Osteochondral defect repair using a polyvinyl alcohol-polyacrylic acid (PVA-PAAc) hydrogel

Revision Surgery for Failed Polyvinyl Alcohol Hydrogel Implant in the First MTP Joint: A Case Report and Comprehensive Review

Background

Hallux rigidus is a degenerative condition of the first metatarsophalangeal (MTP) joint that can significantly impair function and quality of life. The introduction of polyvinyl alcohol (PVA) hydrogel implants, such as Cartiva, offered an alternative to arthrodesis by preserving joint motion. However, failures of these implants, often resulting in bone loss and joint instability, present a challenge for revision surgery.

Methods

We report the case of a 43-year-old woman with persistent pain and functional limitations after a failed PVA hydrogel implant in the first MTP joint. The revision surgery involved a biologic resurfacing using the Osteochondral Autograft Transfer System (OATS) with a graft harvested from the ipsilateral femoral condyle, complemented by interpositional arthroplasty with a dermal graft and a proximal phalanx closing wedge osteotomy to correct residual hallux valgus.

Results

At the 3-year follow-up, the patient-reported complete resolution of pain and returned to full activity with improved range of motion (40 degrees dorsiflexion, 15 degrees plantarflexion). Radiographic evaluation demonstrated graft incorporation and restoration of joint space, confirming the success of the procedure.

Conclusion

This case highlights the potential of OATS combined with interpositional arthroplasty as a viable option for revision surgery in complex cases of failed synthetic cartilage implants in hallux rigidus. By addressing bone loss and preserving joint function, this approach provides a patient-specific alternative to traditional arthrodesis. Further studies are warranted to establish the long-term efficacy of this technique in similar cases.

Level of Evidence

Level V, case report.

Ultramodern natural and synthetic polymer hydrogel scaffolds for articular cartilage repair and regeneration

Articular cartilage injury is a serious bone disease that can result in disabilities. With the rapid increase in the aging population, this disorder has become an increasingly important public health issue. Recently, stem cell-based cartilage tissue engineering has emerged as a promising therapeutic option for treating articular cartilage damage. Cellular scaffolds, which are among three key elements of tissue engineering, play significant roles in the repair of damaged articular cartilage by regulating cellular responses and promoting cartilage tissue regeneration. Biological macromolecules are commonly used as scaffold materials owing to their unique properties. For example, natural and synthetic polymer hydrogel scaffolds can effectively mimic the microenvironment of the natural extracellular matrix; exhibit high cytocompatibility, biocompatibility, and biodegradability; and have attracted increasing attention in bone and cartilage tissue engineering and regeneration medicine. Several types of hydrogel scaffolds have been fabricated to treat articular cartilage abnormalities. This article outlines the recent progress in the field of hydrogel scaffolds manufactured from various biomaterials for repairing damaged articular cartilage, discusses their advantages and disadvantages, and proposes directions for their future development.

Knee Joint Preservation in Tactical Athletes: A Comprehensive Approach Based upon Lesion Location and Restoration of the Osteochondral Unit

The unique physical demands of tactical athletes put immense stress on the knee joint, making these individuals susceptible to injury. In order to ensure operational readiness, management options must restore and preserve the native architecture and minimize downtime, while optimizing functionality. Osteochondral lesions (OCL) of the knee have long been acknowledged as significant sources of knee pain and functional deficits. The management of OCL is predicated on certain injury characteristics, including lesion location and the extent of subchondral disease. Techniques such as marrow stimulation, allograft and autologous chondrocyte implantation are examined in detail, with a focus on their application and suitability in tactical athlete populations. Moreover, the restoration of the osteochondral unit (OCU) is highlighted as a central aspect of knee joint preservation. The discussion encompasses the biomechanical considerations and outcomes associated with various cartilage restoration techniques. Factors influencing procedure selection, including lesion size, location, and patient-specific variables, are thoroughly examined. Additionally, the review underscores the critical role of post-operative rehabilitation and conditioning programs in optimizing outcomes. Strengthening the surrounding musculature, enhancing joint stability, and refining movement patterns are paramount in facilitating the successful integration of preservation procedures. This narrative review aims to provide a comprehensive resource for surgeons, engineers, and sports medicine practitioners engaged in the care of tactical athletes and the field of cartilage restoration. The integration of advanced preservation techniques and tailored rehabilitation protocols offers a promising avenue for sustaining knee joint health and function in this demanding population.

