Calcein Binding to Assess Mineralization in Hydrogel Microspheres.

We describe a method to assess mineralization by osteoblasts within microspheres using calcein. Fluorescence imaging of calcein bound to the calcium in hydroxyapatite permits assessment of the mineralized portion of the extracellular matrix. Colorimetric imaging of Alizarin Red S complexed with calcium also gives measures of mineralization, and in tissue cultures calcein and Alizarin Red S have been shown to bind to the same regions of mineral deposits.

Biomaterials for human space exploration: A review of their untapped potential.

As biomaterial advances make headway into lightweight radiation protection, wound healing dressings, and microbe resistant surfaces, a relevance to human space exploration manifests itself. To address the needs of the human in space, a knowledge of the space environment becomes necessary. Both an understanding of the environment itself and an understanding of the physiological adaptations to that environment must inform design parameters.

Development of an Electroactive Hydrogel as a Scaffold for Excitable Tissues.

For many cells used in tissue engineering applications, the scaffolds upon which they are seeded do not entirely mimic their native environment, particularly in the case of excitable tissues. For instance, muscle cells experience contraction and relaxation driven by the electrical input of an action potential. Electroactive materials can also deform in response to electrical input; however, few such materials are currently suitable as cell scaffolds.

Micropatterning biomineralization with immobilized mother of pearl proteins.

In response to the drawbacks of autograft donor-site morbidity and bone morphogenetic protein type 2 (BMP2) carcinogenesis and ectopic bone formation, there has been an increased research focus towards developing alternatives capable of achieving spatial control over bone formation. Here we show for the first time both osteogenic differentiation and mineralization (from solution or mediated by cells) occurring within predetermined microscopic patterns. Our results revealed that both PEGylated BMP2 and nacre proteins induced stem cell osteodifferentiation in microscopic patterns when these proteins were covalently bonded in patterns onto polyethylene glycol diacrylate (PEGDA) hydrogel substrates; however, only nacre proteins induced mineralization localized to the micropatterns.

Coencapsulation of ISCs and MSCs Enhances Viability and Function of both Cell Types for Improved Wound Healing.

Introduction: We previously demonstrated that insulin secreting cells (ISCs) accelerate healing of chronic wounds, and it is known that mesenchymal stem cells (MSCs) also accelerate wound healing. Here, we report that the combination of both cell types coencapsulated into a synthetic hydrogel dressing accelerates chronic wound healing 3 × faster than control and 2 × faster than each cell type delivered singly. Specifically, insulin released by ISCs activates the PI3/Akt pathway, which is vital to the function and survival of MSCs.

Biomanufacturing for clinically advanced cell therapies.

The achievements of cell-based therapeutics have galvanized efforts to bring cell therapies to the market. To address the demands of the clinical and eventual commercial-scale production of cells, and with the increasing generation of large clinical datasets from chimeric antigen receptor T-cell immunotherapy, from transplants of engineered haematopoietic stem cells and from other promising cell therapies, an emphasis on biomanufacturing requirements becomes necessary. Robust infrastructure should address current limitations in cell harvesting, expansion, manipulation, purification, preservation and formulation, ultimately leading to successful therapy administration to patients at an acceptable cost.

Spatiotemporal Control Strategies for Bone Formation through Tissue Engineering and Regenerative Medicine Approaches.

Global increases in life expectancy drive increasing demands for bone regeneration. The gold standard for surgical bone repair is autografting, which enjoys excellent clinical outcomes; however, it possesses significant drawbacks including donor site morbidity and limited availability. Although collagen sponges delivered with bone morphogenetic protein, type 2 (BMP2) are a common alternative or supplement, they do not efficiently retain BMP2, necessitating extremely high doses to elicit bone formation.

Activin A improves retinal pigment epithelial cell survival on stiff but not soft substrates.

In several retinal degenerative disease pathologies, such as dry age-related macular degeneration (AMD), the retinal pigment epithelium (RPE) cell monolayer becomes dysfunctional. Promising tissue engineering treatment approaches implant RPE cells on scaffolds into the subretinal space. However, these approaches are not without challenges.

