Electrothermal soft manipulator enabling safe transport and handling of thin cell/tissue sheets and bioelectronic devices

“Living” cell sheets or bioelectronic chips have great potentials to improve the quality of diagnostics and therapies. However, handling these thin and delicate materials remains a grand challenge because the external force applied for gripping and releasing can easily deform or damage the materials. This study presents a soft manipulator that can manipulate and transport cell/tissue sheets and ultrathin wearable biosensing devices seamlessly by recapitulating how a cephalopod’s suction cup works. The soft manipulator consists of an ultrafast thermo-responsive, microchanneled hydrogel layer with tissue-like softness and an electric heater layer. The electric current to the manipulator drives microchannels of the gel to shrink/expand and results in a pressure change through the microchannels. The manipulator can lift/detach an object within 10 s and can be used repeatedly over 50 times. This soft manipulator would be highly useful for safe and reliable assembly and implantation of therapeutic cell/tissue sheets and biosensing devices

Poly(ethylene glycol)-poly(lactic-co-glycolic acid) core-shell microspheres with enhanced controllability of drug encapsulation and release rate

Poly(lactic-co-glycolic acid) (PLGA) microspheres have been widely used as drug carriers for minimally invasive, local, and sustained drug delivery. However, their use is often plagued by limited controllability of encapsulation efficiency, initial burst, and release rate of drug molecules, which cause unsatisfactory outcomes and several side effects including inflammation. This study presents a new strategy of tuning the encapsulation efficiency and the release rate of protein drugs from a PLGA microsphere by filling the hollow core of the microsphere with poly(ethylene glycol) (PEG) hydrogels of varying cross-linking density. The PEG gel cores were prepared by inducing in situ cross-linking reactions of PEG monoacrylate solution within the PLGA microspheres. The resulting PEG-PLGA core-shell microspheres exhibited (1) increased encapsulation efficiency, (2) decreased initial burst, and (3) a more sustained release of protein drugs, as the cross-linking density of the PEG gel core was increased. In addition, implantation of PEG-PLGA core-shell microspheres encapsulated with vascular endothelial growth factor (VEGF) onto a chicken chorioallantoic membrane resulted in a significant increase in the number of new blood vessels at an implantation site, while minimizing inflammation. Overall, this strategy of introducing PEG gel into PLGA microspheres will be highly useful in tuning release rates and ultimately in improving the therapeutic efficacy of a wide array of protein drugs.close0

Proangiogenic alginate-g-pyrrole hydrogel with decoupled control of mechanical rigidity and electrically conductivity

Abstract Background An electrically conductive hydrogel has emerged to regulate cellular secretion activities with electrical stimulation. However, the electrical conductivity of typical hydrogel systems decreases with increasing elastic modulus of the hydrogels because of decreased transport of ions through a polymeric cross-linked mesh. Method This study hypothesized that the inverse dependency between electrical conductivity and elastic modulus would be made through the cross-linking of conductive monomer-units conjugated to a hydrophilic polymeric backbone. This hypothesis was examined through the cross-linking of pyrrole groups that were conjugated to an alginate backbone, termed alginate-g-pyrrole. Results Hydrogels with increased degrees of pyrrole substitution exhibited a simultaneous increase in the gels mechanical rigidity and electrical conductivity. The resulting hydrogel could control the adhesion and vascular endothelial growth factor secretion of cells via applied electrical stimulation. Conclusions This material design principle will be broadly useful to fabricating materials used for various actuation, cell culture, and biomedical applications

Cross-Linkable Liposomes Stabilize a Magnetic Resonance Contrast-Enhancing Polymeric Fastener

