Polycaprolactone and poly(glycerol) sebacate polyHIPEs for regeneration of osteochondral defects

According to the Outerbridge grading system and the ICRS grading, osteochondral defects are
described as a cartilage lesion that reaches down the subchondral bone and can penetrate across.
Physiologically, a decrease in the cartilage proteoglycans and an increase in degradative enzymes
lead to loss of motor abilities, pain and over-mineralisation of joints.

Current preventive treatments include pharmacotherapies and cartilage enhancement procedures
while corrective approaches mostly consist of major interventions (transplantations and invasive
tissue engineering techniques). Materials proposed for tissue engineering (TE) and regenerative
medicine (RM) show impressive advances in both production technologies and resilience responses
after implantation, ameliorating the patient’s mobility and lifestyle for years. However, there is
still a huge gap between the number of academic proposals undergoing clinical trials and the product
release to the market. Finally, clinical interventions usually include site morbidity, immune
rejection and tissue regeneration that does not exactly mimic the host environment.

Osteochondral (OC) defects and articular cartilage pathologies are part of the most common
musculoskeletal (MSK) conditions in the UK. They are known due to their low rate of healing
and the concomitant pathologies around them. Almost 20 million people in the country have an MSK
condition; osteoarthritis (OA), avascular necrosis (AVN), osteochondritis dissecans (OCD) and
traumatic OC affects 3 out of 10 citizens over the age of 45. Surprisingly, OC affects mainly mid-leagued high-performance athletes and women. Every year, the NHS develops partial or total one or
two-sided replacements; around 102 000 hip, 109 000 knee replacements, and 7,000 shoulder
replacements. Frome these, over 90% of the patients are diagnosed with osteoarthritis.
With main symptoms as a decrease in the cartilage proteoglycans and an increase on the degradative
enzymes, various treatments have been offered for the last two decades: (i) cartilage enhancement
procedures & pharmacotherapies, (ii) transplantations (AOCT - Mosaicplasty), and (iii) TE
techniques / cellular therapies (MACI – ACI). Despite their advantages in mobility restoration and
symptom elimination, site morbidity, low availability of cell and tissue supply, fibrocartilage
formation and allogeneic graft materials still limit their effectiveness.
The present work has as main objective to propose an alternative material or group of materials for
the creation of porous structures that, when implanted, could support the formation of novel
osteochondral tissue. For this;

i) The first chapter explores the literature regarding the anatomy of the knee and its connections
with OC defects. Additionally, an analysis of current treatments for OC defects is presented.
ii) Materials and methods used through this work are mainly condensed in Chapter II.
iii) The third chapter discusses polycaprolactone methacrylate (PCLMA) as a candidate for the
formation of porous structures through emulsion templating (polyHIPEs), with a special
focus on the chemical and mechanical characterisation of the material, as well as the study of
their microstructure through scan electron microscopy (SEM) microscopy and microcomputed tomography (micro-CT).
iv) The fourth chapter proposes poly(glycerol sebacate) methacrylate (PGSM) as a candidate for
the formation of polyHIPEs through emulsion templating, with a special focus on the
understanding and optimisation of the emulsification process, and the chemical and
mechanical characterisation of the material, as well as the study of their microstructure
through SEM, LightSheet microscopy and micro-CT.
v) The fifth chapter explores blends of PCLMA and PGSM as biodegradable polymers and as
HIPE material. A multi-layered scaffold is also displayed. The mechanical characterisation
of the materials was explored through tensile and compressive tests, and the overall
morphology was imaged through LighSheet microscopy and micro-CT.
vi) The sixth chapter proposes a variety of techniques for the treatment of polyHIPEs to tune
their wettability, bioactivity and biodegradability, as well as their attractiveness to cellular
environments. The chapter also discusses the use of hydrogels as part of the internal phase of
emulsions, and as carriers of molecules as sugars and cells for TE applications.
vii) The seventh chapter collects cell experiments developed using materials previously discussed.
The cellular lines (hES-MPs, BACs, Y201, MLO5) were selected due to their proximity to
the tissues of interest (cartilage, osteochondral) and cell culture was done on 2D and 3D,
using both qualitative and quantitative assays to measure cellular metabolic activity,
extracellular matrix (ECM) production, and early differentiation.
viii) The eight chapter represents a final reflection on future work on both the biomaterial and TE
approaches. Additionally, it also explores the feasibility of polyHIPEs for their commercial
application as scaffolds for novel tissues, especially for the food industry.

It can be concluded that PCLMA and PGSM as individual or as a blend, are suitable polymers
for TE applications. Additionally, that stable polyHIPEs can be formed from these materials, that
can be functionalised and treated to increase their attractiveness to cellular environments in the
macro and micro structural level and support metabolic activities that can lead to the production
of ECM and new tissues