Effects of precipitate agents on temperature-responsive sol–gel transitions of PLGA–PEG–PLGA copolymers in water

Reshapable polymeric hydrogel for controlled soft-tissue expansion: In vitro and in vivo evaluation

Tissue expansion is the process by which extra skin is generated using a device that applies pressure from underneath the skin. Over the course of weeks to months, stretching by this pressure creates a flap of extra tissue that can be used to cover a defect area or enclose a permanent implant. Conventional tissue expanders require a silicone shell inflated either by external injections of saline solution or air, or by internal osmotic pressure generated by a hydrophilic polymer. In this study, a shell-free tissue expander comprised only of a chemically cross-linked biocompatible polymeric hydrogel is developed. The cross-linked network of hydrophilic polymer provides for intrinsically controlled swelling in the absence of an external membrane. The new type of hydrogel expanders were characterized in vitro as well as in vivo using a rat-skin animal model. It was found that increasing the hydrophobic polyester content in the hydrogel reduced the swelling velocity to a rate and volume that eliminate the danger of premature swelling rupturing the sutured area. Additionally, increasing the crosslinking density resulted in enough mechanical strength of the hydrogel to allow for complete post-swelling removal, without the hydrogel cracking or crumbling. No systemic toxicity was noted with the expanders and histology showed the material to be highly biocompatible. These expanders have an advantage of tissue expansion without requiring an external silicone membrane, and thus, they can be cut or reshaped at the time of implantation for applications in small or physically constrained regions of the body.

Injectable Polypeptide Thermogel as a Tissue Engineering System for Hepatogenic Differentiation of Tonsil-Derived Mesenchymal Stem Cells

A poly(ethylene glycol)-b-poly(l-alanine) (PEG-l-PA) hydrogel incorporating tonsil-derived mesenchymal stem cells (TMSCs), tauroursodeoxycholic acid (TUDCA), hepatocyte growth factor (HGF), and fibroblast growth factor 4 (FGF4) was prepared through thermal gelation of an aqueous polymer solution for an injectable tissue engineering application. The thermal gelation accompanied conformational changes of both PA and PEG blocks. The gel modulus at 37 °C was controlled to be 1000 Pa by using a 14.0 wt % aqueous polymer solution. The gel preserved its physical integrity during the 3D culture of the cells. TUDCA, HGF, and FGF4 were released from the PEG-l-PA hydrogel over 21 days of the 3D cell culture period. TMSCs initially exhibited a spherical shape, whereas some fibers protruded from the cells on days 14-21 of 3D culture. The injectable system exhibited pronounced expressions of the hepatic biomarkers at both mRNA and protein levels, which are significantly better than the commercially available hyaluronic acid gel. In particular, the hepatogenically differentiated cells from the TMSCs in the injectable system demonstrated hepatic biofunctions comparable to HepG2 cells for the uptakes of low density lipoproteins (52%) and indocyanine green (76%), and the production of albumin (40%) and urea (52%), which are also significantly better than the 3D-cultured cells in the commercially available hyaluronic acid gel. Our studies suggest that the PEG-l-PA thermogel incorporating TMSCs, TUDCA, and growth factors is highly promising as an in situ forming tissue engineering system.

Platelet-Rich Plasma-Loaded Poly(d,l-lactide)-Poly(ethylene glycol)-Poly(d,l-lactide) Hydrogel Dressing Promotes Full-Thickness Skin Wound Healing in a Rodent Model

Traditional therapeutic methods for skin wounds have many disadvantages, and new wound dressings that can facilitate the healing process are thus urgently needed. Platelet-rich plasma (PRP) contains multiple growth factors (GFs) and shows a significant capacity to heal soft tissue wounds. However, these GFs have a short half-life and deactivate rapidly; we therefore need a sustained delivery system to overcome this shortcoming. In this study, poly(d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (PDLLA-PEG-PDLLA: PLEL) hydrogel was successfully created as delivery vehicle for PRP GFs and was evaluated systematically. PLEL hydrogel was injectable at room temperature and exhibited a smart thermosensitive in situ gel-formation behavior at body temperature. In vitro cell culture showed PRP-loaded PLEL hydrogel (PRP/PLEL) had little cytotoxicity, and promoted EaHy926 proliferation, migration and tube formation; the factor release assay additionally indicated that PLEL realized the controlled release of PRP GFs for as long as 14 days. When employed to treat rodents’ full-thickness skin defects, PRP/PLEL showed a significantly better ability to raise the number of both newly formed and mature blood vessels compared to the control, PLEL and PRP groups. Furthermore, the PRP/PLEL-treated group displayed faster wound closure, better reepithelialization and collagen formation. Taken together, PRP/PLEL provides a promising strategy for promoting angiogenesis and skin wound healing, which extends the potential of this dressing for clinical application.

Hydrolytic stability of end-linked hydrogels from PLGA–PEG–PLGA macromonomers terminated by α,ω-itaconyl groups

Biodegradable amphiphilic PLGA–PEG–PLGA triblock copolymers end-terminated with itaconic acid (ITA) having reactive double bond were end-linked by light and swelled in water. Hydrolytical stability of prepared hydrogels was evaluated.