High biocompatible polyacrylamide hydrogels fabricated by surface mineralization for subchondral bone tissue engineering

The subchondral bone is an important part of cartilage which contains a large amount of hydroxyapatite. The mineral components of subchondral bone is the key factor which determines the biomechanical strength, and then affects the biological function of articular cartilage. Here, a mineralized polyacrylamide (PAM-Mineralized) hydrogel with good ALP activity, cell adhesion and biocompatibility was fabricated for subchondral bone tissue engineering. The micromorphology, composition and mechanical properties of PAM and PAM-Mineralized hydrogels were studied. The PAM hydrogels showed a porous structure, while the PAM-Mineralized hydrogels had well-distributed layers of hydroxyapatite mineralization on the surface. The XRD results show that the characteristic peak of hydroxyapatite (HA) was measured in PAM-Mineralized, indicating that the main component of the mineralized structure formed on the surface of the hydrogel after mineralization is HA. The formation of HA ectively decreased the rate of equilibrium swelling of the PAM hydrogel, with PAM-M reaching swelling equilibrium at 6 h. Meanwhile, compressive strength of PAM-Mineralized hydrogel (moisture state) reached 290 ± 30 kPa, compressive modulus reached 130 ± 4 kPa. PAM-Mineralized hydrogels did not affect the growth and proliferation of MC3T3-E1 cells. Surface mineralization of PAM hydrogel could significantly improve osteogenic differentiation of MC3T3-E1 cells. These results showed that PAM-Mineralized hydrogel could possess potential application in the field of subchondral bone tissue engineering.

Hydrogel Tissue Bioengineered Scaffolds in Bone Repair: A Review

Large bone defects due to trauma, infections, and tumors are difficult to heal spontaneously by the body's repair mechanisms and have become a major hindrance to people's daily lives and economic development. However, autologous and allogeneic bone grafts, with their lack of donors, more invasive surgery, immune rejection, and potential viral transmission, hinder the development of bone repair. Hydrogel tissue bioengineered scaffolds have gained widespread attention in the field of bone repair due to their good biocompatibility and three-dimensional network structure that facilitates cell adhesion and proliferation. In addition, loading natural products with nanoparticles and incorporating them into hydrogel tissue bioengineered scaffolds is one of the most effective strategies to promote bone repair due to the good bioactivity and limitations of natural products. Therefore, this paper presents a brief review of the application of hydrogels with different gel-forming properties, hydrogels with different matrices, and nanoparticle-loaded natural products loaded and incorporated into hydrogels for bone defect repair in recent years.

Regeneration of articular cartilage defects: Therapeutic strategies and perspectives

Articular cartilage (AC), a bone-to-bone protective device made of up to 80% water and populated by only one cell type (i.e. chondrocyte), has limited capacity for regeneration and self-repair after being damaged because of its low cell density, alymphatic and avascular nature. Resulting repair of cartilage defects, such as osteoarthritis (OA), is highly challenging in clinical treatment. Fortunately, the development of tissue engineering provides a promising method for growing cells in cartilage regeneration and repair by using hydrogels or the porous scaffolds. In this paper, we review the therapeutic strategies for AC defects, including current treatment methods, engineering/regenerative strategies, recent advances in biomaterials, and present emphasize on the perspectives of gene regulation and therapy of noncoding RNAs (ncRNAs), such as circular RNA (circRNA) and microRNA (miRNA).

Adhesive Gelatin-Catechol Complex Reinforced Poly(Acrylic Acid) Hydrogel with Enhanced Toughness and Cell Affinity for Cartilage Regeneration

The repair of cartilage damage caused by trauma, wear, or degenerative deformation remains a major challenge in modern medicine. Therefore, it is essential to develop a mechanically compatible and bioactive scaffold for cartilage tissue regeneration. In this study, a mussel-inspired, tough, adhesive polydopamine/gelatin-poly(acrylic acid) (PDA/Gel-PAA) composite hydrogel was developed for cartilage regeneration. The hydrogel achieved a high compressive strength of up to 0.67 MPa and a toughness of 420 J/m2 because of the unique chemical-physical cross-linking structure by introducing the PDA/Gel complex into the PAA network. PAA chains with rich carboxyl groups mimic the negatively charged glycosaminoglycans (GAGs) in the natural cartilage extracellular matrix (ECM), leading to strong water retention in the hydrogel. The incorporation of the PDA/Gel complex with catechol groups on PDA and arginine-glycine-aspartic acid (RGD) sequences on gelatin chains provided abundant adhesive motifs to improve the cell affinity and tissue adhesiveness of PAA, thereby facilitating the adhesion and proliferation of bone marrow stromal cells (BMSCs). In addition, transforming growth factor-β3 (TGFβ3) was stably immobilized and released from the PDA/Gel-PAA hydrogel. Thus, adhesive hydrogels can provide a suitable microenvironment to promote cell migration in the defect area and induce chronogenesis for cartilage regeneration.

