Elsevier

Applied Surface Science

Volume 494, 15 November 2019, Pages 335-352
Applied Surface Science

Full length article
Synthesis and characterization of biocompatible polymer-ceramic film structures as favorable interface in guided bone regeneration

https://doi.org/10.1016/j.apsusc.2019.07.098Get rights and content

Highlights

  • Cellulose acetate and hydroxyapatite composite films for guided bone regeneration

  • Influence of the ultrasonication time on the bioceramic particles dispersion

  • Influence of ceramic particles size, quantity and dispersion on composite film assembly

  • Surface features attained by morphology, roughness, wettability and in vitro study

Abstract

The bone regeneration field targeted lately the development of new products based on precursors of natural origin. This study aimed to obtain the optimal design of polymer-ceramic composites for guided bone regeneration application from cellulose acetate (CA) and hydroxyapatite (HA) by varying three relevant parameters: the amount of HA powder added to the CA matrix (in the 20–40 wt% range), the HA particles size (max. 20 μm vs. max. 40 μm) and the homogenization time required for HA powder dispersion in the CA matrix (1 min vs. 4 min).

For polymer-ceramic film structures preparation, the phase inversion by immersion in water method was used. This involved the deposition of composite solution (i.e. CA with 20–40 wt% HA) on a glass support, followed by sizing it at a thickness of 0.2 mm. The obtained film structures were investigated in terms of morpho-compositional and structural properties. The surface features evaluation was achieved by surface wettability, roughness, water permeation, protein retention and in vitro evaluation of MC3T3-E1 morphology and viability. Further, ceramic particle distribution throughout samples volume was provided by computed tomography methods. These investigations targeted the validation of the prepared composite film structures as viable solutions for guided bone regeneration.

Introduction

Periodontal diseases, tumors extraction, congenital defects, alveolar bone resorption, or pathological causes lead to large bone tissue defects which may result in total or partial loss of dental crown [1,2]. One aided solution for partially edentulous maxillae rehabilitation [3], both functional and aesthetic, can be represented by the dental implant. However, in some cases this stands as a temporary fixing due to reported inflammatory processes of peri-implant tissue (e.g. peri-implant mucositis, peri-implantitis) caused by plaque concentration around the mucosa surrounding the implant and further related to dental implants failure [4]. The exposure of the root surface resulting from the migration of the gingival margin beyond the enamel-cement junction, namely the gingival recession, is one of the most common problems encountered by the dentist and the patient. This has led to the improvement of mucogingival surgery techniques, primarily due to the aesthetic needs of the patient, but also to the comfort of both patient and clinician during the treatment period. Root cover solves root caries, root sensitivity and aesthetic aspects [5].

To avoid or to improve periodontal plastic surgery, a procedure who involve various surgical techniques [6] like interpositional grafts, the ridge split technique or ridge expansion, distraction osteogenesis, onlay block bone grafting [3] aimed to correct and prevent various dental problems. There are techniques that can reduce these types of interventions, and in addition help to improve bone tissue regeneration, like vertically and horizontally bone augmentation [3], coronally advanced flap, free gingival graft, rotational flap, connective tissue graft, guided bone regeneration [5], maxillary sinus floor elevation [3,7], delivery of growth factors [8], and the combination of two or more of these techniques. The guided bone regeneration strategy (GBR), the most used alveolar bone grafting technique [2], allows for a proper implant support mimicking the same anatomical position as the replaced segment and aesthetic aspects, both quickly and efficiently achieved [9]. Although GBR was initially used for periodontal tissue restoration, later improvements in bone tissue engineering field led to its development as bone augmentation technique around dental implants [10].

As compared to autogenous bone or other substitution materials used alone, GBR relies on the restoration of bone tissue through a mechanical barrier (a thin film) which could also integrate a bone substitution material [11,12]. These barriers are mainly addressed for bone defect area isolation from the surrounding connective soft tissue and migration of gingival epithelium [13,14], and possible blood clots, thereby creating an adequate space for alveolar bone regeneration and facilitating the new bone formation [11]. When using bone fillers or block grafting products, barrier materials act toward keeping them in the area of interest and facilitate a better resorption [15]. However, the bone regeneration process is strongly dependent on a compatible matrix for new tissue formation, good blood circulation, signaling agents (e.g. growth factors) and osteoblasts (bone-forming cells) colonization in the implantation area [1,15].

