection of the breaching of sutures, in as little as 3 hours in intestinal leak scenarios and 15 minutes in gastric leak conditions. This technology paves the way for next-generation suture support materials that seal and offer disambiguation in cases of anastomotic leaks based on point-of-need monitoring, without reliance on complex electronics or bulky (bio)electronic implantables.

Growing Pains: The Need for Engineered Platforms to Study Growth Plate Biology

Growth plates, or physis, are highly specialized cartilage tissues responsible for longitudinal bone growth in children and adolescents. Chondrocytes that reside in growth plates are organized into three distinct zones essential for proper function. Modeling key features of growth plates may provide an avenue to develop advanced tissue engineering strategies and perspectives for cartilage and bone regenerative medicine applications and a platform to study processes linked to disease progression. In this review, a brief introduction of the growth plates and their role in skeletal development is first provided. Injuries and diseases of the growth plates as well as physiological and pathological mechanisms associated with remodeling and disease progression are discussed. Growth plate biology, namely, its architecture and extracellular matrix organization, resident cell types, and growth factor signaling are then focused. Next, opportunities and challenges for developing 3D biomaterial models to study aspects of growth plate biology and disease in vitro are discussed. Finally, opportunities for increasingly sophisticated in vitro biomaterial models of the growth plate to study spatiotemporal aspects of growth plate remodeling, to investigate multicellular signaling underlying growth plate biology, and to develop platforms that address key roadblocks to in vivo musculoskeletal tissue engineering applications are described.

In vivo non-invasive monitoring of tissue development in 3D printed subcutaneous bone scaffolds using fibre-optic Raman spectroscopy

The development of novel biomaterials for regenerative therapy relies on the ability to assess tissue development, quality, and similarity with native tissue types in in vivo experiments. Non-invasive imaging modalities such as X-ray computed tomography offer high spatial resolution but limited biochemical information while histology and biochemical assays are destructive. Raman spectroscopy is a non-invasive, label-free and non-destructive technique widely applied for biochemical characterization. Here we demonstrate the use of fibre-optic Raman spectroscopy for in vivo quantitative monitoring of tissue development in subcutaneous calcium phosphate scaffolds in mice over 16 weeks. Raman spectroscopy was able to quantify the time dependency of different tissue components related to the presence, absence, and quantity of mesenchymal stem cells. Scaffolds seeded with stem cells produced 3-5 times higher amount of collagen-rich extracellular matrix after 16 weeks implantation compared to scaffolds without. These however, showed a 2.5 times higher amount of lipid-rich tissue compared to implants with stem cells. Ex vivo micro-computed tomography and histology showed stem cell mediated collagen and bone development. Histological measures of collagen correlated well with Raman derived quantifications (correlation coefficient in vivo 0.74, ex vivo 0.93). In the absence of stem cells, the scaffolds were largely occupied by adipocytes. The technique developed here could potentially be adapted for a range of small animal experiments for assessing tissue engineering strategies at the biochemical level.

Three-Dimensional Culture of Cartilage Tissue on Nanogel-Cross-Linked Porous Freeze-Dried Gel Scaffold for Regenerative Cartilage Therapy: A Vibrational Spectroscopy Evaluation

This study presents a set of vibrational characterizations on a nanogel-cross-linked porous freeze-dried gel (NanoCliP-FD gel) scaffold for tissue engineering and regenerative therapy. This scaffold is designed for the in vitro culture of high-quality cartilage tissue to be then transplanted in vivo to enable recovery from congenital malformations in the maxillofacial area or crippling jaw disease. The three-dimensional scaffold for in-plate culture is designed with interface chemistry capable of stimulating cartilage formation and maintaining its structure through counteracting the dedifferentiation of mesenchymal stem cells (MSCs) during the formation of cartilage tissue. The developed interface chemistry enabled high efficiency in both growth rate and tissue quality, thus satisfying the requirements of large volumes, high matrix quality, and superior mechanical properties needed in cartilage transplants. We characterized the cartilage tissue in vitro grown on a NanoCliP-FD gel scaffold by human periodontal ligament-derived stem cells (a type of MSC) with cartilage grown by the same cells and under the same conditions on a conventional (porous) atelocollagen scaffold. The cartilage tissues produced by the MSCs on different scaffolds were comparatively evaluated by immunohistochemical and spectroscopic analyses. Cartilage differentiation occurred at a higher rate when MSCs were cultured on the NanoCliP-FD gel scaffold compared to the atelocollagen scaffold, and produced a tissue richer in cartilage matrix. In situ spectroscopic analyses revealed the cell/scaffold interactive mechanisms by which the NanoCliP-FD gel scaffold stimulated such increased efficiency in cartilage matrix formation. In addition to demonstrating the high potential of human periodontal ligament-derived stem cell cultures on NanoCliP-FD gel scaffolds in regenerative cartilage therapy, the present study also highlights the novelty of Raman spectroscopy as a non-destructive method for the concurrent evaluation of matrix quality and cell metabolic response. In situ Raman analyses on living cells unveiled for the first time the underlying physiological mechanisms behind such improved chondrocyte performance.

