Poly(lactic-co-glycolic acid) Microspheres as an Injectable Scaffold for Cartilage Tissue Engineering

Injectable testosterone PLGA microsphere with different characteristics: effect of preparation method (paddle mixing versus microfluidic device)

The purpose of this study was to compare the characteristics of testosterone polylactic-co-glycolic (PLGA) microspheres prepared by a paddle mixer or microfluidics device. The comparison was conducted by not only in vitro evaluation but also in vivo evaluation which has not been reported up to date. We discovered that, among the steps in microsphere preparation, the solvent removal process strongly impacted drug content, particle size and surface morphology. Spectroscopic measurements suggested that molecular interactions and crystallinity of the drug incorporated in the microspheres differed. For the drug release profile, although both mixer- and microfluidics-prepared samples showed similar sustained release of the incorporated drug for approximately one month in vitro, they exhibited different plasma concentration profiles in vivo. Together, our findings show that the preparation process, especially the solvent removal process, may affect the physicochemical characteristics of testosterone PLGA microspheres, leading to different in vivo performance.

Dexamethasone loaded injectable, self-healing hydrogel microspheresbased on UPy-functionalized Gelatin/ZnHAp physical network promotes bone regeneration

Biopolymer-based injectable hydrogels provide great potential as bone tissue engineering (BTE) scaffolds on account of biocompatibility, and pore interconnectivity that enables delivery of cells and/or signaling molecules for bone repair. Recently, Gelatin hydrogels based on H-bonds were considered in response to concerns around the chemical crosslinking agents. In this study, a self-healing gelatin hydrogel with remarkable compressive and self-healing properties was prepared via formation of quadruple hydrogen bonds between ureidopyrimidinon functional groups, which were substituted on NH₂ groups of gelatin(GelUPy). Degree of substitution controls properties of the resulting hydrogel from a shape- memory hydrogel (100% substitution), to a hydrogel (about 80%), to this self-healing hydrogel (about 40%). We report a strategy that adopts an emulsion synthesis approach to delivery of dexamethasone and Ca/Zn ions from injectable self-healing GelUPy hydrogel (GelUPy-ZnHApUPy-DEX), to induce osteogenic differentiation of adipose-derived stem cells, in vitro, and enhance bone regeneration in a cranial bone defect in a rat model. We show that key properties of the composite hydrogels, including mechanical properties, and release behavior of DEX are a match to the requirements of BTE. Overall, our results demonstrate that this self-healing gelatin approach is a promising strategy to enhance bone regeneration through a minimally invasive procedure.

Poly(lactic acid-co-glycolic acid)-based celecoxib extended-release microspheres for the local treatment of traumatic heterotopic ossification

Traumatic heterotopic ossification (THO) is a serious and common clinical post-traumatic complication for which there is no effective and safe drug treatment. Routine administration of nonsteroidal anti-inflammatory drugs (NSAIDs) after injury is extensively used approach for THO. However, serious adverse events can occur in the event of an overdose of NSAIDs. In our study, we have developed a poly(lactic acid-co-glycolic acid) (PLGA) microsphere by emulsifying solvent volatilization for the prolonged slow delivery of celecoxib (CLX). Three groups of celecoxib-poly(lactic acid-co-glycolic acid) microspheres (CLX-PLGA MPs) were prepared with particle sizes of 3.75±1.28 μm, 49.56±17.15 μm, and 94.98±42.53 μm. Meanwhile, related parameters of microspheres in each group were studied: drug loading (DL), encapsulation rate (EE), and slow-release behavior. The DL and EE of the 3 CLX-PLGA MPs did not vary significantly, and subsequently, we selected the second drug loading microspheres with a retardation period of about 70 days for subsequent experiments. Moreover, cellular and animal experiments suggest that the microspheres are biocompatible and can be safely applied to localized trauma tissue. Finally, it is demonstrated that CLX-PLGA MPs have an effect on inhibiting the osteogenic differentiation of bone marrow mesenchymal stem cells and have the potential to inhibit ectopic bone formation of the THO model in Sprague-Dawley rat. Therefore, this study suggests that CLX-PLGA MPs are expected to be applied topically in the early post-traumatic period to prevent the development of THO.

Type II Collagen-Conjugated Mesenchymal Stem Cells Micromass for Articular Tissue Targeting

The tissue engineering approach in osteoarthritic cell therapy often requires the delivery of a substantially high cell number due to the low engraftment efficiency as a result of low affinity binding of implanted cells to the targeted tissue. A modification towards the cell membrane that provides specific epitope for antibody binding to a target tissue may be a plausible solution to increase engraftment. In this study, we intercalated palmitated protein G (PPG) with mesenchymal stem cells (MSCs) and antibody, and evaluated their effects on the properties of MSCs either in monolayer state or in a 3D culture state (gelatin microsphere, GM). Bone marrow MSCs were intercalated with PPG (PPG-MSCs), followed by coating with type II collagen antibody (PPG-MSC-Ab). The effect of PPG and antibody conjugation on the MSC proliferation and multilineage differentiation capabilities both in monolayer and GM cultures was evaluated. PPG did not affect MSC proliferation and differentiation either in monolayer or 3D culture. The PPG-MSCs were successfully conjugated with the type II collagen antibody. Both PPG-MSCs with and without antibody conjugation did not alter MSC proliferation, stemness, and the collagen, aggrecan, and sGAG expression profiles. Assessment of the osteochondral defect explant revealed that the PPG-MSC-Ab micromass was able to attach within 48 h onto the osteochondral surface. Antibody-conjugated MSCs in GM culture is a potential method for targeted delivery of MSCs in future therapy of cartilage defects and osteoarthritis.