The effect of polymer molecular weight and cell seeding density on viability of cells entrapped within PEGDA hydrogel microspheres.

Cell microencapsulation can be used in tissue engineering as a scaffold or physical barrier that provides immunoisolation for donor cells. When used as a barrier, microencapsulation shields donor cells from the host immune system when implanted for cell therapies. Maximizing therapeutic product delivery per volume of microencapsulated cells necessitates first optimising the viability of entrapped cells.

The effect of low-magnitude, high-frequency vibration on poly(ethylene glycol)-microencapsulated mesenchymal stem cells.

Low-magnitude, high-frequency vibration has stimulated osteogenesis in mesenchymal stem cells when these cells were cultured in certain types of three-dimensional environments. However, results of osteogenesis are conflicting with some reports showing no effect of vibration at all. A large number of vibration studies using three-dimensional scaffolds employ scaffolds derived from natural sources.

Strain and Vibration in Mesenchymal Stem Cells.

Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into any mesenchymal tissue, including bone, cartilage, muscle, and fat. MSC differentiation can be influenced by a variety of stimuli, including environmental and mechanical stimulation, scaffold physical properties, or applied loads. Numerous studies have evaluated the effects of vibration or cyclic tensile strain on MSCs towards developing a mechanically based method of differentiation, but there is no consensus between studies and each investigation uses different culture conditions, which also influence MSC fate.

Scaffolds for retinal pigment epithelial cell transplantation in age-related macular degeneration.

In several retinal degenerative diseases, including age-related macular degeneration, the retinal pigment epithelium, a highly functionalized cell monolayer, becomes dysfunctional. These retinal diseases are marked by early retinal pigment epithelium dysfunction reducing its ability to maintain a healthy retina, hence making the retinal pigment epithelium an attractive target for treatment. Cell therapies, including bolus cell injections, have been investigated with mixed results.

Characterization and optimization of actuating poly(ethylene glycol) diacrylate/acrylic acid hydrogels as artificial muscles.

Large volume deficiencies in skeletal muscle tissue fail to heal with conservative treatments, and improved treatment methods are needed. Tissue engineered scaffolds for skeletal muscle need to mimic the optimal environment for muscle development by providing the proper electric, mechanical, and chemical cues. Electroactive polymers, polymers that change in size or shape in response to an electric field, may be able to provide the optimal environment for muscle growth.

The influence of substrate modulus on retinal pigment epithelial cells.

Although transplantation of retinal pigment epithelial (RPE) cells has shown promise for the treatment of retinal degenerative diseases, this therapeutic approach is not without challenges. Two major challenges are RPE cell dedifferentiation and inflammatory response following transplantation. The aim of this work is to understand how the rigidity of a scaffold, a relatively unexplored design aspect in retinal tissue engineering, affects RPE cells, particularly the pathways associated with the aforementioned challenges.

Polymeric Materials for Cell Microencapsulation.

Mammalian cells have been microencapsulated within both natural and synthetic polymers for over half a century. Specifically, in the last 36 years microencapsulated cells have been used therapeutically to deliver a wide range of drugs, cytokines, growth factors, and hormones while enjoying the immunoisolation provided by the encapsulating material. In addition to preventing immune attack, microencapsulation prevents migration of entrapped cells.

The Effect of Swelling Ratio on the Coulter Underestimation of Hydrogel Microsphere Diameters.

It has been demonstrated that the diameters of porous particles are underestimated by Coulter measurements. This phenomenon has also been observed in hydrogel particles, but not characterized. Since the Coulter principle uses the displacement of electrolyte to determine particle size, electrolyte contained within the swelled hydrogel microparticles results in an underestimate of actual particle diameters.

Hydrogel Microencapsulated Insulin-Secreting Cells Increase Keratinocyte Migration, Epidermal Thickness, Collagen Fiber Density, and Wound Closure in a Diabetic Mouse Model of Wound Healing.

Wound healing is a hierarchical process of intracellular and intercellular signaling. Insulin is a potent chemoattractant and mitogen for cells involved in wound healing. Insulin's potential to promote keratinocyte growth and stimulate collagen synthesis in fibroblasts is well described.

