Three-dimensional biomaterials for the study of human pluripotent stem cells

The Application of Biomaterials to Tissue Engineering Neural Retina and Retinal Pigment Epithelium

The prevalence of degenerative retinal disease is ever increasing as life expectancy rises globally. The human retina fails to regenerate and the use of human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs) to engineer retinal tissue is of particular interest due to the limited availability of suitable allogeneic or autologous tissue. Retinal tissue and its development are well characterized, which have resulted in robust assays to assess the development of tissue-engineered retina. Retinal tissue can be generated in vitro from hESCs and hiPSCs without biomaterial scaffolds, but despite advancements, protocols remain slow, expensive, and fail to result in mature functional tissue. Several recent studies have demonstrated the potential of biomaterial scaffolds to enhance generation of hESC/hiPSC-derived retinal tissue, including synthetic polymers, silk, alginate, hyaluronic acid, and extracellular matrix molecules. This review outlines the advances that have been made toward tissue-engineered neural retina and retinal pigment epithelium (RPE) for clinical application in recent years, including the success of clinical trials involving transplantation of cells and tissue to promote retinal repair; and the evidence from in vitro and animal studies that biomaterials can enhance development and integration of retinal tissue.

Hydrogel-Based Bioprocess for Scalable Manufacturing of Human Pluripotent Stem Cell-Derived Neural Stem Cells

Neural stem cells derived from human pluripotent stem cells (hPSC-NSCs) are of great value for modeling diseases, developing drugs, and treating neurological disorders. However, manufacturing high-quantity and -quality hPSC-NSCs, especially for clinical applications, remains a challenge. Here, we report a chemically defined, high-yield, and scalable bioprocess for manufacturing hPSC-NSCs. hPSCs are expanded and differentiated into NSCs in microscale tubes made with alginate hydrogels. The tubes are used to isolate cells from the hydrodynamic stresses in the culture vessel and limit the radial diameter of the cell mass to less than 400 μm to ensure efficient mass transport during the culture. The hydrogel tubes provide uniform, reproducible, and cell-friendly microspaces and microenvironments for cells. With this new technology, we showed that hPSC-NSCs could be produced in 12 days with high viability (∼95%), high purity (>90%), and high yield (∼5 × 10⁸ cells/mL of microspace). The volumetric yield is about 250 times more than the current state-of-the-art. Whole transcriptome analysis and quantitative real-time polymerase chain reaction showed that hPSC-NSCs made by this process had a similar gene expression to hPSC-NSCs made by the conventional culture technology. The produced hPSC-NSCs could mature into both neurons and glial cells in vitro and in vivo. The process developed in this paper can be used to produce large numbers of hPSC-NSCs for various biomedical applications in the future.

3D Microstructured Scaffolds to Support Photoreceptor Polarization and Maturation

Blinding disorders of the outer retina involve dysfunction and degeneration of photoreceptors. One potential approach to treat these forms of blindness is to repopulate the outer retina via a simple bolus injection of donor photoreceptors. However, this may not be ideal due to the highly polarized organization of photoreceptors that include apical light sensing photopigments and basal axon terminals. Furthermore, bolus injections create uncertainty with regard to the area, density, and retention of donor cells. Here, a novel and robust microfabrication process is developed to create 3D, micrometer-sized complex structures in ultrathin and biocompatible elastomer films (nonbiodegradable polydimethylsiloxane and biodegradable poly(glycerol-sebacate)) that can serve as polarizable photoreceptor delivery scaffolds, consisting of an array of cup-shaped photoreceptor capture wells that funnel into a microchannel. This "wine glass" scaffold design promotes efficient capture of human pluripotent stem-cell-derived photoreceptor cell bodies and guidance of basal axon extensions, ultimately achieving a uniform level of organization and polarization that is not possible with bolus injections or previously described scaffolds. In addition to future therapeutic applications, our scaffold design and materials provide a platform to generate reproducible and scalable in vitro models of photoreceptor-based diseases.

Two-Photon Laser Polymerization: From Fundamentals to Biomedical Application in Tissue Engineering and Regenerative Medicine

Three-dimensional material microstructuring by femtosecond laser-induced two-photon polymerization is emerging as an important tool in biomedicine. During two-photon polymerization, a tightly focused femtosecond laser pulse induces a crosslinking photoreaction in the polymer confined within the focal volume. As a rapid-prototyping technique, two-photon polymerization enables the fabrication of truly arbitrary three-dimensional micro- and nano-structures directly from computer models, with a spatial resolution down to 100 nm. In this review, we discuss the fundamentals, experimental methods, and materials used for two-photon polymerization; in addition, we present some applications of this technology related to microfluidics and to biomaterial scaffolds for tissue engineering and regenerative medicine.

A Scalable and Efficient Bioprocess for Manufacturing Human Pluripotent Stem Cell-Derived Endothelial Cells

Endothelial cells (ECs) are of great value for cell therapy, tissue engineering, and drug discovery. Obtaining high-quantity and -quality ECs remains very challenging. Here, we report a method for the scalable manufacturing of ECs from human pluripotent stem cells (hPSCs). hPSCs are expanded and differentiated into ECs in a 3D thermoreversible PNIPAAm-PEG hydrogel. The hydrogel protects cells from hydrodynamic stresses in the culture vessel and prevents cells from excessive agglomeration, leading to high-culture efficiency including high-viability (>90%), high-purity (>80%), and high-volumetric yield (2.0 × 10⁷ cells/mL). These ECs (i.e., 3D-ECs) had similar properties as ECs made using 2D culture systems (i.e., 2D-ECs). Genome-wide gene expression analysis showed that 3D-ECs had higher expression of genes related to vasculature development, extracellular matrix, and glycolysis, while 2D-ECs had higher expression of genes related to cell proliferation.

