Continuous gradients exist at osteochondral interfaces, which may be engineered by applying spatially patterned gradients of biological cues. In the present study, a protein-loaded microsphere-based scaffold fabrication strategy was applied to achieve spatially and temporally controlled delivery of bioactive signals in three-dimensional (3D) tissue engineering scaffolds. Bone morphogenetic protein-2 and transforming growth factor-β1-loaded poly(d,llactic- co-glycolic acid) microspheres were utilized with a gradient scaffold fabrication technology to produce microsphere-based scaffolds containing opposing gradients of these signals. Constructs were then seeded with human bone marrow stromal cells (hBMSCs) or human umbilical cord mesenchymal stromal cells (hUCMSCs), and osteochondral tissue regeneration was assessed in gradient scaffolds and compared to multiple control groups. Following a 6-week cell culture, the gradient scaffolds produced regionalized extracellular matrix, and outperformed the blank control scaffolds in cell number, glycosaminoglycan production, collagen content, alkaline phosphatase activity, and in some instances, gene expression of major osteogenic and chondrogenic markers. These results suggest that engineered signal gradients may be beneficial for osteochondral tissue engineering.
Osteochondral; Interface; Gradient; Microsphere; Umbilical cord stem cells; PLGA; BMP-2; TGF-β1
Interfacial tissue engineering is an emerging branch of regenerative medicine, where engineers are faced with developing methods for the repair of one or many functional tissue systems simultaneously. Early and recent solutions for complex tissue formation have utilized stratified designs, where scaffold formulations are segregated into two or more layers, with discrete changes in physical or chemical properties, mimicking a corresponding number of interfacing tissue types. This method has brought forth promising results, along with a myriad of regenerative techniques. The latest designs, however, are employing “continuous gradients” in properties, where there is no discrete segregation between scaffold layers. This review compares the methods and applications of recent stratified approaches to emerging continuously graded methods.
Gradient; Stratified; Interface; Tissue engineering; Osteochondral
Calcium-based minerals have consistently been shown to stimulate osteoblastic behavior in vitro and in vivo. Thus, use of such minerals in biomaterial applications has become an effective method to enhance bone tissue engineered constructs. In the present study, for the first time, human bone marrow stromal cells (hBMSC) were osteogenically differentiated on scaffolds consisting only of hydroxyapatite (HAp)-loaded poly(d,l-lactic acid-co-glycolic acid) (PLGA) microspheres of high monodispersity. Scaffold formulations included 0, 5, 10, and 20 wt% Hap, and the hBMSC were cultured for 6 weeks. Results demonstrated suppression of some osteogenic genes during differentiation in the HAp group, but higher end-point glycosaminoglycan and collagen content in 10% and 20% HAp samples, as evidenced by biochemical tests, histology, and immunohistochemistry. After 6 weeks of culture, constructs with 0% and 5% HAp had average compressive moduli of 0.7±0.2 and 1.5±0.9 kPa, respectively, whereas constructs with 10% and 20% HAp had higher average moduli of 17.6±4.6 and 18.9±8.1 kPa, respectively. The results of this study indicate that HAp inclusion in microsphere-based scaffolds could be implemented as a physical gradient in combination with bioactive signal gradients seen in previous iterations of these microsphere-based scaffolds to enhance osteoconduction and mechanical integrity of a healing site.
To date, most interfacial tissue engineering approaches have utilized stratified designs, in which there are two or more discrete layers comprising the interface. Continuously-graded interfacial designs, where there is no discrete transition from one tissue type to another, are gaining attention as an alternative to stratified designs. Given that osteochondral regeneration holds the potential to enhance cartilage regeneration by leveraging the healing capacity of the underlying bone, we endeavored to introduce a continuously graded approach to osteochondral regeneration. The purpose of this study was thus to evaluate the performance of a novel gradient-based scaffolding approach to regenerate osteochondral defects in the New Zealand White rabbit femoral condyle. Bioactive plugs were constructed from poly(d,l-lactic-co-glycolic acid) (PLGA) microspheres with a continuous gradient transition between cartilage-promoting and bone-promoting growth factors. At six and 12 weeks of healing, results suggested that the implants provided support for the neo-synthesized tissue, and the gradient in bioactive signaling may have been beneficial for bone and cartilage regeneration compared to the blank control implant, as evidenced by histology. In addition, the effects of pre-seeding gradient scaffolds with umbilical cord mesenchymal stromal cells (UCMSCs) from the Wharton’s jelly of New Zealand White rabbits were evaluated. Results indicated that there may be regenerative benefits to pre-localizing UCMSCs within scaffold interiors. The inclusion of bioactive factors in a gradient-based scaffolding design is a promising new treatment strategy for defect repair in the femoral condyle.
Osteochondral; Interface; Gradient; Microsphere; Umbilical Cord Stem Cells; PLGA; BMP-2; TGF-β1
Tissue engineering solutions focused on the temporomandibular joint (TMJ) have expanded in number and variety over the past decade to address the treatment of TMJ disorders. The existing literature on approaches for healing small defects in the TMJ condylar cartilage and subchondral bone, however, is sparse. The purpose of this study was thus to evaluate the performance of a novel gradient-based scaffolding approach to regenerate osteochondral defects in the rabbit mandibular condyle.