Liposomes are commonly used to deliver drugs and contrast agents to their target site in a controlled manner. One of the greatest obstacles in the performance of such delivery vehicles is their stability in the presence of serum. Here, we demonstrate a method to stabilize a class of liposomes that load gadolinium, a magnetic resonance (MR) contrast agent, as a model cargo on their surfaces. We hypothesized that the sequential adsorption of a gadolinium-binding chitosan fastener on the liposome surface followed by covalent cross-linking of the lipid bilayer would provide enhanced stability and improved MR signal in the presence of human serum. To investigate this hypothesis, liposomes composed of diyne-containing lipids were assembled and functionalized via chitosan conjugated with a hydrophobic anchor and diethylenetriaminepentaacetic acid (DTPA). This postadsorption cross-linking strategy served to stabilize the thermodynamically favorable association between liposome and polymeric fastener. Furthermore, the chitosan-coated, cross-linked liposomes proved more effective as delivery vehicles of gadolinium than uncross-linked liposomes due to the reduced liposome degradation and chitosan desorption. Overall, this study demonstrates a useful method to stabilize a broad class of particles used for systemic delivery of various molecular payloads

Matrix Rigidity-Modulated Cardiovascular Organoid Formation from Embryoid Bodies

<div><p>Stem cell clusters, such as embryoid bodies (EBs) derived from embryonic stem cells, are extensively studied for creation of multicellular clusters and complex functional tissues. It is common to control phenotypes of ES cells with varying molecular compounds; however, there is still a need to improve the controllability of cell differentiation, and thus, the quality of created tissue. This study demonstrates a simple but effective strategy to promote formation of vascularized cardiac muscle - like tissue in EBs and form contracting cardiovascular organoids by modulating the stiffness of a cell adherent hydrogel. Using collagen-conjugated polyacrylamide hydrogels with controlled elastic moduli, we discovered that cellular organization in a form of vascularized cardiac muscle sheet was maximal on the gel with the stiffness similar to cardiac muscle. We envisage that the results of this study will greatly contribute to better understanding of emergent behavior of stem cells in developmental and regeneration process and will also expedite translation of EB studies to drug-screening device assembly and clinical treatments.</p></div

Decoupled control of stiffness and permeability with a cell-encapsulating poly(ethylene glycol) dimethacrylate hydrogel

Hydrogels are increasingly used as a cell encapsulation and transplantation device. The successful use of a hydrogel greatly relies on an ability to control hydrogel stiffness which affects structural integrity and regulates cellular phenotypes. However, conventional strategies to increase the gel stiffness lead to decrease in the gel permeability and subsequently deteriorate the viability of cells encapsulated in a gel matrix. This study presents a strategy to decouple the inversed dependency of permeability on the stiffness of a hydrogel by chemically cross-linking methacrylic alginate with poly(ethylene glycol) dimethacrylate (PEGDA). As expected, gel stiffness represented by elastic modulus was tuned over one order of magnitude with the concentration of methacrylic alginate and the degree of substitution of methacrylic groups. In contrast, swelling ratio of the hydrogel indicative of gel permeability was minimally changed because of multiple hydrophilic groups of alginate, similar to function of proteoglycans in a natural extracellular matrix. Furthermore, viability of neural cells encapsulated in a hydrogel of PEGDA and methacrylic alginate rather increased with hydrogel stiffness. Overall, the results of this study demonstrate an advanced biomaterial design paradigm which allows one to culture cells in a 3D matrix of varying rigidity. This study will therefore greatly expedite the use of a hydrogel system in both fundamental studies and clinical settings of cell therapies.close333

Additional file 1: of Proangiogenic alginate-g-pyrrole hydrogel with decoupled control of mechanical rigidity and electrically conductivity

Supporting Information. (DOCX 618 kb

Tuning the dependency between stiffness and permeability of a cell encapsulating hydrogel with hydrophilic pendant chains