Injectable open-porous PLGA microspheres as cell carriers for cartilage regeneration

Minimally invasive treatment via injectable delivery of cells has drawn extensive attention for tissue regeneration because it reduces the need for substantial open surgery and fits tissue defects with complex shapes, making it a suitable option for repairing articular cartilage defects. This work presents an alkaline treatment method to fabricate open-porous poly (lactic-co-glycolic acid) microspheres (OPMs) as bone marrow stromal cells (BMSCs) carriers for cartilage regeneration. OPMs have better biodegradation property and the extended pores can provide easier access for cells to the internal space. The BMSCs cultured with OPMs can display enhanced cell proliferation, up-regulated expression of cartilage-related mRNAs and proteins, and improved cartilage regeneration in vitro and in vivo. These results highlight the advantage and potential of using OPMs fabricated via simple alkaline treatment as injectable stem cell carriers for cartilage regeneration through minimally invasive procedures.

Thermo-irreversible glycol chitosan/hyaluronic acid blend hydrogel for injectable tissue engineering

Thermogels that undergo temperature-dependent sol-gel transition have recently attracted attention as a promising biomaterial for injectable tissue engineering. However, conventional thermogels usually suffer from poor physical properties and low cell binding affinity, limiting their practical applications. Here, a simple approach for developing a new thermogel with enhanced physical properties and cell binding affinity is proposed. This thermogel (AcHA/HGC) was obtained by simple blending of a new class of polysaccharide-based thermogel, N-hexanoyl glycol chitosan (HGC), with a polysaccharide possessing good cell binding affinity, acetylated hyaluronic acid (AcHA). Gelation of AcHA/HGC was initially triggered by the thermosensitive response of HGC and gradually intensified by additional physical crosslinking mechanisms between HGC and AcHA, resulting in thermo-irreversible gelation. Compared to the thermos-reversible HGC hydrogel, the thermo-irreversible AcHA/HGC hydrogel exhibited enhanced physical stability, mechanical properties, cell binding affinity, and tissue compatibility. These results suggest that our thermo-irreversible hydrogel is a promising biomaterial for injectable tissue engineering.

In Situ Precipitation of Cluster and Acicular Hydroxyapatite onto Porous Poly(γ-benzyl-l-glutamate) Microcarriers for Bone Tissue Engineering

Bone tissue engineering scaffold based on microcarriers provides an effective approach for the repair of irregular bone defects. The implantation of microcarriers by injection can reduce surgical trauma and fill various irregular shaped bone defects. Microcarriers with porous structure and osteogenic properties have shown great potential in promoting the repair of bone defects. In this study, two kinds of hydroxyapatite/poly-(γ-benzyl-l-glutamate) (HA/PBLG) microcarriers were constructed by emulsion/in situ precipitation method and their structures and properties were studied. First, PBLG porous microcarriers were prepared by an emulsion method. Surface carboxylation of PBLG microcarriers was performed to promote the deposition of HA on PBLG microcarriers. Next, the modified porous PBLG microcarriers were used as the matrix, combined with the in situ precipitation method; the cluster HA and acicular HA were precipitated onto the surface of porous microcarriers in the presence of ammonia water and tri(hydroxymethyl)aminomethane (Tris) solution, respectively. The micromorphology, composition, and element distribution of the two kinds of microcarriers were characterized by TEM, SEM, and AFM. Adipose stem cells (ADSCs) were cultured on the cluster HA/PBLG and acicular HA/PBLG microcarriers, respectively. ADSCs could grow and proliferate normally on both kinds of microcarriers wherein the acicular HA/PBLG microcarriers were more favorable for early cell adhesion and showed a beneficial effect on mineralization and osteogenic differentiation of ADSCs. Successful healing of a rabbit femur defect verified the bone regeneration ability of acicular HA/PBLG microcarriers.

Regenerating infected bone defects with osteocompatible microspheres possessing antibacterial activity

Treatment of infected bone defects still remains a formidable clinical challenge, and the design of bone implants with both anti-bacterial activity and osteogenesis effects is nowadays regarded as a powerful strategy for infection control and bone healing.

A Micro-Ark for Cells: Highly Open Porous Polyhydroxyalkanoate Microspheres as Injectable Scaffolds for Tissue Regeneration

To avoid large open surgery using scaffold transplants, small-sized cell carriers are employed to repair complexly shaped tissue defects. However, most cell carriers show poor cell adherences and viability. Therefore, polyhydroxyalkanoate (PHA), a natural biopolymer, is used to prepare highly open porous microspheres (OPMs) of 300-360 µm in diameter, combining the advantages of microspheres and scaffolds to serve as injectable carriers harboring proliferating stem cells. In addition to the convenient injection to a defected tissue, and in contrast to poor performances of OPMs made of polylactides (PLA OPMs) and traditional less porous hollow microspheres (PHA HMs), PHA OPMs present suitable surface pores of 10-60 µm and interconnected passages with an average size of 8.8 µm, leading to a high in vitro cell adhesion of 93.4%, continuous proliferation for 10 d and improved differentiation of human bone marrow mesenchymal stem cells (hMSCs). PHA OPMs also support stronger osteoblast-regeneration compared with traditional PHA HMs, PLA OPMs, commercial hyaluronic acid hydrogels, and carrier-free hMSCs in an ectopic bone-formation mouse model. PHA OPMs protect cells against stresses during injection, allowing more living cells to proliferate and migrate to damaged tissues. They function like a micro-Noah's Ark to safely transport cells to a defect tissue.

Influence of injectable microparticle size on cardiac progenitor cell response

INTRODUCTION

Injectable scaffolds are emerging as a promising strategy in the field of myocardial tissue engineering. Among injectable scaffolds, microparticles have been poorly investigated. The goal of this study was the development of novel gelatin/gellan microparticles that could be used as an injectable scaffold to repair the infarcted myocardium. In particular, the effect of particle size on cardiac progenitor cell response was investigated.