Poly(3,4-ethylenedioxythiophene) nanoparticle and poly(ɛ-caprolactone) electrospun scaffold characterization for skeletal muscle regeneration.

Injuries to peripheral nerves and/or skeletal muscle can cause scar tissue formation and loss of function. The focus of this article is the creation of a conductive, biocompatible scaffold with appropriate mechanical properties to regenerate skeletal muscle. Poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles (Np) were electrospun with poly(ɛ-caprolactone) (PCL) to form conductive scaffolds.

Cell microencapsulation with synthetic polymers.

The encapsulation of cells into polymeric microspheres or microcapsules has permitted the transplantation of cells into human and animal subjects without the need for immunosuppressants. Cell-based therapies use donor cells to provide sustained release of a therapeutic product, such as insulin, and have shown promise in treating a variety of diseases. Immunoisolation of these cells via microencapsulation is a hotly investigated field, and the preferred material of choice has been alginate, a natural polymer derived from seaweed due to its gelling conditions.

Rapid healing of femoral defects in rats with low dose sustained BMP2 expression from PEGDA hydrogel microspheres.

Current strategies for bone regeneration after traumatic injury often fail to provide adequate healing and integration. Here, we combined the poly (ethylene glycol) diacrylate (PEGDA) hydrogel with allogeneic "carrier" cells transduced with an adenovirus expressing BMP2. The system is unique in that the biomaterial encapsulates the cells, shielding them and thus suppressing destructive inflammatory processes.

Cell-based therapies for spinal fusion.

During spinal fusion procedures, bone grafts are placed to promote bone healing and to provide stability. The autologous graft is the current clinical standard of care due to its ability to initiate bone formation and because it poses no risk of rejection; however, it has drawbacks such as donor site morbidity and limited supply. Due to processing for sterility and storage, allogeneic grafts have reduced osteoinductive properties and thus must be delivered with osteoinductive agents.

Rapid Heterotrophic Ossification with Cryopreserved Poly(ethylene glycol-) Microencapsulated BMP2-Expressing MSCs.

Autologous bone grafting is the most effective treatment for long-bone nonunions, but it poses considerable risks to donors, necessitating the development of alternative therapeutics. Poly(ethylene glycol) (PEG) microencapsulation and BMP2 transgene delivery are being developed together to induce rapid bone formation. However, methods to make these treatments available for clinical applications are presently lacking.

Distraction osteogenesis-induced muscle fibrosis may not be associated with TGF-β1.

Background: Transforming growth factor-β 1 (TGF-β1) participates in the synthesis and deposition of collagen. It has been implicated in fibrosis of tendons in wound-healing models but has never been studied in muscles with respect to distraction osteogenesis.

Methods: Using a rabbit model of distraction osteogenesis, we distracted the left tibias of 36 New Zealand white rabbits at 0.

Cathepsin K-sensitive poly(ethylene glycol) hydrogels for degradation in response to bone resorption.

We propose a new strategy of biomaterial design to achieve selective cellular degradation by the incorporation of cathepsin K-degradable peptide sequences into a scaffold structure so that scaffold biodegradation can be induced at the end of the bone formation process. Poly(ethylene glycol) diacrylate (PEGDA) hydrogels were used as a model biomaterial system in this study. A cathepsin K-sensitive peptide, GGGMGPSGPWGGK (GPSG), was synthesized and modified with acryloyl-PEG-succinimidyl carbonate to produce a cross-linkable cathepsin K-sensitive polymer that can be used to form a hydrogel.

Cell-based gene therapy for repair of critical size defects in the rat fibula.

More than a decade has passed since the first experiments using adenovirus-transduced cells expressing bone morphogenetic protein 2 were performed for the synthesis of bone. Since this time, the field of bone gene therapy has tackled many issues surrounding safety and efficacy of this type of strategy. We present studies examining the parameters of the timing of bone healing, and remodeling when heterotopic ossification (HO) is used for bone fracture repair using an adenovirus gene therapy approach.