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3D bioprinting has recently emerged as a very useful tool in tissue engineering and regenerative medicine. However, developing suitable bioinks to fabricate specific tissue constructs remains a challenging task. Herein, we report on a nanocellulose/chitosan-based bioink, which is compatible with a 3D extrusion-based bioprinting technology, to design and engineer constructs for bone tissue engineering and regeneration applications. Bioinks were prepared using thermogelling chitosan, glycerophosphate, hydroxyethyl cellulose, and cellulose nanocrystals (CNCs). Formulations were optimized by varying the concentrations of glycerophosphate (80-300 mM), hydroxyethyl cellulose (0-0.5 mg/mL), and CNCs (0-2% w/v) to promote fast gelation kinetics (7 s) at 37 °C and retain the shape integrity of constructs post 3D bioprinting. We investigated the effect of CNCs and pre-osteoblast cells (MC3T3-E1) on the rheological properties of bioinks, bioink printability, and mechanical properties of bioprinted scaffolds. We demonstrate that the addition of CNCs and cells (5 million cells/mL) significantly improved the viscosity of bioinks and the mechanical properties of chitosan scaffolds post-fabrication. The bioinks were biocompatible and printable at an optimized range of printing pressures (12-20 kPa) that did not compromise cell viability. The presence of CNCs promoted greater osteogenesis of MC3T3-E1 cells in chitosan scaffolds as shown by the upregulation of alkaline phosphatase activity, higher calcium mineralization, and extracellular matrix formation. The versatility of this CNCs-incorporated chitosan hydrogel makes it attractive as a bioink for 3D bioprinting to engineer scaffolds for bone tissue engineering and other therapeutic applications.

Psoriasis (PsO) is a complex immune-mediated disease that afflicts 100 million people. Omilancor is a locally-acting, small molecule that selectively activates the Lanthionine Synthetase C-like 2 (LANCL2) pathway, resulting in immunoregulatory effects at the intersection of immunity and metabolism. Topical omilancor treatment in an imiquimod-induced mouse model of PsO ameliorates disease severity, epidermal hyperplasia and acanthosis. Further, pharmacological activation of LANCL2 results in significant downregulation of proinflammatory markers including local reduction of IL17, and infiltration of proinflammatory cell subsets. These therapeutic effects were further validated in an IL-23 PsO model. This model reported increased preservation of homeostatic skin structure, accompanied by a decreased infiltration of proinflammatory T cell subsets. In CD4+ T cells and Th17 cells, the LANCL2 pathway regulates proinflammatory cytokine production, proliferation and glucose metabolism. Metabolically, the loss of Lancl2 resulted in increased glycolytic rates, lactate production and upregulated enzymatic activity of hexokinase and lactate dehydrogenase (LDH). Inhibition of LDH activity abrogated the increased proliferation rate in Lancl2−/− CD4+ T cells. Additionally, topical omilancor treatment decreased the metabolic upregulation in keratinocytes, keratinocyte hyperproliferation and expression of inflammatory markers. Omilancor is a promising topical, LANCL2-targeting therapeutic candidate for the treatment of PsO and other dermatology indications.

Lack of adherence is a key barrier to a successful human immunodeficiency virus (HIV) treatment and prevention. We report on an ultra-long-acting (ULA) biodegradable polymeric solid implant (PSI) that can accommodate one or more antiretrovirals (e.g., dolutegravir (DTG) and rilpivirine (RPV)) at translatable human doses (65% wt.) in a single implant. PSIs are fabricated using a three-step process: (a) phase inversion of a drug/polymer solution to form an initial in-situ forming solid implant, (b) micronization of dried drug-loaded solid implants, and (c) compression of the micronized drug-loaded solid powder to generate the PSI. DTG and RPV can be pre-combined in a single PLGA-based solution to make dual-drug PSI; or formulated individually in PLGA-based solutions to generate separate micronized powders and form a bilayer dual-drug PSI. Results showed that in a single or bilayer dual-drug PSI, DTG and RPV exhibited physicochemical properties similar to their pure drug analogues. PSIs were well tolerated in vivo and effectively delivered drug(s) over 180 days with concentrations above 4 × PA-IC90 after a single subcutaneous administration. While biodegradable and do not require removal, these PSIs can safely be removed to terminate the treatment if required. The versatility of this technology makes it attractive as an ULA drug delivery platform for HIV and various therapeutic applications.

