Encapsulation of Osteoblast Seeded Microcarriers into Injectable, Photopolymerizable Three-Dimensional Scaffolds Based ond,l-Lactide and ε-Caprolactone

An Edible, Decellularized Plant Derived Cell Carrier for Lab Grown Meat

Rapidly expanding skeletal muscle satellite cells with cost-effective methods have been presented as a solution for meeting the growing global demand for meat. A common strategy for scaling cell proliferation employs microcarriers, small beads designed to support anchorage-dependent cells in suspension-style bioreactors. No carrier has yet been marketed for the cultivation of lab-grown meat. The objective of this study was to demonstrate a rapid, food safe, decellularization procedure to yield cell-free extracellular matrix scaffolds and evaluate them as cell carriers for lab grown meat. Broccoli florets were soaked in SDS, Tween-20, and bleach for 48 h. The decellularization process was confirmed via histology, which showed an absence of cell nuclei, and DNA quantification (0.0037 ± 0.00961 μg DNA/mg tissue). Decellularized carriers were sorted by cross sectional area (7.07 ± 1.74 mm2, 3.03 ± 1.15 mm2, and 0.49 ± 0.3 mm2) measured for eccentricity (0.73 ± 0.16). Density measurements of decellularized carriers (1.01 ± 0.01 g/cm) were comparable to traditional microcarriers. Primary bovine satellite cells were inoculated into and cultured within a reactor containing decellularized carriers. Cell adhesion was observed and cell death was limited to 2.55 ± 1.09%. These studies suggested that broccoli florets may serve as adequate edible carrier scaffolds for satellite cells.

Modular microcarrier technologies for cell-based bone regeneration

A variety of materials-based approaches to accelerate the regeneration of damaged bone have been developed to meet the important clinical need for improved bone fillers. This comprehensive review covers the materials and technologies used in modular microcarrier-based methods for delivery of progenitor cells in orthopaedic repair applications. It provides an overview of the field and the rationale for using microcarriers combined with osteoprogenitor cells for bone regeneration in particular. The general concepts and methods used in microcarrier-based cell culture and delivery are described, and methods for fabricating and characterizing microcarriers designed for specific indications are presented. A comprehensive review of the current literature on the use of microcarriers in bone regeneration is provided, with emphasis on key developments in the field and their impact. The studies reviewed are organized according to the broad classes of materials that are used for fabricating microcarriers, including polysaccharides, proteins and peptides, ceramics, and synthetic polymers. In addition, composite microcarriers that incorporate multiple material types or that are mineralized biomimetically are included. In each case, the fabrication, processing, characterization, and resulting function of the microcarriers is described, with an emphasis on their ability to support osteogenic differentiation of progenitor cells in vitro, and their effectiveness in healing bone defects in vivo. In addition, a summary of the current state of the field is provided, as are future perspectives on how microcarrier technologies may be enhanced to create improved cell-based therapies for bone regeneration.

Water-Soluble Photoinitiators in Biomedical Applications

Light-initiated polymerization processes are currently an important tool in various industrial fields. The advancement of technology has resulted in the use of photopolymerization in various biomedical applications, such as the production of 3D hydrogel structures, the encapsulation of cells, and in drug delivery systems. The use of photopolymerization processes requires an appropriate initiating system that, in biomedical applications, must meet additional criteria such as high water solubility, non-toxicity to cells, and compatibility with visible low-power light sources. This article is a literature review on those compounds that act as photoinitiators of photopolymerization processes in biomedical applications. The division of initiators according to the method of photoinitiation was described and the related mechanisms were discussed. Examples from each group of photoinitiators are presented, and their benefits, limitations, and applications are outlined.

Nanocomposite Porous Microcarriers Based on Strontium-Substituted HA- g-Poly(γ-benzyl-l-glutamate) for Bone Tissue Engineering

Porous microcarriers have aroused increasing attention recently, which can create a protected environment for sufficient cell seeding density, facilitate oxygen and nutrient transfer, and well support the cell attachment and growth. In this study, porous microcarriers fabricated from the strontium-substituted hydroxyapatite- graft-poly(γ-benzyl-l-glutamate) (Sr10-HA- g-PBLG) hybrid nanocomposite were developed. The surface grating of PBLG, the micromorphology and element distribution, mechanical strength, in vitro degradation, and Sr²⁺ ion release of the obtained Sr10-HA- g-PBLG porous microcarriers were investigated, respectively. The grafting ratio and the molecular weight of the grafted PBLG of Sr10-HA- g-PBLG could be effectively controlled by varying the initial ratio of BLG-NCA to Sr10-HA-NH₂. The microcarriers exhibited a highly porous and interconnected microstructure with the porosity of about 90% and overall density of 1.03-1.06 g/cm³. Also, the degradation rate of Sr10-HA-PBLG microcarriers could be effectively controlled and long-term Sr²⁺ release was obtained. The Sr10-HA-PBLG microcarriers allowed cells adhesion, infiltration, and proliferation and promoted the osteogenic differentiation of rabbit adipose-derived stem cells (ADSCs). Successful healing of femoral bone defect was proved by injection of the ADSCs-seeded Sr10-HA-PBLG microcarriers in a rabbit model.