METHODS

Particles were produced by a water-in-oil emulsion method. Phosphatidylcholine was used as a surfactant. Particles with different diameter ranges (125-300 µm and 350-450 µm) were fabricated using two different surfactant concentrations. Morphological, physicochemical, and functional characterizations were carried out. Cardiac progenitor cell adhesion and growth on microparticles were tested both in static and dynamic suspension culture conditions.

RESULTS

Morphological analysis of the produced particles showed a spherical shape and porous surface. The hydrophilicity of particle matrix and the presence of intermolecular interactions between gellan and gelatin were pointed out by the physicochemical characterization. A weight loss of 75 ± 5 % after 90 days of hydrolytic degradation was observed. Injectability through a narrow needle (26 G) and persistence of the microparticles at the injection site were preliminarily verified by ex vivo test. In vitro cell culture tests showed a preservation of rat cardiac progenitor biologic properties and indicated a preferential cell adherence to microparticles with a smaller size.

CONCLUSION

Overall, the obtained results indicate that the produced gelatin/gellan microparticles could be potentially employed as injectable scaffolds for myocardial regeneration.

Suspended polyhydroxyalkanoate microspheres as 3D carriers for mammalian cell growth

Different forms of biopolyester PHBVHHx microspheres were prepared so as to compare the mammalian cell behaviors in suspension cultivation system. Based on a microbial terpolyester PHBVHHx consisting of 3-hydroxybutyrate (HB), 3-hydroxyvalerate (HV), and 3-hydroxyhexanoate (HHx), solid microspheres (SMSs), hollow microspheres (HMSs), and porous microspheres (PMS) were successfully prepared by a modified solvent evaporation method involving gas-in-oil-in-water (G1/O/W2) double emulsion, water-in-oil-in-water (W1/O/W2) double emulsion and oil-in-water (O/W) single emulsion, respectively. Generally, PMSs have diameters ranging from 330 to 400 μm with pore sizes of 10 to 60 μm. The pores inside the PMSs were found well interconnected compared with PHBVHHx prepared by the traditional solvent evaporation method, resulting in the highest water uptake ratio. When inoculated with human osteoblast-like cells lasting 6 days, PMS showed much better cell attachment and proliferation compared with other less porous microspheres due to its large inner space as a 3 D carrier. Cell migration towards surface and other interconnected inner pores was clearly observable. Dead or apoptotic cells were found more common among less porous SMSs or HMSs compared with highly porous PMSs. It is therefore concluded that porous PHBVHHx microspheres with larger surface open pores and interconnected inner pores can serve as a carrier or scaffold supporting more and better cell growth for either injectable purposes or simply supporting cell growth.

BMP-7-Loaded PGLA Microspheres as a New Delivery System for the Cultivation of Human Chondrocytes in a Collagen Type I Gel: The Common Nude Mouse Model

Purpose

Bone morphogenic protein 7 (BMP-7) released from polylactide (PLGA) microspheres has proven to be a potent system in cartilage tissue engineering in vitro. However, in vivo data are still lacking. The aim of this study was to investigate this BMP-7 release system utilizing the nude mouse as a small animal model.

Methods

Human osteoarthritic chondrocytes of 10 patients were enzymatically released and transferred into a collagen type-I gel. A concentration of 2×105 cells/mL was used. BMP-7 encapsulated in PGLA microspheres was added at an initial concentration of 500 ng BMP-7/mL gel. Untreated specimens and specimens with empty microspheres served as control. Samples were cultivated subcutaneously in nude mice for 6 weeks.

Results

After recovery, chondrocytes of all groups displayed a spheroid morphology without signs of dedifferentiation. The proteoglycan and collagen type II content of the control groups was restricted to the immediate pericellular region, whereas treatment group samples showed enhanced collagen type II production. Collagen type II and aggrecan gene expression was enhanced in treatment group samples with respect to the two control groups (mean ± SD: 0.268 ± 0.450 to 0.152 ± 0.129 and 0.155 ± 0.216 ng/ng β-actin for collagen type II; 0.535 ± 0.731 to 0.367 ± 0.651 and 0.405 ± 0.326 ng/ng β-actin for aggrecan), whereas collagen type I gene expression decreased by a factor of 10. Relative protein quantification of collagen type II, collagen type I and proteoglycan was in accordance.

Conclusions

Our data suggest that BMP-7 release from PGLA microspheres led to an improved tissue-engineered cartilage analogue in vivo with an increase in hyaline-cartilage-specific components.

Functionalizing PLGA and PLGA Derivatives for Drug Delivery and Tissue Regeneration Applications

Poly(lactic-co-glycolic) acid (PLGA) is one of the most versatile biomedical polymers, already approved by regulatory authorities to be used in human research and clinics. Due to its valuable characteristics, PLGA can be tailored to acquire desirable features for control bioactive payload or scaffold matrix. Moreover, its chemical modification with other polymers or bioconjugation with molecules may render PLGA with functional properties that make it the Holy Grail among the synthetic polymers to be applied in the biomedical field. In this review, the physical-chemical properties of PLGA, its synthesis, degradation, and conjugation with other polymers or molecules are revised in detail, as well as its applications in drug delivery and regeneration fields. A particular focus is given to successful examples of products already on the market or at the late stages of trials, reinforcing the potential of this polymer in the biomedical field.

