HA-based Biomaterials Research Articles

The Incorporation of Zinc into Hydroxyapatite and Its Influence on the Cellular Response to Biomaterials: A Systematic Review.

Zinc is known for its role in enhancing bone metabolism, cell proliferation, and tissue regeneration. Several studies proposed the incorporation of zinc into hydroxyapatite (HA) to produce biomaterials (ZnHA) that stimulate and accelerate bone healing. This systematic review aimed to understand the physicochemical characteristics of zinc-doped HA-based biomaterials and the evidence of their biological effects on osteoblastic cells. A comprehensive literature search was conducted from 2022 to 2024, covering all years of publications, in three databases (Web of Science, PUBMED, Scopus), retrieving 609 entries, with 36 articles included in the analysis according to the selection criteria. The selected studies provided data on the material's physicochemical properties, the methods of zinc incorporation, and the biological effects of ZnHA on bone cells. The production of ZnHA typically involves the wet chemical synthesis of HA and ZnHA precursors, followed by deposition on substrates using processes such as liquid precursor plasma spraying (LPPS). Characterization techniques confirmed the successful incorporation of zinc into the HA lattice. The findings indicated that zinc incorporation into HA at low concentrations is non-cytotoxic and beneficial for bone cells. ZnHA was found to stimulate cell proliferation, adhesion, and the production of osteogenic factors, thereby promoting in vitro mineralization. However, the optimal zinc concentration for the desired effects varied across studies, making it challenging to establish a standardized concentration. ZnHA materials are biocompatible and enhance osteoblast proliferation and differentiation. However, the mechanisms of zinc release and the ideal concentrations for optimal tissue regeneration require further investigation. Standardizing these parameters is essential for the effective clinical application of ZnHA.

The Effect of Doping on the Electrical and Dielectric Properties of Hydroxyapatite for Medical Applications: From Powders to Thin Films.

Recently, the favorable electrical properties of biomaterials have been acknowledged as crucial for various medical applications, including both bone healing and growth processes. This review will specifically concentrate on calcium phosphate (CaP)-based bioceramics, with a notable emphasis on hydroxyapatite (HA), among the diverse range of synthetic biomaterials. HA is currently the subject of extensive research in the medical field, particularly in dentistry and orthopedics. The existing literature encompasses numerous studies exploring the physical-chemical, mechanical, and biological properties of HA-based materials produced in various forms (i.e., powders, pellets, and/or thin films) using various physical and chemical vapor deposition techniques. In comparison, there is a relative scarcity of research on the electrical and dielectric properties of HA, which have been demonstrated to be essential for understanding dipole polarization and surface charge. It is noteworthy that these electrical and dielectric properties also offer valuable insights into the structure and functioning of biological tissues and cells. In this respect, electrical impedance studies on living tissues have been performed to assess the condition of cell membranes and estimate cell shape and size. The need to fill the gap and correlate the physical-chemical, mechanical, and biological characteristics with the electrical and dielectric properties could represent a step forward in providing new avenues for the development of the next-generation of high-performance HA-doped biomaterials for future top medical applications. Therefore, this review focuses on the electrical and dielectric properties of HA-based biomaterials, covering a range from powders and pellets to thin films, with a particular emphasis on the impact of the various dopants used. Therefore, it will be revealed that each dopant possesses unique properties capable of enhancing the overall characteristics of the produced structures. Considering that the electrical and dielectric properties of HA-based biomaterials have not been extensively explored thus far, the aim of this review is to compile and thoroughly discuss the latest research findings in the field, with special attention given to biomedical applications.

Molecular weight of hyaluronic acid crosslinked into biomaterial scaffolds affects angiogenic potential.