Global Gene Expression Profiling and Alternative Splicing Events during the Chondrogenic Differentiation of Human Cartilage Endplate-Derived Stem Cells

Low back pain (LBP) is a very prevalent disease and degenerative disc diseases (DDDs) usually account for the LBP. However, the pathogenesis of DDDs is complicated and difficult to elucidate. Alternative splicing is a sophisticated regulatory process which greatly increases cellular complexity and phenotypic diversity of eukaryotic organisms. In addition, the cartilage endplate-derived stem cells have been discovered and identified by our research group. In this paper, we continue to investigate gene expression profiling and alternative splicing events during chondrogenic differentiation of cartilage endplate-derived stem cells. We adopted Affymetrix Human Transcriptome Array 2.0 (HTA 2.0) to compare the transcriptional and splicing changes between the control and differentiated samples. RT-PCR and quantitative PCR are used to validate the microarray results. The GO and KEGG pathway analysis was also performed. After bioinformatics analysis of the data, we detected 1953 differentially expressed genes. In terms of alternative splicing, the Splicing Index algorithm was used to select alternatively spliced genes. We detected 4411 alternatively spliced genes. GO and KEGG pathway analysis also revealed several functionally involved biological processes and signaling pathways. To our knowledge, this is the first study to investigate the alternative splicing mechanisms in chondrogenic differentiation of stem cells on a genome-wide scale.

Highly adjustable biomaterial networks from three-armed biodegradable macromers

Biocompatible material platforms with adjustable properties and option for chemical modification are warranted for site-specific biomedical applications. To this end, three-armed biodegradable macromers of well-defined chemical characteristics were prepared from trivalent alcohols with different degrees of ethoxylation and different lengths of oligoester domains. A platform of 15 different macromers was established. The macromers were designed to exhibit different hydrophilicities and molecular weights and contained various types of oligoesters such as d,l-lactide, l-lactide and ε-caprolactone. Macromers chemical composition was determined and molecular weights ranged from 900 to 3000 Da. Thermally induced cross-linking of methacrylated macromers was monitored by oscillation rheology. A novel variant of the solid lipid templating technique was established to fabricate macroporous tissue engineering scaffolds from these macromers. Scaffold properties were thoroughly investigated regarding mechanical properties, compositional analysis including methacrylic double bond conversion, microstructure and porosity. Material properties could be controlled by macromer chemistry. By variation of the fabrication procedure and processing parameters scaffold porosity was increased up to 88%. Basic cytocompatibility was assessed including indirect and direct contact methods. The established macromers hold promise for various biomedical purposes.

STATEMENT OF SIGNIFICANCE

Specific biomedical applications require tailored biomaterials with defined properties. We established a macromer platform for preparation of tissue engineering scaffolds with adjustable chemical and mechanical characteristics. Macromers were composed of trivalent core alcohols with different degrees of ethoxylation to which biodegradable domains - lactide or ε-caprolactone - were oligomerized before final methacrylation. The solid lipid templating technique was adapted to fabricate macroporous scaffolds with controlled pore structure and porosity from the developed macromers, which can also be processed by solid freeform fabrication techniques. The material platform relies on clinically established chemistries of the biodegradable domains and the macromer concept enables the fabrication of networks in which cross-polymerization kinetics, mechanical properties and surface hydrophobicity is predefined by macromer chemistry. Cytocompatibility was confirmed by indirect and direct cell contact experiments.

Past, present, and future of microcarrier-based tissue engineering

The top issue in tissue engineering is how to obtain more seed cells quickly and to preserve their characteristic morphology during in vitro expansion culture of cells. Microcarriers can help to amplify cell numbers and maintain the appropriate phenotype for tissue repair and restoration of function. In addition, microtissue with cell microcarriers can be used to repair diseased tissues or organs. This review introduces the materials used for, and classification of, microcarriers and the improvements in, and potential applications of, microtissues with cell microcarriers in tissue engineering.

