Biodegradable cell scaffolds and local drug delivery to stimulate cell response are currently receiving much scientific attention. Here we present a nanocomposite that combines biodegradation with controlled release of lithium, which is known to enhance bone growth. Nanogels of lithium neutralized polyacrylic acid were synthesized by microemulsion-templated polymerization and were incorporated into a biodegradable polyhydroxybutyrate (PHB) matrix. Nanogel size was characterized using dynamic light scattering, and the nanocomposites were characterized with regard to structure using scanning electron microscopy, mechanical properties using tensile testing, permeability using tritiated water, and lithium release in PBS using a lithium specific electrode. The nanogels were well dispersed in the composites and the mechanical properties were good, with a decrease in elastic modulus being compensated by increased tolerance to strain in the wet state. Approximately half of the lithium was released over about three hours, with the remaining fraction being trapped in the PHB for subsequent slow release during biodegradation. The prepared nanocomposites seem promising for use as dual functional scaffolds for bone regeneration. Here lithium ions were chosen as model drug, but the nanogels could potentially act as carriers for larger and more complex drugs, possibly while still carrying lithium. 1. Introduction To introduce additional functionality in a biodegradable polyhydroxybutyrate (PHB) matrix, polyacrylic acid (PAA) nanogels were incorporated to form a hybrid solid-gel nanocomposite. This highly designed material structure approach is in line with recent developments in the biomaterials field. Biodegradable materials have long been investigated for use in tissue engineering and drug delivery, as seen from literature [1–3], but attention has turned towards structured and/or multifunctional materials [3, 4]. One material class that has been widely investigated for use in biomedical applications is polyhydroxyalkanoates (PHA), as it incorporates a range of naturally occurring biocompatible aliphatic polyesters, including PHB [5]. The characteristics and material properties of different PHA vary greatly, for example, mechanical properties and degradation rates can be tailored by the monomer composition [2, 3, 5]. When it comes to PHB it has a strong tendency for crystallization [5] and has a slow biodegradation rate compared to most biodegradable polyesters [6]. With regard to mechanical properties it is hard and brittle, where the brittleness is a disadvantage
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