Effects of Type I Collagen Concentration in Hydrogel on the Growth and Phenotypic Expression of Rat Chondrocytes

Characterization of Composite Agarose-Collagen Hydrogels for Chondrocyte Culture

To elucidate the mechanisms of cellular mechanotransduction, it is necessary to employ biomaterials that effectively merge biofunctionality with appropriate mechanical characteristics. Agarose and collagen separately are common biopolymers used in cartilage mechanobiology and mechanotransduction studies but lack features that make them ideal for functional engineered cartilage. In this study, agarose is blended with collagen type I to create hydrogels with final concentrations of 4% w/v or 2% w/v agarose with 2 mg/mL collagen. We hypothesized that the addition of collagen into a high-concentration agarose hydrogel does not diminish mechanical properties. Acellular and cell-laden studies were completed to assess rheologic and compressive properties, contraction, and structural homogeneity in addition to cell proliferation and sulfated glycosaminoglycan production. Over 21 days in culture, cellular 4% agarose-2 mg/mL collagen I hydrogels seeded with primary murine chondrocytes displayed structural and bulk mechanical behaviors that did not significantly alter from 4% agarose-only hydrogels, cell proliferation, and continual glycosaminoglycan production, indicating promise toward the development of an effective hydrogel for chondrocyte mechanotransduction and mechanobiology studies.

Advancements in Chondrocyte 3-Dimensional Embedded Culture: Implications for Tissue Engineering and Regenerative Medicine

Cartilage repair necessitates regenerative medicine because of the unreliable healing mechanism of cartilage. To yield a sufficient number of cells for transplantation, chondrocytes must be expanded in culture. However, in 2D culture, chondrocytes tend to lose their distinctive phenotypes and functionalities after serial passage, thereby limiting their efficacy for tissue engineering purposes. The mechanism of dedifferentiation in 2D culture can be attributed to various factors, including abnormal nuclear strength, stress-induced mitochondrial impairment, chromatin remodeling, ERK-1/2 and the p38/mitogen-activated protein kinase (MAPK) signaling pathway. These mechanisms collectively contribute to the loss of chondrocyte phenotype and reduced production of cartilage-specific extracellular matrix (ECM) components. Chondrocyte 3D culture methods have emerged as promising solutions to prevent dedifferentiation. Techniques, such as scaffold-based culture and scaffold-free approaches, provide chondrocytes with a more physiologically relevant environment, promoting their differentiation and matrix synthesis. These methods have been used in cartilage tissue engineering to create engineered cartilage constructs for transplantation and joint repair. However, chondrocyte 3D culture still has limitations, such as low viability and proliferation rate, and also difficulties in passage under 3D condition. These indicate challenges of obtaining a sufficient number of chondrocytes for large-scale tissue production. To address these issues, ongoing studies of many research groups have been focusing on refining culture conditions, optimizing scaffold materials, and exploring novel cell sources such as stem cells to enhance the quality and quantity of engineered cartilage tissues. Although obstacles remain, continuous endeavors to enhance culture techniques and overcome limitations offer a promising outlook for the advancement of more efficient strategies for cartilage regeneration.

Melatonin hyalurosomes in collagen thermosensitive gel as a potential repurposing approach for rheumatoid arthritis management via the intra-articular route

Despite the fact that several rheumatoid arthritis treatments have been utilized, none of them achieved complete joint healing and has been accompanied by several side effects that compromise patient compliance. This study aims to provide an effective safe RA treatment with minimum side effects through the encapsulation of melatonin (MEL) in hyalurosomes and loading these hyalurosomes in collagen thermos-sensitive poloxamer 407 (PCO) hydrogels, followed by their intra-articular administration in AIA model rats. In vitro characterization of MEL-hyalurosomes and PCO hydrogel along with in vivo evaluation of the selected formulation were conducted. Particle size, PDI and EE % of the selected formulation were 71.5 nm, 0.09 and 90 %. TEM micrographs demonstrated that the particles had spherical shape with no aggregation signs. Loading PCO hydrogels with MEL-hyalurosomes did not cause significant changes in pH although it increased its viscosity and injection time. FTIR analysis showed that no interactions were noted among the delivery system components. In vivo results revealed the superior effect of MEL-hyalurosomes PCO hydrogel over MEL-PCO hydrogel and blank PCO hydrogels in improving joint healing, cartilage repair, pannus formation and cell infiltrations. Also, MEL-hyalurosomes PCO hydrogel group showed comparable levels of TNF-α, IL1, MDA, NRF2 and HO-1 with the negative control group. These findings highlight the MEL encapsulation role in augmenting its pharmacological effects along with the synergistic effect of hyaluronic acid in hyalurosomes and collagen in PCO hydrogel in promoting joint healing.