Thermostabilization of inactivated polio vaccine in PLGA-based microspheres for pulsatile release

Vaccines are a critical clinical tool in preventing illness and death due to infectious diseases and are regularly administered to children and adults across the globe. In order to obtain full protection from many vaccines, an individual needs to receive multiple doses over the course of months. However, vaccine administration in developing countries is limited by the difficulty in consistently delivering a second or third dose, and some vaccines, including the inactivated polio vaccine (IPV), must be injected more than once for efficacy. In addition, IPV does not remain stable over time at elevated temperatures, such as those it would encounter over time in the body if it were to be injected as a single-administration vaccine. In this manuscript, we describe microspheres composed of poly(lactic-co-glycolic acid) (PLGA) that can encapsulate IPV along with stabilizing excipients and release immunogenic IPV over the course of several weeks. Additionally, pH-sensitive, cationic dopants such as Eudragit E polymer caused clinically relevant amounts of stable IPV release upon degradation of the PLGA matrix. Specifically, IPV was released in two separate bursts, mimicking the delivery of two boluses approximately one month apart. In one of our top formulations, 1.4, 1.1, and 1.2 doses of the IPV serotype 1, 2, and 3, respectively, were released within the first few days from 50mg of particles. During the delayed, second burst, 0.5, 0.8, and 0.6 doses of each serotype, respectively, were released; thus, 50mg of these particles released approximately two clinical doses spaced a month apart. Immunization of rats with the leading microsphere formulation showed more robust and long-lasting humoral immune response compared to a single bolus injection and was statistically non-inferior from two bolus injections spaced 1 month apart. By minimizing the number of administrations of a vaccine, such as IPV, this technology can serve as a tool to aid in the eradication of polio and other infectious diseases for the improvement of global health.

Strategies to Optimize Adult Stem Cell Therapy for Tissue Regeneration

Stem cell therapy aims to replace damaged or aged cells with healthy functioning cells in congenital defects, tissue injuries, autoimmune disorders, and neurogenic degenerative diseases. Among various types of stem cells, adult stem cells (i.e., tissue-specific stem cells) commit to becoming the functional cells from their tissue of origin. These cells are the most commonly used in cell-based therapy since they do not confer risk of teratomas, do not require fetal stem cell maneuvers and thus are free of ethical concerns, and they confer low immunogenicity (even if allogenous). The goal of this review is to summarize the current state of the art and advances in using stem cell therapy for tissue repair in solid organs. Here we address key factors in cell preparation, such as the source of adult stem cells, optimal cell types for implantation (universal mesenchymal stem cells vs. tissue-specific stem cells, or induced vs. non-induced stem cells), early or late passages of stem cells, stem cells with endogenous or exogenous growth factors, preconditioning of stem cells (hypoxia, growth factors, or conditioned medium), using various controlled release systems to deliver growth factors with hydrogels or microspheres to provide apposite interactions of stem cells and their niche. We also review several approaches of cell delivery that affect the outcomes of cell therapy, including the appropriate routes of cell administration (systemic, intravenous, or intraperitoneal vs. local administration), timing for cell therapy (immediate vs. a few days after injury), single injection of a large number of cells vs. multiple smaller injections, a single site for injection vs. multiple sites and use of rodents vs. larger animal models. Future directions of stem cell-based therapies are also discussed to guide potential clinical applications.

Porous microcarrier-enabled three-dimensional culture of chondrocytes for cartilage engineering: A feasibility study

Cartilage repair is substantially intractable due to poor self-healing ability. Porous microspheres can be a fascinating three-dimensional matrix for cell culture and injectable carrier in cartilage engineering. In this study, we assessed the feasible use of porous biopolymer microspheres for chondrocyte carriers. When seeded onto the blended biopolymer microspheres and followed by a dynamic spinner flask culture, the chondrocytes showed robust growth behaviors during the culture period. The gene expressions of SOX9, type II collagen, and aggrecan were significantly upregulated after 2-week of culture. Furthermore, immunolocalization of type II collagen and secretion of glycosaminolglycan became prominent. The results suggest the feasible usefulness of the porous microspheres as the cell culture matrix and the subsequent delivery into cartilage defects.

Nanostructured injectable cell microcarriers for tissue regeneration

Biodegradable polymer microspheres have emerged as cell carriers for the regeneration and repair of irregularly shaped tissue defects due to their injectability, controllable biodegradability and capacity for drug incorporation and release. Notably, recent advances in nanotechnology allowed the manipulation of the physical and chemical properties of the microspheres at the nanoscale, creating nanostructured microspheres mimicking the composition and/or structure of natural extracellular matrix. These nanostructured microspheres, including nanocomposite microspheres and nanofibrous microspheres, have been employed as cell carriers for tissue regeneration. They enhance cell attachment and proliferation, promote positive cell-carrier interactions and facilitate stem cell differentiation for target tissue regeneration. This review highlights the recent advances in nanostructured microspheres that are employed as injectable, biomimetic and cell-instructive cell carriers.

Injectable PEGylated fibrinogen cell-laden microparticles made with a continuous solvent- and oil-free preparation method

A new methodology is reported for the continuous, solvent- and oil-free production of photopolymerizable microparticles containing encapsulated human dermal fibroblasts. A precursor solution of cells in photoreactive poly(ethylene glycol) (PEG)-fibrinogen (PF) polymer was transported through a transparent injector exposed to light irradiation before being atomized in a jet-in-air nozzle. Shear rheometry data revealed the crosslinking kinetics of the PF/cell solution, which was then used to determine the amount of irradiation required to partially polymerize the mixture just prior to atomization. The partially polymerized drops of PF/cells fell into a gelation bath for further crosslinking until fully polymerized hydrogel microparticles were formed. As the drops of solution exited the air-in-jet nozzle, their viscosity was designed to be sufficiently high so as to prevent rapid mixing and/or dilution in the gelation bath, but without undergoing complete gelation in the nozzle. Several parameters of this system were varied to control the size and polydispersity of the microparticles, including the cell density, the flow rate and the air pressure in the nozzle. The system was capable of producing cell-laden microparticles with an average diameter of between 88.1 to 347.1 μm, and a dispersity of between 1.1 and 2.4, depending on the parameters chosen. Varying the precursor flow rate and/or cell density was beneficial in controlling the size and polydispersity of the microparticles; all microparticles exhibited very high cell viability, which was not affected by these parameters. In conclusion, this dropwise photopolymerization methodology for preparing cell-laden microparticles is an attractive alternative to existing techniques that use harsh solvents/oils and offer limited control over particle size and polydispersity.