The effect of photoinitiators on intracellular AKT signaling pathway in tissue engineering application

Free-radical photopolymerization initiated by photoinitiators is an important method to make tissue engineering scaffolds. To advance understanding of photoinitiator cytocompatibility, we examined three photoinitiators including 2,2-dimethoxy-2-phenylacetophenone (DMPA), Irgacure 2959 (I-2959), and eosin Y photoinitiating system (EY) in terms of their effects on viability of HN4 cells and expression levels of intracellular AKT and its phosphorylated form p-AKT. Our results show that the photoinitiators and their UV-exposed counterparts affect intracellular AKT signaling, which can be used in conjunction with cell viability for cytocompatibility assessment of photoinitiators.

Density-dependent separation of encapsulated cells in a microfluidic channel by using a standing surface acoustic wave

This study presents a method for density-based separation of monodisperse encapsulated cells using a standing surface acoustic wave (SSAW) in a microchannel. Even though monodisperse polymer beads can be generated by the state-of-the-art technology in microfluidics, the quantity of encapsulated cells cannot be controlled precisely. In the present study, mono-disperse alginate beads in a laminar flow can be separated based on their density using acoustophoresis. A mixture of beads of equal sizes but dissimilar densities was hydrodynamically focused at the entrance and then actively driven toward the sidewalls by a SSAW. The lateral displacement of a bead is proportional to the density of the bead, i.e., the number of encapsulated cells in an alginate bead. Under optimized conditions, the recovery rate of a target bead group (large-cell-quantity alginate beads) reached up to 97% at a rate of 2300 beads per minute. A cell viability test also confirmed that the encapsulated cells were hardly damaged by the acoustic force. Moreover, cell-encapsulating beads that were cultured for 1 day were separated in a similar manner. In conclusion, this study demonstrated that a SSAW can successfully separate monodisperse particles by their density. With the present technique for separating cell-encapsulating beads, the current cell engineering technology can be significantly advanced.

Cell survival and proliferation after encapsulation in a chemically modified Pluronic(R) F127 hydrogel

Pluronic® F127 is a biocompatible, injectable, and thermoresponsive polymer with promising biomedical applications. In this study, a chemically modified form, i.e., Pluronic ALA-L with tailored degradation rate, was tested as an encapsulation vehicle for osteoblastic cells. UV cross-linking of the modified polymer results in a stable hydrogel with a slower degradation rate. Toxicological screening showed no adverse effects of the modified Pluronic ALA-L on the cell viability. Moreover, high viability of embedded cells in the cross-linked Pluronic ALA-L was observed with life/death fluorescent staining during a 7-day-culture period. Cells were also cultured on macroporous, cross-linked gelatin microbeads, called CultiSpher-S® carriers, and encapsulated into the modified cross-linked hydrogel. Also, in this situation, good cell proliferation and migration could be observed in vitro. Preliminary in vivo tests have shown the formation of new bone starting from the injected pre-loaded CultiSpher-S® carriers.

Large-scale production of murine embryonic stem cell-derived osteoblasts and chondrocytes on microcarriers in serum-free media

The generation of tissue-engineered constructs from stem cells for the treatment of musculoskeletal diseases may have immense impact in regenerative medicine, but there are difficulties associated with stem cell culture and differentiation, including the use of serum. Here we present serum-free protocols for the successful production of murine embryonic stem cell (mESC) derived osteoblasts and chondrocytes on CultiSpher S macroporous microcarriers in stirred suspension bioreactors. Various inoculum forms and agitation rates were investigated. Produced osteogenic cells were implanted ectopically into SCID mice and orthotopically into a murine burr-hole fracture model. Osterix, osteocalcin and collagen type I were upregulated in osteogenic cultures, while aggrecan and collagen type II were upregulated in chondrogenic cultures. Histological analysis using alizarin red S, von Kossa and alcian blue staining confirmed the presence of osteoblasts and chondrocytes, respectively in cultured microcarriers and excised tissue. Finally, implantation of derived cells into a mouse fracture model revealed cellular integration without any tumor formation. Overall, microcarriers may provide a supportive scaffold for ESC expansion and differentiation in a serum-free bioprocess for in vivo implantation. These findings lay the groundwork for the development of clinical therapies for musculoskeletal injuries and diseases using hESCs and iPS cells.