While hyaluronic acid (HA)-based hydrogels have been used clinically for decades, the mechanisms by which HA exerts molecular weight-dependent bioactivity and how chemical modification and crosslinking may affect molecular weight-dependent bioactivity remain poorly understood. This knowledge gap presents a significant barrier to designing HA hydrogels with predictable bioactivities. As HA has been widely reported to have molecular weight-dependent effects on endothelial cells (ECs), we investigated how the molecular weight of HA in either soluble or crosslinked forms affects angiogenesis and interrogated CD44 clustering on the surface of endothelial cells as a candidate mechanism for these affects. Using soluble HA, our results show high molecular weight (HMW) HA, but not low molecular weight (LMW) HA, increased viability and tube formation in cultured human cerebral microvascular ECs (HCMVECs). No size of HA affected proliferation. When HCMVECs were cultured with crosslinked HA of varying molecular weights in the form of HA-based microporous annealed particle scaffold (HMAPS), the cell response was comparable to when cultured with soluble HA. Similarly, when implanted subcutaneously, HMAPS with HMW HA were more vascularized than those with LMW HA. We also show that antibody-mediated CD44 clustering resulted in HCMVECs with increased viability and tube-like structure formation in a manner comparable to exposure to HMW HA, suggesting that HMW acts through CD44 clustering. STATEMENT OF SIGNIFICANCE: Biomaterials based on hyaluronic acid (HA), a bioactive extracellular matrix polysaccharide, have been used in clinical products for several years. Despite the knowledge that HA molecular weight heavily influences its bioactivity, molecular weight has been largely ignored in the development of HA-based biomaterials. Given the high viscosity of high molecular weight HA typically found in native tissues, lower molecular weight polysaccharides have been used most commonly for biomaterial fabrication. By comparing the ability of injectable, microporous annealed particle scaffolds (MAPS) fabricated from variably sized HA to promote angiogenesis, this study demonstrates that MAPS with high molecular weight HA better support vascularization, likely through an unique ability to induce clustering of CD44 receptors on endothelial cells.

Temporal characterization of hyaluronidases after peripheral nerve injury.

Hyaluronic acid (HA) is ubiquitously found in biological tissues and mediates wound healing mechanisms after injury by promoting cell migration and proliferation. With the development of tissue-engineered neural therapeutics, including off-the-shelf grafts for peripheral nerve repair, HA is an attractive material for clinical use because of its various biological roles. HA-based biomaterials have been carefully engineered to elicit specific in vivo host responses, however an important design feature that should be considered in these scaffolds is endogenous degradation. Hyaluronidases (HYALs) are the complementary enzymes that are responsible for HA turnover. Although HYAL expression has been widely characterized in various tissues, including the central nervous system, and for different pathologies, there remains a lack of knowledge of HYAL mediated turnover in peripheral nerve tissue. In this work, gene expression of two hyaluronidases, HYAL1 and HYAL2, and HA-binding receptor, CD44, were studied in two injury models: rat sciatic nerve crush and critical gap transection. HYAL2 and CD44 were shown to be upregulated 3 days after crush injury, whereas HYAL1 was upregulated at 3 weeks, which collectively demonstrate temporal patterning of HA breakdown. Additionally, differences were observed between HYAL and HA expression at 3 weeks when compared for both nerve injury models. The activity of HYAL in peripheral nerve tissue was determined to be approximately 0.11 μmol/min, which could be used to further model HA-based biomaterial breakdown for peripheral nerve applications. Overall, this work provides a landscape of HA turnover in peripheral nerve that can be used for future neural applications.

Systemic rifampicin shows accretion to locally implanted hydroxyapatite particles in a rat abdominal muscle pouch model.