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hPSCs can be differentiated into endothelial cells in 3D thermoreversible hydrogels

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The differentiation efficiency is similar to this in 2D cultures

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The global gene expression and phenotypes are similar to ECs made in 2D cultures

New substrates for stem cell control

The capacity to culture stem cells in a controllable, robust and scalable manner is necessary in order to develop successful strategies for the generation of cellular and tissue platforms for drug screening, toxicity testing, tissue engineering and regenerative medicine. Creating substrates that support the expansion, maintenance or directional differentiation of stem cells would greatly aid these efforts. Optimally, the substrates used should be chemically defined and synthetically scalable, allowing growth under defined, serum-free culture conditions. To achieve this, the chemical and physical attributes of the substrates should mimic the natural tissue environment and allow control of their biological properties. Herein, recent advances in the development of materials to study/manipulate stem cells, both in vitro and in vivo, are described with a focus on the novelty of the substrates' properties, and on application of substrates to direct stem cells.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

MBG scaffolds containing chitosan microspheres for binary delivery of IL-8 and BMP-2 for bone regeneration

Biomimetic delivery of chemokines and growth factors based on stem cell recruitment and endochondral ossification, as the key steps in natural regenerative process, has been an area of intense research in recent years. An inflammatory chemokine, interleukin-8 (IL-8), was recently reported with high recruitment efficiency of bone marrow stem cells, chondrogenic inductivity and immune regulatory functions. In this study, the effect of IL-8 action duration on bone morphogenetic protein-2 (BMP-2)-induced bone regeneration was studied to achieve an optimal synergism of these two proteins. Herein, a mesoporous bioactive glass (MBG)-based scaffold with BMP-2 entrapment and IL-8-loaded chitosan microspheres (CMs) was developed. The MBG scaffold with size-matched mesopores was adopted for the long-term sustained delivery of BMP-2; and CMs with different sizes, prepared using a modified ionotropic gelation method, were customized to match the optimal action time of IL-8. The results indicated that CMs of 100 μm diameter and medium crosslinking density exhibited an 85% release of IL-8 in 7 days and the MBG substrate exhibited a long-term sustained release of BMP-2. Furthermore, the binary delivery system exhibited excellent biocompatibility and synergistically enhanced osteoinductivity. In an in situ bone regeneration model of a rabbit radius large segmental defect, the system efficiently accelerated the whole regenerative process, with the highest bone formation amount from an early stage and the highest degree of regenerative completion. Since delivery systems for multiple cytokines have been in great demand due to the requirement of complicated biological processes, we believe that this new binary delivery system could be customized to design other dual delivery systems for improving bone-repairing biomaterials with higher regenerative efficiency.

Effects of 3D culturing conditions on the transcriptomic profile of stem-cell-derived neurons

Understanding neurological diseases requires tractable genetic systems. Engineered 3D neural tissues are an attractive choice, but how the cellular transcriptomic profiles in these tissues are affected by the encapsulating materials and are related to the human-brain transcriptome is not well understood. Here, we report the characterization of the effects of culturing conditions on the transcriptomic profiles of induced neuronal cells, as well as a method for the rapid generation of 3D co-cultures of neuronal and astrocytic cells from the same pool of human embryonic stem cells. By comparing the gene-expression profiles of neuronal cells in culture conditions relevant to the developing human brain, we found that modifying the degree of crosslinking of composite hydrogels can tune expression patterns so they correlate with those of specific brain regions and developmental stages. Moreover, by using single-cell sequencing, we show that our engineered tissues recapitulate transcriptional patterns of cell types in the human brain. The analysis of culturing conditions will inform the development of 3D neural tissues for use as tractable models of brain diseases.

hPSC-Derived Striatal Cells Generated Using a Scalable 3D Hydrogel Promote Recovery in a Huntington Disease Mouse Model

Huntington disease (HD) is an inherited, progressive neurological disorder characterized by degenerating striatal medium spiny neurons (MSNs). One promising approach for treating HD is cell replacement therapy, where lost cells are replaced by MSN progenitors derived from human pluripotent stem cells (hPSCs). While there has been remarkable progress in generating hPSC-derived MSNs, current production methods rely on two-dimensional culture systems that can include poorly defined components, limit scalability, and yield differing preclinical results. To facilitate clinical translation, here, we generated striatal progenitors from hPSCs within a fully defined and scalable PNIPAAm-PEG three-dimensional (3D) hydrogel. Transplantation of 3D-derived striatal progenitors into a transgenic mouse model of HD slowed disease progression, improved motor coordination, and increased survival. In addition, the transplanted cells developed an MSN-like phenotype and formed synaptic connections with host cells. Our results illustrate the potential of scalable 3D biomaterials for generating striatal progenitors for HD cell therapy.

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3D-generated striatal cells rapidly achieve functional maturity

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Transplanted cells delayed disease onset and alleviated symptoms in HD mice

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Transplanted striatal cells increased lifespan in HD mice

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HTT aggregates were observed in striatal cells transplanted into HD mice

Materials for Neural Differentiation, Trans-Differentiation, and Modeling of Neurological Disease

Neuron regeneration from pluripotent stem cells (PSCs) differentiation or somatic cells trans-differentiation is a promising approach for cell replacement in neurodegenerative diseases and provides a powerful tool for investigating neural development, modeling neurological diseases, and uncovering the mechanisms that underlie diseases. Advancing the materials that are applied in neural differentiation and trans-differentiation promotes the safety, efficiency, and efficacy of neuron regeneration. In the neural differentiation process, matrix materials, either natural or synthetic, not only provide a structural and biochemical support for the monolayer or three-dimensional (3D) cultured cells but also assist in cell adhesion and cell-to-cell communication. They play important roles in directing the differentiation of PSCs into neural cells and modeling neurological diseases. For the trans-differentiation of neural cells, several materials have been used to make the conversion feasible for future therapy. Here, the most current applications of materials for neural differentiation for PSCs, neuronal trans-differentiation, and neurological disease modeling is summarized and discussed.

Thermogelling 3D Systems towards Stem Cell-Based Tissue Regeneration Therapies

Stem cell culturing and differentiation is a very important research direction for tissue engineering. Thermogels are well suited for encapsulating cells because of their non-biotoxic nature and mild sol-gel transition as temperature increases. In particular, thermogels provide a 3D growth environment for stem cell growth, which is more similar to the extracellular matrix than flat substrates, so thermogels as a medium can overcome many of the cell abnormalities caused by 2D cell growth. In this review, we summarize the applications of thermogels in cell and stem cell culture in recent years. We also elaborate on the methods to induce stem cell differentiation by using thermogel-based 3D scaffolds. In particular, thermogels, encapsulating specific differentiation-inducing factor and having specific structures and moduli, can induce the differentiation into the desired tissue cells. Three dimensional thermogel scaffolds that control the growth and differentiation of cells will undoubtedly have a bright future in regenerative medicine.