The mechanical stiffness of a hydrogel plays a significant role in regulating the phenotype of cells that adhere to its surface. However, the effect of hydrogel stiffness on cells cultured within its matrix is not well understood, because of the intrinsic inverse dependency between the permeability and stiffness of hydrogels. This study therefore presents an advanced biomaterial design strategy to decrease the inverse dependency between permeability and stiffness of a cell encapsulating hydrogel. Hydrogels were made by cross-linking poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) monoacrylate (PEGMA), with PEGMA acting as a pendant polymer chain. Increasing the mass fraction of PEGMA while keeping the total polymer concentration constant led to a decrease in the elastic modulus (E) of the hydrogel, but caused a minimal increase in the swelling ratio (Q). The size and hydrophobicity of the end groups of pendant PEG chains further fine tuned the dependency between Q and E of the hydrogel. Pure PEGDA hydrogels with varying molecular weights, which show the same range of E but a much greater range of Q were used as a control. Fibroblasts encapsulated in PEGDA-PEGMA hydrogels displayed more significant biphasic dependencies of cell viability and vascular endothelial growth factor (VEGF) expression on E than those encapsulated in pure PEGDA hydrogels, which were greatly influenced by Q. Overall, the hydrogel design strategy presented in this study will be highly useful to better regulate the phenotype and ultimately improve the therapeutic efficacy of a wide array of cells used in various biology studies and clinical settings.close171

Integrative deign of a poly(ethylene glycol)-poly(propylene glycol)-alginate hydrogel to control three dimensional biomineralization

A mineralized polymeric matrix has been extensively studied to understand biomineralization processes and to further regulate phenotypic functions of various cells involved in osteogenesis and physiological homeostasis. It has been often proposed that several matrix variables including charge density, hydrophobicity, and pore size play vital roles in modulating composition and morphology of minerals formed within a three dimensional (3D) matrix. However, the aspects have not yet been systematically examined because a tool enabling the independent control of the matrix variables is lacking. This study presents an advanced integrative strategy to control morphology and composition of biominerals with matrix properties, by using a hydrogel formulated to independently control charge density, hydrophobicity, and porosity. The hydrogel consists of poly(ethylene glycol) monomethacrylate (PEGmM), poly(propylene glycol) monomethacrylate (PPGmM), and methacrylic alginate (MA), so the charge density and hydrophobicity of the hydrogel can be separately controlled with mass fractions of MA and PPGmM. Also, hydrogels which present only nano-sized pores, termed nanoporous hydrogels, are lyophilized and rehydrated to prepare the hydrogels containing micro-sized pores, termed microporous hydrogels. We find that increasing the mass fractions of MA and PPGmM of the microporous hydrogel promotes the growth of apatite layers because of the increases in the charge density, hydrophobicity and pore size. In contrast, increasing mass fractions of MA and PPGmM of the nanoporous hydrogel enhances the formation of calcium carbonate minerals. The dependency of the mineralization on hydrogel variables is related to the change in supersaturation of mineral ions. Overall, the results of this study will be highly useful to better understand the interplay of matrix variables in biomineralization and to design a wide array of mineralized matrix potentially used in cell therapies and tissue engineering.close171

Immunohistochemical analysis of cardiomyogenic and endothelial differentiation within EBs.

<p>(A) Fluorescent images of EBs stained for sarcomeric α-actinin (red) and CD31 (green). (A-1, 5, & 9) EBs cultured in suspended state for 23 days. (A-2, 6 & 10) EBs cultured on the pure collagen gel with <i>E</i> of 0.2 kPa. (A-3, 7, & 11) EBs cultured on the CCP gel with <i>E</i> of 6 kPa. (A-4 & 8) EBs cultured on the CCP gel with <i>E</i> of 40 kPa. Scale bar represents 200 µm. Images on the second row are magnified views of those on the first row. Images on the third row are three-dimensional confocal images of EBs. (B) Percentage of the EB area positively stained by antibodies to sarcomeric α-actinin. The difference of the values between EBs cultured on the gel with <i>E</i> of 6 kPa and other three conditions is statistically significant (*p<0.05). (C) Percentage of EB area positively stained with an antibody to CD31. The difference of the values between EBs cultured on the gel with <i>E</i> of 6 and 40 kPa is statistically not significant (*p>0.1). Values and error bars represent the mean and the standard error of at least 20 EBs, respectively.</p