Categorization of collagen type I and II blend hydrogel using multipolarization SHG imaging with ResNet regression

Previously, the discrimination of collagen types I and II was successfully achieved using peptide pitch angle and anisotropic parameter methods. However, these methods require fitting polarization second harmonic generation (SHG) pixel-wise information into generic mathematical models, revealing inconsistencies in categorizing collagen type I and II blend hydrogels. In this study, a ResNet approach based on multipolarization SHG imaging is proposed for the categorization and regression of collagen type I and II blend hydrogels at 0%, 25%, 50%, 75%, and 100% type II, without the need for prior time-consuming model fitting. A ResNet model, pretrained on 18 progressive polarization SHG images at 10° intervals for each percentage, categorizes the five blended collagen hydrogels with a mean absolute error (MAE) of 0.021, while the model pretrained on nonpolarization images exhibited 0.083 MAE. Moreover, the pretrained models can also generally regress the blend hydrogels at 20%, 40%, 60%, and 80% type II. In conclusion, the multipolarization SHG image-based ResNet analysis demonstrates the potential for an automated approach using deep learning to extract valuable information from the collagen matrix.

Ultrasound-derived mechanical stimulation of cell-laden collagen hydrogels for bone repair

Cell therapy is emerging as an effective treatment strategy for many diseases. Here we describe a novel approach to bone tissue repair that combines hydrogel-based cell therapy with low intensity pulsed ultrasound (LIPUS), an FDA approved treatment for fracture repair. Bone marrow-derived stromal cells (BMSCs) have been encapsulated in type I collagen hydrogels and mechanically stimulated using LIPUS-derived acoustic radiation force (ARF). We observed the expression and upward trend of load-sensitive, osteoblast-specific markers and determined that the extent of cell response is dependent on an optimal combination of both hydrogel stiffness and ARF intensity. Specifically, cells encapsulated in hydrogels of optimal stiffness respond at the onset of ultrasound by upregulating early bone-sensitive markers such as calcium, cyclooxygenase-2, and prostaglandin E2 , and later by supporting mineralized tissue formation after 21 days of culture. In vivo evaluation of a critical size calvarial defect in NOD scid gamma (NSG) mice indicated that the implantation of BMSC-laden hydrogels of optimal stiffness improved healing of calvarial defects after daily administration of ARF over 4 weeks. Collectively, these findings validate the efficacy of our system of localized cell delivery for treating bone defects where undifferentiated BMSCs are induced to the osteoblastic lineage. Further, in vivo healing may be enhanced via non-invasive transdermal mechanical stimulation of implanted cells using ARF.

Controlling Microenvironments with Organs-on-Chips for Osteoarthritis Modelling

Osteoarthritis (OA) remains a prevalent disease affecting more than 20% of the global population, resulting in morbidity and lower quality of life for patients. The study of OA pathophysiology remains predominantly in animal models due to the complexities of mimicking the physiological environment surrounding the joint tissue. Recent development in microfluidic organ-on-chip (OoC) systems have demonstrated various techniques to mimic and modulate tissue physiological environments. Adaptations of these techniques have demonstrated success in capturing a joint tissue's tissue physiology for studying the mechanism of OA. Adapting these techniques and strategies can help create human-specific in vitro models that recapitulate the cellular processes involved in OA. This review aims to comprehensively summarise various demonstrations of microfluidic platforms in mimicking joint microenvironments for future platform design iterations.

3D cell culture model: From ground experiment to microgravity study

Microgravity has been shown to induce many changes in cell growth and differentiation due to offloading the gravitational strain normally exerted on cells. Although many studies have used two-dimensional (2D) cell culture systems to investigate the effects of microgravity on cell growth, three-dimensional (3D) culture scaffolds can offer more direct indications of the modified cell response to microgravity-related dysregulations compared to 2D culture methods. Thus, knowledge of 3D cell culture is essential for better understanding the in vivo tissue function and physiological response under microgravity conditions. This review discusses the advances in 2D and 3D cell culture studies, particularly emphasizing the role of hydrogels, which can provide cells with a mimic in vivo environment to collect a more natural response. We also summarized recent studies about cell growth and differentiation under real microgravity or simulated microgravity conditions using ground-based equipment. Finally, we anticipate that hydrogel-based 3D culture models will play an essential role in constructing organoids, discovering the causes of microgravity-dependent molecular and cellular changes, improving space tissue regeneration, and developing innovative therapeutic strategies. Future research into the 3D culture in microgravity conditions could lead to valuable therapeutic applications in health and pharmaceuticals.