A novel method for differentiation of human mesenchymal stem cells into smooth muscle-like cells on clinically deliverable thermally induced phase separation microspheres

Muscle degeneration is a prevalent disease, particularly in aging societies where it has a huge impact on quality of life and incurs colossal health costs. Suitable donor sources of smooth muscle cells are limited and minimally invasive therapeutic approaches are sought that will augment muscle volume by delivering cells to damaged or degenerated areas of muscle. For the first time, we report the use of highly porous microcarriers produced using thermally induced phase separation (TIPS) to expand and differentiate adipose-derived mesenchymal stem cells (AdMSCs) into smooth muscle-like cells in a format that requires minimal manipulation before clinical delivery. AdMSCs readily attached to the surface of TIPS microcarriers and proliferated while maintained in suspension culture for 12 days. Switching the incubation medium to a differentiation medium containing 2 ng/mL transforming growth factor beta-1 resulted in a significant increase in both the mRNA and protein expression of cell contractile apparatus components caldesmon, calponin, and myosin heavy chains, indicative of a smooth muscle cell-like phenotype. Growth of smooth muscle cells on the surface of the microcarriers caused no change to the integrity of the polymer microspheres making them suitable for a cell-delivery vehicle. Our results indicate that TIPS microspheres provide an ideal substrate for the expansion and differentiation of AdMSCs into smooth muscle-like cells as well as a microcarrier delivery vehicle for the attached cells ready for therapeutic applications.

Bioactivated protein-based porous microcarriers for tissue engineering applications

Lipoaspirate-derived extracellular matrix enrichment was able to provide the necessary cell adhesion receptors and biological factors for improving cell–material interactions of porous OVA microcarriers.

PLGA microspheres by Supercritical Emulsion Extraction: a study on insulin release in myoblast culture

Supercritical Emulsion Extraction in a Continuous operation layout is proposed for the production of poly-lactic-co-glycolic acid (PLGA) microspheres loaded with insulin, selected as a model of bioactive signal. Microspheres with different mean sizes of 2 μm (±0.9 μm) and 3 μm (±2.2 μm) and insulin loadings of 3 and 6 mg/g were obtained by processing different water-oil-water emulsions; an encapsulation efficiency of about 60% w/w was measured in all cases. Insulin release profiles from PLGA microspheres were also characterized in two different media (Phosphate-Buffered Saline and Dulbecco's Modified Eagle Medium) and kinetic constants were estimated by using a model proposed in literature. The produced microspheres were, then, used for the cultivation of rat embryonic ventricular myoblasts in a serum-free medium to monitor the biological effect of the released insulin. The best cell viability and proliferation, supported by released insulin, was monitored when microspheres with mean size of 3 μm loaded with 3 mg/g of insulin were added.

High-density cell systems incorporating polymer microspheres as microenvironmental regulators in engineered cartilage tissues

To address the significant clinical need for tissue-engineered therapies for the repair and regeneration of articular cartilage, many systems have recently been developed using bioactive polymer microspheres as regulators of the chondrogenic microenvironment within high-density cell cultures. In this review, we highlight various densely cellular systems utilizing polymer microspheres as three-dimensional (3D) structural elements within developing engineered cartilage tissue, carriers for cell expansion and delivery, vehicles for spatiotemporally controlled growth factor delivery, and directors of cell behavior via regulation of cell-biomaterial interactions. The diverse systems described herein represent a shift from the more traditional tissue engineering approach of combining cells and growth factors within a biomaterial scaffold, to the design of modular systems that rely on the assembly of cells and bioactive polymer microspheres as building blocks to guide the creation of articular cartilage. Cell-based assembly of 3D microsphere-incorporated structures represents a promising avenue for the future of tissue engineering.

Open porous microscaffolds for cellular and tissue engineering by lipid templating

Porous microspheres fabricated from biodegradable polymers have great potential as microscaffolds in tissue engineering applications, especially for novel strategies such as microtissue fabrication in vitro and microtissue assembly in vivo. Fabrication techniques for microparticulate scaffolds with surface and bulk pore sizes relevant for effective cell intrusion, however, are scarce. This study presents two techniques for the fabrication of open porous microscaffolds from poly(lactide-co-glycolide) in which lipid templating is used for pore formation and combined with either dispersion spraying or a double emulsion technique to determine the size and shape of the particulate structures generated. Both techniques yield microscaffolds with an average size of between 500 and 800 μm, high bulk porosities and open surface pores larger than 50 μm in diameter. Microscaffold morphology was investigated microscopically, particle size distribution was determined and porosity was quantified by intrusion measurements. Particle size and morphology was controlled by the processing parameters and the content and type of lipid porogen. Efficient extraction of the lipid template was shown by thermal analysis. Microscaffold cytocompatibility and in vitro cell culture performance was evaluated with L929 fibroblasts and rat adipose-derived stromal cells (ADSC), respectively. Extracts of different formulations were cytocompatible. Rat ADSC proliferated on the microscaffolds and were differentiated along the adipogenic lineage.

Advancing nasal reconstructive surgery: the application of tissue engineering technology

Cartilage tissue engineering is a rapidly progressing area of regenerative medicine with advances in cell biology and scaffold engineering constantly being investigated. Many groups are now capable of making neocartilage constructs with some level of morphological, biochemical, and histological likeness to native human cartilage tissues. The application of this useful technology in articular cartilage repair is well described in the literature; however, few studies have evaluated its application in head and neck reconstruction. Although there are many studies on auricular cartilage tissue engineering, there are few studies regarding cartilage tissue engineering for complex nasal reconstruction. This study therefore highlighted the challenges involved with nasal reconstruction, with special focus on nasal cartilage tissue, and examined how advancements made in cartilage tissue engineering research could be applied to improve the clinical outcomes of total nasal reconstructive surgery.

