Biocompatible microcapsules with enhanced mechanical strength

Modeling the debonding process of osseointegrated implants due to coupled adhesion and friction

Cementless implants have become widely used for total hip replacement surgery. The long-term stability of these implants is achieved by bone growing around and into the rough surface of the implant, a process called osseointegration. However, debonding of the bone-implant interface can still occur due to aseptic implant loosening and insufficient osseointegration, which may have dramatic consequences. The aim of this work is to describe a new 3D finite element frictional contact formulation for the debonding of partially osseointegrated implants. The contact model is based on a modified Coulomb friction law by Immel et al. (2020), that takes into account the tangential debonding of the bone-implant interface. This model is extended in the direction normal to the bone-implant interface by considering a cohesive zone model, to account for adhesion phenomena in the normal direction and for adhesive friction of partially bonded interfaces. The model is applied to simulate the debonding of an acetabular cup implant. The influence of partial osseointegration and adhesive effects on the long-term stability of the implant is assessed. The influence of different patient- and implant-specific parameters such as the friction coefficient [Formula: see text], the trabecular Young's modulus [Formula: see text], and the interference fit [Formula: see text] is also analyzed, in order to determine the optimal stability for different configurations. Furthermore, this work provides guidelines for future experimental and computational studies that are necessary for further parameter calibration.

Artificial cells for the treatment of liver diseases

Liver diseases have become an increasing health burden and account for over 2 million deaths every year globally. Standard therapies including liver transplant and cell therapy offer a promising treatment for liver diseases, but they also suffer limitations such as adverse immune reactions and lack of long-term efficacy. Artificial cells that mimic certain functions of a living cell have emerged as a new strategy to overcome some of the challenges that liver cell therapy faces at present. Artificial cells have demonstrated advantages in long-term storage, targeting capability, and tuneable features. This article provides an overview of the recent progress in developing artificial cells and their potential applications in liver disease treatment. First, the design of artificial cells and their biomimicking functions are summarized. Then, systems that mimic cell surface properties are introduced with two concepts highlighted: cell membrane-coated artificial cells and synthetic lipid-based artificial cells. Next, cell microencapsulation strategy is summarized and discussed. Finally, challenges and future perspectives of artificial cells are outlined. STATEMENT OF SIGNIFICANCE: Liver diseases have become an increasing health burden. Standard therapies including liver transplant and cell therapy offer a promising treatment for liver diseases, but they have limitations such as adverse immune reactions and lack of long-term efficacy. Artificial cells that mimic certain functions of a living cell have emerged as a new strategy to overcome some of the challenges that liver cell therapy faces at present. This article provides an overview of the recent progress in developing artificial cells and their potential applications in liver disease treatment, including the design of artificial cells and their biomimicking functions, two systems that mimic cell surface properties (cell membrane-coated artificial cells and synthetic lipid-based artificial cells), and cell microencapsulation strategy. We also outline the challenges and future perspectives of artificial cells.

Bio Micro-Nano Technologies of Antioxidants Optimised Their Pharmacological and Cellular Effects, ex vivo, in Pancreatic β-Cells

Introduction

Recent formulation and microencapsulation studies of probucol (PB) using the polymer sodium alginate (SA) and bile acids have shown promising results but PB stability, and pharmacology profiles remain suboptimal. This study aimed to investigate novel polymers for the nano and micro encapsulation of PB, with the anti-inflammatory bile acid ursodeoxycholic acid (UDCA).

Material and methods

Six formulations using three types of polymers were investigated with and without UDCA. The polymers were NM30D, RL30D, and RS30D and they were mixed with SA and PB at set ratios and microencapsulated using oscillating-voltage-mediated nozzle technology coupled with ionic gelation. The microcapsules were examined for physical and biological effects using pancreatic β-cells.