The specialized market offers a wide range of barrier materials, obtained from different polymeric materials with a high success rate in GBR [11,16]. Currently, the development of new barrier materials is based on both degradable and non-degradable polymers, with or without growth factors addition: the most commonly used polymers are the collagen obtained from human or animal tissues [15], the polyethylene glycol hydrogel (PEG) with/without arginylglycylaspartic acid [17], the expanded polytetrafluoroethylene (ePTFE) [10,11,15], chitosan [[18], [19], [20]] and nanocellulose [21,22]. They can be further reinforced with a variety of materials with established purpose in bone regeneration field such as bioactive glasses (e.g. Bio-Oss®) [9,15,23], calcium phosphates (hydroxyapatite (HA, Ca10(PO4)6(OH)2), dicalcium and tricalcium phosphate) [17], or precious metals (gold, silver, platinum) [21]. In addition, metals such as titanium were also targeted as reinforcement material or for the whole barrier materials synthesis [10,24,25].

Overall, bone grafting techniques (e.g. sinus lift procedure) [7,26] involving alloplastic materials display several advantages compared to the autologous bone transplantation, which for the past two decades represented the golden standard [27,28]. In this regard, donor site morbidity or disease transmission avoidance and, additionally, the osteoconductive behavior of used materials, represent key points of this technique [28]. Synthetic HA prevalence in the bone regeneration field is primarily correlated to its biocompatible, osteoconductive and biodegradable properties and also to the capability of mimicking the crystalline phase of the human bone [15,22,[29], [30], [31], [32]]. Nowadays, there is a continuous interest in the use of natural sources such as corals, eggshells, seashells, marble, fish and bovine bone as precursors for hydroxyapatite synthesis [27,[33], [34], [35], [36]]. The natural bone structure contains approximately 10% wt water, up to 30% wt, organic components and 60–70% wt mineral component [37]. Unlike synthetic hydroxyapatite, the biological (natural) one has a Ca/P ratio >1.67, its structure being formed not only from carbonate groups but also from numerous trace elements (e.g. Na, Mg, Si, Mn, Cu) [38].

Compared to synthetic hydroxyapatite, the use of these natural resources for HA achievement has as main advantage the similarity with the human bone, the spread throughout the world, their renewability, the low raw material costs, the rapidity of obtaining with simple devices. From biological safety point of view, the HA synthesis route, namely the heat treatment temperature, provides a complete decontamination [39,40]. The synthesis route of HA powder provides a complete decontamination, thus eliminating the risk of immunological contamination with pathogens and/or the transmission of diseases from animal to patient. Among the plethora of synthesis methods reported in this regard (e.g. precipitation, sol-gel, combustion) [41], the facile and direct extraction from bovine bone leads to HA-based materials with improved morpho-compositional, mechanical and biological properties [33,42].

This study targeted the synthesis of bicomposite materials through an optimized route based on cellulose acetate matrix and bovine bone-derived HA addition. This process involved an optimum variation of key-parameters such as (i) HA particles size (<20 μm and 20–40 μm) and concentration (20–40%) range and (ii) ultrasonic time mandatory for a properly surface-volume dispersion of HA particles. The need for these parameters modulation is raised by several problems related to dimensional irregularities and particles agglomeration, which influences both volume and surface properties of composite materials [24]. Therefore, the current study focused on the development of a user-friendly interface between the additive materials and the adjacent tissues. The obtained composite materials stand as potential solution for barrier materials involved in GBR applications in the dental field.

Section snippets

Bicomposite materials synthesis

The HA preparation from bovine bone was performed according to a previously reported route [33]. The resultant powder was further grounded in a planetary mill with agate balls and bowl, and sorted using standardized sieves (particle size <20 μm and <40 μm) with a Retsch AS 200 device. The cellulose acetate matrix was prepared using 51.49 g of 12% cellulose acetate solution (CA, 67% acetylation degree, Sigma Aldrich) dissolved in 400 ml of N,N′-dimethylformamide (DMF, analytical purity 99.96%,

Morphological and compositional characterization

The morpho-compositional evolution of bicomposite films (formed by a CA matrix with different amount of HA powder addition with different particle sizes) was investigated in comparison with the reference samples (CA matrix) and is presented in Fig. 1. The cellulose acetate matrices (reference samples) obtained at 1 and 4 min dispersion times, presented porous structures with interconnected spherical and polyhedral pores. The addition of various concentrations of HA powders led to aggregates

Conclusions

This study focused on the synthesis route optimization by varying three key-parameters (the ultrasonic dispersion time, the hydroxyapatite particles size and powder concentrations) for the development of the best form of barrier composite material prepared from sustainable resources. The obtained materials were characterized in terms of both surface and volume characteristics, revealed by micro-CT investigations, for the adequate composite material settlement.

The modulation of the

Acknowledgements

The authors are thankful to the Advanced Polymer Materials Group, led by prof. dr. H. Iovu, for the technical support and valuable insights regarding the CT investigations and data interpretation. The micro-CT analyses on SkyScaner 1272 were possible due to European Regional Development Fund through Competitiveness Operational Program 2014-2020, Priority axis 1, Project No. P_36_611, MySMIS code 107066, Innovative Technologies for Materials Quality Assurance in Health, Energy and Environmental

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