pH and Thrombin Concentration Are Decisive in Synthesizing Stiff, Stable, and Open-Porous Fibrin-Collagen Hydrogel Blends without Chemical Cross-Linker

Fibrin-collagen hydrogel blends exhibit high potential for tissue engineering applications. However, it is still unclear whether the underlying cross-linking mechanisms are of chemical or physical nature. It is here hypothesized that chemical cross-linkers play a negligible role and that instead pH and thrombin concentration are decisive for synthetizing blends with high stiffness and hydrolytic stability. Different fibrin-collagen formulations (pure and with additional transglutaminase) are used and the blends' compaction rate, hydrolytic stability, compressive strength, and hydrogel microstructure are investigated. The effect of thrombin concentration on gel compaction is examined and the importance of pH control during synthesis observed. It is revealed that transglutaminase impairs gel stability and it is deduced that fibrin-collagen blends mainly cross-link by mechanical interactions due to physical fibril entanglement as opposed to covalent bonds from chemical cross-linking. High thrombin concentrations and basic pH during synthesis reduce gel compaction and enhance stiffness and long-term stability. Scanning electron microscopy reveals a highly interpenetrating fibrous network with unique, interconnected open-porous microstructures. Endothelial cells proliferate on the blends and form a confluent monolayer. This study reveals the underlying cross-linking mechanisms and presents enhanced fibrin-collagen blends with high stiffness, hydrolytic stability, and large, interconnected pores; findings that offer high potential for advanced tissue engineering applications.

Preparation and Characterization of Extracellular Matrix Hydrogels Derived from Acellular Cartilage Tissue

Decellularized matrices can effectively reduce severe immune rejection with their cells and eliminated nucleic acid material and provide specific environments for tissue repair or tissue regeneration. In this study, we prepared acellular cartilage matrix (ACM) powder through the decellularization method and developed ACM hydrogels by physical, chemical, and enzymatic digestion methods. The results demonstrated that the small size group of ACM hydrogels exhibited better gel conditions when the concentration of ACM hydrogels was 30 and 20 mg/mL in 1N HCl through parameter adjustment. The data also confirmed that the ACM hydrogels retained the main components of cartilage: 61.18% of glycosaminoglycan (GAG) and 78.29% of collagen, with 99.61% of its DNA removed compared to samples without the decellularization procedure (set as 100%). Through turbidimetric gelation kinetics, hydrogel rheological property analysis, and hydrogel tissue physical property testing, this study also revealed that increasing hydrogel concentration is helpful for gelation. Besides, the ex vivo test confirmed that a higher concentration of ACM hydrogels had good adhesive properties and could fill in cartilage defects adequately. This study offers useful information for developing and manufacturing ACM hydrogels to serve as potential alternative scaffolds for future cartilage defect treatment.

A defined heat pretreatment of gelatin enables control of hydrolytic stability, stiffness, and microstructural architecture of fibrin-gelatin hydrogel blends

Fibrin-gelatin hydrogel blends exhibit high potential for tissue engineering in vitro applications. However, the means to tailor these blends in order to control their properties, thus opening up a broad range of new target applications, have been insufficiently explored. We hypothesized that a controlled heat treatment of gelatin prior to blend synthesis enables control of hydrolytic swelling and shrinking, stiffness, and microstructural architecture of fibrin-gelatin based hydrogel blends while providing tremendous long-term stability. We investigated these hydrogel blends' compressive strength, in vitro degradation stability, and microstructure in order to test this hypothesis. In addition, we examined the gel's ability to support endothelial cell proliferation and stretching of encapsulated smooth muscle cells. This research showed that a controlled heat pretreatment of the gelatin component strongly influenced the stiffness, swelling, shrinking, and microstructural architecture of the final blends regardless of identical gelatin mass fractions. All blends offered high long-term hydrolytic stability. In conclusion, the results of this study open the possibility to use this technique in order to tune low-concentrated, open-porous fibrin-based hydrogels, even in long-term tissue engineering in vitro experiments.