Scalable and physiologically relevant microenvironments for human pluripotent stem cell expansion and differentiation

Human pluripotent stem cells (hPSCs) are required in large numbers for various biomedical applications. However, the scalable and cost-effective culturing of high quality hPSCs and their derivatives remains very challenging. Here, we report a novel and physiologically relevant 3D culture system (called the AlgTube cell culture system) for hPSC expansion and differentiation. With this system, cells are processed into and cultured in microscale alginate hydrogel tubes that are suspended in the cell culture medium in a culture vessel. The hydrogel tubes protect cells from hydrodynamic stresses in the culture vessel and limit the cell mass smaller than 400 μm in diameter to ensure efficient mass transport, creating cell-friendly microenvironments for growing cells. This system is simple, scalable, highly efficient, defined and compatible with the current good manufacturing practices. Under optimized culture conditions, the AlgTubes enabled long-term culture of hPSCs (>10 passages, >50 days) with high cell viability, high growth rate (1000-fold expansion over 10 days per passage), high purity (>95% Oct4+) and high yield (5.0 × 10⁸ cells ml^-1), all of which offer considerable advantages compared to current approaches. Moreover, the AlgTubes enabled directed differentiation of hPSCs into various tissue cells. This system can be readily scaled to support research from basic biological study to clinical development and the future industry-scale production.

Strategies Developed to Induce, Direct, and Potentiate Bone Healing

Bone exhibits a great ability for endogenous self-healing. Nevertheless, impaired bone regeneration and healing is on the rise due to population aging, increasing incidence of bone trauma and the clinical need for the development of alternative options to autologous bone grafts. Current strategies, including several biomolecules, cellular therapies, biomaterials, and different permutations of these, are now developed to facilitate the vascularization and the engraftment of the constructs, to recreate ultimately a bone tissue with the same properties and characteristics of the native bone. In this review, we browse the existing strategies that are currently developed, using biomolecules, cells and biomaterials, to induce, direct and potentiate bone healing after injury and further discuss the biological processes associated with this repair.

3D neural tissue models: From spheroids to bioprinting

Three-dimensional (3D) in vitro neural tissue models provide a better recapitulation of in vivo cell-cell and cell-extracellular matrix interactions than conventional two-dimensional (2D) cultures. Therefore, the former is believed to have great potential for both mechanistic and translational studies. In this paper, we review the recent developments in 3D in vitro neural tissue models, with a particular focus on the emerging bioprinted tissue structures. We draw on specific examples to describe the merits and limitations of each model, in terms of different applications. Bioprinting offers a revolutionary approach for constructing repeatable and controllable 3D in vitro neural tissues with diverse cell types, complex microscale features and tissue level responses. Further advances in bioprinting research would likely consolidate existing models and generate complex neural tissue structures bearing higher fidelity, which is ultimately useful for probing disease-specific mechanisms, facilitating development of novel therapeutics and promoting neural regeneration.

A versatile 3D tissue matrix scaffold system for tumor modeling and drug screening

Most of the anticancer drug candidates entering preclinical trials fail to be approved for clinical applications. The following are among the main causes of these failures: studying molecular mechanisms of cancer development, identifying therapeutic targets, and testing drug candidates using inappropriate tissue culture models, which do not recapitulate the native microenvironment where the cancer cells originate. It has become clear that three-dimensional (3D) cell cultures are more biologically and clinically relevant than 2D models. The spatial and mechanical conditions of 3D cultures enable the cancer cells to display heterogeneous growth, assume diverse phenotypes, express distinct gene and protein products, and attain metastatic potential and resistance to drugs that are reminiscent of tumors in humans. However, the current 3D culture systems using synthetic polymers or selected components of the extracellular matrix (ECM) are defective (particularly the biophysical and biochemical properties of the native ECM) and remain distant to optimally support the signaling cue-oriented cell survival and growth. We introduce a reconstitutable tissue matrix scaffold (TMS) system fabricated using native tissue ECM, with tissue-like architecture and resilience. The structural and compositional properties of TMS favor robust cell survival, proliferation, migration, and invasion in culture and vascularized tumor formation in animals. The combination of porous and hydrogel TMS allows compartmental culture of cancerous and stromal cells, which are distinguishable by biomarkers. The response of the cancer cells grown on TMS to drugs well reflects animal and clinical observations. TMS enables more biologically relevant studies and is suitable for preclinical drug screening.

3D Bioprinting Human Induced Pluripotent Stem Cell Constructs for In Situ Cell Proliferation and Successive Multilineage Differentiation

The ability to create 3D tissues from induced pluripotent stem cells (iPSCs) is poised to revolutionize stem cell research and regenerative medicine, including individualized, patient-specific stem cell-based treatments. There are, however, few examples of tissue engineering using iPSCs. Their culture and differentiation is predominantly planar for monolayer cell support or induction of self-organizing embryoids (EBs) and organoids. Bioprinting iPSCs with advanced biomaterials promises to augment efforts to develop 3D tissues, ideally comprising direct-write printing of cells for encapsulation, proliferation, and differentiation. Here, such a method, employing a clinically amenable polysaccharide-based bioink, is described as the first example of bioprinting human iPSCs for in situ expansion and sequential differentiation. Specifically, we have extrusion printed the bioink including iPSCs, alginate (Al; 5% weight/volume [w/v]), carboxymethyl-chitosan (5% w/v), and agarose (Ag; 1.5% w/v), crosslinked the bioink in calcium chloride for a stable and porous construct, proliferated the iPSCs within the construct and differentiated the same iPSCs into either EBs comprising cells of three germ lineages-endoderm, ectoderm, and mesoderm, or more homogeneous neural tissues containing functional migrating neurons and neuroglia. This defined, scalable, and versatile platform is envisaged being useful in iPSC research and translation for pharmaceuticals development and regenerative medicine.