Assessment of Ligament Viscoelastic Properties Using Raman Spectroscopy

Injuries to the ligaments of the knee commonly impact vulnerable and physically active individuals. These injuries can lead to the development of degenerative diseases such as post-traumatic osteoarthritis (PTOA). Non-invasive optical modalities, such as infrared and Raman spectroscopy, provide means for quantitative evaluation of knee joint tissues and have been proposed as potential quantitative diagnostic tools for arthroscopy. In this study, we evaluate Raman spectroscopy as a viable tool for estimating functional properties of collateral ligaments. Artificial trauma was induced by anterior cruciate ligament transection (ACLT) in the left or right knee joint of skeletally mature New Zealand rabbits. The corresponding contralateral (CL) samples were extracted from healthy unoperated joints along with a separate group of control (CNTRL) animals. The rabbits were sacrificed at 8 weeks after ACLT. The ligaments were then harvested and measured using Raman spectroscopy. A uniaxial tensile stress-relaxation testing protocol was adopted for determining several biomechanical properties of the samples. Partial least squares (PLS) regression models were then employed to correlate the spectral data with the biomechanical properties. Results show that the capacity of Raman spectroscopy for estimating the biomechanical properties of the ligament samples varies depending on the target property, with prediction error ranging from 15.78% for tissue cross-sectional area to 30.39% for stiffness. The hysteresis under cyclic loading at 2 Hz (RMSE = 6.22%, Normalized RMSE = 22.24%) can be accurately estimated from the Raman data which describes the viscous damping properties of the tissue. We conclude that Raman spectroscopy has the potential for non-destructively estimating ligament biomechanical properties in health and disease, thus enhancing the diagnostic value of optical arthroscopic evaluations of ligament integrity.

Deciphering pathological remodelling of the human cartilage extracellular matrix in osteoarthritis at the supramolecular level

The extracellular matrix (ECM) of articular cartilage is a three-dimensional network mainly constituted of entangled collagen fibrils and interfibrillar aggrecan aggregates. During the development of osteoarthritis (OA), the most common musculoskeletal disorder, the ECM is subjected to a combination of chemical and structural changes that play a pivotal role in the initiation and the progress of the disease. While the molecular mechanisms involved in the pathological remodelling of the ECM are considered as decisive, they remain, however, not completely elucidated. Herein, we report a relevant way for unravelling the role and nature of OA progress on human cartilage tissues, in terms of chemical composition and morphological and mechanical properties at the level of supramolecular assemblies constituting the cartilage ECM. For this purpose, we used X-ray photoelectron spectroscopy (XPS), and developed an innovative methodological approach that provides the molecular composition of the ECM. Moreover, we used atomic force microscopy (AFM) to probe the tissues at the level of individual collagen fibrils, both imaging and force spectroscopy modes being explored to this end. Taken together, these nanoscale characterization studies reveal the existence of two stages in the OA progress. At the early stage, a marked increase in the aggrecan and collagen content is observed, reflecting the homeostatic chondrocyte activity that tends to repair the cartilage ECM. At the late stage, we observe a failed attempt to stabilize and/or restore the tissue, yielding significant degradation of the supramolecular assemblies. This suggests an imbalance in the chondrocyte activity that turns in favor of catabolic events. Chemical changes are also accompanied by ECM structural changes and stiffening. Interestingly, we showed the possibility to mimic the imbalanced activities of chondrocytes by applying enzymatic digestions of healthy cartilage, through the combined action of hyaluronidase and collagenase. This yields damage strictly analogous to that observed at high OA severity. These findings bring mechanistic insights leading to a better understanding of the mechanism by which OA is initiated and progresses in the cartilage ECM. They offer guidelines for the development of curative treatments, such as targeting the homeostatic balance of chondrocyte metabolism through the control of enzymatic reactions involved in catabolic processes.