A sonication-induced silk-collagen hydrogel for functional cartilage regeneration

Cartilage tissue has limited self-regeneration capacity and current treatment methods often result in fibrocartilage formation. Although collagen has shown the ability to induce chondrogenesis of mesenchymal stem cells (MSCs) and regenerate hyaline cartilage, the application of a pure collagen hydrogel is inherently limited by its fast degradation, poor mechanical properties and excessive cell-mediated shrinkage. To overcome this challenge, we developed a sonication-induced silk-collagen composite hydrogel (COL + SF(S)) and investigated its physicochemical and biological properties compared with a collagen hydrogel (COL) and a non-sonicated silk-collagen composite hydrogel (COL + SF(NS)). The results showed that the sonication treatment of silk fibroin induced antiparallel β-sheet formation and a stronger negative charge on the silk fibroin molecule, which resulted in improved mechanical properties of the COL + SF(S) hydrogel. The COL + SF(S) hydrogel exhibited superior stability during cell culture and promoted the gene expression of SOX9 at the early stage and sulfated glycosaminoglycan (sGAG) deposition without any exogenous growth factor. Moreover, the cartilage regeneration capacity of the COL + SF(S) group was evaluated in rabbit knee defects. The COL + SF(S) group exhibited well-integrated articular hyaline cartilage closely resembling native articular cartilage after 6 months. Overall, the COL + SF(S) hydrogel holds great potential as a scaffold material to regenerate functional hyaline cartilage.

Novel Synthetic Polymer-Based 3D Contraction Assay: A Versatile Preclinical Research Platform for Fibrosis

The driving factors causing fibrosis and scar formation include fibroblast differentiation into myofibroblasts and hampered myofibroblast apoptosis, which ultimately results in collagen accumulation and tissue contraction. Currently, only very few drugs are available for fibrosis treatment, and there is an urgent demand for new pharmaceutical products. High-throughput in vitro fibrosis models are necessary to develop such drugs. In this study, we developed such a novel model based on synthetic polyisocyanide (PIC-RGD) hydrogels. The model not only measures contraction but also allows for subsequent molecular and cellular analysis. Fibroblasts were seeded in small (10 μL) PIC-RGD gels in the absence or presence of TGFβ1, the latter to induce myofibroblast differentiation. The contraction model clearly differentiates fibroblasts and myofibroblasts. Besides a stronger contraction, we also observed α-smooth muscle actin (αSMA) production and higher collagen deposition for the latter. The results were supported by mRNA expression experiments of αSMA, Col1α1, P53, and Ki67. As proof of principle, the effects of FDA-approved antifibrotic drugs nintedanib and pirfenidone were tested in our newly developed fibrosis model. Both drugs clearly reduce myofibroblast-induced contraction. Moreover, both drugs significantly decrease myofibroblast viability. Our low-volume synthetic PIC-RGD hydrogel platform is an attractive tool for high-throughput in vitro antifibrotic drug screening.

Hydrogels: Properties and Applications in Biomedicine

Hydrogels are crosslinked polymer chains with three-dimensional (3D) network structures, which can absorb relatively large amounts of fluid. Because of the high water content, soft structure, and porosity of hydrogels, they closely resemble living tissues. Research in recent years shows that hydrogels have been applied in various fields, such as agriculture, biomaterials, the food industry, drug delivery, tissue engineering, and regenerative medicine. Along with the underlying technology improvements of hydrogel development, hydrogels can be expected to be applied in more fields. Although not all hydrogels have good biodegradability and biocompatibility, such as synthetic hydrogels (polyvinyl alcohol, polyacrylamide, polyethylene glycol hydrogels, etc.), their biodegradability and biocompatibility can be adjusted by modification of their functional group or incorporation of natural polymers. Hence, scientists are still interested in the biomedical applications of hydrogels due to their creative adjustability for different uses. In this review, we first introduce the basic information of hydrogels, such as structure, classification, and synthesis. Then, we further describe the recent applications of hydrogels in 3D cell cultures, drug delivery, wound dressing, and tissue engineering.

Towards Bioinspired Meniscus-Regenerative Scaffolds: Engineering a Novel 3D Bioprinted Patient-Specific Construct Reinforced by Biomimetically Aligned Nanofibers

Introduction

Three of the main requirements that remain major challenges in tissue engineering of the knee meniscus are to engineer scaffolds with compatible anatomical shape, good mechanical properties, and microstructure able to mimic the architecture of the extracellular matrix (ECM). In this context, we presented a new biofabrication strategy to develop a three-dimensional (3D) meniscus-regenerative scaffold with custom-made macroscopic size and microarchitecture bioinspired by the organization of structural fibers of native tissue ECM.