An Artificial PVA-BC Composite That Mimics the Biomechanical Properties and Structure of a Natural Intervertebral Disc

Disc herniation is one of the most ubiquitous healthcare problems in modern cities—severe patients eventually require surgical intervention. However, the existing operations—spinal fusion and artificial disc replacement—alter the biomechanics of the spine, leaving much room for improvement. The appropriateness of polyvinyl alcohol (PVA) for biomedical applications has been recognised due to its high water content, excellent biocompatibility, and versatile mechanical properties. In this study, a newly-designed PVA–bacterial cellulose (PVA-BC) composite was assembled to mimic both the biomechanics and annular structure of natural intervertebral discs (IVDs). PVA-BC composites of various concentrations were fabricated and tested under unconfined compression and compressive creep in order to acquire the values of the normalised compressive stiffness and whole normalised deformation. The normalised compressive stiffness increased considerably with an increasing PVA concentration, spanning from 1.82 (±0.18) to 3.50 (±0.14) MPa, and the whole normalised deformation decreased from 0.25 to 0.13. Formulations of 40% PVA provided the most accurate mimicry of natural human IVDs in normalised whole deformation, and demonstrated higher dimensional stability. The biocompatible results further confirmed that the materials had excellent biocompatibility. The novel bionic structure and formulations of the PVA-BC materials mimicked the biomechanics and structure of natural IVDs, and ensured dimensional stability under prolonged compression, reducing the risk of impingement on the surrounding tissue. The PVA-BC composite is a promising material for third-generation artificial IVDs with integrated construction.

Thermal, Mechanical and Chemical Analysis of Poly(vinyl alcohol) Multifilament and Braided Yarns

Poly(vinyl alcohol) (PVA) in multifilament and braided yarns (BY) forms presents great potential for the design of numerous applications. However, such solutions fail to accomplish their requirements if the chemical and thermomechanical behaviour is not sufficiently known. Hence, a comprehensive characterisation of PVA multifilament and three BY architectures (6, 8, and 10 yarns) was performed involving the application of several techniques to evaluate the morphological, chemical, thermal, and mechanical features of those structures. Scanning electron microscopy (SEM) was used to reveal structural and morphological information. Differential thermal analysis (DTA) pointed out the glass transition temperature of PVA at 76 °C and the corresponding crystalline melting point at 210 °C. PVA BY exhibited higher tensile strength under monotonic quasi-static loading in comparison to their multifilament forms. Creep tests demonstrated that 6BY structures present the most deformable behaviour, while 8BY structures are the least deformable. Relaxation tests showed that 8BY architecture presents a more expressive variation of tensile stress, while 10BY offered the least. Dynamic mechanical analysis (DMA) revealed storage and loss moduli curves with similar transition peaks for the tested structures, except for the 10BY. Storage modulus is always four to six times higher than the loss modulus.

Early Failure of a Polyvinyl Alcohol Hydrogel Implant With Osteolysis and Foreign Body Reactions in an Ovine Model of Cartilage Repair

BACKGROUND

Hemiarthroplasty using a polyvinyl alcohol (PVA) hydrogel synthetic implant has been suggested as a good alternative to arthrodesis for the treatment of hallux rigidus. However, failure rates as high as 20% have been recorded.

PURPOSE

To characterize the pathological processes in bone, cartilage, and the synovial membrane after PVA hemiarthroplasty in an ovine model with 6 months of follow-up.

STUDY DESIGN

Controlled laboratory study.

METHODS

A unilateral osteochondral defect (8-mm diameter × 10-mm depth) was made in the medial femoral condyle in 6 sheep. Animals were randomized to receive a PVA implant (n = 4) or to have an empty defect (n = 2) and were monitored for 6 months. Patellofemoral radiographs were obtained at monthly intervals, and quantitative computed tomography was performed at the end of the study. After death, the joints were macroscopically evaluated and scored. Osteochondral and synovial membrane histological findings were assessed using modified Osteoarthritis Research Society International (OARSI) and aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) scoring systems. Immunohistochemistry using Iba1 was performed to evaluate activated macrophage infiltration.