Introduction: biomaterials combined with antibiotics are routinely used for the management of bone infections. After eluting high concentrations of antibiotics during the first week, sub-inhibitory concentrations of antibiotics may lead to late repopulation of recalcitrant bacteria. Recent studies have shown that systemically given antibiotics like tetracycline and rifampicin (RIF) could seek and bind to locally implanted hydroxyapatite (HA). The aim of this in vivo study was to test if systemically administered rifampicin could replenish HA-based biomaterials with or without prior antibiotic loading to protect the material from late bacterial repopulation. Methods: in vivo accretion of systemically administered RIF to three different types of HA-based materials was tested. In group 1, nano (n)- and micro (m)-sized HA particles were used, while group 2 consisted of a calcium sulfate hydroxyapatite (CaS HA) biomaterial without preloaded antibiotics gentamycin (GEN) or vancomycin (VAN), and in group 3, the CaS HA material contained GEN (CaS HA GEN) or VAN (CaS HA VAN). The above materials were implanted in an abdominal muscle pouch model in rats, and at 7 d post-surgery, the animals were assigned to a control group (i.e., no systemic antibiotic) and a test group (i.e., animals receiving one single intraperitoneal injection of RIF each day (4 mgper rat) for 3 consecutive days). Twenty-four hours after the third injection, the animals were sacrificed and the implanted pellets were retrieved and tested against Staphylococcus aureus ATCC 25923 in an agar diffusion assay. After overnight incubation, the zone of inhibition (ZOI) around the pellets were measured. Results: in the control group, CaS HA GEN pellets had a ZOI, while all other harvested pellets had no ZOI. No pellets from animals in test group 1 had a ZOI. In test group 2, CaS HA pellets showed a ZOI. In test group 3, CaS HA GEN and CaS HA VAN pellets showed a ZOI. Conclusions: in this proof-of-concept study, we have shown that a locally implanted biphasic CaS HA carrier after 1 week can be loaded by systemic RIF administration and exert an antibacterial effect. Further in vivo infection models are necessary to validate our findings.

Embryotoxicity and visual-motor response of functionalized nanostructured hydroxyapatite-based biomaterials in zebrafish (Danio rerio)

Hydroxyapatite (HA) is a biomaterial widely used in biomedical applications. Many studies have shown that ionic substituents can be incorporated into HA to produce a mineral composition more similar to natural bone tissue with more favorable biological characteristics for application in bone regeneration. However, its potentially toxic effects need to be evaluated before full approval for human use. For this purpose, an embryotoxicity test was performed on zebrafish according to OECD guideline 236. Zebrafish embryos were exposed to 1 or 3 microspheres of alginate containing nanoparticles of HA and carbonate (CHA), strontium (SrHA), and zinc-substituted HA (ZnHA) from 4 to 120 h post-fertilization (hpf). Lethality and developmental endpoints were evaluated. In addition, larval behavior at 168 hpf was also analyzed to observe whether biomaterials adversely affect optomotor and avoidance responses (neurotoxicity), as well as the oxidative stress pattern through qPCR. After 120 h exposure to all microspheres with different patterns of crystallinity, porosity, nanoparticle size, surface area, and degradation behavior, there was no mortality rate greater than 20%, indicating the non-embryotoxic character of these biomaterials. All experimental groups showed positive optomotor and avoidance responses, which means that embryo exposure to the tested biomaterials had no neurotoxic effects. Furthermore, larvae exposed to one SrHA microsphere showed a better optomotor response than the control. Furthermore, the biomaterials did not change the pattern of mRNA levels of genes related to oxidative stress even after 120 hpf. The growing number of new HA-based biomaterials produced should be accompanied by increased studies to understand the biosafety of these compounds, especially in alternative models, such as zebrafish embryos. These results reinforce our hypothesis that ion-substituted HA biomaterials do not impose toxicological effects, cause development and neuromotor impairment, or increase oxidative stress in zebrafish embryos being useful for medical devices and in the process of bone regeneration.

Dynamic covalent crosslinked hyaluronic acid hydrogels and nanomaterials for biomedical applications.

Hyaluronic acid (HA), one of the main components of the extracellular matrix (ECM), is extensively used in the design of hydrogels and nanoparticles for different biomedical applications due to its critical role in vivo, degradability by endogenous enzymes, and absence of immunogenicity. HA-based hydrogels and nanoparticles have been developed by utilizing different crosslinking chemistries. The development of such crosslinking chemistries indicates that even subtle differences in the structure of reactive groups or the procedure of crosslinking may have a profound impact on the intended mechanical, physical and biological outcomes. There are widespread examples of modified HA polymers that can form either covalently or physically crosslinked biomaterials. More recently, studies have been focused on dynamic covalent crosslinked HA-based biomaterials since these types of crosslinking allow the preparation of dynamic structures with the ability to form in situ, be injectable, and have self-healing properties. In this review, HA-based hydrogels and nanomaterials that are crosslinked by dynamic-covalent coupling (DCC) chemistry have been critically assessed.