Methods

The concept was based on the combination of bioprinted cell-laden hydrogel (type 1 collagen) reinforced by multilayers of biomimetically aligned electrospun nanofibrous mats (polycaprolactone/carbon nanotubes, PCL/CNT), using a patient-specific 3D digital meniscus model reconstructed from MRI data by free and open-source software.

Results

The results showed that the incorporation of aligned nanofibers sheets between the hydrogel layers enhanced the scaffold's structural integrity and shape fidelity compared to the nanofiber-free collagen hydrogel. Furthermore, mechanical compression tests demonstrated that the presence of nanofiber layers significantly improved the mechanical properties of the bioprinted construct. Importantly, the introduction of PCL/CNT nanofibrous mats between the layers of the bioprinted collagen hydrogel did not negatively affect cell viability, in which mesenchymal stem cells remained viable even after 7 days of culture within the scaffold.

Conclusion

Overall, these findings evidence that this bioengineering approach offers a promising strategy for fabricating biomimetic meniscus scaffolds for tissue engineering.

Pressure Drives Rapid Burst-Like Coordinated Cellular Motion from 3D Cancer Aggregates

A key behavior observed during morphogenesis, wound healing, and cancer invasion is that of collective and coordinated cellular motion. Hence, understanding the different aspects of such coordinated migration is fundamental for describing and treating cancer and other pathological defects. In general, individual cells exert forces on their environment in order to move, and collective motion is coordinated by cell-cell adhesion-based forces. However, this notion ignores other mechanisms that encourage cellular movement, such as pressure differences. Here, using model tumors, it is found that increased pressure drove coordinated cellular motion independent of cell-cell adhesion by triggering cell swelling in a soft extracellular matrix (ECM). In the resulting phenotype, a rapid burst-like stream of cervical cancer cells emerged from 3D aggregates embedded in soft collagen matrices (0.5 mg mL-1 ). This fluid-like pushing mechanism, recorded within 8 h after embedding, shows high cell velocities and super-diffusive motion. Because the swelling in this model system critically depends on integrin-mediated cell-ECM adhesions and cellular contractility, the swelling is likely triggered by unsustained mechanotransduction, providing new evidence that pressure-driven effects must be considered to more completely understand the mechanical forces involved in cell and tissue movement as well as invasion.

Combinations of Hydrogels and Mesenchymal Stromal Cells (MSCs) for Cartilage Tissue Engineering-A Review of the Literature

Cartilage offers limited regenerative capacity. Cell-based approaches have emerged as a promising alternative in the treatment of cartilage defects and osteoarthritis. Due to their easy accessibility, abundancy, and chondrogenic potential mesenchymal stromal cells (MSCs) offer an attractive cell source. MSCs are often combined with natural or synthetic hydrogels providing tunable biocompatibility, biodegradability, and enhanced cell functionality. In this review, we focused on the different advantages and disadvantages of various natural, synthetic, and modified hydrogels. We examined the different combinations of MSC-subpopulations and hydrogels used for cartilage engineering in preclinical and clinical studies and reviewed the effects of added growth factors or gene transfer on chondrogenesis in MSC-laden hydrogels. The aim of this review is to add to the understanding of the disadvantages and advantages of various combinations of MSC-subpopulations, growth factors, gene transfers, and hydrogels in cartilage engineering.

Decellularized kidney extracellular matrix bioinks recapitulate renal 3D microenvironmentin vitro

Decellularized extracellular matrices (ECMs) are able to provide the necessary and specific cues for remodeling and maturation of tissue-specific cells. Nevertheless, their use for typical biofabrication applications requires chemical modification or mixing with other polymers, mainly due to the limited viscoelastic properties. In this study, we hypothesize that a bioink exclusively based on decellularized kidney ECM (dKECM) could be used to bioprint renal progenitor cells. To address these aims, porcine kidneys were decellularized, lyophilized and digested to yield a viscous solution. Then, the bioprinting process was optimized using an agarose microparticle support bath containing transglutaminase for enzymatic crosslinking of the dKECM. This methodology was highly effective to obtain constructs with good printing resolution and high structural integrity. Moreover, the encapsulation of primary renal progenitor cells resulted in high cell viability, with creation of 3D complex structures over time. More importantly, this tissue-specific matrix was also able to influence cellular growth and differentiation over time. Taken together, these results demonstrate that unmodified dKECM bioinks have great potential for bioengineering renal tissue analogs with promising translational applications and/or forin vitromodel systems. Ultimately, this strategy may have greater implications on the biomedical field for the development of bioengineered substitutes using decellularized matrices from other tissues.