Advances and challenges in stem cell culture

Stem cells (SCs) hold great promise for cell therapy, tissue engineering, and regenerative medicine as well as pharmaceutical and biotechnological applications. They have the capacity to self-renew and the ability to differentiate into specialized cell types depending upon their source of isolation. However, use of SCs for clinical applications requires a high quality and quantity of cells. This necessitates large-scale expansion of SCs followed by efficient and homogeneous differentiation into functional derivatives. Traditional methods for maintenance and expansion of cells rely on two-dimensional (2-D) culturing techniques using plastic culture plates and xenogenic media. These methods provide limited expansion and cells tend to lose clonal and differentiation capacity upon long-term passaging. Recently, new approaches for the expansion of SCs have emphasized three-dimensional (3-D) cell growth to mimic the in vivo environment. This review provides a comprehensive compendium of recent advancements in culturing SCs using 2-D and 3-D techniques involving spheroids, biomaterials, and bioreactors. In addition, potential challenges to achieve billion-fold expansion of cells are discussed.

Fast-degrading PLA/ORMOGLASS fibrous composite scaffold leads to a calcium-rich angiogenic environment

The success of scaffold implantation in acellular tissue engineering approaches relies on the ability of the material to interact properly with the biological environment. This behavior mainly depends on the design of the graft surface and, more precisely, on its capacity to biodegrade in a well-defined manner (nature of ions released, surface-to-volume ratio, dissolution profile of this release, rate of material resorption, and preservation of mechanical properties). The assessment of the biological behavior of temporary templates is therefore very important in tissue engineering, especially for composites, which usually exhibit complicated degradation behavior. Here, blended polylactic acid (PLA) calcium phosphate ORMOGLASS (organically modified glass) nanofibrous mats have been incubated up to 4 weeks in physiological simulated conditions, and their morphological, topographical, and chemical changes have been investigated. The results showed that a significant loss of inorganic phase occurred at the beginning of the immersion and the ORMOGLASS maintained a stable composition afterward throughout the degradation period. As a whole, the nanostructured scaffolds underwent fast and heterogeneous degradation. This study reveals that an angiogenic calcium-rich environment can be achieved through fast-degrading ORMOGLASS/PLA blended fibers, which seems to be an excellent alternative for guided bone regeneration.

Human embryonic stem cell dispersion in electrospun PCL fiber scaffolds by coating with laminin-521 and E-cadherin-Fc

Advances in human pluripotent cell cultivation and differentiation protocols have led to production of stem cell-derived progenitors as a promising cell source for replacement therapy. Three-dimensional (3-D) culture is a better mimic of the natural niche for stem cells and is widely used for disease modeling. Here, we describe a nonaggregate culture system of human embryonic stem cells inside electrospun polycaprolactone (PCL) fiber scaffolds combined with defined extracellular proteins naturally occurring in the stem cell niche. PCL fiber scaffolds coated with recombinant human laminin-521 readily supported initial stem cell attachment and growth from a single-cell suspension. The combination of recombinant E-cadherin-Fc and laminin-521 further improved cell dispersion rendering a uniform cell population. Finally, we showed that the cells cultured in E-cadherin-Fc- and laminin-521-coated PCL scaffolds could differentiate into all three germ layers. Importantly, we provided a chemically defined 3-D system in which pluripotent stem cells grown and differentiated avoiding the formation of cell aggregates. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1226-1236, 2018.

Fabrication and Characterization of Three-Dimensional (3D) Core-Shell Structure Nanofibers Designed for 3D Dynamic Cell Culture

Three-dimensional elastic nanofibers (3D eNFs) can offer a suitable 3D dynamic microenvironment and sufficient flexibility to regulate cellular behavior and functional protein expression. In this study, we report a novel approach to prepare 3D nanofibers with excellent mechanical properties by solution-assisted electrospinning technology and in situ polymerization. The obtained 3D eNFs demonstrated excellent biocompatible properties to meet cell culture requirements under a dynamic environment in vitro. Moreover, these 3D eNFs also promoted human bone marrow mesenchymal stem cells (hMSCs) adhesion and collagen expression under biomechanical stimulation. The results demonstrated that this dynamic cell culture system could positively impact cellular collagen but has no significant effect on the proliferation of hMSCs grown in the 3D eNFs. This work may give rise to a new approach for constructing a 3D cell culture for tissue engineering.

Multiparametric quantification of thermal heterogeneity within aqueous materials by water 1H NMR spectroscopy: Paradigms and algorithms

Processes involving heat generation and dissipation play an important role in the performance of numerous materials. The behavior of (semi-)aqueous materials such as hydrogels during production and application, but also properties of biological tissue in disease and therapy (e.g., hyperthermia) critically depend on heat regulation. However, currently available thermometry methods do not provide quantitative parameters characterizing the overall temperature distribution within a volume of soft matter. To this end, we present here a new paradigm enabling accurate, contactless quantification of thermal heterogeneity based on the line shape of a water proton nuclear magnetic resonance (¹H NMR) spectrum. First, the ¹H NMR resonance from water serving as a "temperature probe" is transformed into a temperature curve. Then, the digital points of this temperature profile are used to construct a histogram by way of specifically developed algorithms. We demonstrate that from this histogram, at least eight quantitative parameters describing the underlying statistical temperature distribution can be computed: weighted median, weighted mean, standard deviation, range, mode(s), kurtosis, skewness, and entropy. All mathematical transformations and calculations are performed using specifically programmed EXCEL spreadsheets. Our new paradigm is helpful in detailed investigations of thermal heterogeneity, including dynamic characteristics of heat exchange at sub-second temporal resolution.

Defined and Scalable Differentiation of Human Oligodendrocyte Precursors from Pluripotent Stem Cells in a 3D Culture System

Oligodendrocyte precursor cells (OPCs) offer considerable potential for the treatment of demyelinating diseases and injuries of the CNS. However, generating large quantities of high-quality OPCs remains a substantial challenge that impedes their therapeutic application. Here, we show that OPCs can be generated from human pluripotent stem cells (hPSCs) in a three-dimensional (3D), scalable, and fully defined thermoresponsive biomaterial system. We used CRISPR/Cas9 to create a NKX2.2-EGFP human embryonic stem cell reporter line that enabled fine-tuning of early OPC specification and identification of conditions that markedly increased the number of OLIG2⁺ and NKX2.2⁺ cells generated from hPSCs. Transplantation of 50-day-old OPCs into the brains of NOD/SCID mice revealed that progenitors generated in 3D without cell selection or purification subsequently engrafted, migrated, and matured into myelinating oligodendrocytes in vivo. These results demonstrate the potential of harnessing lineage reporter lines to develop 3D platforms for rapid and large-scale production of OPCs.