Hyaluronic acid as a bioactive component for bone tissue regeneration: Fabrication, modification, properties, and biological functions

Abstract Hyaluronic acid (HA) is widely distributed in the human body, and it is heavily involved in many physiological functions such as tissue hydration, wound repair, and cell migration. In recent years, HA and its derivatives have been widely used as advanced bioactive polymers for bone regeneration. Many medical products containing HA have been developed because this natural polymer has been proven to be nontoxic, noninflammatory, biodegradable, and biocompatible. Moreover, HA-based composite scaffolds have shown good potential for promoting osteogenesis and mineralization. Recently, many HA-based biomaterials have been fabricated for bone regeneration by combining with electrospinning and 3D printing technology. In this review, the polymer structures, processing, properties, and applications in bone tissue engineering are summarized. The challenges and prospects of HA polymers are also discussed.

The Role of Hyaluronic Acid in Intervertebral Disc Regeneration

Intervertebral disc (IVD) degeneration is a leading cause of low back pain worldwide, incurring a significant burden on the healthcare system and society. IVD degeneration is characterized by an abnormal cell-mediated response leading to the stimulation of different catabolic biomarkers and activation of signalling pathways. In the last few decades, hyaluronic acid (HA), which has been broadly used in tissue-engineering, has popularised due to its anti-inflammatory, analgesic and extracellular matrix enhancing properties. Hence, there is expressed interest in treating the IVD using different HA compositions. An ideal HA-based biomaterial needs to be compatible and supportive of the disc microenvironment in general and inhibit inflammation and downstream cascades leading to the innervation, vascularisation and pain sensation in particular. High molecular weight hyaluronic acid (HMW HA) and HA-based biomaterials used as therapeutic delivery platforms have been trialled in preclinical models and clinical trials. In this paper, we reviewed a series of studies focused on assessing the effect of different compositions of HA as a therapeutic, targeting IVD degeneration. Overall, tremendous advances have been made towards an optimal form of a HA biomaterial to target specific biomarkers associated with IVD degeneration, but further optimization is necessary to address regeneration.

In vitro bioactivity and osteoblast cell viability studies of hydroxyapatite-incorporated silica aerogel

Bioactivity and osteoblastic growth of hydroxyapatite (HA)-incorporated silica aerogels (SA) (HAESA) with different ratio of HA/SiO2 (0.1, 0.5, 1.0, and 1.3 HA/SiO2) were investigated. Bioactivity of HAESA was studied by immersing all samples in simulated body fluids (SBF) for 7 and 14 days. The recovered samples were then characterised using Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy combined with energy dispersive X-ray analyser (FESEM–EDX) and the analysis of phosphate loss in the solution. These samples were also investigated for their effect on cell viability and proliferation abilities against normal human osteoblast cells in vitro after 24 and 48 h of exposure times. The HA/SiO2 ratio affected its bioactivity in which the bioactivity increased to 0.5 (HAESA-0.5) and declined at higher ratios (1.0 and 1.3). A similar trend was observed for cell viability and proliferation assays. HAESA-0.5 (HA/SiO2 ratio of 0.5), which possesses the optimal characteristics of SA and HA, resulted in the highest osteoblastic growth due to the synergistic effects between SA and HA. Thus, HAESA-0.5 could be an alternative biomaterial compared to silica- and HA-based biomaterials for bone implant application due to its higher bioactivity in SBF with the improved performance of osteoblast growth. Hydroxyapatite-incorporated silica aerogel with different weight ratio of HA/SiO2 (HAESA) was studied for their bioactivity in simulated body fluid and in vitro osteoblastic growth.

Hyaluronic Acid: Incorporating the Bio into the Material.

In the last few decades, hyaluronic acid (HA) has become increasingly employed as a biomaterial in both clinical and research applications. The abundance of HA in many tissues, together with its amenability to chemical modification, has made HA an attractive material platform for a wide range of applications including regenerative medicine, drug delivery, and scaffolds for cell culture. HA has traditionally been appreciated to modulate tissue mechanics and remodeling through its distinctive biophysical properties and ability to organize other matrix proteins. However, HA can influence cell behavior in much more direct and specific ways by engaging cellular HA receptors, which can trigger signals that influence cell survival, proliferation, adhesion, and migration. In turn, cells modify HA by regulating synthesis and degradation through a dedicated arsenal of enzymes. Optimal design of HA-based biomaterials demands full consideration of these diverse modes of regulation. This review summarizes how HA-based signaling regulates cell behavior and discusses how these signals can be leveraged to create cell-instructive biomaterials.