Human Olfactory Mucosa Stem Cells Delivery Using a Collagen Hydrogel: As a Potential Candidate for Bone Tissue Engineering

For bone tissue engineering, stem cell-based therapy has become a promising option. Recently, cell transplantation supported by polymeric carriers has been increasingly evaluated. Herein, we encapsulated human olfactory ectomesenchymal stem cells (OE-MSC) in the collagen hydrogel system, and their osteogenic potential was assessed in vitro and in vivo conditions. Collagen type I was composed of four different concentrations of (4 mg/mL, 5 mg/mL, 6 mg/mL, 7 mg/mL). SDS-Page, FTIR, rheologic test, resazurin assay, live/dead assay, and SEM were used to characterize collagen hydrogels. OE-MSCs encapsulated in the optimum concentration of collagen hydrogel and transplanted in rat calvarial defects. The tissue samples were harvested after 4- and 8-weeks post-transplantation and assessed by optical imaging, micro CT, and H&E staining methods. The highest porosity and biocompatibility were confirmed in all scaffolds. The collagen hydrogel with 7 mg/mL concentration was presented as optimal mechanical properties close to the naïve bone. Furthermore, the same concentration illustrated high osteogenic differentiation confirmed by real-time PCR and alizarin red S methods. Bone healing has significantly occurred in defects treated with OE-MSCs encapsulated hydrogels in vivo. As a result, OE-MSCs with suitable carriers could be used as an appropriate cell source to address clinical bone complications.

Applications of Biomaterials in 3D Cell Culture and Contributions of 3D Cell Culture to Drug Development and Basic Biomedical Research

The process of evaluating the efficacy and toxicity of drugs is important in the production of new drugs to treat diseases. Testing in humans is the most accurate method, but there are technical and ethical limitations. To overcome these limitations, various models have been developed in which responses to various external stimuli can be observed to help guide future trials. In particular, three-dimensional (3D) cell culture has a great advantage in simulating the physical and biological functions of tissues in the human body. This article reviews the biomaterials currently used to improve cellular functions in 3D culture and the contributions of 3D culture to cancer research, stem cell culture and drug and toxicity screening.

Review of Plastic Surgery Biomaterials and Current Progress in Their 3D Manufacturing Technology

Plastic surgery is a broad field, including maxillofacial surgery, skin flaps and grafts, liposuction and body contouring, breast surgery, and facial cosmetic procedures. Due to the requirements of plastic surgery for the biological safety of materials, biomaterials are widely used because of its superior biocompatibility and biodegradability. Currently, there are many kinds of biomaterials clinically used in plastic surgery and their applications are diverse. Moreover, with the rise of three-dimensional printing technology in recent years, the macroscopically more precise and personalized bio-scaffolding materials with microporous structure have made good progress, which is thought to bring new development to biomaterials. Therefore, in this paper, we reviewed the plastic surgery biomaterials and current progress in their 3D manufacturing technology.

Advances in biomaterials for adipose tissue reconstruction in plastic surgery

Adipose tissue reconstruction is an important technique for soft tissue defects caused by facial plastic surgery and trauma. Adipose tissue reconstruction can be repaired by fat transplantation and biomaterial filling, but there are some problems in fat transplantation, such as second operation and limited resources. The application of advanced artificial biomaterials is a promising strategy. In this paper, injectable biomaterials and three-dimensional (3D) tissue-engineered scaffold materials for adipose tissue reconstruction in plastic surgery are reviewed. Injectable biomaterials include natural biomaterials and artificial biomaterials, which generally have problems such as high absorptivity of fillers, repeated injection, and rejection. In recent years, the technology of new 3D tissue-engineering scaffold materials with adipose-derived stem cells (ADSCs) and porous scaffold as the core has made good progress in fat reconstruction, which is expected to solve the current problem of clinical adipose tissue reconstruction, and various biomaterials preparation technology and transformation research also provide the basis for clinical transformation of fat tissue reconstruction.

