Initial design and physical characterization of a polymeric device for osmosis-driven delayed burst delivery of vaccines

A vertical additive-lathe printing system for the fabrication of tubular constructs using gelatin methacryloyl hydrogel

Reproducing both the mechanical and biological performance of native blood vessels remains an ongoing challenge in vascular tissue engineering. Additive-lathe printing offers an attractive method of fabricating long tubular constructs as a potential vascular graft for the treatment of cardiovascular diseases. Printing hydrogels onto rotating horizontal mandrels often leads to sagging, resulting in poor and variable mechanical properties. In this study, an additive-lathe printing system with a vertical mandrel to fabricate tubular constructs is presented. Various concentrations of gelatin methacryloyl (gelMA) hydrogel were used to print grafts on the rotating mandrel in a helical pattern. The printing parameters were selected to achieve the bonding of consecutive gelMA filaments to improve the quality of the printed graft. The hydrogel filaments were fused properly under the action of gravity on the vertical mandrel. Thus, the vertical additive-lathe printing system was used to print uniform wall thickness grafts, eliminating the hydrogel sagging problem. Tensile testing performed in both circumferential and longitudinal direction revealed that the anisotropic properties of printed gelMA constructs were similar to those observed in the native blood vessels. In addition, no leakage was detected through the walls of the gelMA grafts during burst pressure measurement. Therefore, the current printing setup could be utilized to print vascular grafts for the treatment of cardiovascular diseases.

Controlled release vaccine implants for delivery of booster immunisations

Most current animal vaccine regimes involve a primary vaccination followed sometime later by a booster vaccination. This presents challenges when vaccinating difficult to access animals such as livestock. Mustering livestock to deliver a vaccine boost is costly and stressful for animals. Thus, we have produced a platform system that can be administered at the same time as the priming immunisation and delivers payload after an appropriate delay time to boost the immune response, without need for further handling of animals. A 30 × 2 mm osmotically triggered polymer implant device with burst-release characteristics delivered the booster dose of a tetanus vaccine. Blood samples were collected from an experimental group that received the priming vaccine and implant on day 0 and control group that received the initial vaccine (tetanus toxoid) and then a bolus dose 28 days later via subcutaneous injection. The two groups showed identical weight gain curves. T cell proliferation following in vitro stimulation with antigen was identical between the two groups at all time points. However, serum IgG antibody responses to the tetanus toxoid antigen were significantly higher in the control group at weeks 8 and 12. The implant capsules stayed at the site of implantation and at week 12 there was evidence of tissue integration. No local reactions at the implant site were observed, other than mild thickening of the skin in half of the experimental group animals and no other adverse health events were recorded in either group.

Elastic Bioresorbable Polymeric Capsules for Osmosis-Driven Delayed Burst Delivery of Vaccines

Single-administration vaccine delivery systems are intended to improve the efficiency and efficacy of immunisation programs in both human and veterinary medicine. In this work, an osmotically triggered delayed delivery device was developed that was able to release a payload after a delay of approximately 21 days, in a consistent and reproducible manner. The device was constructed out of a flexible poly(ε-caprolactone) photo-cured network fabricated into a hollow tubular shape, which expelled approximately 10% of its total payload within 2 days after bursting. Characterisation of the factors that control the delay of release demonstrated that it was advantageous to adjust material permeability and device wall thickness over manipulation of the osmogent concentration in order to maintain reproducibility in burst delay times. The photo-cured poly(ε-caprolactone) network was shown to be fully degradable in vitro, and there was no evidence of cytotoxicity after 11 days of direct contact with primary dermal fibroblasts. This study provides strong evidence to support further development of flexible biomaterials with the aim of continuing improvement of the device burst characteristics in order to provide the greatest chance of the devices succeeding with in vivo vaccine booster delivery.

Catalyst-Loaded Capsules that Spontaneously Inflate and Violently Eject their Core

We present a design for polymer capsules that exhibit a range of unusual autonomous behaviors when exposed to a chemical fuel. The capsules have a physically gelled core (alginate-Ca²⁺) loaded with catalytic (silver) particles and a shell composed of a chemically cross-linked gel. In the presence of the fuel (H₂O₂), a catalytic reaction occurs, which generates oxygen (O₂) gas. The gas collects in a zone between the core and the shell, and the resulting gas pressure causes the elastic shell to stretch. This makes the capsule inflate in a process reminiscent of a swelling pufferfish. As the capsule inflates, the polymer chains in the shell continue to stretch until a breaking point is reached, whereupon the shell ruptures. Three rupture modes are documented: gentle, moderate, and violent. The latter involves the gelled core being forcefully ejected out of the shell in a manner similar to the ejection of needles out of nematocysts on jellyfish. The extent and duration of inflation can be tuned by altering the core and shell composition; for example, shells that are more densely cross-linked swell less and rupture faster. Also, instead of a catalytic reaction, capsule inflation can be achieved by combining reactants, one in the capsule and the other in the external solution, that together generate a different gas (e.g., CO₂).

Impact of dose, route, and composition on the immunogenicity of immune polyelectrolyte multilayers delivered on gold templates

Biomaterial vaccines offer new capabilities that can be exploited for both infectious disease and cancer. We recently developed a novel vaccine platform based on self‐assembly of immune signals into immune polyelectrolyte multilayers (iPEMs). These iPEM vaccines are electrostatically assembled from peptide antigens and nucleic acid‐based toll‐like receptor agonists (TLRas) that serve as molecular adjuvants. Gold nanoparticles (AuNPs) coated with iPEMs stimulate effector cytokine secretion in vitro and expand antigen‐specific T cells in mice. Here we investigated how the dose, injection route, and choice of molecular adjuvant impacts the ability of iPEMs to generate T cell immunity and anti‐tumor response in mice. Three injection routes—intradermal, subcutaneous, and intramuscular—and three iPEM dosing levels were employed. Intradermal injection induced the most potent antigen‐specific T cell responses and, for all routes, the level of response was dose‐dependent. We further discovered that these vaccines generate durable memory, indicated by potent, antigen‐specific CD8⁺ T cell recall responses in mice challenged with vaccine 49 days after a prime‐boost immunization regimen. In a common exogenous antigen melanoma model, iPEM vaccines slowed or stopped tumor growth more effectively than equivalent ad‐mixed formulations. Further, iPEMs containing CpG—a TLR9a—were more potent compared with iPEMs containing polyIC, a TLR3a. These findings demonstrate the ability of iPEMs to enhance response to several different classes of vaccine cargos, supporting iPEMs as a simple vaccine platform that mimics attractive features of other nanoparticles using immune signals that can be self‐assembled or coated on substrates. Biotechnol. Bioeng. 2017;114: 423–431. © 2016 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.