Peptide-modified, hyaluronic acid-based hydrogels as a 3D culture platform for neural stem/progenitor cell engineering.

Neural stem/progenitor cell (NS/PC)-based therapies have shown exciting potential for regeneration of the central nervous system (CNS) and NS/PC cultures represent an important resource for disease modeling and drug screening. However, significant challenges limiting clinical translation remain, such as generating large numbers of cells required for model cultures or transplantation, maintaining physiologically representative phenotypes ex vivo and directing NS/PC differentiation into specific fates. Here, we report that culture of human NS/PCs in 3D, hyaluronic acid (HA)-rich biomaterial microenvironments increased differentiation toward oligodendrocytes and neurons over 2D cultures on laminin-coated glass. Moreover, NS/PCs in 3D culture exhibited a significant reduction in differentiation into reactive astrocytes. Many NS/PC-derived neurons in 3D, HA-based hydrogels expressed synaptophysin, indicating synapse formation, and displayed electrophysiological characteristics of immature neurons. While inclusion of integrin-binding, RGD peptides into hydrogels resulted in a modest increase in numbers of viable NS/PCs, no combination of laminin-derived, adhesive peptides affected differentiation outcomes. Notably, 3D cultures of differentiating NS/PCs were maintained for at least 70 days in medium with minimal growth factor supplementation. In sum, results demonstrate the use of 3D, HA-based biomaterials for long-term expansion and differentiation of NS/PCs toward oligodendroglial and neuronal fates, while inhibiting astroglial fates. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 704-718, 2019.

A comparative study of the dissolubility of pure and silicon substituted hydroxyapatite from density functional theory calculations.

Introduction of silicon into hydroxyapatite (HA) is one of the effective ways to modulate the bioactivity of HA-based biomaterials. The bulk and surface structures of silicate-substituted HA (Si-HA) were characterized by using density functional theory calculations. The energetically favorable structures were identified from a number of candidate structures. Particular attention was paid to the surface structures of Si-HA, whose bioactivity is closely relevant to their surface atoms. Compared to the surface of pure HA, the Si-HA surface has similar surface energy but different charge distribution. Under the implicit solvent model, the exposed calcium/oxygen atoms become more positive/negative in net charge, resulting in a considerable change in the surface electrostatic potential at van der Waals distances. However, changes in the dissolution of surface calcium ions are not remarkable, as depicted by their activation energy leaving from the surface. Our calculations reveal that the surface structures and properties of HA were changed to some extent by silicate substitution, which provides some hints for understanding the experimentally observed changes in bioactivity and biodegradability of Si-HA that still remain controversial in many aspects.

Synthesis and characterization of hyaluronic acid hydrogels crosslinked using a solvent-free process for potential biomedical applications

Hyaluronic acid (HA) is a natural linear polysaccharide that has been used extensively in the biomedical field as it is a biocompatible, biodegradable, nontoxic and non-immunogenic polymer with high water affinity. Besides, the presence of multiple acid and hydroxyl groups in the HA molecule makes it an ideal candidate for chemical modification. The present paper describes the synthesis and characterization of HA-based hydrogels. For this purpose, aqueous mixtures containing 5% (w/w) of HA and different concentrations of Gantrez S97 (GAN) (1, 3 and 5% w/w) were used to prepare HA-based hydrogels. The mixtures were dried and the hydrogels were obtained after heating the solid material at 80°C for 24h. GAN is the acid form of an methylvinylether and maleic anhydride copolymer and contains multiple acid groups that can form ester bonds when reacting with the multiple hydroxyl groups present in HA chains. The method described here present potential to be applied for the preparation of HA-based biomaterials with a defined form as the crosslinking reaction between HA and the crosslinker takes place in solid phase. Besides, the method can be considered an environmental-friendly process as no organic solvents or potentially toxic substances were used. The esterification reaction was confirmed by infrared spectroscopy and dynamic scanning calorimetry measurements. The loading and release capabilities of the hydrogels were evaluating by using methylene blue (MB) as a model molecule. The hydrogels showed a high affinity for MB showing loadings up to 0.35mg MB per mg of hydrogel. Moreover, the hydrogels were capable of sustaining the MB release over two days. The use of microwave radiation was evaluated to reduce the crosslinking time from 24h to 1h, but this procedure needs to be optimized in future studies. As the crosslinking procedure takes place in solid state, the HA/GAN hydrogels were used to prepare micro-engineered device, microneedle arrays. Finally, the antimicrobial properties of the hydrogels were evaluated. The results showed that the hydrogels presented anti-infective properties.