MATERIALS AND METHODS
Miniature bioactive plugs for regeneration of small mandibular condylar defects in New Zealand White rabbits were fabricated. The plugs were constructed from poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres with a gradient transition between cartilage-promoting and bone-promoting growth factors.
At six weeks of healing, results suggested that the implants provided support for the neo-synthesized tissue as evidenced by histology and 9.4T magnetic resonance imaging.
The inclusion of bioactive factors in a gradient-based scaffolding design is a promising new treatment strategy for focal defect repair in the TMJ.
TMJ; Osteochondral; Interface; Gradient; Microsphere; PLGA; BMP-2; TGF-β1
Cisplatin (CDDP) intravenous treatments suffer several dose-limiting toxicity issues. Hyaluronan (HA), a naturally occurring biopolymer in the interstitium, is primarily cleared by the lymphatic system. An alteration in input rate and administration route through pulmonary delivery of hyaluronan-cisplatin conjugate (HA-Pt) may increase local lung CDDP concentrations and decrease systemic toxicity.
Sprague-Dawley rats were split into four groups: i.v. CDDP (3.5 mg/kg), i.v. HA-Pt conjugate (3.5 mg/kg equivalent CDDP), lung instillation CDDP and lung instillation HA-Pt conjugate. Total platinum level in the lungs of the HA-Pt lung instillation group was 5.7-fold and 1.2-fold higher than the CDDP intravenous group at 24 h and 96 h, respectively. A 1.1-fold increase of Pt accumulation in lung draining nodes for the HA-Pt lung instillation group was achieved at 24 h relative to the CDDP i.v. group. In the brain and kidneys, the CDDP i.v. group had higher tissue/plasma ratios compared to the HA-Pt lung instillation group. Augmented tissue distribution from CDDP i.v. could translate into enhanced tissue toxicity compared to the altered input rate and distribution of the intrapulmonary nanoformulation.
In conclusion, a local pulmonary CDDP delivery system was developed with increased platinum concentration in the lungs and draining nodes compared to i.v. therapy.
cisplatin; hyaluronan; pharmacokinetics; pulmonary delivery; lung chemotherapeutics
Synthetic nanoparticles are emerging as versatile tools in biomedical applications, particularly in the area of biomedical imaging. Nanoparticles 1 – 100 nm in diameter have dimensions comparable to biological functional units. Diverse surface chemistries, unique magnetic properties, tunable absorption and emission properties, and recent advances in the synthesis and engineering of various nanoparticles suggest their potential as probes for early detection of diseases such as cancer. Surface functionalization has expanded further the potential of nanoparticles as probes for molecular imaging.
To summarize emerging research of nanoparticles for biomedical imaging with increased selectivity and reduced nonspecific uptake with increased spatial resolution containing stabilizers conjugated with targeting ligands.
This review summarizes recent technological advances in the synthesis of various nanoparticle probes, and surveys methods to improve the targeting of nanoparticles for their application in biomedical imaging.
Structural design of nanomaterials for biomedical imaging continues to expand and diversify. Synthetic methods have aimed to control the size and surface characteristics of nanoparticles to control distribution, half-life and elimination. Although molecular imaging applications using nanoparticles are advancing into clinical applications, challenges such as storage stability and long-term toxicology should continue to be addressed.
biomedical imaging; molecular imaging; nanoparticle synthesis; surface modification; targeting
It is well recognized that physical and chemical properties of materials can alter dramatically at nanoscopic scale, and the growing use of nanotechnologies requires careful assessment of unexpected toxicities and biological interactions. However, most in vivo toxicity concerns focus primarily on pulmonary, oral, and dermal exposure to ultrafine particles. As nanomaterials expand as therapeutics and as diagnostic tools, parenteral administration of engineered nanomaterials should also be recognized as a critical aspect for toxicity consideration. Due to the complex nature of nanomaterials, conflicting studies have led to different views of their safety. Here, the physicochemical properties of four representative nanomaterials (dendrimers, carbon nanotubes, quantum dots, and gold nanoparticles) as it relates to their toxicity after systemic exposure is discussed.
nanomaterial; toxicity; in vivo; dendrimer; carbon nanotube; quantum dot; gold nanoparticle; analysis
Diabetes is a set of diseases characterized by defects in insulin utilization, either through autoimmune destruction of insulin-producing cells (Type I) or insulin resistance (Type II). Treatment options can include regular injections of insulin, which can be painful and inconvenient, often leading to low patient compliance. To overcome this problem, novel formulations of insulin are being investigated, such as inhaled aerosols. Sufficient deposition of powder in the peripheral lung to maximize systemic absorption requires precise control over particle size and density, with particles between 1 and 5 μm in aerodynamic diameter being within the respirable range. Insulin nanoparticles were produced by titrating insulin dissolved at low pH up to the pI of the native protein, and were then further processed into microparticles using solvent displacement. Particle size, crystallinity, dissolution properties, structural stability, and bulk powder density were characterized. We have demonstrated that pure drug insulin microparticles can be produced from nanosuspensions with minimal processing steps without excipients, and with suitable properties for deposition in the peripheral lung.
Insulin; Diabetes; Pulmonary Medicine; Crystallinity