Background Biocompatible hydrogel systems with tunable mechanical properties have been reported to influence the behavior and differentiation of mesenchymal stem cells (MSCs). Objective To develop a functionalized hydrogel system with well-defined chemical structures and tunable mechanical property for regulation of stem cell differentiation. Methods An in situ-forming hydrogel system is developed by crosslinking vinyl sulfone functionalized polyamidoamine (PAMAM) dendrimer and multi-armed thiolated polyethylene glycol (PEG) through a thiol-ene Michael addition in aqueous conditions. The viability and differentiation of MSCs in hydrogels of different stiffness are conducted for 21 days under corresponding induction media. Results MSCs are viable in synthesized hydrogels after 48 hours of culture. By varying the concentrations of PAMAM dendrimer and PEG, hydrogels of different gelation time and stiffness are achieved. The MSC differentiation indicates that more osteogenic differentiation is observed in hard gel (5,663 Pa) and more adipogenic differentiation is observed in soft gel (77 Pa) in addition to the differentiation caused by each individual induction media during the process of culture. Conclusions A biocompatible in situ-forming hydrogel system is successfully synthesized. This hydrogel system has shown influences on differentiation of MSCs and may potentially be important in developing therapeutic strategies in medical applications.

We present a long-acting (LA) biodegradable polymeric solid implant (PSI) fabricated using a new process combining in-situ phase inversion and compression. This robust process allows fabrication of solid implants that can have different shapes and sizes, accommodate high drug payloads, and provide sustained drug release over several months. Herein the integrase inhibitor dolutegravir (DTG) was used to develop PSIs for HIV prevention. PSIs were fabricated using a three-step process by (a) phase inversion of DTG-loaded polymer solution to form an initial in-situ forming implant in an aqueous solution, (b) micronization of dried DTG-loaded solid implants, and (c) compression of the micronized DTG-loaded solid implants to form the PSI. High drug loading (up to 85 wt%) was achieved in the PSIs. DTG exhibited minimum burst release in the first 24 h (, Graphical abstract Unlabelled Image

This present work aims to functionalize poly(amidoamine) (PAMAM) dendrimers with various reported adhesive peptides, including Arg-Gly-Asp (RGD), Tyr-Ile-Gly-Ser-Arg (YIGSR), and Ile-Lys-Val-Ala-Val (IKVAV) for enhancing cell responses. The RGD, YIGSR, or IKVAV functionalized PAMAM coated substrate could promote cell adhesion of bone marrow mesenchymal stem cells (BMSCs) within 1 h after incubation. The neurite differentiation and proliferation of pheochromocytoma (PC12) cells were also significantly enhanced after culturing on the peptide functionalized PAMAM dendrimers for two and four days. This peptide functionalized PAMAM dendrimers are considered as the potential candidates for various tissue engineering applications.

A series of alkene functionalized polyamidoamine (PAMAM) dendrimers were synthesized to prepare in situ forming hydrogels with varied gelation time and mechanical properties through crosslinking with thiolated hyaluronic acid (HS-HA). By varying the alkenyl groups on the dendrimers, the gelation time displayed a large range from 8 seconds to 18 hours, and the modulus of the hydrogels ranged from 36 to 183 Pa under experimental conditions. Investigation by 1H-NMR spectroscopy revealed that the gelation time and the stiffness of the hydrogels were governed by the degree of electron deficiency of alkenyl groups on the dendrimers. This research provided a systematic study on the relationship between chemical structures versus gelation time and mechanical properties of hydrogels, which could guide the way to synthesize in situ forming hydrogels with designated gelation time and stiffness for biomedical applications. Further, a RGD peptide was attached to the PAMAM dendrimers to enhance cell attachment and proliferation. Viability assays of Human Umbilical Vein Endothelial Cells (HUVEC) in the synthesized hydrogels demonstrated the biocompatibility of the hydrogels after 48 hours of culturing, and the RGD peptide improved the viability of HUVEC cells in hydrogels. We believe the PAMAM/HA hydrogel system is a tuneable and biocompatible system for diverse biomedical applications.