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A defined and scalable 3D system accelerates the differentiation of OPCs from hPSCs

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A NKX2.2-EGFP hESC reporter line enables optimization of OPC differentiation

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3D-derived OPCs engraft, migrate, and mature after implantation into NOD/SCID mice

Three-dimensional system enabling the maintenance and directed differentiation of pluripotent stem cells under defined conditions

The development of in vitro models for the maintenance and differentiation of pluripotent stem cells (PSCs) is an active area of stem cell research. The strategies used so far are based mainly on two-dimensional (2D) cultures, in which cellular phenotypes are regulated by soluble factors. We show that a 3D culture system with atelocollagen porous scaffolds can significantly improve the outcome of the current platforms intended for the maintenance and lineage specification of mouse PSCs (mPSCs). Unlike 2D conditions, the 3D conditions maintained the undifferentiated state of mouse embryonic stem cells (mESCs) without exogenous stimulation and also supported endoderm, mesoderm, and ectoderm differentiation of mESCs under serum-free conditions. Moreover, 3D mPSC-derived mesodermal cells showed accelerated osteogenic differentiation, giving rise to functional osteoblast-osteocyte populations within calcified structures. The present strategy offers a 3D platform suitable for the formation of organoids that mimic in vivo organs containing various cell types, and it may be adaptable to the generation of ectoderm-, mesoderm-, and endoderm-derived tissues when combined with appropriate differentiation treatments.

Micropatterned co-culture of cardiac myocytes on fibrous scaffolds for predictive screening of drug cardiotoxicities

The spatial arrangement of cardiac myocytes (CMs) and other non-myocytes scaffolds, closely resembling native tissue, is essential to control the CM morphology and function for cardiac tissue regeneration. In the current study, micropatterned fibrous scaffolds were developed to establish a CM co-culture system with cardiac fibroblasts (CFs) and endothelial cells (ECs) as a potential in vitro drug screening model. To pursue a biomimetic approach to influence CM behaviors, strip, oval and wave-patterned mats were constructed by deposition of electrospun fibers on lithographic collectors, followed by precise stacking for cell co-cultures. CMs, CFs, and ECs were located on the patterned scaffolds with controlled cellular distribution in the respective regions and no across condition was found. Compared with those after strip and oval-patterned co-culture, CMs co-cultured on wave-patterned scaffolds displayed significantly greater cell viabilities, larger cell elongation ratios, stronger expressions of cardiac-specific Troponin I, connexin 43 and sarcomeric α-actinin and higher beating rates during 15 days of incubation. The responses of co-cultured CMs to quinidine, erythromycin and sotalol show good correlations with clinical observations in the beating rate and the prolongation of the contraction and relaxation time. The in vivo safety data reflected well with the concentrations for 50% of maximal effect (EC₅₀) after drug treatment on co-cultured CMs, which was determined from the changes in the corrected field potential duration (FPDc) against the drug concentrations. During 15 days of patterned co-culture, the interbeat intervals and fluctuations of the CMs indicated quick changes in response to haloperidol treatment and sufficient restoration of the original beating profiles after drug removal. This study demonstrates the capabilities of micropatterned co-culture of CMs to establish the cardiac function as a reproducible and reliable platform for screening cardiac side effects of drugs.

3D Stem Cell Niche Engineering via Two-Photon Laser Polymerization

A strategy to modulate the behavior of stem cells in culture is to mimic structural aspects of the native cell-extracellular matrix (ECM) interaction. An important example of such artificial microenvironments for stem cell culture is the so-called "synthetic niche." Synthetic niches can be defined as polymeric culture systems mimicking at least one aspect of the interactions between stem cells and the extracellular surroundings, including biochemical factors (e.g., the delivery of soluble factors) and/or biophysical factors (e.g., the microarchitecture of the ECM). Most of the currently available approaches for scaffold fabrication, based on self-assembly methods, do not allow for a submicrometer control of the geometrical structure of the substrate, which might play a crucial role in stem cell fate determination. A novel technology that overcomes these limitations is laser two-photon polymerization (2PP). Femtosecond laser 2PP is a mask-less direct laser writing technique that allows manufacturing three dimensional arbitrary microarchitectures using photosensitive materials. Here, we report on the development of an innovative culture substrate, called the "nichoid," microfabricated in a hybrid organic-inorganic photoresist called SZ2080, to study mesenchymal stem cell mechanobiology.

Advances in nanowire bioelectronics

Semiconductor nanowires represent powerful building blocks for next generation bioelectronics given their attractive properties, including nanometer-scale footprint comparable to subcellular structures and bio-molecules, configurable in nonstandard device geometries readily interfaced with biological systems, high surface-to-volume ratios, fast signal responses, and minimum consumption of energy. In this review article, we summarize recent progress in the field of nanowire bioelectronics with a focus primarily on silicon nanowire field-effect transistor biosensors. First, the synthesis and assembly of semiconductor nanowires will be described, including the basics of nanowire FETs crucial to their configuration as biosensors. Second, we will introduce and review recent results in nanowire bioelectronics for biomedical applications ranging from label-free sensing of biomolecules, to extracellular and intracellular electrophysiological recording.

Injectable, Biomolecule-Responsive Polypeptide Hydrogels for Cell Encapsulation and Facile Cell Recovery through Triggered Degradation

Injectable hydrogels have been widely investigated in biomedical applications, and increasing demand has been proposed to achieve dynamic regulation of physiological properties of hydrogels. Herein, a new type of injectable and biomolecule-responsive hydrogel based on poly(l-glutamic acid) (PLG) grafted with disulfide bond-modified phloretic acid (denoted as PLG-g-CPA) was developed. The hydrogels formed in situ via enzymatic cross-linking under physiological conditions in the presence of horseradish peroxidase and hydrogen peroxide. The physiochemical properties of the hydrogels, including gelation time and the rheological property, were measured. Particularly, the triggered degradation of the hydrogel in response to a reductive biomolecule, glutathione (GSH), was investigated in detail. The mechanical strength and inner porous structure of the hydrogel were influenced by the addition of GSH. The polypeptide hydrogel was used as a three-dimensional (3D) platform for cell encapsulation, which could release the cells through triggered disruption of the hydrogel in response to the addition of GSH. The cells released from the hydrogel were found to maintain high viability. Moreover, after subcutaneous injection into rats, the PLG-g-CPA hydrogels with disulfide-containing cross-links exhibited a markedly faster degradation behavior in vivo compared to that of the PLG hydrogels without disulfide cross-links, implying an interesting accelerated degradation process of the disulfide-containing polypeptide hydrogels in the physiological environment in vivo. Overall, the injectable and biomolecule-responsive polypeptide hydrogels may serve as a potential platform for 3D cell culture and easy cell collection.