Fabrication of Biomaterials and Biostructures Based On Microfluidic Manipulation

Biofabrication technologies are of importance for the construction of organ models and functional tissue replacements. Microfluidic manipulation, a promising biofabrication technique with micro-scale resolution, can not only help to realize the fabrication of specific microsized structures but also build biomimetic microenvironments for biofabricated tissues. Therefore, microfluidic manipulation has attracted attention from researchers in the manipulation of particles and cells, biochemical analysis, tissue engineering, disease diagnostics, and drug discovery. Herein, biofabrication based on microfluidic manipulation technology is reviewed. The application of microfluidic manipulation technology in the manufacturing of biomaterials and biostructures with different dimensions and the control of the microenvironment is summarized. Finally, current challenges are discussed and a prospect of microfluidic manipulation technology is given. The authors hope this review can provide an overview of microfluidic manipulation technologies used in biofabrication and thus steer the current efforts in this field.

Bioink with cartilage-derived extracellular matrix microfibers enables spatial control of vascular capillary formation in bioprinted constructs

Microvasculature is essential for the exchange of gas and nutrient for most tissues in our body. Some tissue structures such as the meniscus presents spatially confined blood vessels adjacent to non-vascularized regions. In biofabrication, mimicking the spatial distribution of such vascular components is paramount, as capillary ingrowth into non-vascularized tissues can lead to tissue matrix alterations and subsequent pathology. Multi-material 3D bioprinting can potentially resolve anisotropic tissue features, although building complex constructs comprising stable vascularized and non-vascularized regions remains a major challenge. Here, we developed endothelial cell(EC)-laden pro- and anti-angiogenic bioinks, supplemented with bioactive matrix-derived microfibers (MFs) that were created from type I collagen sponges (col-1) and cartilage decellularized extracellular matrix (CdECM). EC-driven capillary network formation started two days after bioprinting. Supplementing cartilage-derived MFs to endothelial-cell laden bioinks reduced the total length of neo-microvessels by 29% after 14 days, compared to col-1 MFs-laden bioinks. As a proof of concept, the bioinks were bioprinted into an anatomical meniscus shape with a biomimetic vascularized outer and non-vascularized inner region, using a microgel suspension bath. The constructs were cultured up to 14 days, with in the outer zone the HUVEC-, mural cell-, and col-1 MF-laden pro-angiogenic bioink, and in the inner zone a meniscus progenitor cell (MPC)- and CdECM MF-laden anti-angiogenic bioink, revealing successful spatial confinement of the nascent vascular network only in the outer zone. Further, to co-facilitate both microvessel formation and MPC-derived matrix formation, we formulated cell culture medium conditions with a temporal switch. Overall, this study provides a new strategy that could be applied to develop zonal biomimetic meniscal constructs. Moreover, the use of ECM-derived MFs to promote or inhibit capillary networks opens new possibilities for the biofabrication of tissues with anisotropic microvascular distribution. These have potential for many applications including in vitro models, cancer progression, and testing anti-angiogenic therapies.

Biomimetic approach to articular cartilage tissue engineering using carbon nanotube-coated and textured polydimethylsiloxane scaffolds

There is a significant need to understand the complexity and heterogeneity of articular cartilage to develop more effective therapeutic strategies for diseases such as osteoarthritis. Here, we show that carbon nanotubes (CNTs) are excellent candidates as a material for synthetic scaffolds to support the growth of chondrocytes—the cells that produce and maintain cartilage. Chondrocyte morphology, proliferation, and alignment were investigated as nanoscale CNT networks were applied to macroscopically textured polydimethylsiloxane (PDMS) scaffolds. The application of CNTs to the surface of PDMS‐based scaffolds resulted in an up to 10‐fold increase in cell adherence and 240% increase in proliferation, which is attributable to increased nanoscale roughness and hydrophilicity. The introduction of macroscale features to PDMS induced alignment of chondrocytes, successfully mimicking the cell behavior observed in the superficial layer of cartilage. Raman spectroscopy was used as a noninvasive, label‐free method to monitor extracellular matrix production and chondrocyte phenotype. Chondrocytes on these scaffolds successfully produced collagen, glycosaminoglycan, and aggrecan. This study demonstrates that introducing physical features at different length scales allows for a high level of control over tissue scaffold design and, thus, cell behavior. Ultimately, these textured scaffolds can serve as platforms to improve the understanding of osteoarthritis and for early‐stage therapeutic testing.