In this study, we developed and characterized an injectable hydrogel with physical and mechanical properties that can mimic the bone microenvironment and promote bone regeneration. The injectable hydrogel was prepared with thermogelling biopolymers, chitosan and cellulose nanofibers/nanocrystals (CNFs/CNCs)). The chitosan solution can undergo sol-gel transition at body temperature, and CNFs/CNCs were used as an additive nanomaterial to enhance the mechanical properties of the chitosan gel and mimic bone tissue properties. Cellulose nanocrystals (CNCs) can significantly improve the gelation kinetics (from ~24 s to 7 s) and mechanical properties of the injectable chitosan hydrogel (from ~28 kPa to ~379 kPa). An increase in percent gel fraction corresponding to the weight percent of CNCs incorporated in the hydrogel demonstrated that the incorporated CNCs were completely reacted into the chitosan network, resulting in a high density of crosslinked network as shown by SEM imaging. Fourier-transform infrared spectroscopy (FTIR) analysis used to probe the reinforcement effect of CNCs showed an increase of hydrogen bonding due to the presence of CNCs within the chitosan networks. The hydrogel formulations were biocompatible as demonstrated by high cell viability in the LIVE-DEAD cell staining analysis. Presence of CNCs in the chitosan gel altered cell morphology by inducing spreading morphology due to higher mechanical sensing from the CNCs. The versatility of this formulation to exhibit strong mechanical properties combined with its ability to support cell encapsulation makes it attractive as a biomaterial for bone regeneration. Statement of significance Bone grafting has increasingly been used in surgery with more than two million times per year worldwide to promote bone regeneration. However, bone grafting failures remain the main constraints in this treatment option. In the past decade, the use of cell-based biomaterials has been extensively investigated as alternatives for bone grafting procedures. Yet, biomaterials that can effectively promote bone fracture healing with a minimally invasive procedure remain in high demand. Herein we describe a novel injectable tunable biomaterial using cellulose nanocrystals-hybridized chitosan-based hydrogel that can safely encapsulate pre-osteoblast cells and can potentially use as an injectable bone graft substitute. This research will establish a novel concept for the use of cell-based biomaterials in bone tissue engineering and other regenerative medicines.

This paper presents a dielectric affinity microsensor that consists of an in situ prepared hydrogel attached to a pair of coplanar electrodes for dielectrically based affinity detection of glucose in subcutaneous tissue in continuous glucose monitoring applications. The hydrogel, incorporating N-3-acrylamidophenylboronic acid that recognizes glucose via affinity binding, is synthetically prepared on the electrodes via in situ gelation. When implanted in subcutaneous tissue, glucose molecules in interstitial fluid diffuse rapidly through the hydrogel and bind to the phenylboronic acid moieties. This induces a change in the hydrogel’s permittivity and hence in the impedance between the electrodes, which can be measured to determine the glucose concentration. The in situ hydrogel preparation allows for a reduced hydrogel thickness (~10 µm) to enable the device to respond rapidly to glucose concentration changes in tissue, as well as covalent electrode attachment of the hydrogel to eliminate the need for semipermeable membranes that would otherwise be required to restrain the sensing material within the device. Meanwhile, the use of coplanar electrodes is amenable to the in situ preparation and facilitates glucose accessibility of the hydrogel, and combined with dielectrically based transduction, also eliminates mechanical moving parts often found in existing affinity glucose microsensors that can be fragile and complicated to fabricate. Testing of the device in phosphate-buffered saline at pH 7.4 and 37 °C has shown that at glucose concentrations ranging from 0 to 500 mg/dL, the hydrogel-based microsensor exhibits a rapid, repeatable, and reversible response. In particular, in the glucose concentration range of 40–100 mg/dL, which is of great clinical interest to monitoring normal and low blood sugar levels, the device response is approximately linear with a resolution of 0.32 mg/dL based on effective capacitance and 0.27 mg/dL based on effective resistance, respectively. Thus, the device holds the potential to enable reliable and accurate continuous monitoring of glucose in subcutaneous tissue.