RESULTS

Overall, 2 sheep with PVA implants were euthanized at 1 and 5 months because of uncontrollable pain and lameness (failed implants). Quantitative computed tomography showed that sheep with failed implants had 2.1-fold more osteolysis than those with successful implants. The sheep with failed implants had osteoarthritis with extensive glycosaminoglycan loss and cartilage fibrillation of the condyle and opposing tibial surface on histological examination. A foreign body reaction with severe chronic lymphoplasmacytic and granulomatous inflammation with giant cells was detected surrounding the implant. The synovial membrane ALVAL score was 9 of 19 and 14 of 19 in failed implants with synovial hyperplasia and lymphoplasmacytic and macrophage infiltration. In contrast, the synovial membrane in successful implants and empty defects was normal (ALVAL score = 0/19). Immunolabeling for Iba1 in failed implants confirmed extensive and dense macrophage infiltration within the condyle and synovial membrane, with the highest immunoreactive score (9/9).

CONCLUSION

PVA hydrogel implants had a 50% failure rate with uncontrollable pain, severe osteolysis, inflammation, and foreign body reactions.

CLINICAL RELEVANCE

The failure rate and pathological characteristics of the PVA implants suggest that their use should not be continued in human patients without further in vivo safety studies.

An Engineered Protein Adhesive with Properties of Tissue Integration and Controlled Release for Efficient Cartilage Repair

Cartilage damage is a prevalent health concern among humans. The inertness of cartilage, the absence of self-healing properties, and the lack of appropriate repair materials that integrate into the tissue pose a significant challenge for cartilage repair. Thus, it is important to develop novel soft biomaterials with strong tissue adhesion and chondrogenic capabilities for cartilage repair. Herein, a new type of protein adhesive is reported that exhibits superior cartilage repair performance. The material is fabricated by the electrostatic combination of chondroitin sulfate (CS) and positively charged elastin-like protein, which is derived from natural components of the extracellular matrix (ECM). The adhesive showed robust adhesion properties on different tissue substrates, offering a favorable environment for cartilage tissue integration. Noncovalent bonding between CS molecules in the glue allows for its controlled release, which is required for efficient chondrogenic differentiation. When implanted into a rat model of cartilage defect, this protein adhesive exhibited beneficial healing effects, as evidenced by enhanced chondrogenesis, sufficient ECM production, and lateral integration. Therefore, this engineered protein complex is a promising candidate for translational application in the field of cartilage repair.

High strength polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel fabricated by Cold-Drawn method for cartilage tissue substitutes

Poly (vinyl alcohol) (PVA) hydrogel has been considered as promising cartilage replacement materials due to its excellent characteristics such as high water content, low frictional behavior and excellent biocompatibility. However, lack of sufficient mechanical properties and cytocompatibility are two key obstacles for PVA hydrogel to be applied as cartilage substitutes. Herein, Polyacrylic acid (PAA) has been introduced into PVA hydrogel to balance these problems. Compared with pure PVA hydrogel, PVA/PAA hydrogel has the equal excellent biocompatibility, and its cell adhesion is significantly improved. In order to further improve the mechanical properties of hydrogels, Cold-Drawn treatment of hydrogels is performed in this paper. Compared to pure 12% PVA hydrogel, 40.8-fold, 50.8-fold, and 46.8-fold increase in tensile strength, tensile modulus, and toughness, respectively, which can be obtained from 12% PVA/PAA Cold-Drawn hydrogel. These biocompatible composite hydrogels have a great application potential as cartilage tissue substitutes.

Nanoscale zero-valent iron (nZVI) immobilization onto graphene oxide (GO)-incorporated electrospun polyvinylidene fluoride (PVDF) nanofiber membrane for groundwater remediation via gravity-driven membrane filtration

Nanoscale zero-valent iron (nZVI), with its high reactivity towards a broad range of contaminants, has been a promising material for groundwater remediation. Membrane-supported nZVI can both avoid nZVI agglomeration for better reactivity and recycle nZVI to lower the risk of secondary pollution. In this study, we successfully fabricated a PVDF-GO membrane via electrospinning technology and employed the functionalized nanofiber membrane to immobilize nZVI particles. The addition of GO into PVDF nanofibers can both increase the hydrophilicity to improve membrane flux and offer -COOH as a binder to immobilize nZVI particles. PVDF-GO-nZVI membranes with different GO loadings (0%, 0.5%, 1%, 3% of PVDF) were tested with two typical nZVI-targeted contaminants (Cd(II) and trichloroethylene (TCE)) via gravity-driven membrane filtration. The results show that membrane with 1% GO had the best nZVI distribution against the aggregation and a better performance in both Cd removal (100%) and TCE removal (82%). The nZVI membrane had a high flux in gravity-driven filtration at 255 LMH for Cd(II) and 265 LMH for TCE respectively. Generally, the developed PVDF-GO-nZVI electrospun nanofiber membrane had an excellent performance in the gravity-driven membrane filtration system for groundwater remediation.