Nondestructive testing of native and tissue-engineered medical products: adding numbers to pictures

Traditional destructive tests are used for quality assurance and control within manufacturing workflows. Their applicability to biomanufacturing is limited due to inherent constraints of the biomanufacturing process. To address this, photo- and acoustic-based nondestructive testing has risen in prominence to interrogate not only structure and function, but also to integrate quantitative measurements of biochemical composition to cross-correlate structural, compositional, and functional variances. We survey relevant literature related to single-mode and multimodal nondestructive testing of soft tissues, which adds numbers (quantitative measurements) to pictures (qualitative data). Native and tissue-engineered articular cartilage is highlighted because active biomanufacturing processes are being developed. Included are recent efforts and prominent trends focused on technologies for clinical and in-process biomanufacturing applications.

Design and clinical application of injectable hydrogels for musculoskeletal therapy

Musculoskeletal defects are an enormous healthcare burden and source of pain and disability for individuals. With an aging population, the proportion of individuals living with these medical indications will increase. Simultaneously, there is pressure on healthcare providers to source efficient solutions, which are cheaper and less invasive than conventional technology. This has led to an increased research focus on hydrogels as highly biocompatible biomaterials that can be delivered through minimally invasive procedures. This review will discuss how hydrogels can be designed for clinical translation, particularly in the context of the new European Medical Device Regulation (MDR). We will then do a deep dive into the clinically used hydrogel solutions that have been commercially approved or have undergone clinical trials in Europe or the United States. We will discuss the therapeutic mechanism and limitations of these products. Due to the vast application areas of hydrogels, this work focuses only on treatments of cartilage, bone, and the nucleus pulposus. Lastly, the main steps toward clinical translation of hydrogels as medical devices are outlined. We suggest a framework for how academics can assist small and medium MedTech enterprises conducting the initial clinical investigation and post‐market clinical follow‐up required in the MDR. It is evident that the successful translation of hydrogels is governed by acquiring high‐quality pre‐clinical and clinical data confirming the device mechanism of action and safety.

Raman spectroscopic insight into osteoarthritic cartilage regeneration by mRNA therapeutics encoding cartilage-anabolic transcription factor Runx1

While joint arthroplasty remains nowadays the most popular option available to repair chronically degenerated osteoarthritic joints, possibilities are recently emerging for regeneration of damaged cartilage rather than its replacement with artificial biomaterials. This latter strategy could allow avoiding the quite intrusive surgical procedures associated with total joint replacement. Building upon this notion, we first apply Raman spectroscopy to characterize diseased cartilage in a mice model of instability-induced knee osteoarthritis (OA) upon medial collateral ligament (MCL) and medial meniscus (MM) transections. Then, we examine the same OA model after cartilage regeneration by means of messenger RNA (mRNA) delivery of a cartilage-anabolic runt-related transcription factor 1 (RUNX1). Raman spectroscopy is shown to substantiate at the molecular scale the therapeutic effect of the Runx1 mRNA cartilage regeneration approach. This study demonstrates how the Raman spectroscopic method could support and accelerate the development of new therapies for cartilage diseases.

The ultrastructure of cartilage tissue and its swelling response in relation to matrix health

This multi-length scale anatomical study explores the influence of mild cartilage structural degeneration on the tissue swelling response. While the swelling response of cartilage has been studied extensively, this is the first study to reveal and correlate tissue microstructure and ultrastructure, with the swelling induced cartilage tissue strains. Cartilage sample strips (n = 30) were obtained from the distal-lateral quadrant of thirty mildly degenerate bovine patellae and, following excision from the bone, the cartilage strips were allowed to swell freely for 2 h in solutions of physiological saline and distilled water successively. The swelling response of this group of samples were compared with that of healthy cartilage, with (n = 20) and without the surface layer (n = 20). The subsequent curling response of cartilage showed that in healthy tissue it was highly variable, and with the surface removed some samples curved in the opposite direction, while in the mildly degenerate tissue group, virtually all tissue strips curved in a consistent upward manner. A significant difference in strain was observed between healthy samples with surface layer removed and mildly degenerate samples, illustrating how excision of the surface zone from pristine cartilage is insufficient to model the swelling response of tissue which has undergone natural degenerative changes. On average, total tissue thickness increased from 940 µm (healthy) to 1079 µm (mildly degenerate), however, looking at the zonal strata, surface and transition zone thicknesses both decreased while deep zone thickness increased from healthy to mildly degenerate tissue. Morphologically, changes to the surface zone integrity were correlated with a diminished surface layer which, at the ultrastructural scale, correlated with a decreased fibrillar density. Similarly, fibrosity of the general matrix visible at the microscale was associated with a loss of later interconnectivity resulting in large, aggregated fibril bundles. The microstructural and ultrastructural investigation revealed that the key differences influencing the tissue swelling strain response was (1) the thickness and extent of disruption to the surface layer and (2) the amount of fibrillar network destructuring, highlighting the importance of the collagen and tissue matrix structure in restraining cartilage swelling.