Cell-laden microfluidic microgels for tissue regeneration

Regeneration of diseased tissue is one of the foremost concerns for millions of patients who suffer from tissue damage each year. Local delivery of cell-laden hydrogels offers an attractive approach for tissue repair. However, due to the typical macroscopic size of these cell constructs, the encapsulated cells often suffer from poor nutrient exchange. These issues can be mitigated by incorporating cells into microscopic hydrogels, or microgels, whose large surface-to-volume ratio promotes efficient mass transport and enhanced cell-matrix interactions. Using microfluidic technology, monodisperse cell-laden microgels with tunable sizes can be generated in a high-throughput manner, making them useful building blocks that can be assembled into tissue constructs with spatially controlled physicochemical properties. In this review, we examine microfluidics-generated cell-laden microgels for tissue regeneration applications. We provide a brief overview of the common biomaterials, gelation mechanisms, and microfluidic device designs that are used to generate these microgels, and summarize the most recent works on how they are applied to tissue regeneration. Finally, we discuss future applications of microfluidic cell-laden microgels as well as existing challenges that should be resolved to stimulate their clinical application.

Three-Dimensional Stem Cell Bioprinting

Stem cells have become a revived biotechnology that is beginning to expand the field of regenerative medicine. Although stem cells are capable of regenerating tissues, current research trends tend to side on developing fully functional organs and other clinical uses including in situ stem cell repair through three-dimensional printing methods. Through several tests and techniques, it can be shown that most stem cell printing methods are possible and that most tests come out with high cell viability. Furthermore, the importance of bioprinting is to benefit the field of regenerative medicine, which looks into artificial organ transplants for the thousands of patients without donors. Although the field is not brand new, understanding the integration and use of additive manufacturing with biomaterials is essential in developing fully functional organs. There is a heavy emphasis on the biomaterials themselves since they have a crucial role in creating an organ that is mechanically robust and adaptable in vivo. Covered in this review article are many featured tests, which also touch on the importance of including a biomaterial that is capable of maintaining a viable microenvironment. These include biomaterials such as hydrogels, biopolymers, and synthetic extra cellular matrices (ECM) built for stem cells to proliferate, differentiate, and give freedom to cell communication after printing.

Two-photon polymerized "nichoid" substrates maintain function of pluripotent stem cells when expanded under feeder-free conditions

Background

The use of pluripotent cells in stem cell therapy has major limitations, mainly related to the high costs and risks of exogenous conditioning and the use of feeder layers during cell expansion passages.

Methods

We developed an innovative three-dimensional culture substrate made of “nichoid” microstructures, nanoengineered via two-photon laser polymerization. The nichoids limit the dimension of the adhering embryoid bodies during expansion, by counteracting cell migration between adjacent units of the substrate by its microarchitecture. We expanded mouse embryonic stem cells on the nichoid for 2 weeks. We compared the expression of pluripotency and differentiation markers induced in cells with that induced by flat substrates and by a culture layer made of kidney-derived extracellular matrix.

Results

The nichoid was found to be the only substrate, among those tested, that maintained the expression of the OCT4 pluripotency marker switched on and, simultaneously, the expression of the differentiation markers GATA4 and α-SMA switched off. The nichoid promotes pluripotency maintenance of embryonic stem cells during expansion, in the absence of a feeder layer and exogenous conditioning factors, such as the leukocyte inhibitory factor.

Conclusions

We hypothesized that the nichoid microstructures induce a genetic reprogramming of cells by controlling their cytoskeletal tension. Further studies are necessary to understand the exact mechanism by which the physical constraint provided by the nichoid architecture is responsible for cell reprogramming. The nichoid may help elucidate mechanisms of pluripotency maintenance, while potentially cutting the costs and risks of both feed-conditioning and exogenous conditioning for industrial-scale expansion of stem cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0387-z) contains supplementary material, which is available to authorized users.

Autonomous osteogenic differentiation of hASCs encapsulated in methacrylated gellan-gum hydrogels

Methacrylated gellan-gum (GG-MA) alone and combined with collagen type I (Coll) is suggested here for the first time as a cell-laden injectable biomaterial for bone regeneration. On-chip high-throughput studies allowed rapidly assessing the suitability of 15 biomaterials/media combinations for the osteodifferentiation of human adipose stem cells (hASCs). Hydrogels composed solely of GG-MA (GG100:0Coll) led hASCs from three different donors into the osteogenic lineage after 21days of cell culture, in the absence of any osteogenic or osteoconductive factors. Hydrogels containing more than 30% of Coll promoted increased cellular proliferation and led hASCs into osteogenic differentiation under basal conditions. Studies using isolated individual hydrogels - excluding eventual on-chip crosstalk - and standard biochemical assays corroborated such findings. The formation of focal adhesions of hASCs on GG100:0Coll hydrogels was verified. We hypothesize that the hydrogels osteogenic effect could be guided by mechanotransduction phenomena. Indeed, the hydrogels showed elastic modulus in ranges previously reported as osteoinductive and the inhibition of the actin-myosin contractility pathway impaired hASCs' osteodifferentiation. GG-MA hydrogels also did not promote hASCs' adipogenesis while used in basal conditions. Overall, GG-MA showed promising properties as an innovative and off-the shelf self-inducing osteogenic injectable biomaterial.

STATEMENT OF SIGNIFICANCE

Methacrylated gellan gum (GG-MA) is here suggested for the first time as a widely available polysaccharide to easily prepare hydrogels with cell adhesion properties and capability of inducing the autonomous osteogenic differentiation of human adipose-derived stem cells (hASCs). GG-MA was processed as stand-alone hydrogels or in different combinations with collage type I. All hydrogel formulations elicited the osteogenic differentiation of hASCs, independently of the addition of any osteoconductive or osteogenic stimuli, i.e. in basal/growth medium. Effective cellular adhesion to methacrylated gellan gum hydrogels in the absence of any cell-ligand peptide/protein was here proved for the first time. Moreover, we showed that the encapsulated hASCs underwent osteogenic differentiation due to a mechanotransduction phenomenon dependent on the actin-myosin contractility pathway.