Results and discussion

UDCA addition did not adversely affect the morphology and physical features of the microcapsules. Despite thermal stability remaining unchanged, bile acid incorporation did enhance the electrokinetic stability of the formulation system for NM30D and RL30D polymers. Mechanical stability remained similar in all groups. Enhanced uptake of PB from the microcapsule by pancreatic β-cells was only seen with NM30D-UDCA-intercalated microcapsules and this effect was sustained at both glucose levels of 5.5 and 35.5 mM.

Conclusion

UDCA addition enhanced PB delivery and biological effects in a formulation-dependent manner.

Investigation of a New Microcapsule Membrane Combining Alginate, Chitosan, Polyethylene Glycol and Poly-L-Lysine for Cell Transplantation Applications

Microencapsulation of living cells may serve as an alternative therapy for patients requiring organ transplants. One of the limiting factors in the progress of such therapy is attaining a biocompatible and mechanically stable polymer. The current study investigates the potential of a novel membrane combining alginate, chitosan, polyethylene glycol (PEG) and poly-L-lysine (PLL) with the objective of proposing a membrane suitable for cell entrapment that may overcome some of the shortcomings of the widely studied alginate-poly-L-lysine-alginate (APA) capsules. The novel microcapsule was formulated using a 1.5% alginate solution coated with 0.05% chitosan, 0.1% PEG and 0.05% poly-L-lysine with a final layer of 0.1% alginate. Microcapsules having a diameter of 450 ± 30 μm were prepared. Upon citrate treatment, the membrane remained intact and retained its spherical structure. The membrane was able to support liver cell proliferation and the encapsulated cells were capable of secreting proteins. The study demonstrated that the new membrane can be used for cell entrapment. However, further investigations are needed to assess its potential for long term transplantation and usage in the development of bioartificial organs.

Inhibition of HeLa cell growth by doxorubicin-loaded and tuftsin-conjugated arginate-PEG microparticles

In order to improve the release pattern of chemotherapy drug and reduce the possibility of drug resistance, poly(ethylene glycol amine) (PEG)-modified alginate microparticles (ALG-PEG MPs) were developed then two different mechanisms were employed to load doxorubicin (Dox): 1) forming Dox/ALG-PEG complex by electrostatic attractions between unsaturated functional groups in Dox and ALG-PEG; 2) forming Dox-ALG-PEG complex through EDC-reaction between the amino and carboxyl groups in Dox and ALG, respectively. Additionally, tuftsin (TFT), a natural immunomodulation peptide, was conjugated to MPs in order to enhance the efficiency of cellular uptake. It was found that the Dox-ALG-PEG-TFT MPs exhibited a significantly slower release of Dox than Dox/ALG-PEG-TFT MPs in neutral medium, suggesting the role of covalent bonding in prolonging Dox retention. Besides, the release of Dox from these MPs was pH-sensitive, and the release rate was observably increased at pH 6.5 compared to the case at pH 7.4. Compared with Dox/ALG-PEG MPs and Dox-ALG-PEG MPs, their counterparts further conjugated with TFT more efficiently inhibited the growth of HeLa cells over a period of 48 h, implying the effectiveness of TFT in enhancing cellular uptake of MPs. Over a period of 48 h, Dox-ALG-PEG-TFT MPs inhibited the growth of HeLa cells less efficiently than Dox/ALG-PEG-TFT MPs but the difference was not significant (p > 0.05). In consideration of the prolonged and sustained release of Dox, Dox-ALG-PEG-TFT MPs possess the advantages for long-term treatment.

•

Dox-ALG-PEG-TFT exhibited slower release of Dox than Dox/ALG-PEG-TFT.

•

Release of Dox from Dox-ALG-PEG-TFT and Dox/ALG-PEG-TFT was pH-sensitive.

•

Further conjugation with TFT enhanced the efficiency of Dox/ALG-PEG and Dox-ALG-PEG in inhibiting HeLa cell growth.

•

Dox-ALG-PEG-TFT MPs possess the advantages for long-term treatment over Dox/ALG-PEG-TFT MPs.