Nondestructive assessment of tissue engineered cartilage based on biochemical markers in cell culture media: application of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy

ATR spectral data obtained from cell culture medium discards can be used to assess glucose and lactate content, which are shown here to be a surrogate for matrix development in tissue engineered cartilage.

Label-free quantification of soft tissue alignment by polarized Raman spectroscopy

The organization of proteins is an important determinant of functionality in soft tissues. However, such organization is difficult to monitor over time in soft tissue with complex compositions. Here, we establish a method to determine the alignment of proteins in soft tissues of varying composition by polarized Raman spectroscopy (PRS). Unlike most conventional microscopy methods, PRS leverages non-destructive, label-free sample preparation. PRS data from highly aligned muscle layers were utilized to derive a weighting function for aligned proteins via principal component analysis (PCA). This trained weighting function was used as a master loading function to calculate a principal component score (PC1 Score) as a function of polarized angle for tendon, dermis, hypodermis, and fabricated collagen gels. Since the PC1 Score calculated at arbitrary angles was insufficient to determine level of alignment, we developed an Amplitude Alignment Metric by fitting a sine function to PC1 Score with respect to polarized angle. We found that our PRS-based Amplitude Alignment Metric can be used as an indicator of level of protein alignment in soft tissues in a non-destructive manner with label-free preparation and has similar discriminatory capacity among isotropic and anisotropic samples compared to microscopy-based image processing method. This PRS method does not require a priori knowledge of sample orientation nor composition and appears insensitive to changes in protein composition among different tissues. The Amplitude Alignment Metric introduced here could enable convenient and adaptable evaluation of protein alignment in soft tissues of varying protein and cell composition. STATEMENT OF SIGNIFICANCE: Polarized Raman spectroscopy (PRS) has been used to characterize the of organization of soft tissues. However, most of the reported applications of PRS have been on collagen-rich tissues and reliant on intensities of collagen-related vibrations. This work describes a PRS method via a multivariate analysis to characterize alignment in soft tissues composed of varying proteins. Of note, the highly aligned muscle layer of mouse skin was used to train a master function then applied to other soft tissue samples, and the degree of anisotropy in the PRS response was evaluated to obtain the level of alignment in tissues. We have demonstrated that this method supports convenient and adaptable evaluation of protein alignment in soft tissues of varying protein and cell composition.

Biophotonic tools for probing extracellular matrix mechanics

The complex, hierarchical and heterogeneous biomechanics of the extracellular matrix (ECM) are central to the health of multicellular organisms. Characterising the distribution, dynamics and above all else origins of ECM biomechanics are challenges that have captivated researchers for decades. Recently, a suite of biophotonics techniques have emerged as powerful new tools to investigate ECM biomechanics. In this mini-review, we discuss how the non-destructive, sub-micron resolution imaging capabilities of Raman spectroscopy and nonlinear microscopy are being used to interrogate the biomechanics of thick, living tissues. These high speed, label-free techniques are implemented during mechanical testing, providing unprecedented insight into the compositional and structural response of the ECM to changes in the mechanical environment.

Non-Destructive Spatial Mapping of Glycosaminoglycan Loss in Native and Degraded Articular Cartilage Using Confocal Raman Microspectroscopy