Bone regeneration is still one of the greatest challenges for the treatment of bone defects since no current clinical approach has been proven effective. To develop an alternative biodegradable bone graft material, multiarm polyethylene glycol (PEG) crosslinked hyaluronic acid (HA) hydrogels are synthesized and applied to promote osteogenesis of mesenchymal stem cells (MSCs) with the ultimate goal for bone defect repair. The multiarm PEG-HA hydrogels provide a significant improvement of alkaline phosphatase (ALP) activity and calcium mineralization of the in vitro encapsulated MSCs under osteogenic condition after 3, 7, and 28 days. In addition, the multiarm PEG-HA hydrogels also facilitate healing of the cranial bone defects more effectively in a Sprague Dawley rat model after 10 weeks of implantation based on histological evaluations and microcomputed tomography analysis. These promising results set the stage for the development of innovative biodegradable hydrogels to provide a more effective and versatile treatment option for bone regeneration.

This study aims to investigate the effect of the structures of cross-linkers on the in vitro chondrogenic differentiation of bone mesenchymal stem cells (BMSCs) in hyaluronic acid (HA)-based hydrogels. The hydrogels were prepared by the covalent cross-linking of methacrylated HA with different types of thiol-tailored molecules, including dithiothreitol (DTT), 4-arm poly(ethylene glycol) (PEG), and multiarm polyamidoamine (PAMAM) dendrimer using thiol-ene "click" chemistry. The microstructure, mechanical properties, diffusivity, and degradation rates of the resultant hydrogels were controlled by the structural feature of different cross-linkers. BMSCs were then encapsulated in the resulting hydrogels and cultured in chondrogenic conditions. Overall, chondrogenic differentiation was highly enhanced in the PEG-cross-linked HA hydrogels, as measured by glycosaminoglycan (GAG) and collagen accumulation. The physical properties of hydrogels, especially the mechanical property and microarchitecture, were resulted from the structures of different cross-linkers, which subsequently modulated the fate of BMSC differentiation.

We present a hydrogel-based affinity microsensor for continuous glucose measurements. The microsensor is based on microelectromechanical systems (MEMS) technology, and incorporates a synthetic hydrogel that is attached to the device surface via in situ polymerization. Glucose molecules that diffuses into and out of the device binds reversibly with boronic acid groups in the hydrogel via affinity binding, and causes changes in the dielectric properties of the hydrogel, which can be measured using a MEMS capacitive transducer to determine the glucose concentration. The use of the in situ polymerized hydrogel eliminates mechanical moving parts found in other types of affinity microsensors, as well as mechanical barriers such as semipermeable membranes that are otherwise required to hold the glucose-sensitive material. This facilitates the miniaturization and robust operation of the microsensor, and can potentially improve the tolerance of the device, when implanted subcutaneously, to biofouling. Experimental results demonstrate that in a glucose concentration range of 0-500 mg/dL and with a resolution of 0.35 mg/dL or better, the microsensor exhibits a repeatable and reversible response, and can potentially be useful for continuous glucose monitoring in diabetes care.

Hydrogels possess great potential in biofabrication because they allow cell encapsulation and proliferation in a highly hydrated three-dimensional environment, and they provide biologically relevant chemical and physical signals. However, development of hydrogel systems that mimic the complexity of natural extracellular matrix remains a challenge. In this study, we report the development of a binary hydrogel system containing a synthetic poly(amido amine) (PAMAM) dendrimer and a natural polymer, i.e., hyaluronic acid (HA), to form a fast cross-linking hydrogel. Live cell staining experiment and cell viability assay of bone marrow stem cells demonstrated that cells were viable and proliferating in the in situ formed PAMAM/HA hydrogel system. Furthermore, introduction of a Arginylglycylaspartic acid (RGD) peptide into the hydrogel system significantly improved the cell viability, proliferation, and attachment. Therefore, this PAMAM/HA hydrogel system could be a promising platform for various applications in biofabrication.