Hyaluronan size alters chondrogenesis of adipose-derived stem cells via the CD44/ERK/SOX-9 pathway.

HA-based biomaterials have been studied in stem cell-based articular cartilage tissue engineering. However, little is known about the optimal HA size for stem cell chondrogenesis and the mechanism of how HA size modulates stem cell chondrogenesis. Accordingly, we used HAs with various Mws (80-2000 kDa) as culture substrates and tested their chondrogenic effect on ADSCs. Our results demonstrated that HAs with a Mw of 2000 kDa showed the optimal effect for chondrogenesis of ADSCs. Moreover, we found that HA size can regulate ADSC chondrogenesis via the CD44/ERK/SOX-9 pathway. This finding provides new information regarding the biochemical control of chondrogenesis by HA substrates that may add value to the development of HA-based biomaterials for articular cartilage regeneration.

Influence of hydroxyapatite granule size, porosity, and crystallinity on tissue reaction invivo. Part B: a comparative study with biphasic synthetic biomaterials.

The aim of this study was to compare the influence of the physical-chemical properties of synthetic hydroxyapatite (HA) and biphasic commercial materials on the biological behavior of study materials through material characterization and SEM analysis before and after application in rabbit tibias. Two defects were performed in each tibiae for a total of 180 defects: Group I HA granules (2000-4000μm), Group II HA granules (1000-2000μm), Group III HA granules (600-1000μm), Group IV Ossceram® nano (Bredent medical GmbH & Co. KG, Senden, Germany), Group V 4Bone® granules (MIS Implants Technologies Ltd, Shlomi, Israel), and Group VI: empty defect acted as control. Comparison was performed by mean of material characterization, SEM, and EDX. 4Bone: Pores between 300μm and 100μm with intra- and interparticle spaces. Ossceram show also interparticle and intraparticle pores, between 100μm and 26μm, but the proportion of interparticles in the 4Bone is clearly minor than in the Ossceram. Related with pure HA, Group III has the greatest porosity (69.3%). For Group I, the intraparticle pores (0.71μm) are about 8 times larger than those of the other two samples. The analysis of the images of invivo SEM shown as biphasic groups has presented a more gradual resorption of the material. HA-based biomaterials, both pure and biphasic, are an effective means for bone regeneration processes; of these, materials with higher initial and secondary porosimetry allow greater cell colonization and therefore more effective substitution by new bone. The two-phase materials have a higher ion release to the environment in the early stages and thus allow greater colonization by collagen fibers that can be matured into new bone.

Influence of hydroxyapatite granule size, porosity, and crystallinity on tissue reaction invivo. Part A: synthesis, characterization of the materials, and SEM analysis.

