## 2 Description and Challenges of a Customized Biomedical Implantable Device
### Research Challenges in Implantable Devices
#### 2.2.2 The Encapsulation of the System
\begin{table}
\begin{tabular}{|p{113.8 pt}|p{113.8 pt}|p{113.8 pt}|p{113.8 pt}|p{113.8 pt}|} \hline  & **Material** & **Abbreviation** & **Specification** & **Manufacturer** \\ \hline \multirow{4}{*}{Encapsulation Materials} & \multirow{2}{*}{Sylgard 184} & \multirow{2}{*}{PDMS} & \multirow{2}{*}{Polydimethylsiloxane} & \multirow{2}{*}{Dow Corning Corp., Midland, MI} \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \hline \multirow{4}{*}{Membrane Materials} & \multirow{2}{*}{Cellulose ester Materials} & \multirow{2}{*}{Cm} & \multirow{2}{*}{Ultrafiltration membrane (MWCO 5000 Da, - 2.5 nm)} & \multirow{2}{*}{Spectrum Laboratories Europe B.V., Breda, Netherlands} \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \hline \multirow{4}{*}{Sensor Carrier Materials} & \multirow{2}{*}{CeramTec GC Materials} & \multirow{2}{*}{CT} & \multirow{2}{*}{Low temperature coifercamic (LTCC)} & \multirow{2}{*}{Ceramtec AG, Plochingen, Germany} \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \hline \multirow{4}{*}{Sealing Materials} & \multirow{2}{*}{Silicone 3145 adhesive Epo-Tek 353 ND ETek Epoxy resin Epoxy Technol., Billerica, MA} & \multicolumn{1}{p{113.8 pt}}{} & \multicolumn{1}{p{113.8 pt}}{} & \multicolumn{1}{p{113.8 pt}}{} \\ \cline{3-3} \cline{5-5}  & & & & \\ \cline{3-3} \cline{5-5}  & & & & \\ \hline \end{tabular}
\end{table} 
Table 2: Candidate materials for implementation in the glucose sensor [79]. Other biocompatible materials include collagen layer for encapsulation [81], or gold, silicon nitride, silicon dioxide and SU-8 for coating use, able to reduce biofouling [82]. Coating of silicon carbide for example, can be used to significantly reduce thrombus formation on the surface of the devices, especially if the device is exposed to blood [83]. [PERSON] _et al._[84] have also mentioned the use of phosphorous glass (SiPOC) for cell adhesion in BioMEMS. The application of NDGA-crosslinked collagen scaffolds is also a good method for enhancing the function and lifetime of implantable bio-sensors by minimizing the _in vivo_ foreign body response. [PERSON] _et al._[85] have developed a 3D porous and bio-stable collagen scaffold for implantable glucose sensors. The scaffolds were fabricated around the sensors and crosslinked using nordihydroguiaretic acid (NDGA) or glutaraldehyde (GA) to enhance physical and biological stability. [PERSON] _et al._[86] reported an implantable sensor for real-time monitoring of the changes in bladder volume with PDMS and parylene-C. They find that both can be used as safe coating materials for the implantable bladder volume sensor reported. A novel polymer coating consisting of poly(lactic-co-glycolic) acid (PLGA) microsphere dispersed in poly(vinyl alcohol) (PVA) hydrogels was evaluated in combination with dummy sensors as a \"smart\" drug eluting bio-compatible coating for implantable biosensors to prevent the foreign body response, and thus enhance sensor performance _in vivo_[80]. Single or multiple electro-spun layers can be used to address mass-transport limiting and additional membranes for improving biocompatibility of implantable biosensors and other biomedical devices requiring analyte transport, especially the first generation implantable glucose biosensors [87]. In summary, packaging techniques used must assure a long-term stability and surgical risks must be avoided. To fulfil these requirements, available implants in the market typically use hermetic packaging in laser-welded enclosures [88]. Nevertheless, for the envisaged miniaturized implants, where cans and micro-lids are used, this solution takes too much space.