Electrospun poly(3-hydroxybutyrate-co-3-hydroxyvalerate) scaffolds - a step towards ligament repair applications

The incidence of anterior cruciate ligament (ACL) ruptures is approximately 50 per 100,000 people. ACL rupture repair methods that offer better biomechanics have the potential to reduce long term osteoarthritis. To improve ACL regeneration biomechanically similar, biocompatible and biodegradable tissue scaffolds are required. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), with high 3-hydroxyvalerate (3HV) content, based scaffold materials have been developed, with the advantages of traditional tissue engineering scaffolds combined with attractive mechanical properties, e.g., elasticity and biodegradability. PHBV with 3HV fractions of 0 to 100 mol% were produced in a controlled manner allowing specific compositions to be targeted, giving control over material properties. In conjunction electrospinning conditions were altered, to manipulate the degree of fibre alignment, with increasing collector rotating speed used to obtain random and aligned PHBV fibres. The PHBV based materials produced were characterised, with mechanical properties, thermal properties and surface morphology being studied. An electrospun PHBV fibre mat with 50 mol% 3HV content shows a significant increase in elasticity compared to those with lower 3HV content and could be fabricated into aligned fibres. Biocompatibility testing with L929 fibroblasts demonstrates good cell viability, with the aligned fibre network promoting fibroblast alignment in the axial fibre direction, desirable for ACL repair applications. Dynamic load testing shows that the 50 mol% 3HV PHBV material produced can withstand cyclic loading with reasonable resilience. Electrospun PHBV can be produced with low batch variability and tailored, application specific properties, giving these biomaterials promise in tissue scaffold applications where aligned fibre networks are desired, such as ACL regeneration.   .

Date seed characterisation, substrate extraction and process modelling for the production of polyhydroxybutyrate by Cupriavidus necator

Poly-3-hydroxybutrate (PHB) is a biodegradable polymer synthesised via bacterial fermentation as a means of storing carbon and energy under unbalanced growth conditions. The production cost of petroleum-based plastics is currently lower than that for biopolymers, and the carbon source is the most significant contributor to biopolymer production cost. A feasibility study to assess the suitability of using a date seed derived media as an alternative for PHB production under various stress conditions was investigated. Results include fructose extraction from date seeds and a mass transfer model to describe the process, demonstrating that the high nutrient content of date seeds makes them a promising raw material for microbial growth and that a meaningful amount of PHB can be produced without supplementation. Maximum dry cell weight and PHB concentrations were 6.3g/l and 4.6g/l respectively, giving a PHB content of 73%, when an initial fructose concentration of 10.8g/l was used.

Effect of limonene on the heterotrophic growth and polyhydroxybutyrate production by Cupriavidus necator H16

The inhibitory effect of limonene on polyhydroxybutyrate (PHB) production in Cupriavidus necator H16 was studied. Firstly, results demonstrate the feasibility of using orange juicing waste (OJW) as a substrate for PHB production. An intracellular PHB content of 81.4% (w/w) was attained for a total dry matter concentration of 9.58gL^-1, when the OJW medium was used. Later, a mineral medium designed to mimic the nutrient levels found in the complex medium derived from OJW was used to study the effect of limonene on the production of PHB. Results showed a drop in specific growth rate (μ) of more than 50% when the initial limonene concentration was 2% (v/v) compared to the limonene free medium. This work highlights the importance of a limonene recovery stage prior to fermentation, to maintain levels below 1% (v/v) in the medium, adding value to the OJW and enhancing the fermentation process productivity.