Applications of Hydrogels with Special Physical Properties in Biomedicine

As a polymer matrix containing a large amount of water, hydrogels have been widely used in many fields such as biology and medicine due to its similarity to extracellular matrix components, and its contact with blood, body fluids, and human tissue does not affect the metabolic processes of living organisms. However, due to the lack of unique physical properties of traditional polymer hydrogels, its further application in the high-end field is limited. With the progress of study, a series of hydrogels with special structures, such as double network hydrogel, composite hydrogel, Tetra-PEG gel, and topological gel, have improved the situation to a large extent. At the same time, the progress of research on the biocompatibility and biodegradability of hydrogels, which are expected to be used in biomedical fields, is also worthy of attention. This review introduces four such types of high-strength polymeric hydrogels and the mechanisms for improving their mechanical strength. Moreover, a discussion will be made around specific methods for imparting special physical properties to hydrogels and applications in the field of biomedicine such as cell culture, medical surgery, tissue engineering, and biosensing. At the end of the review, the main reasons and contradictions for the limits of the current applications are explained. An outlook on the future research in related fields and the importance of carrying out research in this area to promote medical progress are emphasized.

Tissue Engineering Strategies for Osteochondral Repair

Tissue engineering strategies have been pushing forward several fields in the range of biomedical research. The musculoskeletal field is not an exception. In fact, tissue engineering has been a great asset in the development of new treatments for osteochondral lesions. Herein, we overview the recent developments in osteochondral tissue engineering. Currently, the treatments applied in a clinical scenario have shown some drawbacks given the difficulty in regenerating a fully functional hyaline cartilage. Among the different strategies designed for osteochondral regeneration, it is possible to identify cell-free strategies, scaffold-free strategies, and advanced strategies, where different materials are combined with cells. Cell-free strategies consist in the development of scaffolds in the attempt to better fulfill the requirements of the cartilage regeneration process. For that, different structures have been designed, from monolayers to multilayered structures, with the intent to mimic the osteochondral architecture. In the case of scaffold-free strategies, they took advantage on the extracellular matrix produced by cells. The last strategy relies in the development of new biomaterials capable of mimicking the extracellular matrix. This way, the cell growth, proliferation, and differentiation at the lesion site are expedited, exploiting the self-regenerative potential of cells and its interaction with biomolecules. Overall, despite the difficulties associated with each approach, tissue engineering has been proven a valuable tool in the regeneration of osteochondral lesions and together with the latest advances in the field, promises to revolutionize personalized therapies.

Hydrogels for Cartilage Regeneration, from Polysaccharides to Hybrids

The aims of this paper are: (1) to review the current state of the art in the field of cartilage substitution and regeneration; (2) to examine the patented biomaterials being used in preclinical and clinical stages; (3) to explore the potential of polymeric hydrogels for these applications and the reasons that hinder their clinical success. The studies about hydrogels used as potential biomaterials selected for this review are divided into the two major trends in tissue engineering: (1) the use of cell-free biomaterials; and (2) the use of cell seeded biomaterials. Preparation techniques and resulting hydrogel properties are also reviewed. More recent proposals, based on the combination of different polymers and the hybridization process to improve the properties of these materials, are also reviewed. The combination of elements such as scaffolds (cellular solids), matrices (hydrogel-based), growth factors and mechanical stimuli is needed to optimize properties of the required materials in order to facilitate tissue formation, cartilage regeneration and final clinical application. Polymer combinations and hybrids are the most promising materials for this application. Hybrid scaffolds may maximize cell growth and local tissue integration by forming cartilage-like tissue with biomimetic features.