Synthesis and characterization of dual stimuli responsive macromers based on poly(N-isopropylacrylamide) and poly(vinylphosphonic acid)

Stimulus responsive materials hold great promise in biological applications as they can react to changes in physiological stimuli to produce a desired effect. Stimulus responsive macromers designed to respond to temperature changes at or around 37 degrees C and the presence of divalent cations were synthesized from N-isopropylacrylamide, pentaerythritol diacrylate monostearate, 2-hydroxyethyl acrylate, and vinylphosphonic acid by free radical polymerization. Monomers were incorporated into the macromers in ratios approximating the molar feed ratios, and macromers underwent thermogelation around normal body temperature (36.2-40.5 degrees C) as determined by rheology and differential scanning calorimetry. Macromers containing vinylphosphonic acid interacted with calcium ions in solution, displaying decreased sol-gel transition temperatures (27.6-34.4 degrees C in 100 mM CaCl(2)), with decreases of greater magnitude observed for macromers with higher relative vinylphosphonic acid content. Critical micellar concentrations also decreased in a dose-dependent manner with increased vinylphosphonic acid incorporation in solutions with CaCl(2) but not in solutions with NaCl. These dually responsive macromers allow examination of the effect of increasing vinylphosphonic acid content in a macromer, which holds promise in biological applications such as drug and cell delivery or tissue engineering due to the macromer responsiveness at physiological temperatures and concentrations of calcium.

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.

Dynamic mechanical analysis and esterase degradation of dentin adhesives containing a branched methacrylate

A study of the dynamic mechanical properties and the enzymatic degradation of new dentin adhesives containing a multifunctional methacrylate are described. Adhesives contained 2-hydroxyethyl methacrylate, 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy) phenyl]-propane, and a new multifunctional methacrylate with a branched side chain-trimethylolpropane mono allyl ether dimethacrylate (TMPEDMA). Adhesives were photopolymerized in the presence of 0, 8, and 16 wt % water to simulate wet bonding conditions in the mouth and compared with control adhesives. The degree of conversion as a function of irradiation time was comparable for experimental and control adhesives. In dynamic mechanical analysis, broad tan delta peaks were obtained for all samples, indicating that the polymerized networks are heterogeneous; comparison of the full-width-at-half-maximum values obtained from the tan delta curves indicated increased heterogeneity for samples cured in the presence of water and/or containing TMPEDMA. The experimental adhesive showed higher T(g) and higher rubbery modulus indicating increased crosslink density when compared with the control. The improvement in esterase resistance afforded by adhesives containing the TMPEDMA is greater when this material is photopolymerized in the presence of water, suggesting better performance in the moist environment of the mouth. The improved esterase resistance of the new adhesive could be explained in terms of the densely crosslinked network structure and/or the steric hindrance of branched alkyl side chains.

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.

A novel gellan gel-based microcarrier for anchorage-dependent cell delivery

Competent vehicles are highly sought after as a means to transplant cells for tissue regeneration. In this study, novel hydrogel-based microspherical cell carriers are designed and developed with an FDA-approved natural polysaccharide, gellan gum. The bulk fabrication of these microspheres is performed via a water-in-oil (W/O) emulsion process followed by a series of redox (oxidation-reduction) crosslinking treatments; this enables the microspherical dimensions to be precisely manipulated in terms of injectability, and simultaneously ensures the structural stability. To acquire adhesion affinity with anchorage-dependent cells (ADCs), a covalent coating of gelatin is further applied on the microspherical surfaces. The final product is constructed as a variety of gelatin-grafted-gellan microspherical cell carriers, abbreviated as "TriG" microcarriers. The cell-loading tests are conducted, respectively, with human dermal fibroblasts (HDFs) and human fetal osteoblasts (hFOBs). Morphological observation from optical microscopy and field emission scanning electron microscopy indicates that the HDFs spread well and populate rapidly on surfaces of TriG microcarriers. Immunofluorescent staining reveals the activation of focal adhesion and subsequent organization of F-actin from the attached cell surfaces, which suggests the TriG microspherical substrate is favorable to ADC adhesion and therefore capable of promoting HDF proliferation to achieve confluence by turning over three times within 10 days. The hFOBs are also cultivated on the TriG carriers, where ideal viability and clear potentials for osteogenesis are demonstrated by fluorescent "Live/Dead" screening and specific histobiochemical indications. All these findings suggest that the TriG microcarriers are suitable to provide open platforms for therapeutic ADC proliferation and differentiation.

Evaluation of an injectable, photopolymerizable three-dimensional scaffold based on D: ,L: -lactide and epsilon-caprolactone in a tibial goat model

An in situ crosslinkable, biodegradable, methacrylate-encapped porous bone scaffold composed of D: ,L: -lactide, epsilon-caprolactone, 1,6-hexanediol and poly(ortho-esters), in which crosslinkage is achieved by photoinitiators, was developed for bone tissue regeneration. Three different polymer mixtures (pure polymer and 30% bioactive glass or alpha-tricalcium phosphate added) were tested in a uni-cortical tibial defect model in eight goats. The polymers were randomly applicated in one of four (6.0 mm diameter) defects leaving a fourth defect unfilled. Biocompatibility and bone healing properties were evaluated by serial radiographies, histology and histomorphometry. The pure polymer clearly showed excellent biocompatibility and moderate osteoconductive properties. The addition of alpha-TCP increased the latter characteristics. This product offers potentials as a carrier for bone healing promoter substances.