Effect of initial cell seeding density on 3D-engineered silk fibroin scaffolds for articular cartilage tissue engineering

The repair of articular cartilage defects poses a continuing challenge. Cartilage tissue engineering through the culture of chondrocytes seeded in 3D porous scaffolds has the potential for generating constructs that repair successfully. It also provides a platform to study scaffold-cell and cell-cell interactions. The scaffold affects the growth and morphology of cells growing on it, and concomitantly, cells affect the properties of the resultant tissue construct. Silk fibroin protein from Antheraea mylitta, a non-mulberry Indian tropical tasar silkworm, is a potential biomaterial for diverse applications due to its widespread versatility as a mechanically robust, biocompatible, tissue engineering material. Analysis of silk fibroin scaffolds seeded with varying initial densities (25, 50 and 100 million cells/ml) and cultured for 2 weeks showed that thickness and wet weight increased by 60-70% for the highest cell density, and DNA, GAG and collagen content of the cartilaginous constructs increased with increasing cell density. Mechanical characterization of the constructs elucidated that the highest density constructs had compressive stiffness and modulus 4-5 times that of cell-free scaffolds. The present results indicate the importance of cell seeding density in the rapid formation of a functional cartilaginous tissue.

Enhanced attachment, growth and migration of smooth muscle cells on microcarriers produced using thermally induced phase separation

Microcarriers are widely used for the expansion of cells in vitro, but also offer an approach for combining cell transplantation and tissue bulking for regenerative medicine in a minimally invasive manner. This could be beneficial in conditions associated with muscle damage or atrophy, such as faecal incontinence, where the use of bulking materials or cell transplantation alone has proven to be ineffective. Microcarriers currently available have not been designed for this purpose and are likely to be suboptimal due to their physical and biochemical properties. The aim of this study was to investigate macroporous microspheres of polylactide-co-glycolide (PLGA), prepared using a thermally induced phase separation technique, for their suitability as cell microcarriers for the transplantation of smooth muscle cells. Cell attachment, growth and migration were studied and compared with commercially available porcine gelatin microcarriers (Cultispher-S) in suspension culture. Smooth muscle cells attached more rapidly to the PLGA microcarriers, which also significantly enhanced the rate of cell growth compared with Cultispher-S microcarriers. The majority of smooth muscle cells attached to the PLGA microcarriers in suspension culture were able to migrate away over a 15 day period of static culture, unlike Cultispher-S microcarriers which retained the majority of cells. The ability of PLGA microcarriers to enhance cell growth combined with their capacity to release cells at the sites of delivery are features that make them ideally suited for use as a cell transplantation delivery device in tissue engineering and regenerative medicine.

Functional Cells Cultured on Microcarriers for Use in Regenerative Medicine Research

Microcarriers have been successfully used for many years for growing anchorage-dependent cells and as a means of delivering cells for tissue repair. When cultured on microcarriers, the number of anchorage-dependent cells, including primary cells, can easily be scaled up and controlled to generate the quantities of cells necessary for therapeutic applications. Recently, stem cell technology has been recognized as a powerful tool in regenerative medicine, but adequate numbers of stem cells that retain their differentiation potential are still difficult to obtain. For anchorage-dependent stem cells, however, microcarrier-based suspension culture using various types of microcarriers has proven to be a good alternative for effective ex vivo expansion. In this article, we review studies reporting the expansion, differentiation, or transplantation of functional anchorage-dependent cells that were expanded with the microcarrier culture system. Thus, the implementation of technological advances in biodegradable microcarriers, the bead-to-bead transfer process, and appropriate stem cell media may soon foster the ability to produce the numbers of stem cells necessary for cell-based therapies and/or tissue engineering.

A novel cylinder-type poly(L-lactic acid)-collagen hybrid sponge for cartilage tissue engineering

The development of porous scaffolds having both high porosity and strong mechanical strength for tissue engineering and regenerative medicine has been quite challenging. A novel hybrid poly(L-lactic acid) (PLLA)-collagen hybrid sponge was developed by enclosing collagen sponge in a cup-shaped PLLA sponge to meet the necessary requirements. Collagen sponge was formed in the center of the PLLA sponge cup, and collagen microsponges were formed in the pores of the PLLA sponge cup. The PLLA-collagen hybrid sponge showed higher mechanical strength than did those of the PLLA sponge cup and collagen sponge. The porosity of the PLLA-collagen hybrid sponge was greater than that of the PLLA sponge cup. The cup-shaped PLLA sponge skeleton provided the hybrid sponge with high mechanical strength and protected against cell leakage during cell seeding, while the central collagen sponge contributed to high porosity, and facilitated cell adhesion and distribution in the hybrid sponge. Cartilaginous tissue was successfully regenerated when chondrocytes were cultured in the hybrid sponge. This method of hybridization will provide a new technique for the preparation of functional porous scaffolds for tissue engineering.

Strategies for articular cartilage lesion repair and functional restoration

Injury of articular cartilage due to trauma or pathological conditions is the major cause of disability worldwide, especially in North America. The increasing number of patients suffering from joint-related conditions leads to a concomitant increase in the economic burden. In this review article, we focus on strategies to repair and replace knee joint cartilage, since knee-associated disabilities are more prevalent than any other joint. Because of inadequacies associated with widely used approaches, the orthopedic community has an increasing tendency to develop biological strategies, which include transplantation of autologous (i.e., mosaicplasty) or allogeneic osteochondral grafts, autologous chondrocytes (autologous chondrocyte transplantation), or tissue-engineered cartilage substitutes. Tissue-engineered cartilage constructs represent a highly promising treatment option for knee injury as they mimic the biomechanical environment of the native cartilage and have superior integration capabilities. Currently, a wide range of tissue-engineering-based strategies are established and investigated clinically as an alternative to the routinely used techniques (i.e., knee replacement and autologous chondrocyte transplantation). Tissue-engineering-based strategies include implantation of autologous chondrocytes in combination with collagen I, collagen I/III (matrix-induced autologous chondrocyte implantation), HYAFF 11 (Hyalograft C), and fibrin glue (Tissucol) or implantation of minced cartilage in combination with copolymers of polyglycolic acid along with polycaprolactone (cartilage autograft implantation system), and fibrin glue (DeNovo NT graft). Tissue-engineered cartilage replacements show better clinical outcomes in the short term, and with advances that have been made in orthopedics they can be introduced arthroscopically in a minimally invasive fashion. Thus, the future is bright for this innovative approach to restore function.