Articular cartilage is a collagen-rich tissue that provides a smooth, lubricated surface for joints and is also responsible for load bearing during movements. The major components of cartilage are water, collagen, and proteoglycans. Osteoarthritis is a degenerative disease of articular cartilage, in which an early-stage indicator is the loss of proteoglycans from the collagen matrix. In this study, confocal Raman microspectroscopy was applied to study the degradation of articular cartilage, specifically focused on spatially mapping the loss of glycosaminoglycans (GAGs). Trypsin digestion was used as a model for cartilage degradation. Two different scanning geometries for confocal Raman mapping, cross-sectional and depth scans, were applied. The chondroitin sulfate coefficient maps derived from Raman spectra provide spatial distributions similar to histological staining for glycosaminoglycans. The depth scans, during which subsurface data were collected without sectioning the samples, can also generate spectra and GAG distributions consistent with Raman scans of the surface-to-bone cross sections. In native tissue, both scanning geometries demonstrated higher GAG content at the deeper zone beneath the articular surface and negligible GAG content after trypsin degradation. On partially digested samples, both scanning geometries detected an ∼100 μm layer of GAG depletion. Overall, this research provides a technique with high spatial resolution (25 μm pixel size) to measure cartilage degradation without tissue sections using confocal Raman microspectroscopy, laying a foundation for potential in vivo measurements and osteoarthritis diagnosis.

Collagen orientation probed by polarized Raman spectra can serve as differential diagnosis indicator between different grades of meniscus degeneration

The purpose of the present study was to analyze normal and degenerated menisci with Raman methodology on thin sections of formalin fixed paraffin embedding tissues and to correlate the Raman findings with the grade of meniscus degeneration. Menisci (n = 27) were removed from human knee joints after total knee replacement or meniscectomy. Following routine histopathological analysis to determine the grade of meniscal lesions obtained from healthy and degenerated formaline fixed paraffin embedded (FFPE) meniscal sections, Raman polarization approach was applied to evaluate the orientation of collagen fibrils in different levels of the same 5 μm thick FFPE meniscal tissue sections, used for histopathological assessment. We collected Raman spectra in two different polarization geometries, v-HH and v-VV, and calculated the mean value of the v-HH/v-VV intensity ratio of two Raman bands, sensitive and non-sensitive to the molecular orientation. The collagen specific amide I band at 1665 cm^-1, has the higher sensitivity dependence on the Raman polarization. The mean values of ratio v-HH/v-VV of the 1665 cm^-1 peak intensity was significantly higher in healthy, mean ± SD: 2.56 ± 0.46, compared to degenerated menisci, mean ± SD: 1.85 ± 0.42 (p = 0.0014). The mean values of v-HH/v-VV intensity ratio were 2.18 and 1.50 for low and high degenerated menisci, respectively (p < 0.0001). The difference of peak intensities in the two laser polarizations is decreased in the degenerated meniscus; this difference is diminishing as the degeneration increases. The v-HH/v-VV ratio was also of significant difference in low as compared to control and high grade meniscus lesions (p = 0.036 and p < 0.0001, respectively) offering valuable information for the approach of its biology and function. In the present study we showed that the 5 μm thick sections can be used for Raman analysis of meniscal tissue with great reliability, in terms of sensitivity, specificity, false-negative and false-positive results. Our data introduce the interesting hypothesis that compact portable Raman microscopy on tissue sections can be used intra-operatively for fast diagnosis and hence, accurate procedure design in the operating room.

Fabrication of porous chitosan particles using a novel two-step porogen leaching and lyophilization method with the label-free multivariate spectral assessment of live adhered cells

Porous chitosan (CS) particles were fabricated using a novel two-step technique that employed a porogen leaching phase followed by lyophilization or freeze-drying. Poly(ethylene glycol) (PEG) was mixed as a porogen in two different quantities with the CS solution before particle synthesis via coacervation. After the PEG leached out into deionized (DI) water at an elevated constant temperature, the final freeze-dried CS particles revealed surface features that resembled pore pockets. A three-dimensional (3D) culture of murine osteoblast cell line (OB-6) was seeded on these particles to analyze the effect of the porous structure on the cell activity, as compared to a control group with no added porogen. The results highlighted an enhancement in cell adhesion and proliferation on the two porous sample groups. A Raman spectroscopy-based label-free technique for live cell biomarker analysis was applied using multivariate spectral analysis. Results of the spectral analysis in the molecular fingerprint region corresponding to the Raman shift between 900 cm^-1 and 1700 cm^-1inferred inter-group variations. The bands at 1005 cm^-1 and 1375 cm^-1 were assigned to the live cell biomarkers phenylalanine and glycosaminoglycan, respectively, and were assessed during the multivariate spectral analysis. The corresponding score plot and loading information generated from the Principal Component Analysis (PCA) of the Raman spectrum at day 7 and day 14, pointed at inter-group spectral variations related to cell adhesion and proliferation between the two porous CS particle groups and the control.