Gelatin-based microcarriers as embryonic stem cell delivery system in bone tissue engineering: an in-vitro study

Mouse embryonic stem cells were cultured on commercially available biodegradable macroporous microcarriers. A culture period of 1-2 weeks was needed to colonize the microcarriers. Embryonic stem cells retained their pluripotency for up to 14 days when cultured in medium supplemented with leukemia inhibitory factor. Replacing this medium by differentiation medium for 2 weeks initiated osteogenic differentiation. Encapsulation of the cell-loaded microcarriers in photopolymerizable polymers (methacrylate-endcapped poly-D,L-lactide-co-caprolactone), triacetin/hydroxyethylmethacrylate (HEMA) as solvent and with/without gelatin as porogen, resulted in a homogeneous distribution of the microcarriers in the polymer. As observed by transmission electron microscopy, viability of the cells was optimal when gelatin was omitted and when using triacetin instead of HEMA.

Modeling and experimental investigation of rheological properties of injectable poly(lactide ethylene oxide fumarate)/hydroxyapatite nanocomposites

Injectable multiphasic polymer/ceramic composites are attractive as bioresorbable scaffolds for bone regeneration because they can be cross-linked in situ and are osteoconductive. The injectability of the composite depends on the nanoparticle content and the energetic interactions at the polymer/particle interface. The objective of this research was to determine experimentally the rheological properties of the PLEOF/apatite composite as an injectable biomaterial and to compare the viscoelastic response with the predictions of a linear elastic dumbbell model. A degradable in situ cross-linkable terpolymer based on low molecular weight poly(L-lactide) and poly(ethylene oxide) linked by unsaturated fumarate groups is synthesized. The poly(L-lactide-co-ethylene oxide-co-fumarate) (PLEOF) terpolymer interacts with the surface of the apatite nanoparticles by polar interactions and hydrogen bonding. A kinetic model is developed that takes into account the adsorption/desorption of polymer chains to/from the nanoparticle surface. Rheological properties of the aqueous dispersion of PLEOF terpolymer reinforced with nanosized hydroxyapatite (HA) particles are investigated using mechanical rheometry. To this end, we performed a series of rheological experiments on un-cross-linked PLEOF reinforced with different volume fractions of HA nanoparticles. The results demonstrate that the observed nonlinear viscoelasticity at higher shear rates is controlled by the energetic interactions between the polymer chains and dispersed particle aggregates and by the rate of the adsorption/desorption of the chains to/from the surface of the nanoparticles.

Microcarriers in the engineering of cartilage and bone

A major problem in tissue engineering is the availability of a sufficient number of cells with the appropriate phenotype for delivery to damaged or diseased cartilage and bone; the challenge is to amplify cell numbers and maintain the appropriate phenotype for tissue repair and restoration of function. The microcarrier bioreactor culture system offers an attractive method for cell amplification and enhancement of phenotype expression. Besides serving as substrates for the propagation of anchorage-dependent cells, microcarriers can also be used to deliver the expanded undifferentiated or differentiated cells to the site of the defect. The present article provides an overview of the microcarrier culture system, its utility as an in vitro research tool and its potential applications in tissue engineering, particularly in the repair of cartilage and bone.

Artificial extracellular matrix proteins contain heparin-binding and RGD-containing domains to improve osteoblast-like cell attachment and growth

Through the recombinant DNA technology, it is possible to create artificial extracellular matrix (aECM) proteins with domains chosen to modulate cellular behaviors. In this study, we constructed three aECM proteins containing both heparin-binding and RGD-containing domains (387RGDS, Tri-FN10, and TNC-FN3) produced in Escherichia coli. Promotion of MG-63 cell attachment and growth in two-dimensional (2D) cultures (tissue culture plate, polycaprolactone membrane) and 3D cultures (Cytodex 1 and Plastic Plus microcarriers) were demonstrated on these three aECM protein-coated surfaces. These three aECM proteins improved MG-63 cell attachment and growth in the order TNC-FN3 > Tri-FN10 > 387RGDS in both 2D and 3D cultures. This study is the first report of the construction of aECM proteins that contain both heparin-binding and RGD-containing domains used in osteoblast tissue engineering applications.