Osteogenic differentiation of human mesenchymal stem cells through alginate-graft-poly(ethylene glycol) microsphere-mediated intracellular growth factor delivery

The intracellular delivery of growth factors increases opportunities for controlling cell behavior and maintaining tissue homeostasis. Recently, VEGFA was reported to enhance osteogenic differentiation of mesenchymal stem cells (MSCs) through an intracrine mechanism, suggesting a new strategy to promote bone tissue formation in osteoporotic patients. The goal of this study was to design and fabricate ligand-conjugated alginate-graft-poly(ethylene glycol) microspheres for intracellular delivery and release of VEGFA in primary human MSCs to enhance osteogenic differentiation as a potential therapeutic. Three types of microspheres were synthesized and characterized by scanning electron microscopy, in vitro drug release kinetics, MSC uptake and internalization: alginate alone (Alg), alginate-graft-poly(ethylene glycol) (Alg-g-PEG) and alginate-graft-poly(ethylene glycol)-S-S-arginine-glycine-aspartic acid (Alg-g-RGD). Each of the different microsphere formulations successfully transported bioactive VEGFA into primary human MSCs within 48h of culture, and significantly enhanced osteogenic differentiation compared to control treatments with empty microspheres (intracellular control) or non-encapsulated VEGFA (extracellular control). Adipogenic differentiation was not affected by the presence of VEGFA intracellularly or extracellularly. These results demonstrating the internalization of alginate-based microspheres and intracellular delivery of VEGFA support the efficacy of using this drug delivery and intracrine mechanism to control the fate of human MSCs and enhance osteogenic differentiation.

Drug and cell encapsulation: alternative delivery options for the treatment of malignant brain tumors

Malignant brain tumors including glioblastoma are incurable cancers. Over the last years a number of promising novel treatment approaches have been investigated including the application of inhibitors of receptor tyrosine kinases and downstream targets, immune-based therapies and anti-angiogenic agents. Unfortunately so far the major clinical trials in glioblastoma patients did not deliver clear clinical benefits. Systemic brain tumor therapy is seriously hampered by poor drug delivery to the brain. Although in glioblastoma, the blood brain barrier is disrupted in the tumor core, the major part of the tumor is largely protected by an intact blood brain barrier. Active cytotoxic compounds encapsulated into liposomes, micelles, and nanoparticles constitute novel treatment options because they can be designed to facilitate entry into the brain parenchyma. In the case of biological therapeutics, encapsulation of therapeutic cells and their implantation into the surgical cavity represents another promising approach. This technology provides long term release of the active compound at the tumor site and reduces side effects associated with systemic delivery. The proof of principle of encapsulated cell factories has been successfully demonstrated in experimental animal models and should pave the way for clinical application. Here we review the challenges associated with the treatment of brain tumors and the different encapsulation options available for drugs and living cells, with an emphasis on alginate based cell encapsulation technology.

Polymers in cell encapsulation from an enveloped cell perspective

In the past two decades, many polymers have been proposed for producing immunoprotective capsules. Examples include the natural polymers alginate, agarose, chitosan, cellulose, collagen, and xanthan and synthetic polymers poly(ethylene glycol), polyvinyl alcohol, polyurethane, poly(ether-sulfone), polypropylene, sodium polystyrene sulfate, and polyacrylate poly(acrylonitrile-sodium methallylsulfonate). The biocompatibility of these polymers is discussed in terms of tissue responses in both the host and matrix to accommodate the functional survival of the cells. Cells should grow and function in the polymer network as adequately as in their natural environment. This is critical when therapeutic cells from scarce cadaveric donors are considered, such as pancreatic islets. Additionally, the cell mass in capsules is discussed from the perspective of emerging new insights into the release of so-called danger-associated molecular pattern molecules by clumps of necrotic therapeutic cells. We conclude that despite two decades of intensive research, drawing conclusions about which polymer is most adequate for clinical application is still difficult. This is because of the lack of documentation on critical information, such as the composition of the polymer, the presence or absence of confounding factors that induce immune responses, toxicity to enveloped cells, and the permeability of the polymer network. Only alginate has been studied extensively and currently qualifies for application. This review also discusses critical issues that are not directly related to polymers and are not discussed in the other reviews in this issue, such as the functional performance of encapsulated cells in vivo. Physiological endocrine responses may indeed not be expected because of the many barriers that the metabolites encounter when traveling from the blood stream to the enveloped cells and back to circulation. However, despite these diffusion barriers, many studies have shown optimal regulation, allowing us to conclude that encapsulated grafts do not always follow nature's course but are still a possible solution for many endocrine disorders for which the minute-to-minute regulation of metabolites is mandatory.