Modeling psychiatric disorders: from genomic findings to cellular phenotypes

Major programs in psychiatric genetics have identified >150 risk loci for psychiatric disorders. These loci converge on a small number of functional pathways, which span conventional diagnostic criteria, suggesting a partly common biology underlying schizophrenia, autism and other psychiatric disorders. Nevertheless, the cellular phenotypes that capture the fundamental features of psychiatric disorders have not yet been determined. Recent advances in genetics and stem cell biology offer new prospects for cell-based modeling of psychiatric disorders. The advent of cell reprogramming and induced pluripotent stem cells (iPSC) provides an opportunity to translate genetic findings into patient-specific in vitro models. iPSC technology is less than a decade old but holds great promise for bridging the gaps between patients, genetics and biology. Despite many obvious advantages, iPSC studies still present multiple challenges. In this expert review, we critically review the challenges for modeling of psychiatric disorders, potential solutions and how iPSC technology can be used to develop an analytical framework for the evaluation and therapeutic manipulation of fundamental disease processes.

Biological functionality and mechanistic contribution of extracellular matrix-ornamented three dimensional Ti-6Al-4V mesh scaffolds

The 3D printed metallic implants are considered bioinert in nature because of the absence of bioactive molecules. Thus, surface modification of bioinert materials is expected to favorably promote osteoblast functions and differentiation. In this context, the objective of this study is to fundamentally elucidate the effect of cell-derived decellularized extracellular matrix (dECM) ornamented 3D printed Ti-6Al-4V scaffolds on biological functions, involving cell adhesion, proliferation, and synthesis of vinculin and actin proteins. To mimic the natural ECM environment, the mineralized ECM of osteoblasts was deposited on the Ti-6Al-4V porous scaffolds, fabricated by electron beam melting (EBM) method. The process comprised of osteoblast proliferation, differentiation, and freeze-thaw cycles to obtain decellularized extra cellular matrix (dECM), in vitro. The dECM provided a natural environment to restore the natural cell functionality of osteoblasts that were cultured on dECM ornamented Ti-6Al-4V scaffolds. In comparison to the bare Ti-6Al-4V scaffolds, a higher cell functionality such as cell adhesion, proliferation, and growth including cell-cell and cell-material interaction were observed on dECM ornamented Ti-6Al-4V scaffolds, which were characterized by using markers for focal adhesion and cytoskeleton such as vinculin and actin. Moreover, electron microscopy also indicated higher cell-material interaction and enhanced proliferation of cells on dECM ornamented Ti-6Al-4V scaffolds, supported by MTT assay. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2751-2763, 2016.

Sliced Magnetic Polyacrylamide Hydrogel with Cell-Adhesive Microarray Interface: A Novel Multicellular Spheroid Culturing Platform

Cell-adhesive properties are of great significance to materials serving as extracellular matrix mimics. Appropriate cell-adhesive property of material interface can balance the cell-matrix interaction and cell-cell interaction and can promote cells to form 3D structures. Herein, a novel magnetic polyacrylamide (PAM) hydrogel fabricated via combining magnetostatic field induced magnetic nanoparticles assembly and hydrogel gelation was applied as a multicellular spheroids culturing platform. When cultured on the cell-adhesive microarray interface of sliced magnetic hydrogel, normal and tumor cells from different cell lines could rapidly form multicellular spheroids spontaneously. Furthermore, cells which could only form loose cell aggregates in a classic 3D cell culture model (such as hanging drop system) were able to be promoted to form multicellular spheroids on this platform. In the light of its simplicity in fabricating as well as its effectiveness in promoting formation of multicellular spheroids which was considered as a prevailing tool in the study of the microenvironmental regulation of tumor cell physiology and therapeutic problems, this composite material holds promise in anticancer drugs or hyperthermia therapy evaluation in vitro in the future.

Synthetic niche substrates engineered via two-photon laser polymerization for the expansion of human mesenchymal stromal cells

The present study reports on the development of an innovative culture substrate, micro-fabricated by two-photon laser polymerization (2PP) in a hybrid organic-inorganic photoresin. It was previously demonstrated that this substrate is able to guide spontaneous homing and colonization of mesenchymal stromal cells by the presence of synthetic microniches. Here, the number of niches covering the culture substrate was increased up to 10% of the total surface. Human bone marrow-derived mesenchymal stromal cells were expanded for 3 weeks and then their proliferation, clonogenic capacity and bilineage differentiation potential towards the osteogenic and adipogenic lineage were evaluated, both by colorimetric assays and by real-time polymerase chain reaction. Compared with cells cultured on glass substrates, cells expanded on 2PP substrates showed a greater colony diameter, which is an index of clonogenic potential. Following medium conditioning on 2PP-cultured cells, the expression of RUNX2 and BSP genes, as well as PPAR-gamma, was significantly greater than that measured on glass controls. Thus, human cells expanded on the synthetic niche substrate maintained their proliferative potential, clonogenic capacity and bilineage differentiation potential more effectively than cells expanded on glass substrates and in some aspects were comparable to non-expanded cells. © 2016 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd.

Pluripotent stem cell derived hepatocytes: using materials to define cellular differentiation and tissue engineering

Pluripotent stem cell derived liver cells (hepatocytes) represent a promising alternative to primary tissue for biological and clinical applications. To date, most hepatocyte maintenance and differentiation systems have relied upon the use of animal derived components. This serves as a significant barrier to large scale production and application of stem cell derived hepatocytes. Recently, the use of defined biologics has overcome those limitations in two-dimensional monolayer culture. In order to improve the cell phenotype further, three-dimensional culture systems have been employed to better mimic the in vivo situation, drawing upon materials chemistry, engineering and biology. In this review we discuss efforts in the field, to differentiate pluripotent stem cells towards hepatocytes under defined conditions.