The aim of this study was the synthesis and analysis of the tissue reaction to three different Hydroxyapatite (HA)-based bone substitute materials differing only in granule size, porosity, and crystallinity through an animal experimental model at 60days. Three different HA-based biomaterials were synthesized and characterized by X-ray diffraction, SEM, and EDS analysis, the resultant product was ground in three particle sizes: Group I (2000-4000μm), Group II (1000-2000μm), and Group III (600-1000μm). Critical size defects were created in both tibias of 15 rabbits. Four defects per rabbit for a total of 60 defects were grafted with the synthesized materials as follows: Group I (15 defects), Group II (15 defects), Group III (15 defects), and empty (15 defects control). After animals sacrifice at 60days samples were obtained and processed for SEM and EDS evaluation of Ca/P ratios, elemental mapping was performed to determine the chemical degradation process and changes to medullary composition in all the four study groups. The tendency for the density was to increase with the increasing annealing temperature; in this way it was possible to observe that the sample that shows highest crystallinity and crystal size corresponding to that of group I. The SEM morphological examination showed that group III implant showed numerous resorption regions, group II implant presented an average resorption rate of all the implants. The group I displayed smoother surface features, in comparison with the other two implants. The data from this study show that changing the size, porosity, and crystallinity of one HA-based bone substitute material can influence the integration of the biomaterials within the implantation site and the new bone formation.

Biomaterials for cartilage regeneration.

Osteoarthritis (OA), rheumatoid arthritis (RA) or cartilage damage resulting from severe injuries are among the most prevalent chronic conditions that may lead to disability, resulting in high healthcare costs and a major economic burden to society.1 Current articular or hyaline cartilage repair therapies include nonsteroidal anti-inflammatory drugs, such as cyclooxygenase-2 inhibitors, for pain relief; chondroprotective agents to stimulate chondrogenesis and chondrocyte synthesis of collagen and proteoglycans (eg, hyaluronan, chondroitin sulfate, glucosamine);2 and surgical approaches (eg, microfracture, mosaicplasty, osteochondral autologous transplantation, autologous chondrocyte implantation, matrix-induced autologous chondrocyte implantation).3,4 The major challenge in selecting a cartilage regeneration technique for clinical applications is to find a method that demonstrates significant advantage over the others for improving joint function. However, so far, clinical outcomes have not produced histologically comparable cartilage that mimics the complex zonal architecture of native hyaline cartilage with optimal long-term implications.4-7 Ideally, cartilage regeneration techniques must be cost effective, single stage, and patient friendly.4 Biomaterials are an interesting choice because they not only provide in situ three dimensional space-filing properties to facilitate regeneration in medium- or large-sized cartilage defects, but they also can be tailored to increase cell-anchorage sites by incorporating biophysical/biochemical cues for cell guidance.1,5 In addition, mechanical compatibility is another crucial criterion that plays an integral role in stimulating chondrocytes to deposit cartilaginous extracellular matrix (ECM). Therefore, scaffolds are valuable in maintaining the mechanical integrity of constructs during the regeneration process. Furthermore, functional scaffolds have been designed to induce chondrogenic differentiation through a cascade of signaling events and regulatory cytokines.1 All of these key factors demonstrate that biomaterials possess advantageous characteristics that set them apart from other competitors in the field of articular cartilage regeneration. Biomaterials for Cartilage Regeneration Research on tissue-engineered products for hyaline cartilage regeneration is ongoing. In 2011, the market size of surgical procedures for cartilage regeneration reached €25 billion (US$33.5 billion) worldwide.8 In the United States alone, 250,000 to 300,000 symptomatic cartilage injuries receive surgical treatment every year; 70% of these injuries are treated with lavage/débridement, 20% with microfracture, and 10% with other methods (eg, autologous chondrocyte implantation, allografts, autografts).9,10 To date, collagen, alginate, fibrin, chitosan, hyaluronic acid (HA), and synthetic polymers have been the main components of commercial products used for cartilage regeneration. Therefore, based on their success rate, collagen-based scaffolds, commercially known as Carticel (collagen I/III; Genzyme) and CaReS (collagen I; Arthrokinetics) have been widely used to improve the structural and biologic performance of grafts.11,12 HA alone as a chondroprotective agent has excellent viscoelastic properties, with the ability to promote chondrocyte phenotype via CD44 molecular markers; nonetheless, when injected into the defect site, it degrades rapidly. However, commercially available HA-based biomaterials, including Hyalograft-C (Anika Therapeutics) and Hyalgan (Fidia Pharma), have been shown to promote the regeneration of cartilage with improved mobility.5,13 Cartipatch (Xizia Biotech), composed of alginate/agarose hydrogel, has been clinically proven to regenerate hyaline cartilage.14 In addition, synthetic polymers, such as the TruFit plug (composed of poly[lactic-co-glycolic acid]/calcium sulfate/polyglycolic acid [PGA] fibers; Smith & Nephew) and Chondrotissue (composed of PGA/HA sponge; BioTissue) have been used for filling osteochondral defects with satisfactory outcomes. All the above-mentioned commercial products are approved by the FDA and the Medical Devices Directorate in the EU. Unmet Expectations of Biomaterials and Future Perspectives Biomaterials are designed to be flexible in order to take the shape and size of the defect site upon implantation or injection.5 Apart from satisfying the fundamental requirement of biocompatibility, scaffolds must also mimic the in-depth heterogeneity of native cartilage and simultaneously promote cell adhesion, proliferation, and ECM deposition in situ.15 Hydrogels and sponges have been shown to have interconnected pores or fibers (optimum pore size, 150 to 250 µm),16 through which diffusion of nutrients and other biologic signaling molecules can facilitate complete integration with the host cartilage and subchondral bone.17 Lack of integration may deteriorate regenerated cartilage.18 In addition, altering mechanical properties (including strength, stiffness, and roughness) has also been shown to have an effect on the stability of the scaffold.19,20 Various studies have shown cell-seeded scaffolds to aid deposition of cartilaginous ECM; however, lack of maturation has led to inferior qualities and subsequent clinical failure. Summary Although researchers have been successful in restoring the surface of articular cartilage via preloaded growth factors (eg, transforming growth factor–β) and cells in situ, constructing fully functional cartilage is still in progress.21 Henceforth, using extrinsic biologic, chemical, structural, and mechanical cues, intensive research is now under way to fabricate new biologically inspired materials.19 If these fundamental parameters are met, tissue engineered scaffolds will be able to restore cartilage functions more efficiently and effectively for clinical applications.