Synthesis and Properties of Amphipathic Poly(D,L-lactide-co-glycolide)-polyethylene glycol-poly(D,L-lactide-co-glycolide) Triblock Copolymers

In this paper, amphipathic poly(d,l-lactide-co-glycolide)-polyethylene glycol-poly(d,l-lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymers were synthesized via bulk ring-opening polymerization with d,l-lactide (d,l-LA), glycolide (GA), and polyethylene glycol (PEG) as raw materials and tin(ii) bis(2-ethylhexanoate) (Sn(Oct)2) as catalyst. The synthesis and purification processes were free from organic solvent. The chemical structure of PLGA-PEG-PLGA was characterized by Fourier transform infrared spectroscopy, 1H NMR, gel permeation chromatography, differential scanning calorimetry, and thermo gravimetric analysis. The thermo-sensitivity of PLGA-PEG-PLGA aqueous solution was examined, and the results showed that the copolymers concentration, mass ratio of d,l-LA/GA, and molecular weight of PEG played important parts in controlling the sol–gel transition temperature. The sol–gel transition occurred at lower temperatures with higher copolymer concentrations and mass ratios of d,l-LA/GA. In contrast, the sol–gel transition temperature increased with higher molecular weights of PEG. In vitro drug release studies were carried out using ceftibuten as a model drug. The results indicated that PLGA-PEG-PLGA prepared with 30 wt-% PEG1500 and 70 wt-% PLGA (mass ratio of d,l-LA/GA = 2 : 1) was an effective system for achieving long-sustained controlled release. The drug release from the hydrogel showed a higher initial release followed by a slower pattern up to 120 h, and the mean retention time was ~50 h.

Hydrogels for tissue engineering and regenerative medicine

Injectable hydrogels have become an incredibly prolific area of research in the field of tissue engineering and regenerative medicine, because of their high water content, mechanical similarity to natural tissues, and ease of surgical implantation, hydrogels are at the forefront of biomedical scaffold and drug carrier design.

Poly(ethylene glycol)-poly(lactic-co-glycolic acid) based thermosensitive injectable hydrogels for biomedical applications

Stimuli triggered polymers provide a variety of applications related with the biomedical fields. Among various stimuli triggered mechanisms, thermoresponsive mechanisms have been extensively investigated, as they are relatively more convenient and effective stimuli for biomedical applications. In a contemporary approach for achieving the sustained action of proteins, peptides and bioactives, injectable depots and implants have always remained the thrust areas of research. In the same series, Poloxamer based thermogelling copolymers have their own limitations regarding biodegradability. Thus, there is a need to have an alternative biomaterial for the formulation of injectable hydrogel, which must remain biocompatible along with safety and efficacy. In the same context, poly(ethylene glycol) (PEG) based copolymers play a crucial role as a biomedical material for biomedical applications, because of their biocompatibility, biodegradability, thermosensitivity and easy controlled characters. This review stresses on the physicochemical property, stability and composition prospects of smart PEG/poly(lactic-co-glycolic acid) (PLGA) based thermoresponsive injectable hydrogels, recently utilized for biomedical applications. The manuscript also highlights the synthesis scheme and stability characteristics of these copolymers, which will surely help the researchers working in the same area. We have also emphasized the applied use of these smart copolymers along with their formulation problems, which could help in understanding the possible modifications related with these, to overcome their inherent associated limitations.

Cell-material interactions revealed via material techniques of surface patterning

Cell-material interactions constitute a key fundamental topic in biomaterials study. Various cell cues and matrix cues as well as soluble factors regulate cell behaviors on materials. These factors are coupled with each other as usual, and thus it is very difficult to unambiguously elucidate the role of each regulator. The recently developed material techniques of surface patterning afford unique ways to reveal the underlying science. This paper reviews the pertinent material techniques to fabricate patterns of microscale and nanoscale resolutions, and corresponding cell studies. Some issues are emphasized, such as cell localization on patterned surfaces of chemical contrast, and effects of cell shape, cell size, cell-cell contact, and seeding density on differentiation of stem cells. Material cues to regulate cell adhesion, cell differentiation and other cell events are further summed up. Effects of some physical properties, such as surface topography and matrix stiffness, on cell behaviors are also discussed; nanoscaled features of substrate surfaces to regulate cell fate are summarized as well. The pertinent work sheds new insight into the cell-material interactions, and is stimulating for biomaterial design in regenerative medicine, tissue engineering, and high-throughput detection, diagnosis, and drug screening.

A long-acting formulation of a polypeptide drug exenatide in treatment of diabetes using an injectable block copolymer hydrogel

This study is aimed to develop a long-acting injectable formulation in treatment of type II diabetes. A glucoregulatory polypeptide, exenatide (EXT), was chosen as the model drug, and an aqueous block copolymer system with a sol-gel transition upon the increase of temperature was selected as the delivery matrix of EXT. The thermoreversible hydrogel composed of poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) triblock copolymers was found to slower the degradation of the polypeptide to a large extent. However, the initial formulation in this study exhibited a significant drug burst effect, which is a common problem to load a hydrophilic small or medium-size polypeptide into a hydrogel. Zinc acetate was then introduced to slow down the EXT release by formation of insoluble Zn-EXT complexes in the thermogel matrix. Yet an incomplete release became another crucial problem, which is also common for peptide and protein delivery. The synergistic effect of three excipients (zinc acetate, PEG, and sucrose) under an appropriate condition overcame these two problems simultaneously, and the sustained release of drug lasted for 1 week. In vivo experiments via mice oral glucose tolerance tests demonstrated an improved glucose tolerance for 1 week after a single subcutaneous injection of the optimal EXT formulation. As a result, a formulation of antidiabetic drugs was set up, and meanwhile a strategy using synergistic excipients to adjust release profiles of peptides from hydrogels was put forward.