Engineering Embryonic Stem Cell Microenvironments for Tailored Cellular Differentiation

The rapid progress of embryonic stem cell (ESCs) research offers great promise for drug discovery, tissue engineering, and regenerative medicine. However, a major limitation in translation of ESCs technology to pharmaceutical and clinical applications is how to induce their differentiation into tailored lineage commitment with satisfactory efficiency. Many studies indicate that this lineage commitment is precisely controlled by the ESC microenvironment in vivo. Engineering and biomaterial-based approaches to recreate a biomimetic cellular microenvironment provide valuable strategies for directing ESCs differentiation to specific lineages in vitro. In this review, we summarize and examine the recent advances in application of engineering and biomaterial-based approaches to control ESC differentiation. We focus on physical strategies (e.g., geometrical constraint, mechanical stimulation, extracellular matrix (ECM) stiffness, and topography) and biochemical approaches (e.g., genetic engineering, soluble bioactive factors, coculture, and synthetic small molecules), and highlight the three-dimensional (3D) hydrogel-based microenvironment for directed ESC differentiation. Finally, future perspectives in ESCs engineering are provided for the subsequent advancement of this promising research direction.

Controlled assembly of heterotypic cells in a core-shell scaffold: organ in a droplet

This paper reports a droplet-based microfluidic approach to fabricate a large number of monodisperse, portable microtissues, each in an individual drop. We use water-water-oil double emulsions as templates and spatially assemble hepatocytes in the core and fibroblasts in the shell, forming a 3D liver model in a drop.

Composite Hydrogels for Bone Regeneration

Over the past few decades, bone related disorders have constantly increased. Among all pathological conditions, osteoporosis is one of the most common and often leads to bone fractures. This is a massive burden and it affects an estimated 3 million people only in the UK. Furthermore, as the population ages, numbers are due to increase. In this context, novel biomaterials for bone fracture regeneration are constantly under development. Typically, these materials aim at favoring optimal bone integration in the scaffold, up to complete bone regeneration; this approach to regenerative medicine is also known as tissue engineering (TE). Hydrogels are among the most promising biomaterials in TE applications: they are very flexible materials that allow a number of different properties to be targeted for different applications, through appropriate chemical modifications. The present review will focus on the strategies that have been developed for formulating hydrogels with ideal properties for bone regeneration applications. In particular, aspects related to the improvement of hydrogels' mechanical competence, controlled delivery of drugs and growth factors are treated in detail. It is hoped that this review can provide an exhaustive compendium of the main aspects in hydrogel related research and, therefore, stimulate future biomaterial development and applications.

Biomaterials for pluripotent stem cell engineering: From fate determination to vascularization

Recent advancements in material science and engineering may hold the key to overcoming reproducibility and scalability limitations currently hindering the clinical translation of stem cell therapies. Biomaterial assisted differentiation commitment of stem cells and modulation of their in vivo function could have significant impact in stem cell-centred regenerative medicine approaches and next gen technological platforms. Synthetic biomaterials are of particular interest as they provide a consistent, chemically defined, and tunable way of mimicking the physical and chemical properties of the natural tissue or cell environment. Combining emerging biomaterial and biofabrication advancements may finally give researchers the tools to modulate spatiotemporal complexity and engineer more hierarchically complex, physiologically relevant tissue mimics. In this review we highlight recent research advancements in biomaterial assisted pluripotent stem cell (PSC) expansion and three dimensional (3D) tissue formation strategies. Furthermore, since vascularization is a major challenge affecting the in vivo function of engineered tissues, we discuss recent developments in vascularization strategies and assess their ability to produce perfusable and functional vasculature that can be integrated with the host tissue.

Bioinspired trimodal macro/micro/nano-porous scaffolds loading rhBMP-2 for complete regeneration of critical size bone defect

Critical size bone defects raise great demands for efficient bone substitutes. Mimicking the hierarchical porous architecture and specific biological cues of natural bone has been considered as an effective strategy to facilitate bone regeneration. Herein, a trimodal macro/micro/nano-porous scaffold loaded with recombinant human bone morphogenetic protein-2 (rhBMP-2) was developed. With mesoporous bioactive glass (MBG) as matrix, a trimodal MBG scaffold (TMS) with enhanced compressive strength (4.28 MPa, porosity of 80%) was prepared by a "viscosity controlling" and "homogeneous particle reinforcing" multi-template process. A 7.5 nm, 3D cubic (Im3m) mesoporous structure was tailored for a "size-matched entrapment" of rhBMP-2 to achieve sustained release and preserved bioactivity. RhBMP-2-loaded TMS (TMS/rhBMP-2) induced excellent cell attachment, ingrowth and osteogenesis in vitro. Further in vivo ectopic bone formation and orthotopic rabbit radius critical size defect results indicated that compared to the rhBMP-2-loaded bimodal macro/micro- and macro/nano-porous scaffolds, TMS/rhBMP-2 exhibited appealing bone regeneration capacity. Particularly, in critical size defect, complete bone reconstruction with rapid medullary cavity reunion and sclerotin maturity was observed on TMS/rhBMP-2. On the basis of these results, TMS/rhBMP-2 developed here represents a promising bone substitute for clinical application and the concepts proposed in this study might provide new thoughts on development of future orthopedic biomaterials.

STATEMENT OF SIGNIFICANCE

Limited self-regenerating capacity of human body makes the reconstruction of critical size bone defect a significant challenge. Current bone substitutes often exhibit undesirable therapeutic efficacy due to poor osteoconductivity or low osteoinductivity. Herein, TMS/rhBMP-2, an advanced mesoporous bioactive glass (MBG) scaffold with osteoconductive trimodal macro/micro/nano-porosity and osteoinductive rhBMP-2 delivery was developed. The preparative and mechanical problems of hierarchical MBG scaffold were solved without affecting its excellent biocompatibilities, and rhBMP-2 immobilization in sizematched mesopores was first explored. Combining structural and biological cues, TMS/rhBMP-2 achieved a complete regeneration with rapid medullary cavity reunion and sclerotin maturity in rabbit radius critical size defects. The design conceptions proposed in this study might provide new thoughts on development of future orthopedic biomaterials.

Using carbohydrate-based biomaterials as scaffolds to control human stem cell fate

This review describes the current state and applications of several important and extensively studied natural polysaccharide and glycoprotein scaffolds that can control the stem cell fate.