Evaluation of an injectable rhGDF-5/PLGA construct for minimally invasive periodontal regenerative procedures: a histological study in the dog

AIM

To evaluate the injectability, biocompatibility, safety, and periodontal wound healing/regeneration following application of a novel bioresorbable recombinant human growth/differentiation factor-5 (rhGDF-5)/poly(lactic-co-glycolic acid) (PLGA) construct.

MATERIAL AND METHODS

Periodontal pockets (3 x 6 mm, width x depth) were surgically created over the buccal roots of the second and fourth mandibular pre-molars in eight adult Hound Labrador mongrel dogs. Surgeries including injection of the rhGDF-5/PLGA construct into the pockets were sequenced that four animals provided 2-/4-week and four animals 6-/8-week observations of sites receiving rhGDF-5/PLGA or serving as sham-surgery control.

RESULTS

The rhGDF-5/PLGA construct was easy to prepare and apply. Approximately 0.2 ml (93 microg rhGDF-5)/tooth was used. Clinical and radiographic healing was exemplary without adverse events. Healing was characterized by a non-specific connective tissue attachment, acellular/cellular cementum, periodontal ligament (PDL), bone regeneration, and a junctional epithelium. PLGA fragments were observed in 4/7, 2/8, and 1/8 sites at 2, 4, and 6 weeks, respectively. Associated inflammatory reactions exhibited no limiting effect on periodontal wound healing/regeneration. Root resorption/ankylosis was not observed. Bone formation showed apparent increased maturity (lamellar bone) at 6 weeks in sites receiving rhGDF-5/PLGA compared with the control. Both protocols exhibited significant increases in PDL, cementum, and bone regeneration over time, without significant differences between treatments. In time, PDL and cementum regeneration was twofold greater for the control at 4 weeks (p=0.04) while increased bone formation was observed at sites receiving rhGDF-5/PLGA (p<0.01).

CONCLUSIONS

In conclusion, the rhGDF-5/PLGA construct appears to be a safe technology for injectable, ease-of-use application of rhGDF-5-stimulated periodontal wound healing/regeneration. Additional work to optimize the polymer carrier and rhGDF-5 release kinetics/dose might be required before evaluating the efficacy of this technology in clinical settings using minimally invasive approaches.

Gelatinized copper-capillary alginate gel functions as an injectable tissue scaffolding system for stem cell transplants

In severe hypoxic-ischemic brain injury, cellular components such as neurons and astrocytes are injured or destroyed along with the supporting extracellular matrix. This presents a challenge to the field of regenerative medicine since the lack of extracellular matrix and supporting structures makes the transplant milieu inhospitable to the transplanted cells. A potential solution to this problem is the use of a biomaterial to provide the extracellular components needed to keep cells localized in cystic brain regions, allowing the cells to form connections and repair lost brain tissue. Ideally, this biomaterial would be combined with stem cells, which have been proven to have therapeutic potentials, and could be delivered via an injection. To study this approach, we derived a hydrogel biomaterial tissue scaffold from oligomeric gelatin and copper-capillary alginate gel (GCCAG). We then demonstrated that our multipotent astrocytic stem cells (MASCs) could be maintained in GCCAG scaffolds for up to 2 weeks in vitro and that the cells retained their multipotency. We next performed a pilot transplant study in which GCCAG was mixed with MASCs and injected into the brain of a neonatal rat pup. After a week in vivo, our results showed that: the GCCAG biomaterial did not cause a significant reactive gliosis; viable cells were retained within the injected scaffolds; and some delivered cells migrated into the surrounding brain tissue. Therefore, GCCAG tissue scaffolds are a promising, novel injectable system for transplantation of stem cells to the brain.

Neural network analysis identifies scaffold properties necessary for in vitro chondrogenesis in elastin-like polypeptide biopolymer scaffolds

The successful design of biomaterial scaffolds for articular cartilage tissue engineering requires an understanding of the impact of combinations of material formulation parameters on diverse and competing functional outcomes of biomaterial performance. This study sought to explore the use of a type of unsupervised artificial network, a self-organizing map, to identify relationships between scaffold formulation parameters (crosslink density, molecular weight, and concentration) and 11 such outcomes (including mechanical properties, matrix accumulation, metabolite usage and production, and histological appearance) for scaffolds formed from crosslinked elastin-like polypeptide (ELP) hydrogels. The artificial neural network recognized patterns in functional outcomes and provided a set of relationships between ELP formulation parameters and measured outcomes. Mapping resulted in the best mean separation amongst neurons for mechanical properties and pointed to crosslink density as the strongest predictor of most outcomes, followed by ELP concentration. The map also grouped formulations together that simultaneously resulted in the highest values for matrix production, greatest changes in metabolite consumption or production, and highest histological scores, indicating that the network was able to recognize patterns amongst diverse measurement outcomes. These results demonstrated the utility of artificial neural network tools for recognizing relationships in systems with competing parameters, toward the goal of optimizing and accelerating the design of biomaterial scaffolds for articular cartilage tissue engineering.

