Sufficient Mechanical Support Research Articles

Biocompatible encapsulation and interconnection technology for implantable electronic devices

A biocompatible packaging process for implantable electronic systems is under development at imec, combining biocompatibility, hermeticity, extreme miniaturization and cost aspects. In a first phase of this packaging sequence, hermetic chip sealing is performed by encapsulating all chips to realize a bi-directional diffusion barrier preventing body fluids to leach into the package causing corrosion, and preventing IC materials such as Cu to diffuse into the body, causing various adverse effects. For cost effectiveness, this chip sealing is performed as post-processing at wafer level, using modifications of standard clean room (CR) fabrication techniques. Well known conductive and insulating CR materials are investigated with respect to their biocompatibility, biostability, diffusion barrier properties and sensitivity to corrosion. Material selection and integration aspects are modified until good properties are obtained. In a second phase of the packaging process, all chips of the final device should be electrically connected, applying a biocompatible metallization scheme. We selected the use of Pt due to its excellent biocompatibility and corrosion resistance. Since Pt is very expensive, a cost effective Pt-selective plating process is developed. During the third packaging step, all system components such as electronics, passives, a battery,… will be interconnected. To provide sufficient mechanical support, all components are finally embedded using a medical grade elastomer such as PDMS or Poly-urethane.

Design and characterization of a biocompatible packaging concept for implantable electronic devices

A biocompatible packaging process for implantable electronic systems is described, combining biocompatibility and hermeticity with extreme miniaturization. In a first phase of the total packaging sequence, all chips are encapsulated in order to realize a bi-directional diffusion barrier preventing body fluids to leach into the package causing corrosion, and preventing IC materials such as Cu to diffuse into the body, causing various adverse effects. For cost effectiveness, this hermetic chip sealing is performed as post-processing at wafer level, using modifications of standard clean room (CR) fabrication techniques. Well known conductive and insulating CR materials are investigated with respect to their biocompatibility, diffusion barrier properties and sensitivity to corrosion. In a second phase of the packaging process, all chips of the final device should be electrically connected, applying a biocompatible metallization scheme using eg. gold or platinum. For electrodes being in direct contact with the tissue after implantation, IrOx metallization is proposed. Device assembly is the final packaging step, during which all system components such as electronics, passives, a battery,… will be interconnected. To provide sufficient mechanical support, all these components are embedded using a biocompatible elastomer such as PDMS.

The mechanical characteristics and in vitro biocompatibility of poly(glycerol sebacate)-Bioglass ® elastomeric composites

Biodegradable elastomeric materials have gained much recent attention in the field of soft tissue engineering. Poly(glycerol sebacate) (PGS) is one of a new family of elastomers which are promising candidates used for soft tissue engineering. However, PGS has a limited range of mechanical properties and has drawbacks, such as cytotoxicity caused by the acidic degradation products of very soft PGS and degradation kinetics that are too fast in vivo to provide sufficient mechanical support to the tissue. However, the development of PGS/based elastomeric composites containing alkaline bioactive fillers could be a method for addressing these drawbacks and thus may pave the way towards wide clinical applications. In this study, we synthesized a new PGS composite system consisting of a micron-sized Bioglass ® filler. In addition to much improved cytocompatibility, the PGS/Bioglass ® composites demonstrated three remarkable mechanical properties. First, contrary to previous reports, the addition of microsized Bioglass ® increases the elongation at break from 160 to 550%, while enhancing the Young’s modulus of the composites by up to a factor of four. Second, the modulus of the PGS/Bioglass ® composites drops abruptly in a physiological environment (culture medium), and the level of drop can be tuned such that the addition of Bioglass ® does not harden the composite in vivo and thus the desired compliance required for soft tissue engineering are maintained. Third, after the abrupt drop in modulus, the composites exhibited mechanical stability over an extended period. This latter observation is an important feature of the new composites, because they can provide reliable mechanical support to damaged tissues during the lag phase of the healing process. These mechanical properties, together with improved biocompatibility, make this family of composites better candidates than plastic and related composite biomaterials for the applications of tissue engineering.