Synthesis and Characterization of Hyaluronic Acid for Biomedical Application

Hyaluronic acid is a linear polysaccharide composed of glucuronic acid and N-acetylglucosamine. HA-based biomaterials secure wide-range applications in the healthcare industry. The material is found in cartilage, skin, umbilical cord, synovial fluid, as well as in the cell wall of bacteria such a Streptococcus zooepidemicus. As a consequence of these wide applications, HA production from microbial fermentation is receiving increased attention for avoiding the risk of cross-species viral infection, to have lower production cost and to favor a more efficient purification. The molecular weight is increased by adding poly-γ-glutamic acid, which inhibits hyaluronidase of medium, and the degree of purity is enhanced by a purification process using the means of dialysis membrane and organic solvent.

Preservation of Viscoelastic Properties of Rabbit Vocal Folds after Implantation of Hyaluronic Acid‐Based Biomaterials

To compare the rheological characteristics of structurally different hyaluronic acid (HA)-based biomaterials that are presently used for phonosurgery and to investigate their influence on the viscoelastic properties of vocal folds after implantation in an in vivo rabbit model. In vitro and in vivo rheometric investigation. Experimental laboratory, Inha and Seoul National Universities. Viscoelastic shear properties of 3 HA-based biomaterials (Rofilan, Restylane, and Reviderm) were measured with a strain-controlled rheometer. These biomaterials were injected into the deep layers of rabbit vocal folds, and viscoelastic moduli of the injected vocal folds were determined 2 months after the injection. The vocal fold specimens were observed using a light microscope and a transmission electron microscope. All HA-based biomaterials showed similar levels of shear viscosity, which were slightly higher than that of human vocal folds reported in previous studies. Compared with noninjected control vocal folds, there were no significant differences in the magnitudes of both elastic shear modulus (G') and viscous modulus (G") of injected vocal folds among all of the materials. Light microscopic images showed that all materials were observed in the deep layers of vocal folds and electron scanning images revealed that injected HA particles were homogeneously distributed in regions of collagenous fibers. HA-based biomaterials could preserve the viscoelastic properties of the vocal folds, when they were injected into vocal folds in an in vivo rabbit model. However, further studies on the influence of the biomaterials on the viscoelasticity of human vocal folds in ECM surroundings are still needed.