RGD modified PLGA/gelatin microspheres as microcarriers for chondrocyte delivery

Poly(lactide-co-glycotide) (PLGA)/gelatin composite microspheres were prepared by an emulsion solvent evaporation technique. RGDS peptides were further immobilized under the catalyzation of water soluble carbodiimide (EDAC). Confocal laser scanning microscopy and transmission electron microscopy revealed that the gelatin was entrapped in the PLGA/gelatin microspheres with a manner of separated domains. The contents of the entrapped gelatin and immobilized RGDS peptides were quantified as 0.9 mg/20 mg and approximately 2.1 microg/20 mg microspheres by hydroxyproline analysis and bicinchoninic acid protein assay, respectively. Moreover, difference in morphology of PLGA, PLGA/gelatin and RGDS modified PLGA/gelatin (PLGA/gelatin-RGDS) microspheres was observed by scanning electron microscopy. The PLGA/gelatin and PLGA/gelatin-RGDS microspheres lost their weight rapidly in PBS, but slowly in DMEM/fetal bovine serum. Rabbit auricular chondrocytes were seeded onto the microspheres in vitro to assess their biological performance and applicability as cell carriers. Results show that amongst the PLGA, PLGA/gelatin and PLGA/gelatin-RGDS microspheres, the latter ones have the best performance in terms of chondrocyte attachment, proliferation, viability and sulfated glycosaminoglycans secretion.

Optimization of scaled-up chitosan microparticles for bone regeneration

The aim of this study was to scale-up and optimize the chitosan (CS) microparticles (MPs) from 1x batch (41-85 mg) to 4x batch (270-567 mg) to be used in bone regeneration. The MPs used in the present study were prepared by double emulsification technique using CS as a base material under physiologically friendly conditions throughout the process. Structural integrity of MPs was improved creating cross-links between amine groups in CS and phosphate groups in tripolyphosphate (TPP) which has been used as an ionic cross-linking agent. The cross-linking density was varied using different amounts of TPP to CS such as 0%, 8%, 32%, 64% and 110% (w/w). The CS MPs were approximately spherical in shape with a size of 30-50 microm according to scanning electron microscopy results. X-ray diffraction data revealed having TPP in the CS MPs. The evidence of ionic cross-links in the CS MPs was analyzed using Fourier Transform Infra Red. When we scaled-up the yield of MPs, we investigated that 64% TPP cross-linking density provided the best quality MPs. In addition, those MPs provided the yield from 75 mg to 310 mg when scaled up from 1x to 4x batch, respectively. The MPs developed have a great potential to be used as an injectable scaffold for bone regeneration including orthopedic and craniofacial applications using minimally invasive conditions compared with conventional three-dimensional scaffolds.

Bilayered scaffolds for osteochondral tissue engineering

Osteoarthritis (OA) is a prevalent degenerative joint disease that places a significant burden on the socioeconomic efficacy of communities around the world. Tissue engineering repair of articular cartilage in synovial joints represents a potential OA treatment strategy superior to current surgical techniques. In particular, osteochondral tissue engineering, which promotes the simultaneous regeneration of articular cartilage and underlining subchondral bone, may be a clinically relevant approach toward impeding OA progression. The unique and complex functional demands of the two contrasting tissues that comprise osteochondral tissue require the use of bilayered scaffolds to promote individual growth of both on a single integrated implant. This paper reviews the three current bilayered scaffold strategies applied to solve this challenging problem, with a focus on the need for an innovative approach to design and fabrication of new optimized scaffold combinations to reinforce materials science as an important element of osteochondral tissue engineering.

Injectable biomaterials for regenerating complex craniofacial tissues

Engineering complex tissues requires a precisely formulated combination of cells, spatiotemporally released bioactive factors, and a specialized scaffold support system. Injectable materials, particularly those delivered in aqueous solution, are considered ideal delivery vehicles for cells and bioactive factors and can also be delivered through minimally invasive methods and fill complex 3D shapes. In this review, we examine injectable materials that form scaffolds or networks capable of both replacing tissue function early after delivery and supporting tissue regeneration over a time period of weeks to months. The use of these materials for tissue engineering within the craniofacial complex is challenging but ideal as many highly specialized and functional tissues reside within a small volume in the craniofacial structures and the need for minimally invasive interventions is desirable due to aesthetic considerations. Current biomaterials and strategies used to treat craniofacial defects are examined, followed by a review of craniofacial tissue engineering, and finally an examination of current technologies used for injectable scaffold development and drug and cell delivery using these materials.

Open macroporous poly(lactic-co-glycolic Acid) microspheres as an injectable scaffold for cartilage tissue engineering

Non-porous poly(lactic-co-glycolic acid) (PLGA) microspheres have been previously proposed as an injectable scaffold for in vivo cartilage tissue engineering. In this study, we tested whether using open macroporous PLGA microspheres as an injectable scaffold for in vivo cartilage tissue engineering provides a larger surface area for cell adhesion and a larger void space for cartilage tissue regeneration and, thus, regeneration of higher quality cartilage than non-porous PLGA microspheres. Rabbit chondrocytes were mixed with non-porous or macroporous PLGA microspheres and injected immediately through 18-gauge needles into subcutaneous sites in athymic mice. Six weeks after implantation, chondrocytes implanted using both types of PLGA microspheres formed solid, white cartilaginous tissues. Histological analysis of the implants with hematoxylin and eosin, safranin O and Masson's trichrome staining confirmed cartilaginous tissue formation. The portion of cartilage tissue area in the implant cross-sectional area was significantly higher in the macroporous PLGA microsphere group than in the non-porous PLGA microsphere group (88.9% versus 34.6%, P < 0.001). Importantly, the collagen (P < 0.01) and glycosaminoglycan (P < 0.01) contents of the implants were significantly higher in the macroporous PLGA microsphere group than in the non-porous PLGA microsphere group. We conclude that an open macroporous PLGA microsphere scaffold may be useful in cartilage regeneration through minimally-invasive surgical procedures in orthopedic applications.