Biomimetically Reinforced Polyvinyl Alcohol-Based Hybrid Scaffolds for Cartilage Tissue Engineering

Articular cartilage has a very limited regeneration capacity. Therefore, injury or degeneration of articular cartilage results in an inferior mechanical stability, load-bearing capacity, and lubrication capability. Here, we developed a biomimetic scaffold consisting of macroporous polyvinyl alcohol (PVA) sponges as a platform material for the incorporation of cell-embedded photocrosslinkable poly(ethylene glycol) diacrylate (PEGDA), PEGDA-methacrylated chondroitin sulfate (PEGDA-MeCS; PCS), or PEGDA-methacrylated hyaluronic acid (PEGDA-MeHA; PHA) within its pores to improve in vitro chondrocyte functions and subsequent in vivo ectopic cartilage tissue formation. Our findings demonstrated that chondrocytes encapsulated in PCS or PHA and loaded into macroporous PVA hybrid scaffolds maintained their physiological phenotypes during in vitro culture, as shown by the upregulation of various chondrogenic genes. Further, the cell-secreted extracellular matrix (ECM) improved the mechanical properties of the PVA-PCS and PVA-PHA hybrid scaffolds by 83.30% and 73.76%, respectively, compared to their acellular counterparts. After subcutaneous transplantation in vivo, chondrocytes on both PVA-PCS and PVA-PHA hybrid scaffolds significantly promoted ectopic cartilage tissue formation, which was confirmed by detecting cells positively stained with Safranin-O and for type II collagen. Consequently, the mechanical properties of the hybrid scaffolds were biomimetically reinforced by 80.53% and 210.74%, respectively, compared to their acellular counterparts. By enabling the recapitulation of biomimetically relevant structural and functional properties of articular cartilage and the regulation of in vivo mechanical reinforcement mediated by cell⁻matrix interactions, this biomimetic material offers an opportunity to control the desired mechanical properties of cell-laden scaffolds for cartilage tissue regeneration.

In vitro development and evaluation of a polyacrylic acid-silicone device intended for gradual occlusion of portosystemic shunts in dogs and cats

OBJECTIVE

To develop a device intended for gradual venous occlusion over 4 to 6 weeks.

SAMPLE

Silicone tubing filled with various inorganic salt and polyacrylic acid (PAA) formulations and mounted within a polypropylene or polyether ether ketone (PEEK) outer ring.

PROCEDURES

15 polypropylene prototype rings were initially filled with 1 of 5 formulations and placed in PBSS. In a second test, 10 polypropylene and 7 PEEK prototype rings were filled with 1 formulation and placed in PBSS. In a third test, 2 formulations were loaded into 6 PEEK rings each, placed in physiologic solution, and incubated. In all tests, ring luminal diameter, outer diameter, and luminal area were measured over 6 weeks.

RESULTS

In the first test, 2 formulations had the greatest changes in luminal area and diameter, and 1 of those had a greater linear swell rate than the other had. In the second test, 6 of 7 PEEK rings and 6 of 10 polypropylene rings closed to a luminal diamater < 1 mm within 6 weeks. Polypropylene rings had a greater increase in outer diameter than did PEEK rings between 4.5 and 6 weeks. In the third test, 11 of 12 PEEK rings gradually closed to a luminal diameter < 1 mm within 6 weeks.

CONCLUSIONS AND CLINICAL RELEVANCE

A PAA and inorganic salt formulation in a prototype silicone and polymer ring resulted in gradual occlusion over 4 to 6 weeks in vitro. Prototype PEEK rings provided more reliable closure than did polypropylene rings.

Spatially organized differentiation of mesenchymal stem cells within biphasic microparticle-incorporated high cell density osteochondral tissues

Giving rise to both bone and cartilage during development, bone marrow-derived mesenchymal stem cells (hMSC) have the unique capacity to generate the complex tissues of the osteochondral interface. Utilizing a scaffold-free hMSC system, biphasic osteochondral constructs are incorporated with two types of growth factor-releasing microparticles to enable spatially organized differentiation. Gelatin microspheres (GM) releasing transforming growth factor-β1 (TGF-β1) combined with hMSC form the chondrogenic phase. The osteogenic phase contains hMSC only, mineral-coated hydroxyapatite microparticles (MCM), or MCM loaded with bone morphogenetic protein-2 (BMP-2), cultured in medium with or without BMP-2. After 4 weeks, TGF-β1 release from GM within the cartilage phase promotes formation of a glycosaminoglycan- and type II collagen-rich matrix, and has a local inhibitory effect on osteogenesis. In the osteogenic phase, type X collagen and osteopontin are produced in all conditions. However, calcification occurs on the outer edges of the chondrogenic phase in some constructs cultured in media containing BMP-2, and alkaline phosphatase levels are elevated, indicating that BMP-2 releasing MCM provides better control over region-specific differentiation. The production of complex, stem cell-derived osteochondral tissues via incorporated microparticles could enable earlier implantation, potentially improving outcomes in the treatment of osteochondral defects.