CHITOSAN IN APPLICATIONS OF BIOMEDICAL DEVICES

Chitosan is a natural polysaccharide with great potential for biomedical applications due to its biocompatibility, biodegradable capability, and nontoxicity. Various techniques used for preparing chitosan microspheres/membranes and evaluations of these fabrications have also been reviewed. The hydrophilicity of chitosan provides unique characteristics of hydrogel formation with the acidic media and may entrap the drug content inside of the matrix for controlled release. In order to improve upon the scope of preparation of chitosan microspheres, we had successfully employed and incorporated a high-voltage system into the direct pumping injection process. The wide range of drug release profiles could be attributed to the surface characteristics, porosities, and various structures of chitosan microspheres upon treatment with Na5P3O10/NaOH solutions of various volume ratios. We also demonstrated that with the addition of chitosan/β-TCP microspheres as a constituent into the PMMA cement significantly decreases the curing peak temperature and increases the setting time. The excellent gelforming property of chitosan offers another biomedical application in membrane separation fields. Chitosan membranes were prepared by a thermal induced phase separation method, following treatment with nontoxic NaOH gelating and Na5P3O10, Na2SO3 crosslinking agents. In order to further improve the mechanical strength and biocompatibility and to expand the potential of chitosan GTR membranes in periodontal applications, various chitosan membranes incorporating with negatively charged alginate, bioactive tricalcium phosphate, and platelet rich plasma, respectively, were also prepared and characterized. Moreover, we had also utilized chitosan, which with good blood-clotting, cheap, and easy preparation characteristics, as the raw material to prepare rapid clotting wound dressing and tooth plug.

Hydrogels used for cell-based drug delivery

Stem cells, progenitor cells, and lineage-committed cells are being considered as a new generation of drug depots for the sustained release of therapeutic biomolecules. Hydrogels are often used in conjunction with the therapeutic secreting cells to provide a physical barrier to protect the cells from hostile extrinsic factors. Although the hydrogels significantly improve the therapeutic efficacy of transplanted cells, there have been no successful products commercialized based on these technologies. Recently, biomaterials are increasingly designed to provide cells with both a physical barrier and an extracellular matrix to further improve the secretion of therapeutic proteins from cells. This review will discuss (1) the cell encapsulation process, (2) the immunogenicity of the encapsulating hydrogel, (3) the transport properties of the hydrogel, (4) the hydrogel mechanical properties, and will propose new strategies to improve the hydrogel and cell interaction for successful cell-based drug delivery strategies.

Development of two alginate-based wound dressings

Two types of new alginate-based wound dressings, Type-AP and Type-AE, were fabricated by the EDC-activated crosslinking of alginate with Polyethyleneimine and Ethylenediamine, respectively. As compared with the commercial non-woven wound dressing, Kaltostat, both Type-AP and Type-AE dressings had higher degradation temperature, lower calcium content, and a sponge-like macroporous structure. In addition, these two alginate-based dressings had higher mechanical stress (12.37 +/- 1.72 and 6.87 +/- 0.5 MPa for Type-AP and -AE, respectively) and higher water vapor transmission rates (both about 3,500 g/m2/day) than Kaltostat (0.87 +/- 0.12 MPa and 2,538 g/m2/day). Fibroblasts proliferated faster on these two newly developed wound dressings at a higher rate as compared with that on Kalostat dressing. The results of animal study showed that the wounds treated with either Type-AP or Type-AE dressings healed faster than Kaltostat with less encapsulation of residuals by fibrous tissue and more neo-capillary formation. These two newly developed Type-AP and Type-AE porous wound dressings thus have great potential for clinical applications.