One step bulk modification of poly(L-lactic acid) composites with functional additives to improve mechanical and biological properties for cardiovascular implant applications

Poly(L-lactic acid) (PLLA) has been widely used as a promising biomaterial in biomedical applications due to its biodegradability and high mechanical strength. However, because of the inherent brittleness, low impact resistance, and weak thermal stability of PLLA, the modification process is usually required to utilize it for biomedical devices. Furthermore, acidic byproducts resulting from the hydrolysis of PLLA after implantation reduce the pH of the surrounding environment and cause inflammatory responses in the implanted area, leading to the failure of their clinical applications. To this end, here, we demonstrate a novel modification process for the PLLA composite with various functional additives, such as cis-aconitic anhydride (AA), triacetin (TA), isosorbide derivative (ISB), and/or Pluronic® F127 (F). The modified PLLA composite with TA and F (PLLA/TF) showed significantly improved elongation at break and Young's modulus and retained tensile strength. Moreover, incorporating magnesium hydroxide (MH) nanoparticles (PLLA/TFMH) significantly reduced acid-induced inflammation responses caused by the acidic degradation products of PLLA. Reduced plasma protein adsorption was observed in the PLLA/TFMH. These results suggest that the one step bulk modification of biodegradable PLLA using TA, F, and MH will have great potential in cardiovascular implant applications.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Polypeptide Thermogels as Three-Dimensional Scaffolds for Cells

BACKGROUND

Thermogel is an aqueous solution that exhibits a sol-to-gel transition as the temperature increases. Stem cells, growth factors, and differentiating factors can be incorporated in situ in the matrix during the sol-to-gel transition, leading to the formation of a three-dimensional (3D) cell-culture scaffold.

METHODS

The uses of thermogelling polypeptides, such as collagen, Matrigel™, elastin-like polypeptides, and synthetic polypeptides, as 3D scaffolds of cells, are summarized in this paper.

RESULTS

The timely supply of growth factors to the cells, cell survival, and metabolite removal is to be insured in the cell culture matrix. Various growth factors were incorporated in the matrix during the sol-to-gel transition of the thermogelling polypeptide aqueous solutions, and preferential differentiation of the incorporated stem cells into specific target cells were investigated. In addition, modulus of the matrix was controlled by post-crosslinking reactions of thermogels or employing composite systems. Chemical functional groups as well as biological factors were selected appropriately for targeted differentiation of the incorporated stem cells.

CONCLUSION

In addition to all the advantages of thermogels including mild conditions for cell-incorporation and controlled supplies of the growth factors, polypeptide thermogels provide neutral pH environments to the cells during the degradation of the gel. Polypeptide thermogels as an injectable scaffold can be a promising system for their eventual in vivo applications in stem cell therapy.

Electrostatically Interactive Injectable Hydrogels for Drug Delivery

BACKGROUND

Several injectable hydrogels have been developed extensively for a broad range of biomedical applications. Injectable hydrogels forming in situ through the change in external stimuli have the distinct properties of easy management and minimal invasiveness, and thus provide the advantage of bypassing surgical procedures for administration resulting in better patient compliance.

METHODS

The injectable in situ-forming hydrogels can be formed irreversibly or reversibly under physiological stimuli. Among several external stimuli that induce formation of hydrogels in situ, in this review, we focused on the electrostatic interactions as the most simple and interesting stimulus.

RESULTS

Currently, numerous polyelectrolytes have been reported as potential electrostatically interactive in situ-forming hydrogels. In this review, a comprehensive overview of the rapidly developing electrostatically interactive in situ-forming hydrogels, which are produced by various anionic and cationic polyelectrolytes such as chitosan, celluloses, and alginates, has been outlined and summarized. Further, their biomedical applications have also been discussed.

CONCLUSION

The review concludes with perspectives on the future of electrostatically interactive in situ-forming hydrogels.

Injectable Biomaterials in Plastic and Reconstructive Surgery: A Review of the Current Status

BACKGROUND

Injectable biomaterials have attracted increasing attention for volume restoration and tissue regeneration. The main aim of this review is to discuss the current status of the injectable biomaterials for correction of tissue defects in plastic and reconstructive surgery.

METHODS

Requirements of injectable biomaterials, mechanism of in situ gelation, characteristics, and the combinational usage of adipose-derived stem cells (ADSCs) and growth factors were reviewed.

RESULTS

The ideal injectable biomaterials should be biocompatible, non-toxic, easy to use, and cost-effective. Additionally, it should possess adequate mechanical properties and stability. In situ gelation method includes physical, chemical, enzymatic and photo-initiated methods. Natural and synthetic biomaterials carry their pros and cons due to their inherent properties. The combined use of ADSCs and growth factors provides enhanced potential for adipose tissue regeneration.