Wafer-Level hermetic packaging for bio-medical applications

Introduction Packaging of medical implants has been always a challenging topic due to the strong requirements in term of sizes, biocompatibility and safety [1, 2]. This is often required for placing an implant at a specific location of the body, without disturbing the surrounding tissues, and aiming at avoiding discomfort for the patient. The implants should be packaged in order to have a hermetic closed shield around the device, protecting the human body from diffusion of materials from inside the package into the body [3, 4]. Moreover, in order to ensure the functionality of the implanted device, the package should also protect the device from any insertion of body fluids into the implant, especially for active electronics. An implantable device could consist of several subdevices connected each other and integrated in a single package. These sub-devices could be one or more CMOS chips, a battery, a sensor, etc. They need to be electrically connected with each other and if required be accessible through the guest body by dedicated electrodes. We present here a process flow (Figure 1) aiming at encapsulating single dies as commodity Integrated Circuits (IC). The encapsulation consists of a stack of layers, to prevent diffusion of metal contaminant, prior to final encapsulation in a bio-compatible package. The reported process relies on classical CMOS and 3D wafer-level packaging processes. The test devices for encapsulation consist in test silicon chips with Cu metal structures designed to be characterized in a standard daisy chain configuration. A double diffusion barrier is created on the top side of the chip to avoid Cu diffusion. The first barrier consists on a thick layer of Silicon nitride which offers superior performance with respect to Cu diffusion in the immediate vicinity of the interconnect layers. After this step the wafer is processed with Dicing-BeforeGrinding (DBG) technique. A thick silicon oxide is deposited on the sidewalls of the pre-grooved wafers to protect the edge of the IC dies, prior to thinning the wafer down to ~80μm. The sharp edges from the backside of IC dies are then rounded and a 3μm thick oxide deposited at low temperature is deposited to complete the encapsulation. Finally, the test chips are de-bonded and cleaned. The functionality of the encapsulation process as diffusion barrier is tested by various experiments as cell culture test and leaching test followed by TXRF analysis of the elution. After the hermetic encapsulation of single dies, the next step would be the assembly of the final device. The various sub-devices will be connected through a bio-compatible inter-die metallization (e.g. gold, platinum or other) that will have access to the die’s active site by electrodes also them metalized with biocompatible materials (Figure 2a). The total system will be then further encapsulated by using embedding technique where a flexible and biocompatible material [6] will be used to provide the dies a sufficient mechanical support (Figure 2b).

Preparation of porous 45S5 Bioglass®-derived glass–ceramic scaffolds by using rice husk as a porogen additive

Bioactive glass is currently regarded as the most biocompatible material in the bone regeneration field because of its bioactivity, osteoconductivity and even osteoinductivity. In the present work porous glass-ceramic scaffolds, which were prepared from the 45S5 Bioglass by foaming with rice husks and sintering at 1050 degrees C for 1 h, have been developed. The produced scaffolds were characterized for their morphology, properties and bioactivity. Micrographs taken using a scanning electron microscope (SEM) were used for analysis of macropores, mesopores and micropores, respectively. The bioactivity of the porous glass-ceramic scaffolds was investigated using simulated body fluid (SBF) and characterized by SEM, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). A great potential scaffold that provides sufficient mechanical support temporarily while maintaining bioactivity, and that can biodegrade at later stages is achievable with the developed 45S5 Bioglass-derived scaffolds.

Cyclical Wave-Bolt

The conceptual possibilities of the design of thin absorbing (non-reflecting) coatings are considered using simple acoustical and mechanical models. Coating presents a thin layer with microscale stratification and fast time binary modulation of parameters following several algorithms of so-called cyclical wave-bolts. Algorithms of space-time modulation of the controlled layer's structure are thoroughly investigated for the one-dimensional boundary problem. These algorithms present: (a) control of boundary conditions in the discrete points; (b) control of the velocity of wave propagation; (c) control of the viscosity in layers. The algorithms do not require any measurements of the wave field and this removes the traditional stability problem for active systems. All kinds of control assume the existence of sufficient mechanical support or «vibrostat». Most of the algorithms of parametric control considered are converting low frequency incident waves into high frequency waves of technological range for which the waveguiding medium is assumed nontransparent (absorptive). Conditions for the effective application of all algorithms suggested have been formulated. It is shown that the absorbing layer can be arbitrarily thin relating to the minimum space scale of the incident wave and ensures effective absorption over a wide frequency range (beginning from zero frequency) limited only by finite space-time resolution of parametric control operations. On the base of one-dimensional boundary problems the structure of a 3-dimensional «black» parametric coating is formulated. The effectiveness of the absorbing coating does not depend on the incident wave direction. A general solution of the diffraction problem for this coating has been obtained through consideration of the object of disk shape. The possibilities of cyclical wave-bolt realization are based on the surplus of modern high space-time resolution in control, which is growing every year, relating to the space-time scales of location waves for instance remaining the same as years ago due to constant real conditions of far propagation.

Reconstruction of proximal femoral defects with a vascular-pedicled graft.

A new method of treating large bony defects of the proximal femur is described. The defect is filled with a large vascular-pedicled bone graft from the iliac crest. The graft, being nourished by the deep circumflex iliac vessels, remains viable and therefore induces rapid healing of the bone. This method of bony replacement encourages adequate excision of potentially malignant bone lesions and provides sufficient mechanical support to allow early walking. Six clinical cases are presented to illustrate its application.