Dendritic structures of poly(ethylene glycol) on silicon nitride and gold surfaces

A hydrophilic silicon nitride surface was grafted with poly(ethylene glycol) monomethyl ether (average formula weight of 5000 Da) in a one-step protocol. The domains of stable dendritic structures of self-assembled monolayer islands on a silicon nitride surface were observed with atomic force microscopy. The moduli of elasticity of these dendritic structures in air and in KCl aqueous solution were compared. The value of the Young's modulus of these structures is reduced by more than 3 orders of magnitude, from approximately 12 GPa measured in air to approximately 5 MPa in KCl solution. This dramatic reduction in elasticity was attributed to the swelling of the dendritic structures in aqueous solution, which was verified by the increased film thickness. These dendritic structures were not stable in the aqueous environment and could be removed by soaking in water for 22 h because of the hydrolysis of the silicate bonds. This fact was confirmed by the reduction of the C1s signal in the X-ray photoelectron spectroscopy experiments. These morphologies are not unique to silicon nitride substrate; similar features were also observed for thiolated poly(ethylene glycol) monomethyl ether molecules absorbed on a gold surface.

Microencapsulation of parathyroid tissue with photosensitive poly(L-lysine) and short chain alginate-co-MPEG

Human parathyroid glands were encapsulated using the alginate-PLL system in this study. In order to improve the mechanical strength and the biocompatibility, the microcapsules were fabricated with a three-layer structure that consisted of alginate/photosensitive poly(L-lysine)/short chain alginate-co-MPEG. These modified microcapsules were used for encapsulating human parathyroid tissue. In vitro experiments revealed that microencapsulated parathyroid glands maintained differentiative properties in culture, and the capsular membrane was freely permeable to the human parathyroid hormone. For in vivo experiments, these capsules were transplanted into parathyroidectomized SD-rats. After parathyroidectomy, serum calcium decreased from 2.25 to 1.68 mmol/L and remained in a constantly low concentration until transplantation. Parathyroidectomized SD-rats were normocalcemic after transplant of encapsulated parathyroid tissue. The microcapsules were then explanted at 12 weeks for examination. Histological evaluations of excised transplants revealed that the microcapsules remained intact structurally and were free of cell adhesions. The results demonstrated that human parathyroid tissue microencapsulated by this system retains stability and is functional both in vitro and in vivo. This encapsulating system will have valuable application for endocrine surgery in the future.

Modification of porous aminopropyl-silicate microcapsule membrane by electrically-bonded external anionic polymers

Biocompatibility and permeability of a microcapsule membrane governs the function of a microcapsule-shaped bioartificial pancreas. We have previously developed an alginate/sol-gel-synthesized aminopropyl-silicate/alginate microcapsule (Alg/AS/Alg), which had insufficient biocompatibility. The purpose of this study was to investigate whether the biocompatibility could improve by modifying the external surface with other anionic polymers and to investigate an influence of the modification on the permeability of the membrane. Four kinds of anionic polymers, poly(oxyethylene)diglycolic acid (3 kDa), heparin (15 kDa), Alg (54 kDa) and carboxymethylcellulose (CMC, 60 kDa) were used as the external anionic polymers. The heparin-bonded gel bead had the largest resistance to the diffusion of small molecules. The molecular mass cut-off point of 150 kDa required for immunoisolation was maintained for all anionic polymers. Cellular overgrowth to the implanted islet-enclosing microcapsule, a sign of insufficient biocompatibility, was suppressed by altering the external surface material from Alg to CMC. These results suggest that the biocompatibility of the Alg/AS/anionic polymer membrane can be improved by using a biocompatible anionic polymer. At the same time, it is suggested the influence on the permeability has to be investigated to develop an optimal microcapsule for bioartificial pancreas.