CONCLUSIONS

The usage of injectable biomaterials has been increasing for the tissue restoration and regeneration. The future of incorporating ADSCs and growth factors into the injectable biomaterials is promising.

Tonsil-derived mesenchymal stem cell-embedded in situ crosslinkable gelatin hydrogel therapy recovers postmenopausal osteoporosis through bone regeneration

We investigated therapeutic potential of human tonsil-derived mesenchymal stem cells (TMSC) subcutaneously delivered to ovariectomized (OVX) mice for developing more safe and effective therapy for osteoporosis. TMSC were isolated from tonsil tissues of children undergoing tonsillectomy, and TMSC-embedded in situ crosslinkable gelatin-hydroxyphenyl propionic acid hydrogel (TMSC-GHH) or TMSC alone were delivered subcutaneously to the dorsa of OVX mice. After 3 months, three-dimensionally reconstructed micro-computed tomographic images revealed better recovery of the femoral heads in OVX mice treated with TMSC-GHH. Serum osteocalcin and alkaline phosphatase were also recovered, indicating bone formation only in TMSC-GHH-treated mice, and absence in hypercalcemia or other severe macroscopic deformities showed biocompatibility of TMSC-GHH. Additionally, visceral fat reduction effects by TMSC-GHH further supported their therapeutic potential. TMSC provided therapeutic benefits toward osteoporosis only when embedded in GHH, and showed potential as a supplement or alternative to current therapies.

The Application of Fibrin/Hyaluronic Acid-Poly(l-Lactic-co-Glycolic Acid) Construct in Augmentation Rhinoplasty

Although many graft materials have been used for augmentation rhinoplasty, an ideal graft has not yet been developed. As the field of tissue engineering has been developing, it has been applied to the reconstruction of many organs, but its application in the rhinoplasty field is still limited. This study evaluated the utility of allogenic chondrocytes with fibrin/hyaluronic acid (HA)-poly(l-lactic-co-glycolic acid) (PLGA) constructs in augmentation rhinoplasty. Chondrocytes from rabbit auricular cartilage were isolated and cultured with fibrin/HA hydrogels and implanted into PLGA scaffolds. After 8 weeks of in vitro culture, the scaffolds were implanted in the nasal dorsum of six rabbits. Eight weeks postoperatively, the implanted sites were evaluated with gross, radiologic, and histologic analysis. In vitro, more than 90% of the seeded chondrocytes in the PLGA scaffolds survived for 2 weeks, and they produced a large amount of extracellular matrix and were well differentiated. The grafts maintained their initial shape for 8 weeks after implantation. Radiological and histological evaluations showed that the structure was well maintained with minimal inflammatory response and appropriate elevation levels. However, the formation of neo-chondrocytes was not observed. PLGA scaffolds seeded with fibrin/HA and allogenic chondrocytes can be a biocompatible augmentation material in rhinoplasty in the future.

Efficacy of collagen and alginate hydrogels for the prevention of rat chondrocyte dedifferentiation

Dedifferentiation of chondrocytes remains a major problem in cartilage tissue engineering. The development of hydrogels that can preserve chondrogenic phenotype and prevent chondrocyte dedifferentiation is a meaningful strategy to solve dedifferentiation problem of chondrocytes. In the present study, three gels were prepared (alginate gel (Alg gel), type I collagen gel (Col gel), and their combination gel (Alg/Col gel)), and the in vitro efficacy of chondrocytes culture while preserving their phenotypes was investigated. While Col gel became substantially contracted with time, the cells encapsulated in Alg gel preserved the shape over the culture period of 14 days. The mechanical and cell-associated contraction behaviors of Alg/Col gel were similar to those of Alg. The cells in Alg and Alg/Col gels exhibited round morphology, whereas those in Col gel became elongated (i.e. fibroblast-like) during cultures. The cells proliferated with time in all gels with the highest proliferation being attained in Col gel. The expression of chondrogenic genes, including SOX9, type II collagen, and aggrecan, was significantly up-regulated in Alg/Col gel and Col gel, particularly in Col gel. However, the chondrocyte dedifferentiation markers, type I collagen and alkaline phosphatase (ALP), were also expressed at significant levels in Col gel, which being contrasted with the events in Alg and Alg/Col gels. The current results suggest the cells cultured in hydrogels can express chondrocyte dedifferentiation markers as well as chondrocyte markers, which draws attention to choose proper hydrogels for chondrocyte-based cartilage tissue engineering.